What causes respiratory alkalosis?

Respiratory Alkalosis Causes

Respiratory alkalosis results from hyperventilation that eliminates CO2 faster than tissues produce it, and the causes can be systematically categorized into psychological, pulmonary, central nervous system, iatrogenic, and compensatory mechanisms.

Psychological and Behavioral Causes

• Anxiety disorders, panic attacks, and hyperventilation syndrome are among the most common causes, particularly in emergency department settings, characterized by abnormal breathing patterns with impressive hyperventilation and decreased PaCO2 1, 2.
• These represent diagnoses of exclusion after ruling out organic pathology 3.
• Severe cases can produce life-threatening alkalosis with pH >7.6, leading to hypocalcemia, extreme adrenergic sensitivity, and cerebral/myocardial vasoconstriction 4.

Pulmonary Causes

• Hypoxemia stimulates peripheral chemoreceptors, triggering compensatory hyperventilation in conditions such as:
  • Pneumonia 1
  • Pulmonary embolism 1
  • Pulmonary edema 1
• Any pulmonary disorder that stimulates ventilation can produce respiratory alkalosis through this mechanism 1, 3.

Central Nervous System Causes

• Direct stimulation of the medullary respiratory center causes hyperventilation in:
  • Head injury 1
  • Cerebrovascular accidents (stroke) 1
  • CNS infections (meningitis, encephalitis) 1
• These conditions bypass normal respiratory control mechanisms 3.

Iatrogenic Causes

• Mechanical ventilation with excessive minute ventilation settings is a common cause in critical care 1.
• Inappropriate ventilator management, particularly excessive tidal volumes or respiratory rates, directly causes respiratory alkalosis 1.

Compensatory Mechanisms

• Physiological hyperventilation occurs as compensation for metabolic acidosis to maintain pH near normal, as recognized by the American Thoracic Society 1.
• Heart failure with Cheyne-Stokes breathing creates respiratory alkalosis that may actually protect the failing heart from decompensation 1.

Critical Management Pitfall

Avoid disrupting compensatory respiratory alkalosis in patients with underlying metabolic acidosis 1. If mechanical ventilation is required in these patients:

• Target oxygen saturation of 88-92% rather than higher levels 1
• Avoid excessive oxygen therapy that could eliminate the hypoxic drive maintaining compensatory hyperventilation 1
• The American College of Chest Physicians and European Respiratory Society emphasize preserving these protective mechanisms 1

Metabolic Consequences

Respiratory alkalosis produces multiple systemic effects including:

• Electrolyte disturbances (hypokalemia, hypophosphatemia, hypocalcemia) 3
• Mild lactic acidosis 3
• Cardiac effects including tachycardia, arrhythmias, and chest pain 3
• Altered gastrointestinal perfusion and motility 3