Respiratory Alkalosis Clinical Presentation

Clinical manifestations of respiratory alkalosis depend on its duration, its severity, and the underlying disease process. Note the following:

• The hyperventilation syndrome can mimic many conditions that are more serious. Symptoms may include paresthesia, circumoral numbness, chest pain or tightness, dyspnea, and tetany. ^[11]

• Acute onset of hypocapnia can cause cerebral vasoconstriction. An acute decrease in PaCO₂ reduces cerebral blood flow and can cause neurologic symptoms, including dizziness, mental confusion, syncope, and seizures. Hypoxemia need not be present for the patient to experience these symptoms. ^[5]

• The first cases of spontaneous hyperventilation with dizziness and tingling leading to tetany were described in 1922 in patients with cholecystitis, abdominal distention, and hysteria. ^[12]

• Haldane and Poulton described painful tingling in the hands and feet, numbness and sweating of the hands, and cerebral symptoms following voluntary hyperventilation. ^[13]

• Respiratory alkalosis may impair vitamin D metabolism, which may lead to vitamin D deficiency and cause symptoms such as fibromyalgia. ^[14]

Physical examination findings in patients with respiratory alkalosis are nonspecific and are typically related to the underlying illness or cause of the respiratory alkalosis. Note the following:

• Many patients with hyperventilation syndrome appear anxious and are frequently tachycardic. Understandably, tachypnea is a frequent finding.

• In acute hyperventilation, chest wall movement and breathing rate increase. In patients with chronic hyperventilation, these physical findings may not be as obvious.

• Positive Chvostek and Trousseau signs may be elicited. ^[4]

• Patients with underlying pulmonary disease may have signs suggestive of pulmonary disease, such as crackles, wheezes, or rhonchi. Cyanosis may be present if the patient is hypoxic.

• If the underlying pathology is neurologic, the patient may have focal neurologic signs or a depressed level of consciousness. ^[15]

• Cardiovascular effects of hypocapnia in healthy and alert patients are minimal, but in patients who are anesthetized, critically ill, or receiving mechanical ventilation, the effects can be more significant. Cardiac output and systemic blood pressure may fall as a result of the effects of sedation and positive-pressure ventilation on venous return, systemic vascular resistance, and heart rate. ^[5]

• Cardiac rhythm disturbances may occur because of increased tissue hypoxia related to the leftward shift of the hemoglobin-oxygen dissociation curve. ^[5]

The differential diagnosis of respiratory alkalosis is broad; therefore, a thorough history, physical examination, and laboratory evaluation are helpful in arriving at the true diagnosis.

Central nervous system causes are as follows:

• Pain

• Hyperventilation syndrome

• Anxiety

• Panic disorders

• Psychosis

• Fever

• Cerebrovascular accident

• Meningitis

• Encephalitis

• Tumor

• Trauma

Hypoxia-related causes are as follows:

• High altitude

• Right-to-left shunts

Drug-related causes are as follows:

• Progesterone

• Methylxanthine toxicity

• Salicylate toxicity

• Catecholamines

• Nicotine

Endocrine-related causes are as follows:

• Pregnancy

• Hyperthyroidism

Pulmonary causes are as follows:

• Pneumothorax/hemothorax

• Pneumonia

• Pulmonary edema

• Pulmonary embolism

• Aspiration

• Interstitial lung disease

• Asthma

• Emphysema

• Chronic bronchitis

Miscellaneous causes are as follows:

• Sepsis

• Severe anemia

• Hepatic failure

• Mechanical ventilation

• Heat exhaustion

• Recovery phase of metabolic acidosis

• Congestive heart failure