overventilation

Overventilation, or excessive ventilation, is a state in which alveolar ventilation exceeds the body's metabolic CO2 production. The result is a reduction in arterial carbon dioxide (hypocapnia), which leads to respiratory alkalosis in the short term. Lower PaCO2 also causes cerebral vasoconstriction, reducing cerebral blood flow and potentially causing lightheadedness, dizziness, and fainting.

Causes of overventilation include voluntary hyperventilation from anxiety, pain, or panic, as well as medical settings where ventilator settings are too aggressive. In mechanical ventilation, high tidal volumes, high respiratory rates, or inadequate triggering can excessively remove CO2. Other situations include intensive care, perioperative care, and, in divers, rapid or forced breathing before descent. Chronic permissive hyperventilation can occur in certain disease states but is less common.

Clinical features typically reflect hypocapnia and reduced cerebral perfusion and may include perioral tingling, paresthesias of the hands and feet, dizziness, lightheadedness, chest tightness, and occasionally syncope. In patients on mechanical ventilation, low end-tidal CO2 readings and arterial blood gas showing low PaCO2 with high pH support the diagnosis.

Diagnosis relies on capnography or arterial blood gas analysis. Management focuses on correcting the underlying cause and reducing ventilatory drive. This involves adjusting ventilator settings to lower tidal volume and/or respiratory rate, providing reassurance and anxiolysis when appropriate, and monitoring with capnography and repeated ABG as needed. In spontaneous cases, coaching to slow breathing and ensuring adequate oxygenation are important. Overventilation is typically reversible with careful management; severe or prolonged hypocapnia can risk cerebral ischemia and other complications.