Which of the following statements are true of CO₂ and cerebral blood flow?
I.Increased PCO₂ dilates cerebral vessels, raising cerebral blood flow.
II.Normal ICP is less than 10 mm Hg.
III.To sustain the cerebral blood flow, a cerebral perfusion pressure (CPP) of approximately 60 mm Hg must be maintained.
IV.Increased PCO₂ constricts cerebral vessels, decreasing cerebral blood flow.

Question

Quizplus · Accepted Answer

CO₂ plays an important role in regulating cerebral blood flow. Its effect is mediated through CO₂'s formation of hydrogen ions. 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 injury (TBI), the brain swells acutely; this raises the intracranial pressure (ICP) in the rigid skull to such high levels that blood supply to the brain might be cut off, causing cerebral hypoxia (ischemia). That is, high ICP may exceed cerebral arterial pressure and stop blood flow. Normal ICP is less than 10 mm Hg; a pressure of 20 mm Hg places the brain at risk for ischemia and requires active treatment to lower the ICP. The brain has a high oxygen requirement; it accounts for approximately 20% of the entire body's resting oxygen consumption. To meet this oxygen demand, the body maintains a constant cerebral blood flow of approximately 50 to 60 mL per 100 g of brain tissue per minute; a cerebral blood flow less than 18 mL/100 g/min is the threshold for cerebral ischemia. To sustain the cerebral blood flow, a cerebral perfusion pressure (CPP) of approximately 60 mm Hg must be maintained. The CPP is the difference between mean arterial pressure and the ICP; cerebral ischemia is likely to occur if CPP falls below 55 mm Hg.

Which of the Following Statements Are True of CO2 and Cerebral

Which of the Following Statements Are True of CO₂ and Cerebral