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Emergency And Acute Medicine – Alkalosis
Core Overview
Alkalosis refers to disorders in which blood pH is elevated above normal. This may occur due to excessive loss of carbon dioxide from hyperventilation (respiratory alkalosis) or from an increase in serum bicarbonate concentration (metabolic alkalosis). Respiratory alkalosis results from increased alveolar ventilation leading to reduced PaCO₂, commonly triggered by hypoxemia, metabolic acidosis, or direct stimulation of central or peripheral chemoreceptors. It is rarely life-threatening and typically occurs with pH values below 7.50.
Metabolic alkalosis develops when hydrogen ions are lost or bicarbonate is gained. Persistence requires impaired renal excretion of bicarbonate, often due to volume depletion, electrolyte abnormalities, or hormonal influences. Severe alkalemia carries high mortality, particularly when pH exceeds 7.55–7.65.
Underlying Causes
Respiratory alkalosis may arise from central nervous system conditions such as anxiety, pain, fever, stroke, infection, or intracranial lesions. Hypoxemia from altitude exposure, anemia, or pulmonary shunting is a frequent trigger. Drugs and hormones including salicylates, catecholamines, nicotine, progesterone, pregnancy, and hyperthyroidism may also contribute. Thoracic conditions such as pulmonary embolism, pneumonia, pneumothorax, sepsis, hepatic failure, and heat exhaustion are additional causes.
Metabolic alkalosis is commonly due to gastrointestinal hydrogen loss from vomiting, nasogastric suction, bulimia, or chloride-losing diarrhea. Renal losses occur with diuretics, mineralocorticoid excess, post-hypercapnia states, and inherited tubulopathies such as Bartter or Gitelman syndromes. Other mechanisms include intracellular hydrogen shifts, extracellular volume contraction, bicarbonate administration, and massive transfusions.
Clinical Manifestations
Symptoms result from reduced cerebral blood flow, electrolyte disturbances, and the underlying disease process. Neuromuscular irritability due to hypocalcemia is common and may present with weakness, myalgias, tetany, paresthesias, carpal–pedal spasm, seizures, or altered mental status. Cardiac arrhythmias may occur in association with hypokalemia. Signs of dehydration, hypoxemia, and neuromuscular excitability such as Chvostek or Trousseau signs may be present.
Initial Evaluation
Assessment begins with serum electrolytes demonstrating elevated bicarbonate in metabolic alkalosis and evaluation for hypokalemia or hypocalcemia. Renal function testing helps identify dehydration or renal failure. Blood gas analysis confirms alkalemia and distinguishes respiratory from metabolic causes. Expected compensatory responses should be calculated to detect mixed acid–base disorders. Measurement of urine chloride is essential in metabolic alkalosis to differentiate saline-responsive from saline-resistant causes.
Diagnostic Studies
Additional laboratory testing may include glucose, ionized calcium, magnesium, pregnancy testing, and targeted studies based on clinical suspicion such as CBC, cultures, liver function tests, aspirin levels, toxicology screening, renin, aldosterone, cortisol, and thyroid studies. Imaging with chest radiography may reveal pulmonary or cardiac pathology. Electrocardiography is useful for identifying conduction abnormalities related to electrolyte disturbances.
Conditions To Consider
Respiratory alkalosis requires exclusion of organic pathology before diagnosing anxiety-related hyperventilation. Metabolic alkalosis may be categorized as saline responsive (e.g., gastric losses, diuretics, post-hypercapnia states) or saline resistant (e.g., hyperaldosteronism, Cushing syndrome, inherited renal disorders, exogenous alkali exposure).
Emergency Management Principles
Initial stabilization focuses on airway, breathing, and circulation with oxygen, IV access, and cardiac monitoring. Altered mental status warrants administration of glucose, thiamine, and naloxone as indicated.
Respiratory alkalosis is managed by treating the underlying cause, with cautious use of anxiolytics when appropriate.
Management of metabolic alkalosis depends on urine chloride. Volume-depleted patients benefit from isotonic saline and potassium repletion. Saline-resistant cases require treatment of the underlying endocrine or renal disorder, potassium supplementation, aldosterone antagonists, or acetazolamide. Severe refractory alkalosis may rarely require dilute hydrochloric acid infusion or hemodialysis.
Pharmacologic Therapy
Therapeutic agents may include dextrose for hypoglycemia, potassium supplementation, naloxone, thiamine, acetazolamide, spironolactone, antiemetics, and proton pump inhibitors. Dilute hydrochloric acid infusion is reserved for life-threatening alkalemia and must be administered via a central line with close monitoring.
Disposition And Follow-Up
Hospital admission is required for severe alkalemia, altered mental status, dysrhythmias, significant electrolyte abnormalities, hemodynamic instability, or serious underlying disease. ICU care is indicated for pH values greater than 7.55. Patients may be discharged once alkalosis resolves and contributing factors are corrected.
Key Clinical Insights And Common Errors
Respiratory alkalosis is driven by increased minute ventilation resulting in low PaCO₂ and elevated pH. Metabolic alkalosis typically reflects increased bicarbonate retention due to volume, potassium, or chloride depletion. Contraction alkalosis occurs with extracellular fluid loss concentrating serum bicarbonate. Mixed acid–base disorders should be suspected when pH appears normal despite abnormal PaCO₂ or bicarbonate, or when compensatory responses are inappropriate.
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