Causes of Respiratory Alkalosis
Respiratory alkalosis results from hyperventilation that eliminates CO2 faster than tissues produce it, with the most common causes being anxiety/panic disorders, hypoxemia from pulmonary disease, CNS stimulation, and iatrogenic mechanical ventilation. 1
Psychological and Behavioral Causes
- Anxiety reactions, panic disorders, and hyperventilation syndrome are the most common causes in emergency settings, characterized by abnormal breathing patterns with impressive hyperventilation, increased respiratory frequency, and decreased PaCO2. 1
- These conditions produce true hyperventilation with respiratory alkalosis, where increased respiratory frequency eliminates CO2 below the normal range. 2
- Hyperventilation syndrome is a diagnosis of exclusion after ruling out organic causes. 3
Pulmonary Causes
- Hypoxemia stimulates peripheral chemoreceptors leading to increased ventilation, and pulmonary disorders that trigger this response include pneumonia, pulmonary embolism, and pulmonary edema. 1
- Pulmonary vasodilation occurs as a direct effect of respiratory alkalosis. 3
Important caveat: In acute respiratory disease with COPD exacerbations, patients may appear to hyperventilate but actually have ineffective ventilation with CO2 retention, not elimination—this produces respiratory acidosis, not alkalosis. 2
Central Nervous System Causes
- Stimulation of the respiratory center in the medulla causes hyperventilation, with common CNS causes including head injury, cerebrovascular accidents, and CNS infections. 1
- Therapeutic hyperventilation is deliberately used for treatment of elevated intracranial pressure. 3
Cardiovascular and Compensatory Mechanisms
- Physiological hyperventilation occurs as a compensatory mechanism in heart failure with Cheyne-Stokes breathing, creating respiratory alkalosis that may protect the failing heart from decompensation. 1
- Compensatory response to metabolic acidosis maintains pH near normal through increased ventilation. 1
Iatrogenic Causes
- Mechanical ventilation with excessive settings and inappropriate ventilator management in critical care settings is a common iatrogenic cause. 1
- In patients with compensatory respiratory alkalosis from metabolic disorders, avoid disrupting the compensatory mechanism—if assisted ventilation is necessary, target oxygen saturation of 88-92%. 1
Metabolic and Systemic Effects
- Respiratory alkalosis produces multiple metabolic abnormalities including changes in potassium (initial hyperkalemia due to alpha-adrenergic stimulation), phosphate, calcium, and development of mild lactic acidosis. 3, 4
- Cardiac effects include tachycardia, ventricular and atrial arrhythmias, and ischemic chest pain from cerebral and myocardial vasoconstriction. 3, 5
- Severe respiratory alkalosis (pH >7.6) induces hypocalcemia and extreme adrenergic sensitivity, creating a life-threatening condition. 5
Critical pitfall: Avoid excessive oxygen therapy that could disrupt compensatory mechanisms in patients with chronic respiratory alkalosis. 1