Physiology and Pathophysiology of Hypoxia and Hypercapnia

Definition and Classification of Hypercapnia

Hypercapnia refers to an elevated concentration of carbon dioxide (CO₂) in the bloodstream, typically defined as an arterial partial pressure of CO₂ (PaCO₂) above 45 mmHg. This condition arises due to impaired respiratory function and can be classified based on its underlying causes and severity.

Causes of Hypercapnia

• Hypoventilation: Reduced air exchange due to neuromuscular disorders, chronic obstructive pulmonary disease (COPD), or respiratory muscle fatigue.
• Increased CO₂ Production: Excess metabolic activity, fever, or sepsis can contribute.
• Impaired Gas Exchange: Lung diseases such as pulmonary fibrosis and edema hinder CO₂ clearance.

Classification of Hypercapnia

Acute Hypercapnia

Develops rapidly due to conditions like airway obstruction, drug overdose (leading to respiratory depression), or acute exacerbation of COPD.

Chronic Hypercapnia

Occurs over a longer duration, often seen in patients with progressive respiratory disorders such as long-standing COPD or obesity hypoventilation syndrome.

Compensated vs. Uncompensated Hypercapnia

In compensated hypercapnia, the kidneys respond by retaining bicarbonate (HCO₃⁻) to balance pH levels. Uncompensated hypercapnia, on the other hand, leads to respiratory acidosis with severe physiological consequences.

Clinical Manifestations and Management

Symptoms include dyspnea, confusion, drowsiness, headache, and in severe cases, coma. Treatment strategies focus on improving ventilation, addressing underlying disorders, and employing interventions like mechanical ventilation in critical cases.