A 55-year-old man with upper gastrointestinal bleeding (HR 122/min, BP 84/50 mmHg) requires emergency intubation. Compared with a healthy adult, his thiopentone requirement is drastically reduced chiefly because:

• A Reduced plasma protein binding increases free drug fraction
• B Hypovolaemia increases blood-brain barrier permeability to barbiturates
• C Enhanced hepatic extraction prolongs the elimination half-life
• D Reduced cardiac output and a contracted central compartment deliver a larger fraction of the bolus to the brain ✓

Explanation

In hypovolaemic shock, low cardiac output slows delivery of drug to muscle and fat, the sites of redistribution, while the reduced volume of the central compartment means a higher initial arterial concentration reaches the brain. The induction dose may need to be halved or more. Protein binding changes are minor contributors, and altered hepatic clearance affects elimination rather than the onset bolus requirement.

Reference: Stoelting's Pharmacology and Physiology in Anesthetic Practice, 6th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.