1. Definition
Respiratory acidosis is a condition in which carbon dioxide builds up in the bloodstream due to impaired lung function or hypoventilation, leading to a decrease in blood pH. This results in an acid-base imbalance, which can cause symptoms like confusion, shortness of breath, and fatigue.
2. Biochemical Background
Respiratory acidosis occurs due to an imbalance in the carbon dioxide (CO₂) and bicarbonate (HCO₃⁻) equilibrium in the blood, a key aspect of the body’s acid-base regulation. The underlying formula for this balance is:
CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻
In normal conditions, carbon dioxide (CO₂) produced by cellular metabolism is eliminated through the lungs during exhalation. When CO₂ levels increase—due to hypoventilation, lung disease, or impaired gas exchange—more CO₂ dissolves in the blood. This excess CO₂ combines with water (H₂O) to form carbonic acid (H₂CO₃), which dissociates into hydrogen ions (H⁺) and bicarbonate (HCO₃⁻). As the concentration of hydrogen ions rises, the blood’s pH decreases, leading to acidosis.
The kidneys may attempt to compensate for this imbalance by retaining or producing more bicarbonate (HCO₃⁻) to buffer the excess hydrogen ions, but this process is slower than the respiratory response. Thus, the primary cause of respiratory acidosis is insufficient clearance of CO₂ by the lungs, shifting the balance of this equation toward increased acidity and resulting in a decreased blood pH.
3. Classification
3.1. Acute Respiratory Acidosis
Acute respiratory acidosis occurs suddenly, typically due to conditions like respiratory failure, airway obstruction, severe asthma, or drug overdose. This leads to a rapid buildup of carbon dioxide (CO₂) in the blood, causing a swift decrease in blood pH. Because the onset is fast, the kidneys do not have time to compensate by increasing bicarbonate (HCO₃⁻) levels, resulting in a more severe acidosis with symptoms.
3.2. Chronic Respiratory Acidosis
Chronic respiratory acidosis develops gradually over time, typically due to long-term respiratory conditions such as chronic obstructive pulmonary disease (COPD) or neuromuscular disorders that impair breathing. In this form, carbon dioxide (CO₂) accumulates slowly in the blood, allowing the kidneys to compensate by retaining bicarbonate (HCO₃⁻) to help buffer the acid. As a result, the pH levels are more stable compared to the acute form, but prolonged acidosis can still lead to complications. Without proper management, it can eventually result in respiratory failure.