By Channel Your Enthusiasm
A chapter by chapter recap of Burton Rose’s classic, The Clinical Physiology of Acid Base and Electrolyte Disorders, a kidney physiology book for nephrologists, fellows, residents and medical stude
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Outline Chapter 15 — Clinical Use of Diuretics
- Among most commonly used drugs
- Block NaCl reabsorption at different sites along the nephron
- The ability to induce negative balance has made them useful in multiple diseases
- Edematous states
- Hypertension
- Mechanism of action
- Three major classes
- Loop
- NaK2Cl
- Up to 25% of filtered sodium excreted
- Thiazide
- NCC
- Up to 3-5% of filtered sodium excreted
- Potassium sparing
- ENaC
- Up to 1-2% of filtered sodium excreted
- Each segment has a unique sodium channel to allow tubular sodium to flow down a concentration gradient into the cell
- Table 15-1 is interesting
- Most of the sodium 55-655 is reabsorbed in the proximal tubule
- Proximal diuretics would be highly effective if it wasn’t for the loop and other distal sites of Na absorption
- Loop Diuretics
- Furosemide
- Bumetanide
- Torsemide
- Ethacrynic acid
- NaK2Cl activated when all four sites are occupied
- Loop diuretic fits into the chloride slot
- In addition to blocking Na reabsorption results in parallel decrease in calcium resorption
- Increase in stones and nephro albinos is especially premature infants which can increase calcium excretion 10-fold
- Thiazide
- Even though they are less potent than loops they are great for hypertension
- “Not a problem in uncomplicated hypertension where marked fluid loss is neither necessary nor desirable”
- Some chlorothiazide and metolazone also inhibit carbonic anhydrase in the proximal tubule
- Increase Calcium absorption. Mentions that potassium sparing diuretics do this also
- Potassium sparing diuretics
- Amiloride
- Spironolactone
- Triamterene
- Act at principal cells in the cortical collecting tubule,
- Block aldosterone sensitive Na channels.
- Discusses the difference between amiloride and triamterene and spiro
- Mentions that trimethoprim can have a similar effect
- Spiro is surprisingly effective in cirrhosis and ascites
- Talks about amiloride helping in lithium toxicity
- Partially reverse and prevent NDI from lithium
- Trial Terence as nephrotoxin?
- Causes crystaluria and casts
- These crystals are pH independent
- Faintly radio opaque
- Acetazolamide
- Blocks carbonic anhydrase
- Causes both NaCl and NaHCO3 loss
- Modest diuresis de to distal sodium reclamation
- Mannitol
- Nonreabsorbable polysaccharide
- Acts mostly in proximal tubule and Loop of Henle
- Causes water diuresis
- Was used to prevent ATN
- Can cause hyperosmolality directly and through the increased water loss
- This hyperosmolality will be associated with osmotic movement of water from cells resulting in hyponatremia, like in hyperglycemia.
- Docs must treat the hyperosmolality not the hyponatremia
- Time course of Diuresis
- Efficacy of a diuretic related to
- Site of action
- Dietary sodium action
- 15-1 shows patient with good short diuretic response but other times of low urine Na resulting in no 24 hour net sodium excretion.
- Low sodium diets work with diuretics to minimize degree of sodium retension while diuretic not working
- Also minimizes potassium losses
- Increase frequency
- Increase dose
- What causes compensatory anti-diuresis
- Activation of RAAS and SNS
- ANG II, aldo, norepi all promote Na reabsorption
- But even when prazosin to block alpha sympathetic and capto[pril to block RAAS sodium retention occurs
- Decrease in BP retains sodium with reverse pressure natriuresis
- Even with effective diuresis there is reestablishment of a new steady state
- Diuresis is countered by
- Increases in tubular reabsorption at non-diuretic sensitive sites (neurohormonal mediated)
- Flow mediated in creases in Tubular reabsorption distal to the diuretic from increased sodium delivery.
- Hypertrophy
- Increased Na-K-ATPase activity
- Decreased tubular secretion of diuretic if renal perfusion is impaired
- Getting to steady state requires
- Diuretic dose and sodium intake be constant
- Sodium balance is reestablished with 3 days of a fixed diuretic dose
- K balance in 6-9 days
- Figure 15-2
- Which means that people on stable doses of diuretics don’t need regular labs, the abnormalities will emerge quickly.
- Maximum diuresis happens with first dose
- Figure 15-3
- Fluid and Electrolyte complications
- Volume depletion
- “Effective circulating volume depletion also can develop in patients who remain edematous. Although fluid persists, there may be a sufficient reduction in intracranial filling pressures and cardiac output to produce a clinically important reduction in tissue perfusion.”
- Azotemia
- Decreased effective circulating volume with diuretic therapy also can diminish renal perfusion and secondarily the GFR.
- Describes the traditional reason for increased BUN:Cr ratio
- Then states that as much as a third of of the rise in BUN may reflect increased urea production; it is possible, for example, that reduced skeletal muscle perfusion leads to enhanced local proteolysis. This increases urea production.
- Hypokalemia
- Loop and thiazide increase urinary potassium losses
- Often lead to hypokalemia
- 50 mg of HCTZ drop K by 0.4 to 0.6 mEq/L with 15% falling below 3.5
- He uses “associated” I think this is a place where we can use cause
- 50 mg of chlorthalidone
- K falls 0.8 to 0.9 mEq/L
- Etiology
- Increased distal delivery of Na and water
- Increased aldo
- From volume depletion
- Underlying disease: cirrhosis and heart failure
- Talk a lot about significance.
- Info sounds dated
- Increased risk of SCD in MRFIT trial
- Association with increased ventricular arrhythmia with hypokalmia
- Increased PVC and complex PVC by 27% with each drop in K of 0.5 mEq/L
- Says that stress can induce epinephrine which can shift potassium inside cells leading to fatal arrhythmia especially if the patient begins at a low potassium concentration
- Says v-fib two fold likely in MI patients with hypokalemia
- Talks about crazy doses of HCTZ and Chlorthalidone 50+mg
- Recommends 12.5 to 15 mg respectively
- Metabolic alkalosis
- Caused by loop and thiazide diuretics
- Two factors cause this
- Increased urinary H loss
- Partly UE to secondary hyperaldo
- Contraction of extracellular volume around remaining bicarb
- Why not contraction hypernatremia, contraction hyperkalemia, etc?
- Aldosterone contributes by stimulate ing H-ATPase
- Stimulating Sodium reabsorption creating lumen negative charge that promotes Hydrogen secretion
- Loop diuretics can also stimulate net H loss by increased Hsecretion in the cortical aspect of the thick limb
- This segment has two luminal entry points for na, the traditional NaK2Cl and Na-H exchanger
- Blocking NaK2Cl with loop diuretic stimulates the Na-H exchanger
- Can use NaCl or acetazolamide to treat
- Metabolic acidosis
- K-sparing diuretics reduce both K and H secretion in the collecting tubule
- Avoid if renal failure or on an ACEi
- Good advice to avoid K supplement with the K sparing diuretic
- Hyponatremia
- Diuretics can cause volume depletion leading to enhanced secretion of ADH and to increased water intake
- Almost always due to a thiazide
- Loops destroy the concentrated medullary gradient making ADH less effective
- Hyperdrive is
- Increased urate reabsorption in the proximal tubule
- Process mediated by parallel Na-H and urate OH exchangers see figure 3-13a
- Urate reabsorption varies directly with proximal Na transport and in patients with diuretic-induced volume deficiency both Na and urate excretion are reduced.
- May be related to Ang II
- Do not need to treat the hyperuricemia in asymptomatic patients
- Do not develop urate nephropathy because tubular urateis actually low
- Hypomagnesemia
- Generally mild
- Loop diuretics since most reabsorbed in the loop
- Thiazides don’t affect Mg (why with gitelmans?)
- Hypokalemia may directly inhibit tubular cell mg uptake
- Aldosterone increases Mg excretion, so K sparing diuretics decrease Mg secretion
- Determinants of Diuretic responsiveness
- 2 important determinants of diuretic response
- Site of action
- Presence of counterbalancing antinatriuretic forces
- Ang2
- Aldo
- Low systemic BP
- Adds rate of drug excretion as # 2 and a half
- Almost all diuretics are protein bound
- So not well filtered
- Enter tubule through organic anion and organic cation transporter
- This can limit diuretic effectiveness
- Natriuretic response plateaus at higher rates of diuretic excretion due to complete inhibition of the diuretic target
- This plateau in normal people is 1 mg of bumetanide and 40 mg of furosemide given IV
- Double this for oral furosemide, no adjustment needed for bumetanide
- 15-6
- Refractory edema
- Start with a loop diuretic
- Initial aim is to find the effective single dose
- From the paragraph this is about threshold dosing
- Double ineffective doses until good effect
- Suggests maximum furosemide dose is 200 mg IV and 400 mg oral
- Excess sodium intake
- High sodium diet can work to prevent patients from achieving negative sodium balance.
- Suggests diets after leaving the hospital maybe higher in sodium
- Decreased or delayed intestinal absorption
- Decreased intestinal perfusion, reduced intestinal motility and mucosal edema may contribute.
- But why is this worse with furosemide than with bumetidine or torsemide?
- Decreased drug entry into the tubular lumen
- Thiazides don’t work below a GFR of 20
- CLICK
- Renal failure
- Increased organic anions compete for diuretic secretion
- Bumetidine isn’t as dependent as furosemide on GFR
- Use 1/20th rather than 1/40th the dose
- Maximum of 8 to 10 mg
- Furosemide has ototoxicirty at high doses, he advises against 2400 mg/day
- There is a Na-K-2Cl carrier in the endolymph producing cells
- Ethacrynic acid has the most ototoxicity
- Only loop or thiazide that isn’t a sulfonamide derivative
- Cirrhosis
- Spiro is diuretic of choice
- More effective than loops alone
- Does not induce hypokalemia that can cause hepatic encephalopathy
- Cirrhosis causes marked hyperaldo
- Loop diuretics have to compete with bile salts for secretion in the proximal tubule
- Spiro does not need to be secreted in the proximal tubule
- Recommends to 100 to 40 spiro to furosemide ratio
- And can double this to 200 and 80/day
- and a maximum of of 400/160
- Hypoalbuminemia
- <2 g/dL associated with decreased diuretic entry into the lumen
- Protein binding keeps diuretics in the blood, reduces the volume of distribution
- This maximizes the delivery to the kidney
- In nephrotic syndrome tubular albumin can bind diuretic and prevent its activity
- Co administration of albumin with diuretic has resulted in modest improvements in diuretic effectiveness in various studies
- Intravenous infusion of loop diuretics
- Infusions are greater than bolus
- But if patient is not responding to blouses unlikely to respond to infusions since bolus provides a temporary spike in plasma level
- Increased distal reabsorption
- Increased distal sodium reabsorption decreases the effectiveness of proximal diuretics
- Due to aldo and increased sodium delivery
- Mentions that thiazides have a proximal effect (is that inhibition of carbonic anhydrase?)
- 15-8 is very cool
- Says all thiazides are created equal
- Article from 1972 is why people use metolazone in advanced renal disease
- When doing sequential nephron blocked be careful
- Loss of lots of fluid
- Loss of lots of potassium
- Loss of 5 liters and 200 mEq of K a day is possible with sequential nephron blockade
- Decreased loop sodium delivery
- With heart failure and cirrhosis increased proximal resorption mediated by Ang II markedly reduces delivery of fluid to the diuretic sensitive sites.
- Acetazolamide makes sense here
- Supine or 10 degree head down can increase cardiac output possibly increased venous return
- Can double Na excretion
- Increase CrCl 40%
- CAVH enters the chat!
- Other uses of diuretics
- Met alk, RTA, DI, hyponatremia due to SIADH, hypokalemia
- Diuretics and prostaglandins
- Loops and thiazides increase renal generation of prostaglandins
- Can cause venous dilation may help with acute pulmonary edema
- Can help without increased diuresis
- NSAIDS counter the effect of loop diuretics
- Is this natriuretic effect of PGE? Or due to renal ischemia due to unopposed Ang2 and norepi
- They also raise BP and reduce cardiac output due to increased vascular resistance
- Vasoconstrictor effect of loop diuretics
- One hour after loop diuretics increase vasoconstriction and rise in systemic blood pressure
- Increased Renin and norepinephrine, resolved 4 hours later
- Seen in heart failure and cirrhosis
- In cirrhosis decrease in RPF and GFR of 30-40% with furosemide
References
Melanie noted that thiazide diuretics were the Project MUSE - Releasing the Flood Waters: Diuril and the Reshaping of Hypertension
Furosemide early review of furosemide effect in a range of different clinical conditions.
Na+, K+, and BP homeostasis in man during furosemide: Effects of prazosin and captopril This article is quoted in Rose’s book-(Figure 2 is 5-1). The authors provide a figure with a balance study that shows how an initial “diuresis” is followed
Thiazide-Associated Hyponatremia: Clinical Manifestations and Pathophysiology - American Journal of Kidney Diseases
https://jasn.asnjournals.org/content/30/2/216
Thiazide induced hyponatremia, a detailed phenotypic and genotypic analysis (NephJC) https://www.sciencedirect.com/science/article/pii/B9780126356908500025
Classic paper on diuretics in NEJM from Craig Brater: https://www.nejm.org/doi/full/10.1056/NEJM199808063390607
Diagnosis and management of Bartter syndrome: executive summary of the consensus and recommendations from the European Rare Kidney Disease Reference Network Working Group for Tubular Disorders https://linkinghub.elsevier.com/retrieve/pii/S0085253820314046
Nephrocalcinosis of 17% in preemies: https://pubmed.ncbi.nlm.nih.gov/35348900/
Nephrocalcinosis with loop diuretics in neonates: https://pubmed.ncbi.nlm.nih.gov/38296790/ and https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6941622/
We wondered whether the effect of hypercalemia on loop is complete –did we go too far saying that loop diuretics have no effect
Anna’s VOG on hypercalciuria and lasix, etc. NEJM Paper describing the dose of lasix needed for calciuria Meta analysis of lasix used for calciuric effects . David Ellison and Robert Schrier experiment showing NCC activation with chronic loops. NCC activation occurs with hypercalcemia as well via CASR
Thiazide Treatment in Primary Hyperparathyroidism—A New Indication for an Old Medication? | The Journal of Clinical Endocrinology & Metabolism | Oxford Academic
Thiazide-Associated Hypercalcemia: Incidence and Association With Primary Hyperparathyroidism Over Two Decades - PMC
Major Outcomes in High-Risk Hypertensive Patients Randomized to Angiotensin-Converting Enzyme Inhibitor or Calcium Channel Blocker vs Diuretic: The Antihypertensive and Lipid-Lowering Treatment to Prevent Heart Attack Trial (ALLHAT) | Acute Coronary Syndromes | JAMA
Uromodulin upregulates TRPV5 by impairing caveolin-mediated endocytosis - University of Iowa
Acetazolamide to increase natriuresis in congestive heart failure at high risk for diuretic resistance
Regulation of Potassium Homeostasis | American Society of Nephrology Biff Palmer’s review.
Distal Convoluted Tubule - PMC we did not discuss this paper by Subramanya and Ellison but it is a gem
It Is Chloride Depletion Alkalosis, Not Contraction Alkalosis | American Society of Nephrology
Thiazide Effects and Adverse Effects | Hypertension
A comparison of the potassium and magnesium-sparing properties of amiloride and spironolactone in diuretic-treated normal subjects. - PMC
SGLT2i case series for hypomag: SGLT2 Inhibitors for Treatment of Refractory Hypomagnesemia: A Case Report of 3 Patients - PMC
Elevated serum magnesium associated with SGLT2 inhibitor use in type 2 diabetes patients: a meta-analysis of randomized controlled trials
Anti-EGFR monoclonal antibody-induced hypomagnesaemia - The Lancet Oncology
Outline Chapter 14 — Treatment
- Treatment
- Both oral and IV treatment can be used for volume replacement
- The goal of therapy are to restore normovolemia
- And to correct associated acid-base and electrolyte disorders
- Oral Therapy
- Usually can be accomplished with increased water and dietary sodium
- May use salt tablets
- Glucose often added to resuscitation fluids
- Provides calories
- Promotes intestinal Na reabsorption since there is coupled Na and Glucose similar to that seen in the proximal tubule
- Rice based solutions provide more calories and amino acids which also promote sodium reabsorption
- 80g/L of glucose with rice vs 20 g/L with glucose alone
- IV therapy
- Dextrose solutions
- Physiologically equivalent to water
- For correcting hypernatremia
- For covering insensible losses
- Watch for hyperglycemia
- Footnote warns against giving sterile water
- Saline solutions
- Most hypovolemic patients have a water and a sodium deficit
- Isotonic saline has a Na concentration of 154, similar to that of plasma see page 000
- Half-isotonic saline is equivalent to 550 ml of isotonic saline and 500 of free water. Is that a typo?
- 3% is a liter of hypertonic saline and 359 extra mEq of Na
- Dextrose in saline solutions
- Give a small amount of calories, otherwise useless
- Alkalinizing solutions
- 7.5% NaHCO3 in 50 ml ampules 44 mEq of Na and 44 mEq of HCO3
- Treat metabolic acidosis or hyperkalemia
- Why 44 mEq and not 50?
- Do not give with calcium will form insoluble CaCO3
- Polyionic solutions
- Ringers contains physiologic K and Ca
- Lactated Ringers adds 28 mEq of lactate
- Spreads myth of LR in lactic acidosis
- Potassium chloride
- Available as 2 mEq/mL
- Do not give as a bolus as it can cause fatal hyperkalemia
- Plasma volume expanders
- Albumin, polygelastins, hetastarch are restricted to vascular space
- 25% albumin can pull fluid into the vascular space
- 25% albumin is an albumin concentration of 25 g/dL compare to physiologic 4 g/dL
- Says it pulls in several times its own volume
- 5% albumin is like giving plasma
- Blood
- Which fluid?
- Look at osmolality, give hypotonic fluids to people with high osmolality
- Must include all electrolytes
- Example of adding 77 mEw of K to 0.45 NS and making it isotonic
- DI can be replaced with dextrose solutions, pure water deficit
- Case 14-3
- Diarrhea with metabolic acidosis
- He chooses 0.25 NS with 44 mEq of NaCl and 44 NaHCO3
- Talks about blood and trauma
- Some studies advocate delaying saline until penetrating trauma is corrected APR about to. Keep BP low to prevent bleeding. Worry about diluting coagulation factors
- Only do this if the OR is quickly available
- Volume deficit
- Provides formula for water deficit and sodium deficit
- Do not work for isotonic losses
- Provides a table to adjust fluid loss based on changes in Hgb or HCTZ
- Says difficult to estimate it from lab findings and calculations
- Follow serial exams
- Serial urine Na
- Rate of replacement
- Goal is not to give fluid but to induce a positive balance
- Suggests 50-100 ml/hr over what is coming out of the body
- Urine
- Insensibles 30-50
- Diarrhea
- Tubes
- Hypovolemic shock
- Due to bleeding
- Sequesting in third space
- Why shock?
- Progressive volume depletion leads to
- Increased sympathetic NS
- Increased Ang 2
- Initially this maintains BP, cerebral and coronary circulation
- But this can decrease splanchnic, renal and mucocutaneous perfusion
- This leads to lactic acicosis
- This can result in intracellular contents moving into circulation or translocation of gut bacteria
- Early therapy to prevent irreversible shock
- In dogs need to treat with in 2 hours
- In humans may need more than 4 hours
- Irreversible shock associated with pooling of blood in capillaries
- Vasomotor paralysis
- Hyperpolarization of vascular smooth muscle as depletion of ATP allows K to flowing out from K channels opening. Ca flows out too leading to vasodilation
- Glyburide is an K-ATP channel inhibitor (?) caused increased vasoconstriction and BP
- Pluggin of capillaries by neutrophils
- Cerebral ischemia
- Increased NO generation
- Which Fluids?
- Think of what is lost and replace that.
- Bleeding think blood
- Raise the hct but not above 35
- Acellular blood substitutes, looked bad at the time of this writing
- Di aspirin cross linked hemoglobin had increased 2 and 28 day mortality vs saline
- Colloids sound great but they fail in RCTs
- SAFE
- FEAST
- Points out that saline replaces the interstitial losses why do we think those losses are unimportant
- Pulmonary circulation issue
- Pulmonary circulation is more leaky so oncotic pressure less effective there
- Talks about the lungs be naturally protected from pulmonary edema
- Rate of fluid
- 1-2 liters in first hour
- Suggests CVP or capillary wedge pressure during resuscitation
- No refs in the rate of fluid administration section
- Lactic acidosis
- Points out that HCO can impair lactate utilization
- Also states that arterial pH does not point out what is happening at the tissue level. Suggests mixed-venous sample.
References
Why is Gonorrhea Called the Clap? - Nurx™
Here’s the piece we celebrated from David Goldfarb: The Normal Saline Ceremony - PMC
Potency of Oral Rehydration Solution in Inducing Fluid Absorption is Related to Glucose Concentration | Scientific Reports an interesting report on how
Isotonic versus hypotonic solutions for maintenance intravenous fluid administration in children
Here’s a study in the Lancet that explored use the bicarbonate infusion in severe metabolic acidosis. https://www.sciencedirect.com/science/article/pii/S0140673618310808
Joel briefly reviewed the issues with normal saline vs balanced solution and alluded to some of these reports: SMART Balanced Crystalloids versus Saline in Critically Ill Adults | NEJM And SALT-ED https://www.nejm.org/doi/10.1056/NEJMoa1711586
We did not discuss this article on LR in cirrhotics but this study lower incidence of adverse outcomes and did not show higher lactate levels Lactated Ringer's vs Saline Among Critically Ill Adults With Cirrhosis: A Secondary Analysis of the Isotonic Solutions and Major Adverse Renal Events Trial
Joel mentioned a Cochrane review of albumin that showed increased mortality: Human albumin administration in a critically ill patients: systematic review of randomised controlled trials
The SAFE Trial that exonerated albumin: A Comparison of Albumin and Saline for Fluid Resuscitation in the Intensive Care Unit | NEJM
Intravenous albumin infusion is an effective therapy for hyponatremia in patient with malignant ascites - PMC
JC mentioned this study: Comparison of 5% human albumin and normal saline for fluid resuscitation in sepsis induced hypotension among patients with cirrhosis (FRISC study): a randomized controlled trial and then this one: A randomized-controlled trial comparing 20% albumin to plasmalyte in patients with cirrhosis and sepsis- induced hypotension plus here is the CONFIRM Terlipressin plus Albumin for the Treatment of Type 1 Hepatorenal Syndrome | NEJM and ATTIRE A Randomized Trial of Albumin Infusions in Hospitalized Patients with Cirrhosis | NEJM
Amy taught us that the military do use hetastarch in emergencies- up to 1 liter. Here’s a study that looked at its use. Hydroxyethyl Starch or Saline for Fluid Resuscitation in Intensive Care | NEJM
And here’s a cool resource: Fluid resuscitation in haemorrhagic shock in combat casualties | Disaster and Military Medicine | Full Text
Anna reviewed European guidelines on volume resuscitation- Timing and volume of fluid administration for patients with bleeding - Kwan, I - 2014 | Cochrane Library
The Third International Consensus Definitions for Sepsis and Septic Shock (Sepsis-3) | Critical Care Medicine | JAMA
Studies on the renin-angiotensin-aldosterone system in patients with cirrhosis and ascites: effect of saline and albumin infusion
Anna’s VOG on SIRS being out the door
Outline
Chapter 14
- Hypovolemic States
- Etiology
- True volume depletion occurs when fluid is lost from from the extracellular fluid at a rate exceeding intake
- Can come the GI tract
- Lungs
- Urine
- Sequestration in the body in a “third space” that is not in equilibrium with the extracellular fluid.
- When losses occur two responses ameliorate them
- Our intake of Na and fluid is way above basal needs
- This is not the case with anorexia or vomiting
- The kidney responds by minimizing further urinary losses
- This adaptive response is why diuretics do not cause progressive volume depletion
- Initial volume loss stimulates RAAS, and possibly other compensatory mechanisms, resulting increased proximal and collecting tubule Na reabsorption.
- This balances the diuretic effect resulting in a new steady state in 1-2weeks
- New steady state means Na in = Na out
- GI Losses
- Stomach, pancreas, GB, and intestines secretes 3-6 liters a day.
- Almost all is reabsorbed with only loss of 100-200 ml in stool a day
- Volume depletion can result from surgical drainage or failure of reabsorption
- Acid base disturbances with GI losses
- Stomach losses cause metabolic alkalosis
- Intestinal, pancreatic and biliary secretions are alkalotic so losing them causes metabolic acidosis
- Fistulas, laxative abuse, diarrhea, ostomies, tube drainage
- High content of potassium so associated with hypokalemia
- [This is a mistake for stomach losses]
- Bleeding from the GI tract can also cause volume depletion
- No electrolyte disorders from this unless lactic acidosis
- Renal losses
- 130-180 liters filtered every day
- 98-99% reabsorbed
- Urine output of 1-2 liters
- A small 1-2% decrease in reabsorption can lead to 2-4 liter increase in Na and Water excretion
- 4 liters of urine output is the goal of therapeutic diuresis which means a reduction of fluid reabsorption of only 2%
- Diuretics
- Osmotic diuretics
- Severe hyperglycemia can contribute to a fluid deficit of 8-10 Iiters
- CKD with GFR < 25 are poor Na conservers
- Obligate sodium losses of 10 to 40 mEq/day
- Normal people can reduce obligate Na losses down to 5 mEq/day
- Usually not a problem because most people eat way more than 10-40 mEq of Na a day.
- Salt wasting nephropathies
- Water losses of 2 liters a day
- 100 mEq of Na a day
- Tubular and interstitial diseases
- Medullary cystic kidney
- Mechanism
- Increased urea can be an osmotic diuretic
- Damage to tubular epithelium can make it aldo resistant
- Inability to shut off natriuretic hormone (ANP?)
- The decreased nephro number means they need to be able to decrease sodium reabsorption per nephron. This may not be able to be shut down acutely.
- Experiment, salt wasters can stay in balance if sodium intake is slowly decreased. (Think weeks)
- Talks about post obstruction diuresis
- Says it is usually appropriate rather than inappropriate physiology.
- Usually catch up solute and water clearance after releasing obstruction
- Recommends 50-75/hr of half normal saline
- Talks briefly about DI
- Skin and respiratory losses
- 700-1000 ml of water lost daily by evaporation, insensible losses (not sweat)
- Can rise to 1-2 liters per hour in dry hot climate
- 30-50 mEq/L Na
- Thirst is primary compensation for this
- Sweat sodium losses can result in hypovolemia
- Burns and exudative skin losses changes the nature of fluid losses resulting in fluid losses more similar to plasma with a variable amount of protein
- Bronchorrhea
- Sequestration into a third space
- Volume Deficiency produced by the loss of interstitial and intravascular fluid into a third space that is not in equilibrium with the extracellular fluid.
- Hip fracture 1500-2000 into tissues adjacent to fxr
- Intestinal obstruction, severe pancreatitis, crush injury, bleeding, peritonitis, obstruction of a major venous system
- Difference between 3rd space and cirrhosis ascities
- Rate of accumulation, if the rate is slow enough there is time for renal sodium and water compensation to maintain balance.
- So cirrhotics get edema from salt retension and do not act as hypovolemia
- Hemodynamic response to volume depletion
- Initial volume deficit reduced venous return to heart
- Detected by cardiopulmonary receptors in atria and pulmonary veins leading to sympathetic vasoconstriction in skin and skeletal muscle.
- More marked depletion will result in decreased cardiac output and decrease in BP
- This drop in BP is now detected by carotid and aortic arch baroreceptors resulting in splanchnic and renal circulation vasoconstriction
- This maintains cardiac and cerebral circulation
- Returns BP toward normal
- Increase in BP due to increased venous return
- Increased cardiac contractility and heart rate
- Increased vascular resistance
- Sympathetic tone
- Renin leading to Ang2
- These can compensate for 500 ml of blood loss (10%)
- Unless there is autonomic dysfunction
- With 16-25% loss this will not compensate for BP when patient upright
- Postural dizziness
- Symptoms
- Three sets of symptoms can occur in hypovolemic patients
- Those related to the manner in which the fluid loss occurs
- Vomiting
- Diarrhea
- Polyuria
- Those due to volume depletion
- Those due to the electrode and acid base disorders that can accompany volume depletion
- The symptoms of volume depletion are primarily related to the decrease in tissue perfusion
- Early symptoms
- Lassitude
- Fatiguability
- Thirst
- Muscle cramps
- Postural dizziness
- As it gets more severe
- Abdominal pain
- Chest pain
- Lethargy
- Confusion
- Symptomatic hypovolemia is most common with isosmotic Na and water depletion
- In contrast pure water loss, causes hypernatremia, which results in movement of water from the intracellular compartment to the extracellular compartment, so that 2/3s of volume loss comes from the intracellular compartment, which minimizes the decrease in perfusion
- Electrolyte disorders and symptoms
- Muscle weakness from hypokalemia
- Polyuria/poly dips is from hyperglycemia and hypokalemia
- Lethargy, confusion, Seizures, coma from hyponatremia, hypernatremia, hyperglycemia
- Extreme salt craving is unique to adrenal insufficiency
- Eating salt off hands ref 18
- Evaluation of the hypovolemic patient
- Know that if the losses are insensible then the sodium should rise
- Volume depletion refers to extracellular volume depletion of any cause, while dehydration refers to the presence of hypernatremia due to pure water loss. Such patients are also hypovolemic.
- Physical exam is insensitive and nonspecific
- Finding most sensitive and specific finding for bleeding is postural changes in blood pressure
- I don’t find this very specific at all!
- Recommends laboratory confirmation regardless of physical exam
- Skin and mucous membranes
- Should return too shape quickly
- Elastic property is called Turgur
- Not reliable is patients older than 55 to 60
- Dry axilla
- Dry mucus membranes
- Dark skin in Addison’s disease Frim increased ACTH
- Arterial BP
- As volume goes down so does arterial BP
- Marked fluid loss leads to quiet korotkoff signs
- Interpret BP in terms of the patients “normal BP”
- Venous pressure
- Best done by looking at the JVP
- Right atrial and left atrial pressure
- LV EDP is RAP + 5 mmHg
- Be careful if valvular disease, right heart failure, cor pulmonare,
- Figure 14-2
- Shock
- 30% blood loss
- Lab Data
- Urine Na concentration
- Should be less than 25 mmol/L, can go as low as 1 mmol/L
- Metabolic alkalosis can throw this off
- Look to the urine chloride
- Figure 14-3
- Renal artery stenosis can throw this off
- FENa
- Mentions that it doesn’t work so well at high GFR
- Urine osmolality
- Indicates ADH
- Volume depletion often associated with urine osm > 450
- Impaired by
- Renal disease
- Osmotic diuretic
- Diuretics
- DI
- Mentions that severe volume depletion and hypokalemia impairs urea retension in renal medulla
- Points out that isotonic urine does not rule out hypovolemia
- Mentions specific gravity
- BUN and Cr concentration
- Normal ratio is 10:1
- Volume depletion this goes to 20:1
- Serum Na
- Talks about diarrhea
- Difference between secretory diarrhea which is isotonic and just causes hypovolemia
- And osmotic which results in a lower electrolyte content and development of hypernatremia
- Talks about hyperglycemia
- Also can cause the sodium to rise from the low electrolyte content of the urine
- But the pseudohyponatraemia can protect against this
- Plasma potassium
- Treatment
- Both oral and IV treatment can be used for volume replacement
- The goal of therapy are to restore normovolemia
- And to correct associated acid-base and electrolyte disorders
- Oral Therapy
- Usually can be accomplished with increased water and dietary sodium
- May use salt tablets
- Glucose often added to resuscitation fluids
- Provides calories
- Promotes intestinal Na reabsorption since there is coupled Na and Glucose similar to that seen in the proximal tubule
- Rice based solutions provide more calories and amino acids which also promote sodium reabsorption
- 80g/L of glucose with rice vs 20 g/L with glucose alone
- IV therapy
- Dextrose solutions
- Physiologically equivalent to water
- For correcting hypernatremia
- For covering insensible losses
- Watch for hyperglycemia
- Footnote warns against giving sterile water
- Saline solutions
- Most hypovolemic patients have a water and a sodium deficit
- Isotonic saline has a Na concentration of 154, similar to that of plasma see page 000
- Half-isotonic saline is equivalent to 550 ml of
isotonic saline and 500 of free water. Is that a typo?
- 3% is a liter of hypertonic saline and 359 extra mEq of Na
- Dextrose in saline solutions
- Give a small amount of calories, otherwise useless
- Alkalinizing solutions
- 7.5% NaHCO3 in 50 ml ampules 44 mEq of Na and 44 mEq of HCO3
- Treat metabolic acidosis or hyperkalemia
- Why 44 mEq and not 50?
- Do not give with calcium will form insoluble CaCO3
- Polyionic solutions
- Ringers contains physiologic K and Ca
- Lactated Ringers adds 28 mEq of lactate
- Spreads myth of LR in lactic acidosis
- Potassium chloride
- Available as 2 mEq/mL
- Do not give as a bolus as it can cause fatal hyperkalemia
- Plasma volume expanders
- Albumin, polygelastins, hetastarch are restricted to vascular space
- 25% albumin can pull fluid into the vascular space
- 25% albumin is an albumin concentration of 25 g/dL compare to physiologic 4 g/dL
- Says it pulls in several times its own volume
- 5% albumin is like giving plasma
- Blood
- Which fluid?
- Look at osmolality, give hypotonic fluids to people with high osmolality
- Must include all electrolytes
- Example of adding 77 mEw of K to 0.45 NS and making it isotonic
- DI can be replaced with dextrose solutions, pure water deficit
- Case 14-3
- Diarrhea with metabolic acidosis
- He chooses 0.25 NS with 44 mEq of NaCl and 44 NaHCO3
- Talks about blood and trauma
- Some studies advocate delaying saline until penetrating trauma is corrected APR about to. Keep BP low to prevent bleeding. Worry about diluting coagulation factors
- Only do this if the OR is quickly available
- Volume deficit
- Provides formula for water deficit and sodium deficit
- Do not work for isotonic losses
- Provides a table to adjust fluid loss based on changes in Hgb or HCTZ
- Says difficult to estimate it from lab findings and calculations
- Follow serial exams
- Serial urine Na
- Rate of replacement
- Goal is not to give fluid but to induce a positive balance
- Suggests 50-100 ml/hr over what is coming out of the body
- Urine
- Insensibles 30-50
- Diarrhea
- Tubes
- Hypovolemic shock
- Due to bleeding
- Sequesting in third space
- Why shock?
- Progressive volume depletion leads to
- Increased sympathetic NS
- Increased Ang 2
- Initially this maintains BP, cerebral and coronary circulation
- But this can decrease splanchnic, renal and mucocutaneous perfusion
- This leads to lactic acicosis
- This can result in intracellular contents moving into circulation or translocation of gut bacteria
- Early therapy to prevent irreversible shock
- In dogs need to treat with in 2 hours
- In humans may need more than 4 hours
- Irreversible shock associated with pooling of blood in capillaries
- Vasomotor paralysis
- Hyperpolarization of vascular smooth muscle as depletion of ATP allows K to flowing out from K channels opening. Ca flows out too leading to vasodilation
- Glyburide is an K-ATP channel inhibitor (?) caused increased vasoconstriction and BP
- Pluggin of capillaries by neutrophils
- Cerebral ischemia
- Increased NO generation
- Which Fluids?
- Think of what is lost and replace that.
- Bleeding think blood
- Raise the hct but not above 35
- Acellular blood substitutes, looked bad at the time of this writing
- Di aspirin cross linked hemoglobin had increased 2 and 28 day mortality vs saline
- Colloids sound great but they fail in RCTs
- SAFE
- FEAST
- Points out that saline replaces the interstitial losses why do we think those losses are unimportant
- Pulmonary circulation issue
- Pulmonary circulation is more leaky so oncotic pressure less effective there
- Talks about the lungs be naturally protected from pulmonary edema
- Rate of fluid
- 1-2 liters in first hour
- Suggests CVP or capillary wedge pressure during resuscitation
- No refs in the rate of fluid administration section
- Lactic acidosis
- Points out that HCO can impair lactate utilization
- Also states that arterial pH does not point out what is happening at the tissue level. Suggests mixed-venous sample.
References
JCI - Phenotypic and pharmacogenetic evaluation of patients with thiazide-induced hyponatremia and a nice review of this topic: Altered Prostaglandin Signaling as a Cause of Thiazide-Induced Hyponatremia
The electrolyte concentration of human gastric secretion. https://physoc.onlinelibrary.wiley.com/doi/10.1113/expphysiol.1960.sp001428
A classic by Danovitch and Bricker: Reversibility of the “Salt-Losing” Tendency of Chronic Renal Failure | NEJM
Osmotic Diuresis Due to Retained Urea after Release of Obstructive Uropathy | NEJM
Is This Patient Hypovolemic? | Cardiology | JAMA
And by the same author, a textbook: Steven McGee. 5th edition. Evidence-Based Physical Diagnosis Elsevier Philadelphia 2022. ISBN-13: 978-0323754835
The clinical course and pathophysiological investigation of adolescent gestational diabetes insipidus: a case report | BMC Endocrine Disorders
Sensitivity and specificity of clinical signs for assessment of dehydration in endurance athletes | British Journal of Sports Medicine
Diagnostic performance of serum blood urea nitrogen to creatinine ratio for distinguishing prerenal from intrinsic acute kidney injury in the emergency department | BMC Nephrology
The meaning of the blood urea nitrogen/creatinine ratio in acute kidney injury - PMC
Language guiding therapy: the case for dehydration vs volume depletion https://www.acpjournals.org/doi/10.7326/0003-4819-127-9-199711010-00020?url_ver=Z39.88-2003&rfr_id=ori:rid:crossref.org&rfr_dat=cr_pub%20%200pubmed
Validation of a noninvasive monitor to continuously trend individual responses to hypovolemia
References for Anna’s voice of God on Third Spacing : Shires Paper from 1964 (The ‘third space’ – fact or fiction? )
References for melanie’s VOG:
1. Appraising the Preclinical Evidence of the Role of the Renin-Angiotensin-Aldosterone System in Antenatal Programming of Maternal and Offspring Cardiovascular Health Across the Life Course: Moving the Field Forward: A Scientific Statement From the American Heart Association
2. excellent review of RAAS in pregnancy: The enigma of continual plasma volume expansion in pregnancy: critical role of the renin-angiotensin-aldosterone system
https://journals-physiology-org.ezp-prod1.hul.harvard.edu/doi/full/10.1152/ajprenal.00129.2016
3. 10.1172/JCI107462- classic study in JCI of AngII responsiveness during pregnancy
4. William’s Obstetrics 26th edition!
5. Feto-maternal osmotic balance at term. A prospective observational study
References
JC mentioned that the diagnostic accuracy of 24 hour urine collection increases with more collections! Metabolic evaluation of patients with recurrent idiopathic calcium nephrolithiasis
We didn't refer to a particular study on sodium intake and the 24 hour urine but this meta-analysis Comparison of 24‐hour urine and 24‐hour diet recall for estimating dietary sodium intake in populations: A systematic review and meta‐analysis - PMC 24‐hour diet recall underestimated population mean sodium intake.
Anna looking up ace i and urinary sodium Effects of ACE inhibition on proximal tubule sodium transport | American Journal of Physiology-Renal Physiology
The original FENa paper by Espinel: The FeNa Test: Use in the Differential Diagnosis of Acute Renal Failure | JAMA | JAMA Network
Schreir’s replication and expansion of Espinel’s data: Urinary diagnostic indices in acute renal failure: a prospective study
Here’s a report from our own JC on the Diagnostic Utility of Serial Microscopic Examination of the Urinary Sediment in Acute Kidney Injury | American Society of Nephrology
JC shared his journey regarding FENa and refers to his recent paper Concomitant Identification of Muddy Brown Granular Casts and Low Fractional Excretion of Urinary Sodium in AKI
And Melanie’s accompanying editorial Mind the Cast: FENa versus Microscopy in AKI : Kidney360 (with a great image from Samir Parikh)
JC referenced this study from Schrier on FENa with a larger series: Urinary diagnostic indices in acute renal failure: a prospective study
Nonoliguric Acute Renal Failure Associated with a Low Fractional Excretion of Sodium | Annals of Internal Medicine
Urine sodium concentration to predict fluid responsiveness in oliguric ICU patients: a prospective multicenter observational study | Critical Care | Full Text
A classic favorite: Acute renal success. The unexpected logic of oliguria in acute renal failure
Marathon runners had granular casts in their urine without renal failure. Kidney Injury and Repair Biomarkers in Marathon Runners
Cute piece from Rick Sterns on urine electrolytes! Managing electrolyte disorders: order a basic urine metabolic panel
The Urine Anion Gap: Common Misconceptions | American Society of Nephrology
The urine anion gap in context CJASN
Excellent review from Halperin on urine chemistries (including some consideration of the TTKG): Use of Urine Electrolytes and Urine Osmolality in the Clinical Diagnosis of Fluid, Electrolytes, and Acid-Base Disorders - Kidney International Reports
Renal tubular acidosis (RTA): Recognize The Ammonium defect and pHorget the urine pH | SpringerLink
Outline
Chapter 13
- New part: Part 3, Physiologic approach to acid-base and electrolyte disorders
- Do you remember the previous two parts?
- Renal physiology
- Regulation of water and electrolyte balance
- Chapter 13: Meaning and application of urine chemistries
- Measurement of urinary electrolyte concentrations, osmolality and pH helps diagnose some conditions
- There are no fixed normal values
- Kidney varies rate of excretion to match intake and endogenous production
- Example: urine Na of 125/day can be normal if patient euvolemic on a normal diet, and wildly inappropriate in a patient who is volume depleted.
- Urine chemistries are:
- Useful
- Simple
- Widely available
- Usually a random sample is adequate
- 24-hour samples give additional context
- Gives example of urinary potassium, with extra renal loss of K, urine K should be < 25, but if the patient has concurrent volume deficiency and urine output is only 500 mL, then urine K concentration can appropriately be as high as 40 mEq/L
- Table 13-1
- Seems incomplete, see my notes on page 406
- What is Gravity ARF?
- Sodium Excretion
- Kidney varies Na to maintain effective circulating volume (I’d say volume homeostasis)
- Urine Na affected by RAAS and ANP
- Na concentration can be used to determine volume status
- Urine Na < 20 is hypovolemia
- Says it is especially helpful in determining the etiology of hyponatremia
- Calls out SIADH and volume depletion
- Used 40 mEq/L for SIADH
- Also useful in AKI
- Where differential is pre-renal vs ATN
- In addition to urine Na (and FENa) look at urine osmolality
- Again uses 40 mEq/l
- Mentions FENa and urine osmolality
- Urine Na can estimate dietary sodium intake
- Suggests doing this during treatment of hypertension to assure dietary compliance
- 24 hour urine Na is accurate with diuretics as long as the dose is stable and the drugs are chronic
- Diuretics increase Na resorption in other segments of the tubule that are not affected by the diuretic
- Points to increased AT2 induced proximal Na resorption and aldosterone induced DCT resoprtion
- In HTN shoot for less than 100 mEq/Day
- Urine Na useful in stones
- Urine uric acid and urine Ca can cause stones and their handling is dependent on sodium
- Low sodium diet can mask elevated excretion of these stone forming metabolites
- 24-hour Na > 75 and should be enough sodium to avoid this pitfall
- Pitfalls
- Low urine sodium in bilateral renal artery stenosis or acute GN
- High urine sodium with diuretics, aldo deficiency, advanced CKD
- Altered water handling can also disrupt this
- DI with 10 liters of urine and urine sodium excretion of 100 mEq is 10 mEq/L but in this case there is no volume deficiency
- Opposite also important, a lot of water resorption can mask volume deficiency by jacking up the urine sodium
- Advises you to use the FENa
- THE FENA
- < 1% dry
- >2-3% ATN
- It will fail with chronic effective volume depletion
- Heart failure, cirrhosis, and burns
- Suggests that tubular function will be preserved in those situations
- Also with contrast, rhabdo, pigment nephropathy
- Limitations
- Dependent on the amount of Na filtered
- Goes through the math of a normal person with GFR of 125/min and Na of 150 has filtered sodium of 27,000/day so if they eat 125-250 mEq their FENa will be <1%
- Talks about diuretics
- Can use FE lithium
- Mainly reabsorbed in the proximal tubule
- Not affected by loop diuretics
- 20% in healthy controls
- <15% in pre-renal disease
- Can use FE Uric acid
- Also not affected by loop diuretics
- Below 12% is pre-renal
- No FEUrea
- Chloride excretion
- Urine Cl and Na usually move in parallel
- However as many as 30% of hypovolemic patients have more than a 15 mEq/L difference between urine Na and Cl
- Due to Na excretion with another anion, HCO3 or carbenicillin or Cl with another cation, NH4+
- Discusses the metabolic alkalosis issue
- Says the urine Na can be over 100 in volume depleted patients with metabolic alkalosis!
- In metabolic acidosis (normal anion gap)
- Urine Cl should rise to balance out the NH4
- RTA should also have urine pH > 5.3
- Potassium excretion
- Can go as low at 5-25/day
- Low in extra renal losses
- Or after the diuretics have worn off
- More than 25/day indicates renal losses
- Not so helpful in hyperkalemia since chronic hyperkalemia is always due to a defect renal potassium excretion
- Expect always to have inappropriately low K with hyperkalemia due to
- Renal failure
- Hypoaldo
- Urine osmolality
- In hyponatremia it should < 100
- Hyponatremia here should be due to excessive water intake
- In hypernatremia it should be > 600-800
- Urine osm < plasma osm in face of hypernatremia indicates renal water loss due to lack of or resistance to ADH
- In ATN urine OSM < 400
- In pre-renal disease it could be over 500
- Specific but not sensitive due to people with CKD who are unable to concentrate urine
- Specific gravity
- Plasma is 8-10% igher than plasma so specific gravity is 1.008 to 1.010
- Every 30-35 mOsm/L raises urine Osm of 0.001
- so 1.010 is 300-350 mOsm/L H2O
- Glucose raises urine specific gravity more than osmolality
- Same with contrast
- Carbenicillin
- pH
- Normally varies with systemic acid-base status
- PH should fall before 5.3 (usually below 5.0) with systemic metabolic acidosis
- Above 5.3 in adults and 5.6 in children indicate RTA
- PH goal 6.0-6.5
- Separate individual RTAs through FR of HCO3 at various serum HCO3 levels
- Also can monitor urine pH to look for success in treating metabolic alkalosis
- Look for pH > 7
- In treatment of uric acid stone disease
- Want to shift eq: H + urate – <=> uric acid to the left because urate is more soluble
- PH goal 6.0-6.5
References
We considered the complexity of the machinery to excrete ammonium in the context of research on dietary protein and how high protein intake may increase glomerular pressure and contribute to progressive renal disease (many refer to this as the “Brenner hypothesis”). Dietary protein intake and the progressive nature of kidney disease: the role of hemodynamically mediated glomerular injury in the pathogenesis of progressive glomerular sclerosis in aging, renal ablation, and intrinsic renal disease
A trial that studied low protein and progression of CKD The Effects of Dietary Protein Restriction and Blood-Pressure Control on the Progression of Chronic Renal Disease
(and famously provided data for the MDRD eGFR equation A more accurate method to estimate glomerular filtration rate from serum creatinine: a new prediction equation. Modification of Diet in Renal Disease Study Group
We wondered about dietary recommendations in CKD. of note, this is best done in the DKD guidelines from KDIGO Executive summary of the 2020 KDIGO Diabetes Management in CKD Guideline: evidence-based advances in monitoring and treatment.
Joel mentioned this study on red meat and risk of ESKD. Red Meat Intake and Risk of ESRD
We referenced the notion of a plant-based diet. This is an excellent review by Deborah Clegg and Kathleen Hill Gallant. Plant-Based Diets in CKD : Clinical Journal of the American Society of Nephrology
Here’s the review that Josh mentioned on how the kidney appears to sense pH Molecular mechanisms of acid-base sensing by the kidney
Remarkably, Dr. Dale Dubin put a prize in his ECG book Free Car Prize Hidden in Textbook Read the fine print: Student wins T-bird
A review of the role of the kidney in DKA: Diabetic ketoacidosis: Role of the kidney in the acid-base homeostasis re-evaluated
Josh mentioned the effects of infusing large amounts of bicarbonate The effect of prolonged administration of large doses of sodium bicarbonate in man and this study on the respiratory response to a bicarbonate infusion: The Acute Effects In Man Of A Rapid Intravenous Infusion Of Hypertonic Sodium Bicarbonate Solution. Ii. Changes In Respiration And Output Of Carbon Dioxide
This is the study of acute respiratory alkalosis in dogs: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC293311/?page=1
And this is the study of medical students who went to the High Alpine Research Station on the Jungfraujoch in the Swiss Alps https://www.nejm.org/doi/full/10.1056/nejm199105163242003
Self explanatory! A group favorite! It Is Chloride Depletion Alkalosis, Not Contraction Alkalosis
Effects of chloride and extracellular fluid volume on bicarbonate reabsorption along the nephron in metabolic alkalosis in the rat. Reassessment of the classical hypothesis of the pathogenesis of metabolic alkalosis
A review of pendrin’s role in volume homeostasis: The role of pendrin in blood pressure regulation | American Journal of Physiology-Renal Physiology
Infusion of bicarbonate may lead to a decrease in respiratory stimulation but the shift of bicarbonate to the CSF may lag. Check out this review Neural Control of Breathing and CO2 Homeostasis and this classic paper Spinal-Fluid pH and Neurologic Symptoms in Systemic Acidosis.
Outline
Outline: Chapter 11
- Regulation of Acid-Base Balance
- Introduction
- Bicarb plus a proton in equilibrium with CO2 and water
- Can be rearranged to HH
- Importance of regulating pCO2 and HCO3 outside of this equation
- Metabolism of carbs and fats results in the production of 15,000 mmol of CO2 per day
- Metabolism of protein and other “substances” generates non-carbonic acids and bases
- Mostly from sulfur containing methionine and cysteine
- And cationic arginine and lysine
- Hydrolysis of dietary phosphate that exists and H2PO4–
- Source of base/alkali
- Metabolism of an ionic amino acids
- Glutamate and asparatate
- Organic anions going through gluconeogenesis
- Glutamate, Citrate and lactate
- Net effect on a normal western diet 50-100 mEq of H+ per day
- Homeostatic response to these acid-base loads has three stages:
- Chemical buffering
- Changes in ventilation
- Changes in H+ excretion
- Example of H2SO4 from oxidation of sulfur containing AA
- Drop in bicarb will stimulate renal acid secretion
- Nice table of normal cid-base values, arterial and venous
- Great 6 bullet points of acid-base on page 328
- Kidneys must excrete 50-100 of non-carbonic acid daily
- This occurs by H secretion, but mechanisms change by area of nephron
- Not excreted as free H+ due to minimal urine pH being equivalent to 0.05 mmol/L
- No H+ can be excreted until virtually all of th filtered bicarb is reabsorbed
- Secreted H+ must bind buffers (phosphate, NH3, cr)
- PH is main stimulus for H secretion, though K, aldo and volume can affect this.
- Renal Hydrogen excretion
- Critical to understand that loss of bicarb is like addition of hydrogen to the body
- So all bicarb must be reabsorbed before dietary H load can be secreted
- GFR of 125 and bicarb of 24 results in 4300 mEq of bicarb to be reabsorbed daily
- Reabsorption of bicarb and secretion of H involve H secretion from tubular cells into the lumen.
- Thee initial points need to be emphasized
- Secreted H+ ion are generated from dissociation of H2O
- Also creates OH ion
- Which combine with CO2 to form HCO3 with the help of zinc containing intracellular carbonic anhydrase.
- This is how the secretion of H+ which creates an OH ultimately produces HCO3
- Different mechanisms for proximal and distal acidification
- NET ACID EXCRETION
- Free H+ is negligible
- So net H+ is TA + NH4 – HCO3 loss
- Unusually equal to net H+ load, 50-100 mEq/day
- Can bump up to 300 mEq/day if acid production is increased
- Net acid excretion can go negative following a bicarb or citrate load
- Proximal Acidification
- Na-H antiporter (or exchanger) in luminal membrane
- Basolateral membrane has a 3 HCO3 Na cotransporter
- This is electrogenic with 3 anions going out and only one cation
- The Na-H antiporter also works in the thick ascending limb of LOH
- How about this, there is also a H-ATPase just like found in the intercalated cells in the proximal tubule and is responsible for about a third of H secretion
- And similarly there is also. HCO3 Cl exchanger (pendrin-like) in the proximal tubule
- Footnote says the Na- 3HCO3 cotransporter (which moves sodium against chemical gradient NS uses negative charge inside cell to power it) is important for sensing acid-base changes in the cell.
- Distal acidification
- Occurs in intercalated cells of of cortical and medullary collecting tubule
- Three main characteristics
- H secretion via active secretory pumps in the luminal membrane
- Both H-ATPase and H-K ATPase
- H- K ATPase is an exchange pump, k reabsorption
- H-K exchange may be more important in hypokalemia rather than in acid-base balance
- Whole paragraph on how a Na-H exchanger couldn’t work because the gradient that H has to be pumped up is too big.
- H-ATPase work like vasopressin with premise H-ATPase sitting on endocarditis vesicles a=which are then inserted into the membrane. Alkalosis causes them to be recycled out of the membrane.
- H secretory cells do not transport Na since they have few luminal Na channels, but are assisted by the lumen negative tubule from eNaC.
- Minimizes back diffusion of H+ and promotes bicarb resorption
- Bicarbonate leaves the cell through HCO3-Cl exchanger which uses the low intracellular Cl concentration to power this process.
- Same molecule is found on RBC where it is called band 3 protein
- Figure 11-5 is interesting
- Bicarbonate resorption
- 90% in the first 1-22 mm of the proximal tubule (how long is the proximal tubule?)
- Lots of Na-H exchangers and I handed permeability to HCO3 (permeability where?)
- Last 10% happens distally mostly TAL LOH via Na-H exchange
- And the last little bit int he outer medullary collecting duct.
- Carbonic anhydrase and disequilibrium pH
- CA plays central role in HCO3 reabsorption
- After H is secreted in the proximal tubule it combines with HCO# to form carbonic acid. CA then dehydrates it to CO2 and H2O. (Step 2)
- Constantly moving carbonic acid to CO2 and H2O keeps hydrogen combining with HCO3 since the product is rapidly consumed.
- This can be demonstrated by the minimal fall in luminal pH
- That is important so there is not a luminal gradient for H to overcome in the Na-H exchanger (this is why we need a H-ATPase later)
- CA inhibitors that are limited tot he extracellular compartment can impair HCO3 reabsorption by 80%.
- CA is found in S1, S2 but not S3 segment. See consequence in figure 11-6.
- The disequilibrium comes from areas where there is no CA, the HH formula falls down because one of the assumptions of that formula is that H2CO3 (carbonic acid) is a transient actor, but without CA it is not and can accumulate, so the pKa is not 6.1.
- Bicarbonate secretion
- Type B intercalated cells
- H-ATPase polarity reversed
- HCO3 Cl exchanger faces the apical rather than basolateral membrane
- Titratable acidity
- Weak acids are filtered at the glom and act as buffers in the urine.
- HPO4 has PKA of 6.8 making it ideal
- Creatinine (pKa 4.97) and uric acid (pKa 5.75) also contribute
- Under normal cinditions TA buffers 10-40 mEa of H per day
- Does an example of HPO4(2-):H2PO4 (1-) which exists 4:1 at pH of 7.4 (glomerular filtrate)
- So for 50 mEq of Phos 40 is HPO4 and 10 is H2PO4
- When pH drops to 6.8 then the ratio is 1:1 so for 50
- So the 50 mEq is 25 and 25, so this buffered an additional 15 mEq of H while the free H+ concentration increased from 40 to 160 nanomol/L so over 99.99% of secreted H was buffered
- When pH drops to 4.8 ratio is 1:100 so almost all 50 mEq of phos is H2PO4 and 39.5 mEq of H are buffered.
- Acid loading decreases phosphate reabsorption so more is there to act as TA.
- Decreases activity of Na-phosphate cotransporter
- DKA provides a novel weak acid/buffer beta-hydroxybutyrate (pKa 4.8) which buffers significant amount of acid (50 mEq/d).
- Ammonium Excretion
- Ability to excrete H+ as ammonium ions adds an important amount of flexibility to renal acid-base regulation
- NH3 and NH4 production and excretion can be varied according to physiologic need.
- Starts with NH3 production in tubular cells
- NH3, since it is neutral then diffuses into the tubule where it is acidified by the low pH to NH4+
- NH4+ is ionized and cannot cross back into the tubule cells(it is trapped in the tubular fluid)
- This is important for it acting as an important buffer eve though the pKa is 9.0
- At pH of 6.0 the ratio of NH3 to NH4 is 1:1000
- As the neutral NH3 is converted to NH4 more NH3 from theintracellular compartment flows into the tubular fluid replacing the lost NH3. Rinse wash repeat.
- This is an over simplification and that there are threemajor steps
- NH4 is produced in early proximal tubular cells
- Luminal NH4 is partially reabsorbed in the TAL and theNH3 is then recycled within the renal medulla
- The medullary interstitial NH3 reaches highconcentrations that allow NH3 to diffuse into the tubular lumen in the medullary collecting tubule where it is trapped as NH4 by secreted H+
- NH4 production from Glutamine which converts to NH4 and glutamate
- Glutamate is converted to alpha-ketoglutarate
- Alpha ketoglutarate is converted to 2 HCO3 ions
- HCO3 sent to systemic circulation by Na-3 HCO3 transporter
- NH4 then secreted via Na-H exchanger into the lumen
- NH4 is then reabsorbed by NaK2Cl transporter in TAL
- NH4 substitutes for K
- Once reabsorbed the higher intracellular pH causes NH4 to convert to NH3 and the H that is removed is secreted through Na-H exchanger to scavenge the last of the filtered bicarb.
- NH3 diffuses out of the tubular cells into the interstitium
- NH4 reabsorption in the TAL is suppressed by hyperkalemia and stimulated by chronic metabolic acidosis
- NH4 recycling promotes acid clearance
- The collecting tubule has a very low NH3 concentration
- This promotes diffusion of NH3 into the collecting duct
- NH3 that goes there is rapidly converted to NH4 allowing more NH3 to diffuse in.
- Response to changes in pH
- Increased ammonium excretion with two processes
- Increased proximal NH4 production
- This is delayed 24 hours to 2-3 days depending on which enzyme you look at
- Decreased urine pH increases diffusion of ammonia into the MCD
- Occurs with in hours of an acid load
- Peak ammonium excretion takes 5-6 days! (Fig 11-10)
- Glutamine is picked up from tubular fluid but with acidosis get Na dependent peritublar capillary glutamine scavenging too
- Glutamine metabolism is pH dependent with increase with academia and decrease with alkalemia
- NH4 excretion can go from 30-40 mEq/day to > 300 with severe metabolic acidosis (38 NaBicarb tabs)
- Says each NH4 produces equimolar generation of HCO3 but I thought it was two bicarb for every alpha ketoglutarate?
- The importance of urine pH
- Though the total amount of hydrogren cleared by urine pH is insignificant, an acidic urine pH is essential for driving the reactions of TA and NH4 forward.
- Regulation of renal hydrogen excretion
- Net acid excretion vary inverse with extracellular pH
- Academia triggers proximal and distal acidification
- Proximally this:
- Increased Na-H exchange
- Increased luminal H-ATPase activity
- Increased Na:3HCO3 cotransporter on the basolateral membrane
- Increased NH4 production from glutamine
- In the collecting tubules
- Increased H-ATPase
- Reduction of tubular pH promotes diffusion of NH3 which gets converted to NH4…ION TRAPPING
- Extracellular pH affects net acid excretion through its affect on intracellular pH
- This happens directly with respiratory disorders due to movement of CO2 through the lipid bilayer
- In metabolic disorders a low extracellular bicarb with cause bicarb to diffuse out of the cell passively, this lowers intracellular pH
- If you manipulate both low pCO2 and low Bicarb to keep pH stable there will be no change in the intracellular pH and there is no change in renal handling of acid. It is intracellular pH dependent
- Metabolic acidosis
- Ramps up net acid secretion
- Starts within 24 hours and peaks after 5-6 days
- Increase net secretion comes from NH4
- Phosphate is generally limited by diet
- in DKA titratable acid can be ramped up
- Metabolic alkalosis
- Alkaline extracellular pH
- Increased bicarb excretion
- Decrease reabsorption
- HCO3 secretion (pendrin) in cortical collecting tubule
- Occurs in cortical intercalated cells able to insert H-ATPase in basolateral cells (rather than luminal membrane)
- Normal subjects are able to secrete 1000 mmol/day of bicarb
- Maintenance of metabolic alkalosis requires a defect which forces the renal resorption of bicarb
- This can be chloride/volume deficiency
- Hypokalemia
- Hyperaldosteronism
- Respiratory acidosis and alkalosis
- PCO2 via its effect on intracellular pH is an important determinant of renal acid handling
- Ratios he uses:
- 3.5 per 10 for respiratory acidosis
- 5 per 10 for respiratory alkalosis
- Interesting paragraph contrasting the response to chronic metabolic acidosis vs chronic respiratory acidosis
- Less urinary ammonium in respiratory acidosis
- Major differences in proximal tubule cell pH
- In metabolic acidosis there is decreased bicarb load so less to be reabsorbed proximally
- In respiratory acidosis the increased serum bicarb increases the amount of bicarb that must be reabsorbed proximally
- The increased activity of Na-H antiporter returns tubular cell pH to normal and prevents it from creating increased urinary ammonium
- Mentions that weirdly more mRNA for H-Na antiporter in metabolic acidosis than in respiratory acidosis
- Net hydrogen excretion varies with effective circulating volume
- Starts with bicarb infusions
- Normally Tm at 26
- But if you volume deplete the patient with diuretics first this increases to 35+
- Four factors explain this increased Tm for bicarb with volume deficiency
- Reduced GFR
- Activation of RAAS
- Ang2 stim H-Na antiporter proximally
- Ang2 also stimulates Na-3HCO3 cotransporter on basolateral membrane
- Aldosterone stimulates H-ATPase in distal nephron
- ALdo stimulates Cl HCO3 exchanger on basolateral membrane
- Aldo stimulates eNaC producing tubular lumen negative charge to allow H secretion to occur and prevents back diffusion
- Hypochloremia
- Increases H secretion by both Na-dependent and Na-independent methods
- If Na is 140 and Cl is 115, only 115 of Na can be reabsorbed as NaCl, the remainder must be reabsorbed with HCO3 or associated with secretion of K or H to maintained electro neutrality
- This is enhanced with hypochloridemia
- Concurrent hypokalemia
- Changes in K lead to trans cellular shifts that affect inctracellular pH
- Hypokalemia causes K out, H in and in the tubular cell the cell acts if there is systemic acidosis and increases H secretion (and bicarbonate resorption)
- PTH
- Decreases proximal HCO3 resorption
- Primary HyperCard as cause of type 2 RTA
- Does acidosis stim PTH or does PTH stim net acid excretion
The Channelers went where no nephrology podcasters have gone before, recording in front of a live audience at the National Kidney Foundation Clinical Meeting in Austin. We had all eight Channelers doing a live podcast.
We did a Freely Filtered-inspired draft of the best diuretics.
The draft order:
Leticia Rolon
Anna Gaddy
Joel Topf
Roger Rodby
Josh Waitzman
Amy Yau
JC Velez
And Melanie Hoenig
References
JC
Tolvaptan in Later-Stage Autosomal Dominant Polycystic Kidney Disease
Intravenous conivaptan for the treatment of hyponatraemia caused by the syndrome of inappropriate secretion of antidiuretic hormone in hospitalized patients: a single-centre experience
Rapidity of Correction of Hyponatremia Due to Syndrome of Inappropriate Secretion of Antidiuretic Hormone Following Tolvaptan
Tolvaptan, a Selective Oral Vasopressin V2-Receptor Antagonist, for Hyponatremia
Josh
Review on amiloride development https://pubmed.ncbi.nlm.nih.gov/7039345/
Toad bladder: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1351665/
Amiloride derivatives that inhibit flagella: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8544414/
Amiloride as taste sensor: https://www.science.org/doi/10.1126/science.6691151
Batlle on diabetes Insipidus: https://www.nejm.org/doi/full/10.1056/NEJM198502143120705?query=recirc_curatedRelated_article
Amiloride + ddavp for DI https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2518801/
Amy
Treatment of refractory congestive heart failure and normokalemic hypochloremic alkalosis with acetazolamide and spironolactone.
Acetazolamide reversibly inhibits water conduction by aquaporin-4
Inhibition of Human Aquaporin-1 Water Channel Activity by Carbonic Anhydrase Inhibitors
Acetazolamide Attenuates Lithium-Induced Nephrogenic Diabetes Insipidus
Acetazolamide in Lithium-Induced Nephrogenic Diabetes Insipidus
In Vivo Antibacterial Activity of Acetazolamide
Roger
50th anniversary of aldosterone
Joel
Sotagliflozin in Patients with Diabetes and Recent Worsening Heart Failure
The SGLT2 inhibitor empagliflozin in patients hospitalized for acute heart failure: a multinational randomized trial
Effects of Early Empagliflozin Initiation on Diuresis and Kidney Function in Patients With Acute Decompensated Heart Failure (EMPAG-HF)
Empagliflozin and Heart failure: Diuretic and Cardiorenal Effects
Anna
Clinical Results of Treatment of Diabetes Insipidus with Drugs of the Chlorothiazide Series
Treatment of nephrogenic diabetes insipidus with hydrochlorothiazide and amiloride
Influence of renal nerves and sodium balance on the acute antidiuretic effect of bendroflumethiazide in rats with diabetes insipidus
Antidiuretic effect of hydrochlorothiazide in lithium-induced nephrogenic diabetes insipidus is associated with upregulation of aquaporin-2, Na-Cl co-transporter, and epithelial sodium channel
Major Outcomes in High-Risk Hypertensive Patients Randomized to Angiotensin-Converting Enzyme Inhibitor or Calcium Channel Blocker vs Diuretic
Walsh AC, Moyes A. Intractable Congestive Heart Failure Successfully Treated With Southey Tubes. Can Med Assoc J. 1964 Jun 13;90(24):1375-6.
Godwin TF, Gunton RW. Clinical trial of a new diuretic, furosemide: comparison with hydrochlorothiazide and mercaptomerin. Can Med Assoc J. 1965 Dec 18;93(25):1296-300.
Gerber JG. Role of prostaglandins in the hemodynamic and tubular effects of furosemide. Fed Proc. 1983 Apr;42(6):1707-10.
Schlatter E, Salomonsson M, Persson AE, Greger R. Macula densa cells sense luminal NaCl concentration via furosemide sensitive Na+2Cl-K+ cotransport. Pflugers Arch. 1989 Jul;414(3):286-90. doi: 10.1007/BF00584628.
References
We considered the effect of a high protein diet and potential metabolic acidosis on kidney function. This review is of interest by Donald Wesson, a champion for addressing this issue and limiting animal protein: Mechanisms of Metabolic Acidosis-Induced Kidney Injury in Chronic Kidney Disease
Hostetter explored the effect of a high protein diet in the remnant kidney model with 1 ¾ nephrectomy. Rats with reduced dietary acid load (by bicarbonate supplementation) had less tubular damage. Chronic effects of dietary protein in the rat with intact and reduced renal mass
Wesson explored treatment of metabolic acidosis in humans with stage 3 CKD in this study. Treatment of metabolic acidosis in patients with stage 3 chronic kidney disease with fruits and vegetables or oral bicarbonate reduces urine angiotensinogen and preserves glomerular filtration rate
In addition to the effect of metabolic acidosis from a diet high in animal protein, this diet also leads to hyperfiltration. This was demonstrated in normal subjects; ingesting a protein diet had a significantly higher creatinine clearance than a comparable group of normal subjects ingesting a vegetarian diet. Renal functional reserve in humans: Effect of protein intake on glomerular filtration rate.This finding has been implicated in Brenner’s theory regarding hyperfiltration: The hyperfiltration theory: a paradigm shift in nephrology
One of multiple publications from Dr. Nimrat Goraya whom Joel mentioned in the voice over: Dietary Protein as Kidney Protection: Quality or Quantity?
We wondered about the time course in buffering a high protein meal (and its subsequent acid load on ventilation) and Amy found this report:Effect of Protein Intake on Ventilatory Drive | Anesthesiology | American Society of Anesthesiologists
Roger mentioned that the need for acetate to balance the acid from amino acids in parenteral nutrition was identified in pediatrics perhaps because infants may have reduced ability to generate acid. Randomised controlled trial of acetate in preterm neonates receiving parenteral nutrition - PMC
He also recommended an excellent review on the complications of parenteral nutrition by Knochel https://www.kidney-international.org/action/showPdf?pii=S0085-2538%2815%2933384-6 which explained that when the infused amino acids disproportionately include cationic amino acids, metabolism led to H+ production. This is typically mitigated by preparing a solution that is balanced by acetate.
Amy mentioned this study that explored the effect of protein intake on ventilation: Effect of Protein Intake on Ventilatory Drive | Anesthesiology | American Society of Anesthesiologists
Anna and Amy reminisced about a Skeleton Key Group Case from the renal fellow network Skeleton Key Group: Electrolyte Case #7
JC wondered about isolated defects in the proximal tubule and an example is found here: Mutations in SLC4A4 cause permanent isolated proximal renal tubular acidosis with ocular abnormalities
Anna’s Voiceover re: Gastric neobladder → metabolic alkalosis and yes, dysuria. The physiology of gastrocystoplasty: once a stomach, always a stomach but not as common as you might think Gastrocystoplasty: long-term complications in 22 patients
Sjögren’s syndrome has been associated with acquired distal RTA and in some cases, an absence of the H+ ATPase, presumably from autoantibodies to this transporter. Here’s a case report: Absence of H(+)-ATPase in cortical collecting tubules of a patient with Sjogren's syndrome and distal renal tubular acidosis
Can't get enough disequilibrium pH? Check this out- Spontaneous luminal disequilibrium pH in S3 proximal tubules. Role in ammonia and bicarbonate transport.
Acetazolamide secretion was studied in this report Concentration-dependent tubular secretion of acetazolamide and its inhibition by salicylic acid in the isolated perfused rat kidney. | Drug Metabolism & Disposition
In this excellent review, David Goldfarb tackles the challenging case of a A Woman with Recurrent Calcium Phosphate Kidney Stones (spoiler alert, many of these patients have incomplete distal RTA and this problem is hard to treat).
Molecular mechanisms of renal ammonia transport excellent review from David Winer and Lee Hamm.
Outline
Outline: Chapter 11
- Regulation of Acid-Base Balance
- Introduction
- Bicarb plus a proton in equilibrium with CO2 and water
- Can be rearranged to HH
- Importance of regulating pCO2 and HCO3 outside of this equation
- Metabolism of carbs and fats results in the production of 15,000 mmol of CO2 per day
- Metabolism of protein and other “substances” generates non-carbonic acids and bases
- Mostly from sulfur containing methionine and cysteine
- And cationic arginine and lysine
- Hydrolysis of dietary phosphate that exists and H2PO4–
- Source of base/alkali
- Metabolism of an ionic amino acids
- Glutamate and asparatate
- Organic anions going through gluconeogenesis
- Glutamate, Citrate and lactate
- Net effect on a normal western diet 50-100 mEq of H+ per day
- Homeostatic response to these acid-base loads has three stages:
- Chemical buffering
- Changes in ventilation
- Changes in H+ excretion
- Example of H2SO4 from oxidation of sulfur containing AA
- Drop in bicarb will stimulate renal acid secretion
- Nice table of normal cid-base values, arterial and venous
- Great 6 bullet points of acid-base on page 328
- Kidneys must excrete 50-100 of non-carbonic acid daily
- This occurs by H secretion, but mechanisms change by area of nephron
- Not excreted as free H+ due to minimal urine pH being equivalent to 0.05 mmol/L
- No H+ can be excreted until virtually all of th filtered bicarb is reabsorbed
- Secreted H+ must bind buffers (phosphate, NH3, cr)
- PH is main stimulus for H secretion, though K, aldo and volume can affect this.
- Renal Hydrogen excretion
- Critical to understand that loss of bicarb is like addition of hydrogen to the body
- So all bicarb must be reabsorbed before dietary H load can be secreted
- GFR of 125 and bicarb of 24 results in 4300 mEq of bicarb to be reabsorbed daily
- Reabsorption of bicarb and secretion of H involve H secretion from tubular cells into the lumen.
- Thee initial points need to be emphasized
- Secreted H+ ion are generated from dissociation of H2O
- Also creates OH ion
- Which combine with CO2 to form HCO3 with the help of zinc containing intracellular carbonic anhydrase.
- This is how the secretion of H+ which creates an OH ultimately produces HCO3
- Different mechanisms for proximal and distal acidification
- NET ACID EXCRETION
- Free H+ is negligible
- So net H+ is TA + NH4 – HCO3 loss
- Unusually equal to net H+ load, 50-100 mEq/day
- Can bump up to 300 mEq/day if acid production is increased
- Net acid excretion can go negative following a bicarb or citrate load
- Proximal Acidification
- Na-H antiporter (or exchanger) in luminal membrane
- Basolateral membrane has a 3 HCO3 Na cotransporter
- This is electrogenic with 3 anions going out and only one cation
- The Na-H antiporter also works in the thick ascending limb of LOH
- How about this, there is also a H-ATPase just like found in the intercalated cells in the proximal tubule and is responsible for about a third of H secretion
- And similarly there is also. HCO3 Cl exchanger (pendrin-like) in the proximal tubule
- Footnote says the Na- 3HCO3 cotransporter (which moves sodium against chemical gradient NS uses negative charge inside cell to power it) is important for sensing acid-base changes in the cell.
- Distal acidification
- Occurs in intercalated cells of of cortical and medullary collecting tubule
- Three main characteristics
- H secretion via active secretory pumps in the luminal membrane
- Both H-ATPase and H-K ATPase
- H- K ATPase is an exchange pump, k reabsorption
- H-K exchange may be more important in hypokalemia rather than in acid-base balance
- Whole paragraph on how a Na-H exchanger couldn’t work because the gradient that H has to be pumped up is too big.
- H-ATPase work like vasopressin with premise H-ATPase sitting on endocarditis vesicles a=which are then inserted into the membrane. Alkalosis causes them to be recycled out of the membrane.
- H secretory cells do not transport Na since they have few luminal Na channels, but are assisted by the lumen negative tubule from eNaC.
- Minimizes back diffusion of H+ and promotes bicarb resorption
- Bicarbonate leaves the cell through HCO3-Cl exchanger which uses the low intracellular Cl concentration to power this process.
- Same molecule is found on RBC where it is called band 3 protein
- Figure 11-5 is interesting
- Bicarbonate resorption
- 90% in the first 1-22 mm of the proximal tubule (how long is the proximal tubule?)
- Lots of Na-H exchangers and I handed permeability to HCO3 (permeability where?)
- Last 10% happens distally mostly TAL LOH via Na-H exchange
- And the last little bit int he outer medullary collecting duct.
- Carbonic anhydrase and disequilibrium pH
- CA plays central role in HCO3 reabsorption
- After H is secreted in the proximal tubule it combines with HCO# to form carbonic acid. CA then dehydrates it to CO2 and H2O. (Step 2)
- Constantly moving carbonic acid to CO2 and H2O keeps hydrogen combining with HCO3 since the product is rapidly consumed.
- This can be demonstrated by the minimal fall in luminal pH
- That is important so there is not a luminal gradient for H to overcome in the Na-H exchanger (this is why we need a H-ATPase later)
- CA inhibitors that are limited tot he extracellular compartment can impair HCO3 reabsorption by 80%.
- CA is found in S1, S2 but not S3 segment. See consequence in figure 11-6.
- The disequilibrium comes from areas where there is no CA, the HH formula falls down because one of the assumptions of that formula is that H2CO3 (carbonic acid) is a transient actor, but without CA it is not and can accumulate, so the pKa is not 6.1.
- Bicarbonate secretion
- Type B intercalated cells
- H-ATPase polarity reversed
- HCO3 Cl exchanger faces the apical rather than basolateral membrane
- Titratable acidity
- Weak acids are filtered at the glom and act as buffers in the urine.
- HPO4 has PKA of 6.8 making it ideal
- Creatinine (pKa 4.97) and uric acid (pKa 5.75) also contribute
- Under normal cinditions TA buffers 10-40 mEa of H per day
- Does an example of HPO4(2-):H2PO4 (1-) which exists 4:1 at pH of 7.4 (glomerular filtrate)
- So for 50 mEq of Phos 40 is HPO4 and 10 is H2PO4
- When pH drops to 6.8 then the ratio is 1:1 so for 50
- So the 50 mEq is 25 and 25, so this buffered an additional 15 mEq of H while the free H+ concentration increased from 40 to 160 nanomol/L so over 99.99% of secreted H was buffered
- When pH drops to 4.8 ratio is 1:100 so almost all 50 mEq of phos is H2PO4 and 39.5 mEq of H are buffered.
- Acid loading decreases phosphate reabsorption so more is there to act as TA.
- Decreases activity of Na-phosphate cotransporter
- DKA provides a novel weak acid/buffer beta-hydroxybutyrate (pKa 4.8) which buffers significant amount of acid (50 mEq/d).
- Ammonium Excretion
- Ability to excrete H+ as ammonium ions adds an important amount of flexibility to renal acid-base regulation
- NH3 and NH4 production and excretion can be varied according to physiologic need.
- Starts with NH3 production in tubular cells
- NH3, since it is neutral then diffuses into the tubule where it is acidified by the low pH to NH4+
- NH4+ is ionized and cannot cross back into the tubule cells(it is trapped in the tubular fluid)
- This is important for it acting as an important buffer eve though the pKa is 9.0
- At pH of 6.0 the ratio of NH3 to NH4 is 1:1000
- As the neutral NH3 is converted to NH4 more NH3 from theintracellular compartment flows into the tubular fluid replacing the lost NH3. Rinse wash repeat.
- This is an over simplification and that there are threemajor steps
- NH4 is produced in early proximal tubular cells
- Luminal NH4 is partially reabsorbed in the TAL and theNH3 is then recycled within the renal medulla
- The medullary interstitial NH3 reaches highconcentrations that allow NH3 to diffuse into the tubular lumen in the medullary collecting tubule where it is trapped as NH4 by secreted H+
- NH4 production from Glutamine which converts to NH4 and glutamate
- Glutamate is converted to alpha-ketoglutarate
- Alpha ketoglutarate is converted to 2 HCO3 ions
- HCO3 sent to systemic circulation by Na-3 HCO3 transporter
- NH4 then secreted via Na-H exchanger into the lumen
- NH4 is then reabsorbed by NaK2Cl transporter in TAL
- NH4 substitutes for K
- Once reabsorbed the higher intracellular pH causes NH4 to convert to NH3 and the H that is removed is secreted through Na-H exchanger to scavenge the last of the filtered bicarb.
- NH3 diffuses out of the tubular cells into the interstitium
- NH4 reabsorption in the TAL is suppressed by hyperkalemia and stimulated by chronic metabolic acidosis
- NH4 recycling promotes acid clearance
- The collecting tubule has a very low NH3 concentration
- This promotes diffusion of NH3 into the collecting duct
- NH3 that goes there is rapidly converted to NH4 allowing more NH3 to diffuse in.
- Response to changes in pH
- Increased ammonium excretion with two processes
- Increased proximal NH4 production
- This is delayed 24 hours to 2-3 days depending on which enzyme you look at
- Decreased urine pH increases diffusion of ammonia into the MCD
- Occurs with in hours of an acid load
- Peak ammonium excretion takes 5-6 days! (Fig 11-10)
- Glutamine is picked up from tubular fluid but with acidosis get Na dependent peritublar capillary glutamine scavenging too
- Glutamine metabolism is pH dependent with increase with academia and decrease with alkalemia
- NH4 excretion can go from 30-40 mEq/day to > 300 with severe metabolic acidosis (38 NaBicarb tabs)
- Says each NH4 produces equimolar generation of HCO3 but I thought it was two bicarb for every alpha ketoglutarate?
- The importance of urine pH
- Though the total amount of hydrogren cleared by urine pH is insignificant, an acidic urine pH is essential for driving the reactions of TA and NH4 forward.
- Regulation of renal hydrogen excretion
- Net acid excretion vary inverse with extracellular pH
- Academia triggers proximal and distal acidification
- Proximally this:
- Increased Na-H exchange
- Increased luminal H-ATPase activity
- Increased Na:3HCO3 cotransporter on the basolateral membrane
- Increased NH4 production from glutamine
- In the collecting tubules
- Increased H-ATPase
- Reduction of tubular pH promotes diffusion of NH3 which gets converted to NH4…ION TRAPPING
- Extracellular pH affects net acid excretion through its affect on intracellular pH
- This happens directly with respiratory disorders due to movement of CO2 through the lipid bilayer
- In metabolic disorders a low extracellular bicarb with cause bicarb to diffuse out of the cell passively, this lowers intracellular pH
- If you manipulate both low pCO2 and low Bicarb to keep pH stable there will be no change in the intracellular pH and there is no change in renal handling of acid. It is intracellular pH dependent
- Metabolic acidosis
- Ramps up net acid secretion
- Starts within 24 hours and peaks after 5-6 days
- Increase net secretion comes from NH4
- Phosphate is generally limited by diet
- in DKA titratable acid can be ramped up
- Metabolic alkalosis
- Alkaline extracellular pH
- Increased bicarb excretion
- Decrease reabsorption
- HCO3 secretion (pendrin) in cortical collecting tubule
- Occurs in cortical intercalated cells able to insert H-ATPase in basolateral cells (rather than luminal membrane)
- Normal subjects are able to secrete 1000 mmol/day of bicarb
- Maintenance of metabolic alkalosis requires a defect which forces the renal resorption of bicarb
- This can be chloride/volume deficiency
- Hypokalemia
- Hyperaldosteronism
- Respiratory acidosis and alkalosis
- PCO2 via its effect on intracellular pH is an important determinant of renal acid handling
- Ratios he uses:
- 3.5 per 10 for respiratory acidosis
- 5 per 10 for respiratory alkalosis
- Interesting paragraph contrasting the response to chronic metabolic acidosis vs chronic respiratory acidosis
- Less urinary ammonium in respiratory acidosis
- Major differences in proximal tubule cell pH
- In metabolic acidosis there is decreased bicarb load so less to be reabsorbed proximally
- In respiratory acidosis the increased serum bicarb increases the amount of bicarb that must be reabsorbed proximally
- The increased activity of Na-H antiporter returns tubular cell pH to normal and prevents it from creating increased urinary ammonium
- Mentions that weirdly more mRNA for H-Na antiporter in metabolic acidosis than in respiratory acidosis
- Net hydrogen excretion varies with effective circulating volume
- Starts with bicarb infusions
- Normally Tm at 26
- But if you volume deplete the patient with diuretics first this increases to 35+
- Four factors explain this increased Tm for bicarb with volume deficiency
- Reduced GFR
- Activation of RAAS
- Ang2 stim H-Na antiporter proximally
- Ang2 also stimulates Na-3HCO3 cotransporter on basolateral membrane
- Aldosterone stimulates H-ATPase in distal nephron
- ALdo stimulates Cl HCO3 exchanger on basolateral membrane
- Aldo stimulates eNaC producing tubular lumen negative charge to allow H secretion to occur and prevents back diffusion
- Hypochloremia
- Increases H secretion by both Na-dependent and Na-independent methods
- If Na is 140 and Cl is 115, only 115 of Na can be reabsorbed as NaCl, the remainder must be reabsorbed with HCO3 or associated with secretion of K or H to maintained electro neutrality
- This is enhanced with hypochloridemia
- Concurrent hypokalemia
- Changes in K lead to trans cellular shifts that affect inctracellular pH
- Hypokalemia causes K out, H in and in the tubular cell the cell acts if there is systemic acidosis and increases H secretion (and bicarbonate resorption)
- PTH
- Decreases proximal HCO3 resorption
- Primary HyperCard as cause of type 2 RTA
- Does acidosis stim PTH or does PTH stim net acid excretion
References for Chapter 10
We did not mention many references in our discussion today but our listeners may enjoy some of the references below.
Effects of pH on Potassium: New Explanations for Old Observations - PMC although the focus of this article is on potassium, this elegant review by Aronson and Giebisch reviews intracellular shifts as it relates to pH and K+.
Josh swooned for Figure 10-1 is this right? Which figure was it? which shows the relationship between [H+] and pH. You can find this figure in the original reference from Halperin ML and others, Figure 1 here. Factors That Control the Effect of pH on Glycolysis in Leukocytes
Here’s Leticia Rolon’s favorite Henderson-Hasselbalch calculator website: Henderson-Hasselbalch Calculator | Buffer Solutions [hint! for this site, use the bicarbonate (or “total CO2”) for A- and PCO2 for the HA] There’s also a cooking tab for converting units!
Fundamentals of Arterial Blood Gas Interpretation - PMC this review published posthumously from the late but beloved Jerry Yee and his group at Henry Ford Hospital, explores the details and underpinnings of our understandings of arterial blood gas interpretation (and this also addresses how our colleagues in clinical chemistry measure total CO2 - which JC referenced- but JC said “machine” and our colleagues prefer the word “instrument.”)
Amy went deep on bicarbonate in respiratory acidosis. Here are her refs:
Sodium bicarbonate therapy for acute respiratory acidosis
Sodium Bicarbonate in Respiratory Acidosis
Bicarbonate therapy in severe metabolic acidosis
Effect of Intravenous Sodium Bicarbonate on Ventilation, Gas Exchange, and Acid-Base Balance in Patients with Chronic Pulmonary Insufficiency
Bicarbonate Therapy in Severe Metabolic Acidosis | American Society of Nephrology this review article from Sabatini and Kurtzman addresses the issues regarding bicarbonate therapy including theoretical intracellular acidosis.
Bicarbonate in DKA? Don’t do it: Bicarbonate in diabetic ketoacidosis - a systematic review
Here’s a review from Bushinsky and Krieger on the effect acidosis on bone
https://www.sciencedirect.com/science/article/abs/pii/S0085253822002174
Here is the primary resource that Anna used in here investigation of meat replacements Nutritional Composition of Novel Plant-Based Meat Alternatives and Traditional Animal-Based Meats
We enjoyed this paper that Dr. Rose references from the Journal of Clinical Investigation 1955 in which investigators infused HCl into nephrectomized dogs and observed changes in extracellular ions. https://www.jci.org/articles/view/103073/pd
We wondered about the amino acids/protein in some available meat alternatives they are explored in this article in the journal Amino Acids: Protein content and amino acid composition of commercially available plant-based protein isolates - PMC and you may enjoy this exploration of the nutritional value of these foods: Full article: Examination of the nutritional composition of alternative beef burgers available in the United States
Outline
Chapter 10: Acid-Base Physiology
- H concentration regulated tightly
- Normal H+ is 40 nm/L
- This one millionth the concentration of Na and K
- It needs to be this dilute because H+ fucks shit up
- Especially proteins
- Cool foot note H+ actually exists as H3O+
- Under normal conditions the H+ concentration varies little from normal due to three steps
- Chemical buffering by extracellular and intracellular bufffers
- Control of partial pressure of CO2 by alterations of alveolar ventilation
- Control of plasma bicarbonate by changes in renal H+ excretion
- Acid and bases
- Use definition by Bronsted
- Acid can donate protons
- Base can accept protons
- There are two classes of acids**
- Carbonic acid H2CO3
- Each day 15000 mmol of CO2 are generated
- CO2 not acid but combines with water to form carbonic acid H2CO3
- CO2 cleared by the lungs
- Noncarbonic acid
- Formed from metabolism of protein. Sulfur containing AA generate H2SO4. Only 50-100 mEq of acid produced from these sources.
- Cleared by the kidneys
- Law of Mass Action
- Velocity of reaction proportional to the product of the concentrations of the reactants
- Goes through mass action formula for water
- Concludes that water has H of 155 nanoM/L, more than the 40 in plasma
- Says you can do the same mass experiment for every acid in the body
- Can do it also for bases but he is not going to.
- Acids and Bases can be strong or weak
- Strong acids completely dissociate
- Weak acids not so much
- H2PO4 is only 80% dissociated
- Weak acids are the principle buffers in the body
- Then he goes through how H is measured in the blood and it becomes clear why pH is a logical way to measure.
- Then there is a lot of math
- HH equation
- Derives it
- Then uses it to look at phos. Very interesting application
- Buffers
- Goes tot he phosphate well again. Amazing math describing how powerful buffers can be
- Big picture the closer the pKa is to the starting pH the better buffer, i.e. it can absorb lots of OH or H without appreciably changing pH
- HCO3 CO2 system
- H2CO3 to H + HCO3 has a PKA of 2.72 but then lots of Math and the bicarb buffer system has a pKa of 6.1
- But the real power of the bicarb buffer is that it is not a sealed system. The ability to ventilate and keep CO2 constant increases the buffering efficiency by 11 fold and the ability to lower the CO2 below normal increases 18 fold.
- Isohydric principle
- There is only one hydrogen ion concentration and since that is a critical part of the buffer equation, all buffer eq are linked and you can understand all of them by understanding one of them. So we just can look at bicarb and understand the totality of acid base.
- Bicarb is the most important buffer because
- High concentration in plasma
- Ability for CO2 to ventilate
- Other buffers include
- Bone
- Bone is more than just inorganic reaction
- Live bone releases more calcium in response to an acid load than dead bone
- More effect with metabolic acidosis than respiratory acidosis
- Hgb
- Phosphate
- Protein
References for Chapter 9
One of the few papers that Rose wrote as a single author explores electrolyte free water clearance. This seminal paper explores the issue in greater detail than the book. A New approach to disturbances in the plasma sodium concentration
Wondering about the volume of sweat? Josh taught us that the volume of “transepidermal volume loss” is not affected by humidity https://www.jidonline.org/article/S0022-202X(15)48145-X/pdf but is greatly affected by temperature: Skin temperature and transepidermal water loss
Regarding normal sweat physiology, there is a nice review (with figures!) titled Physiological mechanisms determining sweat composition which describes all the important cells and channels which make up sweat glands. And an important follow on paper titled Higher Bioelectric Potentials due to Decreased Chloride Absorption in the Sweat Glands of Patients with Cystic Fibrosis describing specifically the sweat characteristics of patients with cystic fibrosis.
Melanie was enchanted by work from RA McCance who did early experiments to induce sodium deficiency using very low sodium diets and a homemade sauna-like tent. His musings are fascinating. Lancet 1936 Experimental human salt deficiency MEDICAL PROBLEMS IN MINERAL METABOLISM
Age-related decline in urine concentration may not be universal: Comparative study from the US and two small-scale societies from Jeff Sands (of urea transport fame!)
In this initial report, after continually water loading 21 volunteers, the younger group (mean age 31) had a urine osmolality of 52 mOsm/kg compared to in the older group (mean age 84). Influence of age, renal disease, hypertension, diuretics, and calcium on the antidiuretic responses to suboptimal infusions of vasopressin. In a later report older subjects (mean age 72) vs younger controls (mean age 26) drank 20 ml/kg over 40 minutes. The younger group excreted more of the water in the first 2 hours and had a lower mean urine osmolality 86 vs 112 mOsm/kg compared to the older participants. Age-associated Alterations in Thirst and Arginine Vasopressin in Response to a Water or Sodium Load
Howard Furst suggests the urine to plasma electrolyte ratio as a simpler strategy to consider the free water clearance: https://nephrology.edublogs.org/files/2014/03/Water-Restriction-in-Hyponatremia1-1eb8n40.pdf or via pubmed: The urine/plasma electrolyte ratio: a predictive guide to water restriction
Rapidity of Correction of Hyponatremia Due to Syndrome of Inappropriate Secretion of Antidiuretic Hormone Following Tolvaptan
InfoSnack picture of pre and post tolvaptan
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