Acid-Base Disorders USMLE Step 1 Practice Question

A 42-year-old woman with poorly controlled type 2 diabetes mellitus presents to the emergency department with a 2-day history of polyuria, polydipsia, and progressive dyspnea. She reports fruity-smelling breath and denies fever or recent infections. On examination, she is alert but drowsy, breathing deeply and rapidly. Vital signs: BP 98/62 mmHg, HR 118 bpm, RR 28 breaths/min, temperature 37.2°C, SpO2 94% on room air. Arterial blood gas reveals pH 7.24, PCO2 22 mmHg, HCO3− 9 mEq/L. Serum glucose 487 mg/dL, serum β-hydroxybutyrate elevated, serum osmolality 318 mOsm/kg. Urinalysis shows 3+ glucose and 3+ ketones. Which of the following best describes the primary acid-base disturbance and respiratory response?