hypoventilation

Hypoventilation is the opposite of hyperventilation: breathing that is too little for the body's needs. Its hallmark is a rise in arterial carbon dioxide, because the lungs are not clearing it as fast as the body produces it.

The retained carbon dioxide forms acid and lowers blood pH, a state called respiratory acidosis. Because every breath also brings in oxygen, severe hypoventilation lowers blood oxygen as well, especially when a person is breathing room air. The combination of high carbon dioxide and low oxygen is what makes serious hypoventilation dangerous.

Causes include anything that weakens the breathing pump or its drive: sedative or opioid drugs, brainstem injury, nerve or muscle disease, severe obesity pressing on the chest, or advanced airway and lung disease. Treatment targets the cause and supports ventilation, sometimes with non-invasive or mechanical assistance to clear carbon dioxide.