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CMRO2 — FRCA Primary MCQ

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HardPhysiology - NeurophysiologyCMRO2FRCA Primary

Jugular-bulb sampling during stable neuroanaesthesia gives arterial oxygen content 20 mL dL−1 and jugular venous oxygen content 13 mL dL−1. If global cerebral blood flow is 50 mL 100 g−1 min−1, what is CMRO2 by the Fick principle?

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Correct answer: E — 3.5 mL O2 100 g−1 min−1

The best answer is “3.5 mL O2 100 g−1 min−1”. The arteriovenous oxygen-content difference is 7 mL dL−1, or 0.07 mL mL−1. Multiplying by cerebral blood flow of 50 mL 100 g−1 min−1 gives 3.5 mL O2 100 g−1 min−1. This also matches the approximate normal global CMRO2 and demonstrates why units must be converted before applying Fick’s principle.

Reference: Brain vascular and hydrodynamic physiology: https://pmc.ncbi.nlm.nih.gov/articles/PMC3868010/; Royal College of Anaesthetists, Primary FRCA syllabus v2.2: https://www.rcoa.ac.uk/sites/default/files/documents/2026-01/Primary-FRCA-Syllabus.pdf