Causes of Respiratory Alkalosis
Respiratory alkalosis is primarily caused by hyperventilation, which leads to excessive elimination of carbon dioxide relative to its production, resulting in decreased PaCO2 and increased pH. 1, 2
Pathophysiological Mechanisms
- Respiratory alkalosis occurs when alveolar ventilation exceeds metabolic requirements, leading to hypocapnia (PaCO2 < 35 mmHg) and alkalization of body fluids 3
- The condition can be acute or chronic, with different compensatory mechanisms:
Common Causes
Psychogenic/Anxiety-Related
- Anxiety reactions, panic disorders, and hyperventilation syndrome are common causes, especially in emergency department settings 1, 4
- Characterized by abnormal breathing patterns with impressive hyperventilation, increased respiratory frequency, and respiratory alkalosis (decreased PaCO2) 5
- Often presents with an abrupt onset of regular, rapid, shallow breathing disproportionate to metabolic stress 5
Physiological/Compensatory
- Physiological hyperventilation occurs as a compensatory mechanism in various conditions 5
- Compensatory response to metabolic acidosis to maintain pH near normal 6
- Can occur during heart failure with Cheyne-Stokes breathing, creating respiratory alkalosis that may protect the failing heart from decompensation 5
Pulmonary Causes
- Hypoxemia stimulates peripheral chemoreceptors, leading to increased ventilation 5
- Pulmonary disorders that stimulate ventilation:
- Pneumonia
- Pulmonary embolism
- Pulmonary edema
- Asthma 1
Central Nervous System Disorders
- Stimulation of the respiratory center in the medulla can cause hyperventilation 3
- Common CNS causes include:
Drugs and Toxins
- Salicylates, progesterone, and certain stimulants can directly stimulate the respiratory center 7
- Nicotine and xanthines can also trigger hyperventilation 1
Metabolic/Endocrine Disorders
- Hyperthyroidism increases metabolic rate and respiratory drive 1
- Fever increases metabolic demands and stimulates ventilation 1
- Pregnancy (due to progesterone effects) 7
Iatrogenic Causes
- Mechanical ventilation with excessive settings 5
- Inappropriate ventilator management in critical care settings 8
Clinical Manifestations
- Symptoms stem from multiple organ systems and can be caused by low PaCO2 or increased sympathetic tone 4
- Neurological: Lightheadedness, dizziness, paresthesias, tetany, seizures 1
- Cardiovascular: Tachycardia, palpitations, chest pain, arrhythmias 1
- Respiratory: Shortness of breath, chest tightness 4
- Musculoskeletal: Carpopedal spasm, muscle cramps 7
Diagnostic Approach
- Arterial blood gas analysis showing decreased PaCO2 (<35 mmHg) and increased pH (>7.45) 3
- Exclusion of organic causes of hyperventilation is essential before diagnosing hyperventilation syndrome 4
- Evaluation for signs of breathing dysregulation that may lead to hypocapnia 4
Treatment Considerations
- Primary approach is to correct the underlying cause 1
- For hyperventilation syndrome, treatment includes:
- Psychological counseling
- Physiotherapy and relaxation techniques
- Drug therapy in severe cases 4
- In metabolic disorders with compensatory respiratory alkalosis, avoid disrupting the compensatory mechanism 6
- If assisted ventilation is necessary, target appropriate oxygen saturation (88-92%) to avoid worsening the condition 6
Clinical Pitfalls
- Respiratory alkalosis is often underestimated in hospitalized patients despite potential serious consequences 7
- Symptoms may persist even after normalization of PaCO2, as they can be maintained by psychological mechanisms 4
- Avoid excessive oxygen therapy that could disrupt compensatory mechanisms in patients with chronic respiratory alkalosis 5, 6