What are the causes of respiratory alkalosis in patients with respiratory diseases, neurological disorders, or sepsis?

Causes of Respiratory Alkalosis

Respiratory alkalosis results from hyperventilation that reduces PaCO2 below 4.6 kPa (34 mmHg), and the most common causes include anxiety/panic disorders, hypoxemia from pulmonary disease, CNS stimulation, and iatrogenic mechanical ventilation. 1

Primary Etiological Categories

Psychiatric and Behavioral Causes

• Anxiety reactions, panic disorders, and hyperventilation syndrome are among the most frequent causes, characterized by abnormal breathing patterns with impressive hyperventilation, increased respiratory frequency, and decreased PaCO2 1
• Panic disorder specifically 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
• Hyperventilation syndrome is a diagnosis of exclusion commonly seen in emergency department settings 2

Pulmonary Causes

• Hypoxemia stimulates peripheral chemoreceptors, leading to increased ventilation as a compensatory mechanism 1
• Specific pulmonary disorders that stimulate ventilation include:
  • Pneumonia 1
  • Pulmonary embolism 1
  • Pulmonary edema 1, 3
• In acute pulmonary edema, patients hyperventilate to compensate for hypoxemia despite significant respiratory distress, with increased work of breathing causing distress while hyperventilation produces alkalosis 3
• Pulmonary hypertension causes respiratory alkalosis as a compensatory mechanism to reduce pulmonary vascular resistance, where hyperventilation reduces PaCO2 and increases pH to help decrease pulmonary vascular resistance 3

Central Nervous System Causes

• Stimulation of the respiratory center in the medulla can cause hyperventilation 1
• Common CNS causes include:
  • Head injury 1
  • Cerebrovascular accidents 1
  • Central nervous system infections 1

Cardiovascular Causes

• Heart failure with Cheyne-Stokes breathing creates respiratory alkalosis that may protect the failing heart from decompensation 1
• This physiological hyperventilation occurs as a compensatory mechanism and should not be aggressively suppressed 3

Iatrogenic Causes

• Mechanical ventilation with excessive settings and inappropriate ventilator management in critical care settings 1
• Excessive oxygen therapy that disrupts compensatory mechanisms in patients with chronic conditions 1

Drug-Related Causes

• Respiratory dyskinesia from antipsychotic medications can lead to respiratory alkalosis, often undiagnosed, and includes orofacial dyskinesia, dysphonia, and dyspnea 1

Metabolic Compensation

• Compensatory response to metabolic acidosis to maintain pH near normal 1
• In these cases, avoid disrupting the compensatory mechanism; if assisted ventilation is necessary, target appropriate oxygen saturation (88-92% for patients with COPD or risk factors for hypercapnic respiratory failure, 94-98% for most other patients) 1, 3

High-Altitude and Environmental Causes

• High altitude-induced hypobaric hypoxia leads to increased respiratory rate and tidal volume, promoting respiratory alkalosis while simultaneously causing pulmonary vasoconstriction and potentially pulmonary edema 3

Clinical Pitfalls to Avoid

• Do not aggressively correct respiratory alkalosis when it serves as a compensatory mechanism in metabolic acidosis or heart failure with Cheyne-Stokes breathing 1, 3
• Avoid excessive oxygen therapy in patients with chronic respiratory conditions, as this can disrupt compensatory mechanisms 1
• In pulmonary hypertension, maintaining appropriate ventilation without inducing severe respiratory alkalosis is crucial for balancing pulmonary vascular resistance and right ventricular function 3
• Recognize that respiratory alkalosis produces multiple metabolic abnormalities including changes in potassium, phosphate, calcium, and development of mild lactic acidosis 2