Emergency Medical Technician (EMT) Practice Test

What effect do decreased CO2 levels have on intracranial pressure?

1. increased blood flow

2. cerebral vessels constricted

3. decreased blood flow

4. cerebral vessels dilated

The correct answer is: cerebral vessels constricted

Decreased levels of carbon dioxide (CO2) in the blood lead to a condition known as hyperventilation. When CO2 levels drop, it results in respiratory alkalosis, which causes the blood vessels in the brain to constrict, known as cerebral vasoconstriction. This narrowing of the cerebral vessels decreases cerebral blood flow, thereby contributing to a reduction in intracranial pressure. Cerebral vasoconstriction occurs because carbon dioxide acts as a vasodilator in the brain. When CO2 levels are lower than normal, the opposite effect happens leading to decreased blood flow through the cranial vessels. This physiological response helps regulate intracranial pressure, especially in medical situations where increases in pressure could be dangerous. Thus, the correct understanding reflects the relationship between CO2 levels and cerebral vessel behavior, ultimately impacting intracranial pressure management in patients.