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A woman in her twenties, who had vomited daily for a year, developed serious anorexia (BMI 14) and hypokalemia. She was admitted to a local hospital because of listlessness and palpitations. Blood tests showed pH 7.62 (7.35 - 7.45), pCO2: 5.51 kPa (4.70 - 6.00), and potassium 2.3 mmol/l (3.5 - 5.0), later 1.7 mmol/l. She developed tonic-clonic seizures (caused by ventricular tachycardia) and needed assisted ventilation. Upon arrival at the secondary hospital (by air ambulance), she had frequent episodes of ventricular tachycardia, pH was 7.84 (7.37 - 7.45), pCO2: 3.46 kPa (4.3 - 5.7) and QT-time was 775 ms. After onset of assisted ventilation (set to 100 % oxygen and about 20 % of normal minute volume) pH decreased, potassium increased and ventricular arrythmias gradually disappeared. She was extubated seven hours after admission without neurological sequelae. We believe the vomiting was the main cause of hypokalemia and metabolic alkalosis. Hypokalemia prolongs the QT-interval and is a risk factor for Torsades de pointes ventricular tachycardia. Interpretation. The rapid increase of potassium levels in blood upon lowering of pH (approximately 0.5 mmol per 0.1 decline in pH) can be exploited therapeutically as in our case. An anorectic patient developing hypokalemia should be treated in hospital.

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