Thiopentone produces anaesthesia in 'one arm-brain circulation time' (approximately 30–45 seconds). What accounts for the rapid termination of effect after a single induction dose?

• A Rapid hepatic metabolism
• B Rapid renal elimination
• C Plasma pseudocholinesterase hydrolysis
• D Redistribution from highly perfused brain to less perfused muscle and fat compartments ✓

Explanation

Thiopentone is highly lipid-soluble and rapidly redistributes from the brain (vessel-rich group — high blood flow, rapid equilibration) to skeletal muscle and then to fat depots. This redistribution terminates single-dose clinical effect within 5–10 minutes — not hepatic metabolism, which has a slow elimination half-life of 10–12 hours. After multiple doses or prolonged infusion, tissues become saturated and redistribution is impaired, causing cumulative effect ('hangover'). This explains why thiopentone is inappropriate for TIVA and why propofol (which is also redistributed but has faster hepatic clearance) is preferred for infusions.

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

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Written and medically reviewed by the StethoPrep medical team.