Approach to metabolic acidosis Quiz: Ace Your Exams

A 52-year-old man is brought into the emergency department by ambulance after being found confused at home. The patient is unable to provide a reliable history. Per the neighbor who found the patient and called an ambulance, the patient has had nausea and vomiting on and off for the past several days and has not eaten during this time. Emergency medical services brought the patient’s prescription medication bottles to the ED, which include aspirin, ethambutol, isoniazid, pyrazinamide, and rifampin. Temperature is 36.8 ºC (98.2 ºF), pulse is 84/min, respiratory rate is 16/min, blood pressure is 112/74 mm Hg, and SpO₂ is 99% on room air. On physical examination, the patient is confused and oriented only to person. Mucous membranes are dry. Cardiac, pulmonary, and abdominal exams are unremarkable. Arterial blood gas and serum bloodwork are obtained and shown below. Which of the following is the most likely diagnosis?

Serum Laboratory Test	Result	Reference Range
Arterial pH	7.28	7.35-7.45
Arterial pCO2	35 mm Hg	33-45 mm Hg
Sodium	133 mEq/L	136-146 mEq/L
Chloride	98 mEq/L	95-105 mEq/L
Bicarbonate	15 mEq/L	22-28 mEq/L
Glucose	180 mg/dL	70-110 mg/dL
Beta-hydroxybutyrate	0.9 mmol/L	< 0.5 mmol/L