hypercarbia

Hypercarbia, or hypercapnia, is a condition characterized by elevated carbon dioxide (CO2) in the blood. It is usually defined by a partial pressure of CO2 (PaCO2) above 45 mmHg in arterial blood. Hypercarbia can be acute, developing over hours, or chronic, persisting for weeks or longer.

Causes include hypoventilation from central nervous system depression (for example opioid or sedative overdose, anesthesia), neuromuscular disorders (amyotrophic lateral sclerosis, Guillain-Barré syndrome), chest wall abnormalities, obesity hypoventilation syndrome, and ventilation–perfusion mismatch or obstruction from lung disease such as COPD, severe asthma, pneumonia, or pulmonary edema.

Pathophysiology and symptoms: CO2 retention causes respiratory acidosis. In chronic hypercapnia the kidneys compensate by increasing bicarbonate, stabilizing pH toward normal. Clinically, patients may report headaches, sleepiness, confusion or morning headaches; signs include tachycardia and, in severe cases, altered mental status or coma.

Diagnosis: Arterial blood gas analysis shows elevated PaCO2; pH indicates acidosis or compensation; serum bicarbonate may be elevated in chronic cases. Capnography or end-tidal CO2 monitoring can be used at the bedside. Additional workup targets the underlying cause.

Management: Treat the underlying cause and ensure adequate ventilation. Oxygen should be titrated to achieve normoxemia while avoiding excessive oxygen in COPD patients who may rely on hypoxic drive. Noninvasive ventilation is often effective in COPD exacerbations with hypercapnia; invasive mechanical ventilation is used for respiratory failure. In chronic hypercapnia, gradual correction is preferred to minimize complications, and abrupt shifts should be avoided.

Prognosis and prevention: The prognosis depends on the cause and response to treatment. Prevention focuses on managing risk factors for hypoventilation and lung disease, vaccination, pulmonary rehabilitation, and careful monitoring in high-risk patients.