skip to main content

CMRO2 Value — FRCA Primary MCQ

Instant feedback + full explanation. One question, done properly.

HardPhysiology - NeurophysiologyCMRO2 ValueFRCA Primary

A patient with severe brain injury has lost pressure autoregulation. Mean arterial pressure falls from 90 to 65 mmHg while intracranial pressure remains 20 mmHg and arterial oxygen content is unchanged. Which change is most likely?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: E — CPP becomes 45 mmHg while CBF probably falls

The best answer is “CPP becomes 45 mmHg while CBF probably falls”. Cerebral perfusion pressure equals MAP minus ICP: it therefore falls from 70 to 45 mmHg. When pressure autoregulation is impaired, cerebral blood flow becomes pressure dependent, so this reduction threatens cerebral oxygen delivery despite unchanged arterial oxygen content. Increased extraction may be compensatory but cannot make lower perfusion pressure increase flow or guarantee adequate metabolism.

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