USMLE (United States Medical Licensing Examination) Practice Exam 04

A 27-year-old man is brought to the emergency department after being found confused and breathing rapidly. He has type 1 diabetes mellitus and has not taken insulin for 2 days due to gastroenteritis. Temperature is 37.2°C (99.0°F), blood pressure is 102/64 mm Hg, pulse is 118/min, and respirations are 30/min with deep, labored breathing. Labs show: Na+ 130 mEq/L, K+ 5.6 mEq/L, Cl− 96 mEq/L, HCO3− 10 mEq/L, glucose 520 mg/dL. Arterial blood gas shows pH 7.12 and PaCO2 22 mm Hg. Which of the following is the most likely explanation for his low PaCO2?