Causes of Respiratory Alkalosis
Respiratory alkalosis results from hyperventilation that eliminates CO2 faster than tissues produce it, and the causes span pulmonary, neurologic, psychiatric, iatrogenic, and compensatory mechanisms that must be systematically evaluated to guide appropriate management.
Pulmonary Causes
- Hypoxemia from any pulmonary disorder stimulates peripheral chemoreceptors, triggering increased ventilation and includes pneumonia, pulmonary embolism, pulmonary edema, and pulmonary hypertension 1, 2.
- Acute pulmonary edema causes patients to hyperventilate to compensate for hypoxemia, producing respiratory alkalosis despite significant respiratory distress 1.
- Pulmonary hypertension induces hyperventilation as a compensatory mechanism to reduce pulmonary vascular resistance, which is crucial for maintaining cardiac output 1.
- High altitude exposure triggers hypobaric hypoxia, leading to increased respiratory rate and tidal volume that promotes respiratory alkalosis 1.
Central Nervous System Causes
- CNS lesions directly stimulate the respiratory center in the medulla, causing hyperventilation, including head injury, cerebrovascular accidents, and CNS infections 1, 2.
Psychiatric and Behavioral Causes
- Anxiety reactions, panic disorders, and hyperventilation syndrome are among the most common causes in emergency department settings, characterized by abnormal breathing patterns with impressive hyperventilation and increased respiratory frequency 1, 2.
- Panic disorder commonly presents with clustering of suffocating, smothering, and air hunger sensations, occurring even without reduced ventilatory capacity due to excessive ventilatory drive or increased CO2 sensitivity 1, 2.
- Hyperventilation syndrome is a diagnosis of exclusion after ruling out organic causes 3.
Compensatory Mechanisms
- Metabolic acidosis compensation occurs when the respiratory system attempts to maintain pH near normal by hyperventilating to blow off CO2 - this compensatory respiratory alkalosis should not be disrupted 1, 2.
- Heart failure with Cheyne-Stokes breathing creates respiratory alkalosis that may protect the failing heart from decompensation and should not be aggressively suppressed 1, 2.
Iatrogenic Causes
- Mechanical ventilation with excessive settings and inappropriate ventilator management in critical care settings can cause respiratory alkalosis 1, 2.
- Respiratory dyskinesia from antipsychotic medications can lead to respiratory alkalosis, often undiagnosed, including orofacial dyskinesia, dysphonia, and dyspnea 1, 2.
Physiological States
- Pregnancy produces mild respiratory alkalosis with increased ventilation beginning in the first trimester, reaching 20-40% above baseline by term, mediated by elevated serum progesterone levels 1.
Other Causes
- Early sepsis, acute pain, and fever can trigger hyperventilation and respiratory alkalosis 4.
Critical Clinical Pitfalls to Avoid
- Do not disrupt compensatory respiratory alkalosis in patients with underlying metabolic acidosis - if assisted ventilation is necessary, target appropriate oxygen saturation (88-92%) to avoid worsening the condition 1, 2.
- Avoid excessive oxygen therapy that could disrupt compensatory mechanisms in patients with chronic respiratory alkalosis 1, 2.
- In heart failure with Cheyne-Stokes breathing, respiratory alkalosis should not be aggressively suppressed as it serves a protective compensatory function 1, 2.
- Treatment must focus on the underlying cause rather than simply reducing ventilation, as correction requires addressing the etiology 4.