Acute severe metabolic alkalosis: causes, chloride-responsive vs resistant

Also known as Metabolic alkalosis · Alkalosis · Chloride-responsive alkalosis · Chloride-resistant alkalosis · Contraction alkalosis · Hypochloraemic alkalosis

Metabolic alkalosis (pH 7.45, HCO3 26) is common in ICU (vomiting, NG suction, diuretics). SEVERE (pH 7.55) → serious: hypoventilation (compensatory — but causes hypoxia/hypercapnia), hypokalaemia, hypocalcaemia (ionised), arrhythmia, seizures, coronary vasospasm. Classification: CHLORIDE-RESPONSIVE (LOW urine chloride — vomiting, NG suction, diuretics, post-hypercapnia — responds to saline + KCl) vs CHLORIDE-RESISTANT (HIGH urine chloride — mineralocorticoid excess: hyperaldosteronism, Cushing, exogenous steroid, liquorice — responds to treating cause, K-sparing diuretic). KEY: maintenance requires ALDOSTERONE (without it, kidney excretes excess HCO3) + HYPOKALAEMIA (promotes H secretion → HCO3 generation). Treatment: NORMAL SALINE (volume + chloride) + KCl for chloride-responsive; treat cause for chloride-resistant. Severe (pH 7.6) → acetazolamide, acid (HCl/arginine), dialysis.

medium22 referencesUpdated 20 Aug 202625 min readVerification in progress

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Metabolic alkalosis (elevated pH and bicarbonate) becomes dangerous with significant alkalaemia — arrhythmias, confusion and seizures. Split every case by the urine chloride: assessment of metabolic alkalosis begins with measuring urine chloride to decide whether the process is one of chloride depletion (chloride-responsive — vomiting, NG suction, diuretics, post-hypercapnia — corrects with volume and chloride repletion plus potassium) or not (chloride-resistant — e.g., mineralocorticoid excess — needs the cause treated, often with a mineralocorticoid receptor antagonist). Escalate refractory or fluid-restricted disease to acetazolamide (enhances renal bicarbonate excretion), then acid therapy (hydrochloric acid or arginine hydrochloride) — while remembering that aggressive lowering of the pH is usually unnecessary and the alkalosis resolves only once the maintenance factors — volume, chloride, potassium and mineralocorticoid drive — are removed.

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Meet the patient

Mrs K is 68 with severe COPD (baseline PaCO2 68 mmHg, HCO3 38 mmol/L), intubated for an infective exacerbation and now 12 hours into a wean. The gas reads pH 7.58, PaCO2 44 mmHg, HCO3 40 mmol/L, chloride 88 mmol/L, potassium 3.1 mmol/L; she is agitated, triggering hard against the tube, and the monitor shows a short run of supraventricular tachycardia. Hold two questions and the whole topic slots into place: what generated the alkalosis (the kidney's chronically retained bicarbonate, exposed by an over-fast fall in PaCO2), and what maintains it (volume depletion with secondary mineralocorticoid excess, reduced bicarbonate excretion, and hypokalaemia) — and why one urine chloride value decides whether the answer is chloride repletion or a mineralocorticoid block.^[8]^[12]

References22Show

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