Context-sensitive half-time explains why propofol's recovery is faster than thiopentone after prolonged infusions. What does 'context-sensitive' refer to in this pharmacokinetic concept?

• A The drug's half-time depends on the clinical context (type of surgery)
• B The half-time is sensitive to changes in hepatic blood flow in context of general anaesthesia
• C Context refers to the patient's co-morbidities affecting drug clearance
• D The time for plasma drug concentration to halve after stopping infusion depends on the duration of infusion ('context') ✓

Explanation

Context-sensitive half-time (CSHT) refers to the time required for plasma drug concentration to decrease by 50% after terminating an infusion, where 'context' is the duration of that infusion. After short infusions most drugs behave similarly, but with prolonged infusions, peripheral compartment accumulation slows redistribution from the central compartment. Propofol has a CSHT that rises modestly with duration, while thiopentone's CSHT rises sharply — explaining why propofol is preferred for TIVA and thiopentone is unsuitable for infusions.

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

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