Gas Transport — O2 and CO2

A 28-year-old woman at high altitude (4500 m) develops acute mountain sickness with headache, nausea, and mild dyspnea. Her ABG shows: pH 7.48, PaCO₂ 28 mmHg, PaO₂ 55 mmHg, HCO₃⁻ 20 mEq/L, SaO₂ 82%. Vital signs: RR 24/min, HR 110/min, BP 118/82 mmHg. She is conscious and alert. What is the most appropriate immediate management?

A 42-year-old woman with acute pneumonia presents with severe hypoxemia (PaO₂ 55 mmHg on room air) and normal PaCO₂ (40 mmHg). On supplemental O₂ (FiO₂ 0.6), PaO₂ rises only to 65 mmHg. Which investigation would best confirm the suspected pathophysiology?

A 58-year-old male smoker with COPD presents with dyspnea and cyanosis. Arterial blood gas shows pH 7.32, PaCO₂ 58 mmHg, HCO₃⁻ 28 mEq/L, PaO₂ 52 mmHg. To assess the primary mechanism of hypoxemia and guide therapy, which investigation is most appropriate?

Which feature best distinguishes hypoxaemia due to hypoventilation from hypoxaemia due to ventilation–perfusion (V/Q) mismatch?

A 58-year-old man with COPD presents to the emergency department with acute dyspnea, cyanosis, and confusion. ABG shows: pH 7.25, PaCO₂ 72 mmHg, PaO₂ 48 mmHg, HCO₃⁻ 32 mEq/L. Oxygen saturation is 82% on room air. What is the most appropriate immediate next step in management?