In a morbidly obese patient (BMI 48 kg/m2) undergoing laparoscopic bariatric surgery, drug dosing of propofol for total intravenous anaesthesia (TIVA) should be based on which body weight measure for maintenance infusion?

• A Total body weight (TBW), because the volume of distribution is proportional to total mass
• B Ideal body weight (IBW), because propofol distributes primarily in lean tissue
• C Lean body weight (LBW), because propofol clearance correlates with lean mass and cardiac output ✓
• D Adjusted body weight (ABW = IBW + 40% excess weight), as a compromise for most drugs

Explanation

For propofol TIVA maintenance in obese patients, lean body weight (LBW) is the preferred dosing scalar. Propofol clearance is primarily hepatic and correlates with cardiac output and liver perfusion, both of which scale with lean mass rather than total body weight. Using TBW would lead to overdosing and prolonged sedation because the excess adipose tissue contributes minimally to propofol clearance. For the induction bolus, TBW-based dosing is more appropriate to fill the larger initial volume of distribution. For neuromuscular blocking agents, dosing is generally IBW-based to avoid prolonged blockade.

Reference: Morgan & Mikhail's Clinical Anesthesiology, 6th ed.

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Written and medically reviewed by the StethoPrep medical team.