How does hypoventilation affect PaCO2 levels?

Hypoventilation occurs when there is inadequate ventilation to meet the metabolic demands of the body, leading to a reduced exchange of gases in the lungs. When a person hypoventilates, the amount of carbon dioxide (CO2) that is exhaled decreases. As a result, CO2 accumulates in the bloodstream, which causes an increase in the partial pressure of carbon dioxide (PaCO2).

This increase in PaCO2 can lead to respiratory acidosis, as the elevated levels of CO2 result in a higher concentration of carbonic acid in the blood. This physiological response can have several significant effects on the body's acid-base balance and respiratory function.

In contrast, an increase in PaCO2 cannot occur from actions that typically lead to a decrease in CO2 levels, such as hyperventilation, or can maintain normal levels when ventilation is adequate. Therefore, in the case of hypoventilation, an increase in PaCO2 is a clear outcome.