Arm-Brain Time Cardiac Output — FRCA Primary MCQ

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ModeratePharmacology - Intravenous AnaestheticsArm-Brain Time Cardiac OutputFRCA Primary

Regarding the speed of onset of IV induction agents which factor is most important in determining arm-brain circulation time?

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Correct answer: A — Cardiac output

Arm-brain circulation time (the time for drug to travel from the injection site to the brain) is primarily determined by cardiac output. Higher CO = faster delivery = faster onset. In patients with low CO (e.g. shock / heart failure) the arm-brain time is prolonged but the brain receives a higher proportion of the reduced CO so the brain concentration may actually be higher requiring a lower induction dose.

Reference: Peck Hill Williams 2014 Pharmacology for Anaesthesia and Intensive Care