Emergency Medical Technician (EMT) Basic Certification Practice Exam

What effect does decreased CO2 in the blood have on intracranial pressure?

1. Increased blood flow

2. Cerebral vessels dilate

3. Cerebral vessels constrict

4. Loss of consciousness

The correct answer is: Cerebral vessels constrict

Decreased carbon dioxide (CO2) levels in the blood lead to a physiological response known as respiratory alkalosis, which causes constriction of cerebral blood vessels. When CO2 levels drop, the pH of the blood increases, resulting in vasoconstriction due to the fact that CO2 plays a significant role in determining the diameter of blood vessels in the brain. This constriction leads to decreased blood flow to the brain, which subsequently lowers intracranial pressure as there is less volume of blood within the skull. Understanding this mechanism is essential, as the balance of CO2 and the resultant blood vessel response is crucial in managing conditions associated with altered intracranial pressure. In contrast, other potential effects, such as increased blood flow or loss of consciousness, do not directly relate to the specific response of cerebral blood vessels to decreased CO2.