LOW CARBON DIOXIDE’S EFFECT ON BRAIN INJURY

HYPOCAPNIA  AND THE INJURED BRAIN: MORE HARM THAN BENEFIT

Curley J, Cavanaugh BP, Laffey JG Crit Care Med 2010;38(5):1348-1359

This is a retrospective data extraction analysis, not an actual study. Their goal: to chart the effects of lowering carbon dioxide in the circulating blood. Their conclusions are that beyond the immediate concern for the acute management of herniation of the brain, carbon dioxide levels should be normalized as quickly as possible. They claim that outcomes are, in fact, lowered due by keeping a client’s Pco2 in sub normal ranges. The very mechanism that prevents swelling, that lowers blood flow through vasoconstriction also lowers oxygen delivery – especially to those areas of the brain which are already disrupted and have localized edema and bruising.  Further, since the body will buffer this lower Pco2 with less bicarb ions over several days anyway, then, when the the ventilator is set for a normal Pco2, a transient hypercpania may well occur causing vasodilitation in the head and causing swelling.

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