Between a PaCO2 of approximately 20 and 80 mmHg, cerebral blood flow changes linearly with arterial carbon dioxide tension. Within this range, a 1 mmHg change in PaCO2 alters cerebral blood flow by approximately:

• A 0.5 to 1 mL per 100 g brain per minute
• B 2 to 3 mL per 100 g brain per minute ✓
• C 6 to 8 mL per 100 g brain per minute
• D 12 to 15 mL per 100 g brain per minute

Explanation

Cerebrovascular reactivity to carbon dioxide amounts to roughly 2 to 3 mL per 100 g per minute for every 1 mmHg change in PaCO2, equivalent to about 4 percent of baseline flow. This is the physiological basis for hyperventilation as a temporising measure in intracranial hypertension. The larger figures would imply near-total cessation of flow within the physiological range, which does not occur.

Reference: Morgan and Mikhail's Clinical Anesthesiology, 6th ed.

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Written and medically reviewed by the StethoPrep medical team.