A 28-year-old woman from Delhi presents to the emergency department with severe vomiting and abdominal pain for 2 days. On examination, she is tachypneic (RR 28/min) and appears anxious. Arterial blood gas analysis shows: pH 7.52, PaCO₂ 28 mmHg, HCO₃⁻ 24 mEq/L, PaO₂ 95 mmHg. Her hemoglobin is 13 g/dL. A colleague remarks that her oxygen saturation by pulse oximetry is 98%, yet her tissues may be receiving less oxygen than expected. Which of the following best explains the impaired oxygen delivery to tissues in this patient?