Airwayve

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Dr. Cooper a Professor Emeritus in the Faculty of Medicine at the University of Toronto. He spent his career as a Clinical anesthesiologist at University Health Network, Toronto General Hospital from 1981-2019. He was the founder and former Director of the Anesthesia Advanced Airway Fellowship at Toronto General Hospital and the Past President of The Society for Airway Management (SAM) from 2012-14. Join us on this episode as we explore Dr. Cooper's perspectives and reflections on a successful and rewarding career in anesthesia.

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Neuromuscular blocking agents are used to chemically paralyze skeletal muscle during surgery to: 

1. Provide paralysis of the vocal cords for intubation 
2. Enhance operating conditions for surgeons 

How does skeletal muscle work normally? 

An action potential triggers the release of acetylcholine into the neuromuscular junction, which binds to nicotinic receptors on the muscle and causes contraction. As acetylcholine is then degraded, the muscle can begin to respond to stimulation again. 

How do neuromuscular blocking agents work? 

Neuromuscular blocking agents work by interfering with the acetylcholine signaling mechanism and there are two types: 

1. Non-depolarizing (e.g. rocuronium): These are competitive antagonists with acetylcholine and bind to nicotinic receptors preventing muscle contraction. 
2. Depolarizing (e.g. succinylcholine): These act similarly to acetylcholine, as nicotinic receptor agonists, but are not metabolized by acetylcholinesterase and therefore inhibit further acetylcholine-mediated contraction. 

How are neuromuscular blocking agents reversed? 

• Non-Depolarizing 
  • Neostigmine/Glycopyrrolate: This method increases the amount of acetylcholine to outcompete the blockade.
  • Sugammadex: This method directly inactives the non-depolarizing neuromuscular blocking agent 
• Depolarizing 
  • Quickly broken down by plasma cholinesterases and do not require reversal agents 

How to choose a neuromuscular blocking agent? - Questions to consider 

1. Duration of action 
   • Are you doing a RSI or not? 
   • How long do you require skeletal muscle paralysis? 
2. Route of excretion 
   • How is the NMB metabolized/excreted and does you patients have any conditions that would prolong the action? 
3. Adverse reactions and contraindications 
   • Rocuronium: a common cause of allergic reactions in the OR 
   • Succinylcholine (the 4 H’s) 
     1. Malignant Hyperthermia
     2. Hyperkalemia 
     3. High ocular pressure
     4. Higher post-op muscle pain 

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Key principles of pharmacology :

Pharmacokinetics : What the body does to the drug.

A.  Absorption
D. Distribution
M. Metabolism
E. Excretion

Pharmacodynamics: A drug’s biochemical and physiologic effects on the body. 

•  Receptor binding
•  Receptor sensitivity
•  Post-receptor effects

 4 induction agents to familiarize yourself with for the first day in the OR:

1. Propofol

• Inhibitory neurotransmission via the GABA receptor 
• Provides reliable amnesia and anesthesia, but does not have any analgesic properties
• Potent cardiac and respiratory depressant
• Easily titratable due to high volume of distribution and short initial distribution half-life
• Induction dose is 1-2.5 mg/kg

2. Ketamine

• NMDA receptor antagonist
• Has analgesic, amnesia and anesthetic properties.
• Can cause emergence delirium
• Causes central sympathetic stimulation 
• Induction dose 0.5-2 mg/kg

 3. Midazolam

• Enhances the affinity of GABA for its receptor
• Minimal cardiorespiratory depression and produces anxiolysis and anterograde amnesia
• Longer-acting; elimination half-life of 1-4 hours
• Induction doses: 0.02- 0.04 mg/kg (1-2 mg in adults)
• Antagonist available: Flumazenil

4. Etomidate

• Increases the receptor’s affinity for GABA
• Cardio-respiratory stable
• Very fast onset/offset due to high lipophilicity;  an induction dose of 0.1 mg/kg will provide 1.5 minutes of unconsciousness
• Produces a light plane of anesthesia for laryngoscopy
• Can cause adrenocortical insufficiency

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Happy New Year! Airwayve is back to bring you tips for your anesthesia rotations. This episode highlights the importance of professionalism in anesthesia and provides 10 practical tips to help you succeed.  We thought this episode was quite timely as the second-year medical students at our institution, McMaster University, are beginning their clerkship journey.

Our 10 tips for success are:
1. Be on time or even better be early
2. Introduce yourself to the patient
3. Ask your patients how they pronounce their name, and ask them if it is ok if you call them by it
4. Conclude your interviews by asking patients if they have any questions, or if there is anything that you can do for them
5. Get to know your allied health staff 
6. Develop your situational awareness in the OR
7. Be excited to try new things but be aware of the limitations of your technical skills and knowledge
8. Learn more about your preceptor and their preferences
9. Always solicit feedback 
10. If you make a mistake, be honest about it, and learn from it.

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Dr. Dolores McKeen grew up and did her medical training in Newfoundland. She moved
to Halifax to further train at the IWK on a 2-year plan, and ended up staying in Nova
Scotia for the last 21 years with her husband Roger, 3 adult children and a
senior Yorkie-poo named Miss Molly!

She has conducted research in the areas of post-operative pain management, obstetric
anesthesia and health outcomes. Her current research focus is on Patient Centered Care,
Knowledge Translation and Implementation of evidence based clinical care such as
Enhanced Recovery After Surgery (ERAS). She is the current President of the Canadian Anesthesiologists' Society (CAS).

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This is the final episode of this series on general anesthesia! PACU handover can seem complicated, but it's ultimately about transferring professional and care responsibility for your patient after surgery. For this week's episode, remember the acronym "ISBAR" - as always, check out our step-by-step approach below:

1. ID + Introduction: introduce yourself, the surgery team and your patient. This is who YOU are.
2. Situation: identify the type of surgery, whether it was elective/urgent, and under what modality of anesthesia your patient just came from (e.g. "John Doe just underwent an elective laparoscopic appendectomy under general anesthesia)
3. Background: state your patient's pertinent medical history and their risks for anxiety, PONV, changes in baseline cognitive status, etc.
4. Anesthesia/Actions: mention the technique of anesthesia used and share the patient's airway features, and if there were any difficulties during the case. This helps the PACU team anticipate problems EARLY! (e.g. "He was difficult to intubate and experienced potential bronchospasm intraoperatively lasting 10 minutes"). Also state the drugs used and their quantities (e.g. "He was given 2mg midazolam, 150mg propofol, 70mcg fentanyl and 10mg ondansetron). Finally, quantify fluids in/out, any pressors/blood products used and their ongoing needs. 
5. Recommendations: use the PACU order sets to describe what you'd like for your patient (e.g. pain control, PONV medications, IV fluid replacement, hemodynamic management, discharge planning info and when to call the MD for help). (e.g. "We've completed the PACU order set and John is expected to return home today. Any questions?"

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What is emergence? The time from discontinuation of an anesthetic to when the patient can make a non-reflex response to verbal command

 Maneuvers to improve the elimination of inhaled anesthetics:

• Increase FiO2
• Increase gas flow rate
• Increase PEEP to prevent atelectasis

Factors that affect emergence:

• Patient factors (e.g. obesity, advanced age, hepatic or renal insufficiency) 
• Drug factors (e.g. dosage, time of administration, metabolism, excretion) 
• Surgical factors (e.g. length/type of surgery)

 Reversal of neuromuscular blockade:

• Acetylcholinesterase inhibitor (e.g. neostigmine): increases amount of acetylcholine at the neuromuscular junction to reverse paralysis; also increases acetylcholine in the parasympathetic nervous system 
• Muscarinic receptor antagonist (e.g. glycopyrrolate): inhibits the parasympathetic effects of neostigmine

 Postoperative considerations:

• Antiemetics: ondansetron, dexamethasone, aprepitant
• Postoperative pain medications: long-acting narcotics, NSAIDs (e.g. ketorolac), acetaminophen

 Extubation criteria:

• Hemodynamically stable
• Respiratory rate between 8-35
• Adequate oxygenation (PaO2 at least 60 mmHg with FiO2 <50%, or PaCO2 < 50 mmHg)
• Tidal volume > 5 ml/kg
• Negative inspiratory force of at least 25 mmHg, and vital capacity of 15 mL/kg
• Can also look for purposeful movements such as opening eyes or following commands

Respiratory complications are about 3 times more likely to occur during extubation than intubation

 Steps to extubation:

• Deflate the cuff
• Gently remove tube
• Have suction ready, clear secretions prior to extubation and afterwards
• Have oxygenation equipment ready
• Remove monitors from the patient when appropriate (typically remove the oxygen saturation probe last)

 Extubation complications:

• Airway obstruction
• Early postoperative hypoxemia
• Heightened cardiovascular response
• Aspiration
• Emergence delirium

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Two overarching goals for the maintenance phase of an anesthetic:

• Maintain appropriate depth of anesthetic
• Maintain patient’s stability

Inhalational Anesthetics

• Volatile agents: sevoflurane and desflurane (most common), isoflurane (less common)
• Nitrous oxide: low potency, can be used in MH, flammable
• Minimum alveolar concentration (MAC): alveolar concentration of a specific inhaled agent that inhibits motor response to a painful stimulus in 50% of patients

IV infusion

• TIVA: total intravenous anesthetic
• Infusion of a sedative agent (most commonly propofol) +/- other agents (such as opioids or benzodiazepines)
• Advantages: can be used in MH cases, less postoperative nausea and vomiting, can avoid airway instrumentation and aerosolization

 Intraoperative monitoring

• For each physiologic system, consider: 
  • What parameters should I be concerned with?
  • How can I measure or monitor them?
  • What actions can I take to correct an imbalance?

 Temperature

• Monitor: temperature probe
• Adjust: air warming device or IV fluid warmer

Neuromuscular

• Monitor: observe patient movement, check Train-of-Four on peripheral nerve stimulator
• Adjust: give neuromuscular blocker if needed, or reversal if appropriate

Ventilation

• Monitor: observe chest rise, auscultate lungs, end-tidal CO2 tracing, flow-volume loop (this goes in the opposite direction with positive pressure ventilation vs. spontaneous breathing!)
• Adjust: ventilator settings such as PEEP, inspiratory pressure, tidal volume, respiratory rate

Oxygenation

• Monitor: observe lips for cyanosis, pulse oximetry on the monitor
• Adjust: FiO2

Hemodynamics

• Monitor: blood pressure, heart rate, ECG tracing
• Adjust: sedative drugs, analgesics, IV fluids; if necessary, consider rescue drugs such as phenylephrine, ephedrine, and atropine

Volume status

• Monitor: blood pressure, intraoperative blood loss, urine output
• Adjust: IV crystalloid fluids, blood products if needed

Practical things to do during the maintenance phase:

• Come to the OR with some questions in mind; the maintenance phase can be a good time to discuss physiology and other concepts with your staff
• Read up on your patient and try to anticipate any specific issues that could arise
• Catch up on charting, if this is done by hand
• Draw up medications for the next case, and ensure that your syringes are organized and labelled
• Go see your next patient and do a preoperative assessment
• Ask your staff, “How can I help?”

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Overall approach to a difficult airway

• Always ask for help!
• The goal is oxygenation, not intubation
• Your first attempt is your best attempt
• Don’t panic!

Preoperative Assessment (check out Episode 1 of the series for a review!)

• Identify risk factors for a potentially difficult airway:
  • Difficult ventilation
  • Difficult intubation
  • Difficulty with patient cooperation/consent
  • Difficult cricothyrotomy
• One of the best predictors of a difficult airway is a history of difficult airway

 Scenario 1: Can't intubate, can ventilate

• Return to BMV (bag-mask ventilation) to stabilize the patient and give yourself time
• Try something new with each attempt:
  • Switch to a more experienced operator
  • Optimize patient position
  • Ask an assistant to apply BURP (backwards upwards rightwards pressure)
  • Try with different equipment (such as a different size ETT, a Bougie, or videolaryngoscope)
• Minimize the number of attempts (max. 3)
• Consider using a supraglottic airway device or waking the patient up

 Scenario 2: Can't intubate, difficult ventilation

• Improve BMV technique:
  • Use an oropharyngeal or nasopharyngeal airway
  • Optimize patient position
  • Ensure the mask has a tight seal, use 2 hands and ask someone else to bag
• Try inserting a supraglottic airway device
• Once oxygenation is achieved, consider your options for establishing an airway or waking the patient up

 Scenario 3: Can't intubate, can't oxygenate

• Recognize the problem and communicate with the team
• Proceed with cricothyrotomy / surgical airway

 Difficult Airway Society Guidelines: 

• https://das.uk.com/guidelines/das_intubation_guidelines

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