Patient Overview

A 69-year-old female, height 149 cm and weight 54 kg (BMI ≈ 24.3 kg/m²), with a prior right total knee replacement, presented for a left total knee replacement. Comorbidities included hypertension treated with Telvas-AM (telmisartan + amlodipine) and type 2 diabetes mellitus treated with sitagliptin + metformin and gliclazide. Preoperative echocardiography showed normal left ventricular function.

Reference: Kurtz S, Ong K, Lau E, et al. Projections of primary and revision hip and knee arthroplasty in the United States from 2005 to 2030. J Bone Joint Surg Am. 2007;89(4):780–785.

Preoperative Medication Management

Antihypertensive and antidiabetic medications were withheld on the day of surgery.

Telmisartan (part of Telvas-AM) is an angiotensin II type 1 receptor blocker that inhibits vasoconstriction and aldosterone release. Continued angiotensin receptor blockade on the day of anesthesia may precipitate refractory hypotension due to reduced sympathetic compensation and a blunted vasopressin response; hence it was withheld.

Metformin was withheld because it inhibits mitochondrial respiratory chain complex I, promoting anaerobic metabolism and increasing the risk of lactic acidosis during states of hypoperfusion. Sitagliptin (a DPP-4 inhibitor) was withheld because fasting combined with altered incretin action may increase the risk of hypoglycemia in the perioperative period.

Gliclazide (Diamicron XR) was withheld because it stimulates insulin release by blocking ATP-sensitive potassium channels on pancreatic β-cells; in the fasting state under anesthesia, sulfonylureas raise hypoglycemia risk.

References: Weksler N, et al. Can J Anaesth. 2001; Lipska KJ, et al. Diabetes Care. 2011; Joshi GP, et al. Anesth Analg. 2010.

Intraoperative Anesthesia Management

Airway management used an I-gel size 4 supraglottic device.

Induction medications included midazolam 1 mg, fentanyl 100 mcg, and propofol 150 mg. Neuromuscular blockade was provided with atracurium 40 mg.

Maintenance included an atracurium infusion at 10 mg/hr, oxygen, nitrous oxide, and desflurane as volatile anesthetic. An infusion of dexmedetomidine 30 mcg was used. Dexamethasone 8 mg IV was given intraoperatively.

Ventilation settings were a tidal volume of 425 mL, respiratory rate 12/min, and PEEP 5 cm H₂O. Measured airway pressures included a peak inspiratory pressure of 36 cm H₂O and a plateau pressure of 25 cm H₂O, with a normal end-tidal CO₂ waveform.

Molecular and physiologic insights: the elevated peak pressure together with a normal plateau pressure suggests increased airway resistance rather than decreased alveolar compliance. Possible causes include I-gel malposition, secretions, or partial upper airway obstruction. Atracurium is advantageous in older patients because it is eliminated by Hofmann degradation, a temperature- and pH-dependent non-enzymatic process with predictable kinetics independent of renal or hepatic function. Dexmedetomidine is an alpha-2 adrenergic agonist that reduces central sympathetic outflow through inhibition of adenylate cyclase and decreased cAMP, producing sedation and sympatholysis. Desflurane has rapid wash-in and wash-out because of low blood–gas solubility and may occasionally increase airway irritability but does not typically raise plateau pressures.

References: Lumb AB. Nunn’s Applied Respiratory Physiology. 8th ed. Elsevier; Maze M, et al. Br J Anaesth. 2000.

Regional Analgesia

An adductor canal block was performed using 30 mL of 0.2% ropivacaine, targeting the saphenous nerve within the adductor canal. Ropivacaine is an amide local anesthetic that blocks voltage-gated sodium channels in their inactive state, preventing action potential propagation in sensory nerves. It is less lipid-soluble than bupivacaine and is associated with a lower risk of central nervous system and cardiac toxicity. The adductor canal block is relatively motor-sparing compared with femoral nerve block, preserving quadriceps strength and facilitating early mobilization.

Reference: Jaeger P, et al. Reg Anesth Pain Med. 2013.

Analgesia and Adjuncts

Multimodal analgesia and adjuncts used included:

• Intravenous paracetamol 1 g for central analgesic effects possibly via COX-3 inhibition and serotonergic modulation.
• Diclofenac 100 mg per rectum to inhibit COX-1/2 and reduce prostaglandin-mediated inflammation.
• Magnesium sulfate 1 g IV for NMDA receptor antagonism to reduce central sensitization and the risk of chronic post-surgical pain.
• Additional dexmedetomidine 30 mcg IV to lower volatile MAC and blunt sympathetic responses.
• Dexamethasone 8 mg IV for anti-inflammatory effects and prophylaxis against postoperative nausea and vomiting.

Reference: McCartney CJL, Nelligan K. Drugs Ageing. 2014.

Reversal and Extubation

Atracurium infusion was discontinued more than 25 minutes before the end of surgery. Neuromuscular blockade was reversed with neostigmine 2.5 mg and glycopyrrolate 0.4 mg. Neostigmine inhibits acetylcholinesterase, increasing acetylcholine at the neuromuscular junction to antagonize nondepolarizing neuromuscular blockers; glycopyrrolate is an antimuscarinic used to mitigate muscarinic side effects such as bradycardia and excessive secretions.

Reference: Butterworth JF, et al. Morgan & Mikhail’s Clinical Anesthesiology. 6th ed.

Postoperative Care

Antiemetic prophylaxis was provided with ondansetron 4 mg IV, a 5-HT3 receptor antagonist. Rescue analgesia was available with tramadol 50 mg IV, which acts as a weak μ-opioid receptor agonist and inhibits serotonin and norepinephrine reuptake. Nebulized budesonide (Budecort) was used as an anti-inflammatory inhaled steroid to mitigate airway inflammation if needed.

References: White PF, et al. Anesthesiology. 2010; Bhardwaj N, et al. Indian J Anaesth. 2020.

Clinical Pearls

• An I-gel or other supraglottic device can cause increased airway resistance if malpositioned or if secretions obstruct the supraglottic seal; this manifests as elevated peak airway pressures without change in plateau pressure.
• Multimodal analgesia combining NMDA antagonists (magnesium sulfate), COX inhibitors, regional nerve blocks, and dexmedetomidine reduces opioid consumption and lowers the risk of central sensitization.
• Withholding angiotensin receptor blockers such as telmisartan on the day of surgery reduces the risk of intraoperative vasoplegia and refractory hypotension.
• The adductor canal block targets sensory fibers and is motor-sparing, thereby promoting early functional recovery after knee arthroplasty.