Respiratory alkalosis
Respiratory alkalosis is a reduction in arterial Pco2 from increased alveolar ventilation, most often driven by sepsis, hepatic failure, anxiety, hyperventilation, pregnancy, or salicylate toxicity, presenting with tachypnea, lightheadedness, and paresthesia. Diagnosis rests on arterial blood gas confirmation of a primary fall in Pco2 with the expected compensatory drop in bicarbonate, and management targets the underlying driver rather than the blood gas itself, with acetazolamide or controlled hypoventilation reserved for rare severe alkalemia with hemodynamic compromise.
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What this article covers
- Overview
A primary fall in arterial Pco2 from increased alveolar ventilation: respiratory alkalosis is defined by a reduction in Pco2 below the normal range, driving pH up, with a secondary compensatory decrease in serum bicarbonate.
- Epidemiology
Extremely common as a secondary finding because it accompanies many acute illnesses (sepsis, hepatic failure, hypoxemic respiratory conditions) rather than occurring as an isolated primary disorder.
- Risk factors
Sepsis: direct central respiratory stimulation is one of the most common causes of acute respiratory alkalosis in hospitalized patients.
- Pathophysiology
Increased alveolar ventilation lowers Pco2 directly: any process that increases minute ventilation beyond metabolic carbon dioxide (CO2) production drops arterial Pco2, and by the Henderson-Hasselbalch relationship raises pH.
- Clinical features
Tachypnea is the underlying sign that should prompt a blood gas when accompanied by neurologic symptoms.
- Differential diagnosis
Salicylate (aspirin) toxicity: the most dangerous mimic; produces respiratory alkalosis plus an increased anion gap metabolic acidosis with tinnitus, vomiting, and altered mental status; an elevated…
- Diagnosis
Respiratory alkalosis is confirmed on arterial blood gas: a primary decrease in Pco2 below normal, an increased pH, and a compensatory decrease in bicarbonate (only slight acutely, more pronounced…
- Management
First, identify and treat the underlying cause; this resolves the great majority of cases.
- Complications
Cardiac arrhythmias: from severe alkalemia and the accompanying fall in ionized calcium and potassium shifts.
- Prognosis
Prognosis is determined by the underlying cause, not the blood gas abnormality itself: anxiety-driven and pregnancy-related respiratory alkalosis are benign; sepsis- and hepatic failure-driven…
- Prevention
Screen for and treat sepsis promptly using standard sepsis bundles (blood cultures before antibiotics, source control, early broad-spectrum antibiotics) to avoid unrecognized progression.
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