In patients with closed-head injuries, what may happen in the presence of hypercapnia?
a. High CO2 increases the risk of psychotic events.
b. High CO2 levels cause cerebral vasodila-tion and improved oxygenation.
c. Severe cerebral vasoconstriction results in anoxia and stroke.
d. Vasodilation causes increased intracranial pressure and possibly stops blood flow.
ANS: D
Increased PCO2 dilates cerebral vessels, raising cerebral blood flow, whereas decreased PCO2 constricts cerebral vessels and reduces cerebral blood flow. In patients with traumatic brain inju-ry, the brain swells acutely; this raises the intracranial pressure in the rigid skull to such high lev-els that blood supply to the brain might be cutoff, causing cerebral hypoxia (ischemia). That is, high intracranial pressure may exceed cerebral arterial pressure and stop blood flow.
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