Clinical AdvisorClinical Challenge: Vomiting and Weakness

A 38-year-old with two weeks of vomiting presents with tachycardia, weakness, and an ECG showing diffuse ST depression with T-U fusion waves. The pattern points away from ischemia and toward severe hypokalemia, a diagnosis with immediate prescribing implications for NPs/PAs managing vomiting patients across settings.

Clinical Considerations

• Severe hypokalemia (K+ less than 2.5 mEq/L) produces ECG changes including ST depression, T-U fusion, and QRS widening that can mimic ischemia and precede fatal arrhythmia
• Three first-line antiemetics prolong QT and are contraindicated when hypokalemia is suspected: ondansetron, metoclopramide, and prochlorperazine
• Safe antiemetic alternatives include diphenhydramine, benzodiazepines, and dexamethasone, though dexamethasone may worsen metabolic alkalosis
• Epinephrine and sodium bicarbonate both lower serum potassium, critical to know if a hypokalemic patient arrests

Practice Applications

• Reconsider your antiemetic default when vomiting patients present with weakness, tachycardia, or any ECG abnormality
• Order potassium and an ECG together in prolonged vomiting with systemic symptoms; don’t wait for labs to drive the clinical picture
• Admit when K+ is below 2.5 mEq/L, ECG changes are present, or significant muscle weakness exists

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