Respiratory alkalosis

Respiratory alkalosis: Excerpt from Handbook of Diseases

Caused by alveolar hyperventilation, respiratory alkalosis is a condition marked by a decrease in partial pressure of arterial carbon dioxide (Paco₂) to below 35 mm Hg. Uncomplicated respiratory alkalosis leads to a decrease in hydrogen ion concentration, which causes elevated blood pH. Hypocapnia occurs when the elimination of carbon dioxide by the lungs exceeds the production of carbon dioxide at the cellular level.

Causes

Respiratory alkalosis can result from pulmonary or nonpulmonary causes:

❑ Pulmonary causes include pneumonia, interstitial lung disease, pulmonary vascular disease, and acute asthma.

❑ Nonpulmonary causes include anxiety, fever, aspirin toxicity, metabolic acidosis, CNS disease (inflammation or tumor), sepsis, hepatic failure, and pregnancy.

Signs and symptoms

The cardinal sign of respiratory alkalosis is deep, rapid breathing, possibly exceeding 40 breaths/minute and much like the Kussmaul’s respirations that characterize diabetic acidosis.

Such hyperventilation usually leads to CNS and neuromuscular disturbances, such as light-headedness or dizziness (from below-normal carbon dioxide levels that decrease cerebral blood flow), agitation, circumoral and peripheral paresthesia, carpopedal spasms, twitching (possibly progressing to tetany), and muscle weakness. Severe respiratory alkalosis may cause cardiac arrhythmias that fail to respond to conventional treatment, seizures, or both.

Diagnosis

Arterial blood gas (ABG) analysis confirms respiratory alkalosis and rules out respiratory compensation for metabolic acidosis. Findings include a Paco₂ below 35 mm Hg, a pH that’s elevated in proportion to the fall in Paco₂ in the acute stage but that drops toward normal in the chronic stage, and a bicarbonate level that’s normal in the acute stage but below normal in the chronic stage.

Treatment

The goal of treatment is to eradicate the underlying condition — for example, to remove ingested toxins or to treat fever, sepsis, or CNS disease.

CLINICAL TIP: With severe respiratory alkalosis, the patient may be instructed to breathe into a paper bag, which helps relieve acute anxiety and increases carbon dioxide levels.

Prevention of hyperventilation in patients receiving mechanical ventilation requires that ABG values be monitored and dead space or minute ventilation volume be adjusted.

Special considerations

❑ Watch for and report any changes in neurologic, neuromuscular, or cardiovascular function.

❑ Remember that twitching and cardiac arrhythmias may be associated with alkalemia and electrolyte imbalances. Monitor ABG and serum electrolyte levels closely, watching for any variations.

Book Source Details

• Book Title: Handbook of Diseases
• Author(s): Springhouse
• Year of Publication: 2003
• Copyright Details: Handbook of Diseases, Copyright © 2003 Lippincott Williams & Wilkins.

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Copyright notice for book excerpts: Copyright © 2008 Lippincott Williams & Wilkins. All rights reserved.

More About This Book: Title: Handbook of Diseases Authors: Springhouse Publisher: Lippincott Williams & Wilkins Copyright: 2003 ISBN: 1-58255-266-5

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