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Phenylephrine Alpha-1 — FRCA Primary MCQ

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HardPharmacology - CardiovascularPhenylephrine Alpha-1FRCA Primary

Following spinal anaesthesia, phenylephrine restores mean arterial pressure but reduces cardiac output in a patient with fixed stroke volume. Which immediate haemodynamic change most plausibly produced this pattern?

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Correct answer: A — Increased systemic resistance accompanied by reflex heart-rate reduction

The best answer is “Increased systemic resistance accompanied by reflex heart-rate reduction”. Phenylephrine is predominantly an alpha1 agonist, so it raises systemic vascular resistance and arterial pressure. The rise in pressure may evoke reflex bradycardia; with a fixed stroke volume this lowers cardiac output. It does not directly provide beta1 inotropy, reduce afterload or increase venous capacitance. The blood-pressure improvement does not therefore prove increased flow.

Reference: RCoA, Primary FRCA syllabus: https://www.rcoa.ac.uk/sites/default/files/documents/2026-01/Primary-FRCA-Syllabus.pdf; Cardiovascular Anatomy and Pharmacology: https://pmc.ncbi.nlm.nih.gov/articles/PMC7121118/