What causes hypercapnia in patients?

Hypercapnia, the condition characterized by elevated levels of carbon dioxide (CO2) in the blood, primarily results from inadequate ventilation. This occurs when the respiratory system is unable to effectively remove CO2 produced by the body. Inadequate ventilation can stem from various factors such as airway obstruction, depressed central respiratory drive (for example, due to sedatives or neurological conditions), or respiratory muscle weakness.

When ventilation is compromised, the carbon dioxide generated by cellular metabolism accumulates in the bloodstream rather than being expelled through exhalation. This buildup can lead to respiratory acidosis and various physiological responses as the body attempts to correct the imbalance.

Other factors listed, such as excessive oxygen delivery, lung over-expansion, and high altitude, do not directly cause hypercapnia. Excessive oxygen delivery may even result in a decreased respiratory drive in some situations but does not inherently lead to elevated CO2 levels unless ventilation is also inadequate.