A 55-year-old smoker presented with 3 weeks of dyspnea and cough with blood-tinged mucous. Computed tomography of the chest revealed a large mediastinal mass, and bronchoscopy with biopsy confirmed small cell lung carcinoma. There were no adrenal or brain metastases. On admission, laboratory values included potassium of 2.5 mEq/L and serum bicarbonate of 40 mEq/L. Two months prior, both these levels were within the reference ranges. He was treated with normal saline solution infusion and potassium supplementation and was then discharged.