TYK159

Which of the following is the BEST example of context-sensitive half-time?

a) Fentanyl half-life is different in a neonate than in an adult.

b) Propofol bolus redistribution half-life is longer with a dose of 4 mg/kg than with a dose of 1 mg/kg.

c) A patient sedated with a fentanyl infusion at 2 mcg/kg/hr for 2 days will take longer to wake up than a patient sedated with a fentanyl infusion at 2 mcg/kg/hr for 2 hours.

d) Succinylcholine 5 mg/kg IV bolus results in substantially longer paralytic effect (more than 200% longer) than succinylcholine 2.5 mg/kg IV bolus.

e) Pancuronium duration of action is longer in patients with renal failure than patients without.

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Answer

Answer c.

All of the answer choices are true statements with the exception of B; the redistribution half-life of propofol is stable (the longer duration of effect is solely due to the larger dose). However, only answer (c) is an example of context sensitive half-time: longer duration of exposure results in prolonged reduction of effects after discontinuation. The variability in half-life of fentanyl between neonates and adults is related to different volumes of distribution. Succinylcholine at a high dose results in a phase II block that is similar to that seen with nondepolarizing NMBA. The duration of action of pancuronium is different in renal failure patients because of its renal elimination pathway.

Notes

This question originally printed in the Pediatric Anesthesiology Review Topics kindle book series, and appears courtesy of Naerthwyn Press, LLC.

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