Synopsis
Identify chloride-responsive and chloride-resistant metabolic alkalosis, correct its maintenance factors and detect mixed ventilatory or electrolyte danger.
- Metabolic alkalosis is a primary bicarbonate increase; respiratory compensation raises carbon dioxide, but a value outside the expected range reveals an additional respiratory disorder.
- Generation and maintenance are separate: vomiting may initiate acid and chloride loss, while low effective volume, chloride depletion, hypokalaemia and reduced GFR prevent renal bicarbonate excretion.
- A spot urine chloride obtained before treatment helps divide chloride-responsive disease from continuing diuretic or mineralocorticoid-driven chloride-resistant disease, but timing matters.
Key red flags
Perioral tingling, carpopedal spasm, cramps, hyperreflexia, confusion or seizure can result from reduced ionised calcium and altered neuronal excitability.
Investigation priorities
Confirm alkalemia, primary bicarbonate elevation and the adequacy of respiratory compensation.
Management branches
Bicarbonate or base excess is high, pH is alkalemic or symptoms suggest altered ionised calcium.
- Check pH, bicarbonate and carbon dioxide together, compare with expected compensation and identify an additional respiratory acidosis or alkalosis rather than assuming a single process.
- Measure chloride, potassium, magnesium, ionised calcium and renal function, review blood pressure, volume state, ventilation and all gastrointestinal and medicine losses.
Key medicines
Intravenous 0.9% sodium chloridePrescribe through the NICE five-R fluid framework in staged volumes with reassessment, using the patient’s deficit, pressure, urine output, heart failure and renal function rather than a fixed metabolic-alkalosis total.
Potassium chloride replacementChoose oral or approved ready-diluted intravenous potassium chloride from the current measured deficit, symptoms, renal function and local chart, with repeat potassium before further dosing and monitored infusion for high-risk treatment.