A 65-year-old man with a long history of COPD presents to the emergency department with acute worsening of his shortness of breath, increased cough, and purulent sputum. His arterial blood gas shows pH 7.30, PaCO2 65 mmHg, PaO2 55 mmHg, and HCO3 30 mEq/L. What is the most appropriate initial oxygen delivery method for this patient?

The correct answer to the question "A 65-year-old man with a long history of COPD presents to the emergency department with acute worsening of his shortness of breath, increased cough, and purulent sputum. His arterial blood gas shows pH 7.30, PaCO2 65 mmHg, PaO2 55 mmHg, and HCO3 30 mEq/L. What is the most appropriate initial oxygen delivery method for this patient?" is Option C: Venturi mask delivering 24-28% FiO2.

The other options — A) Nasal cannula at 4 L/min, B) Non-rebreather mask at 10 L/min, D) High-flow nasal cannula — are incorrect for this USMLE Exam Prep question. As explained above: In patients with COPD and hypercapnic respiratory failure, precisely controlled oxygen therapy with a Venturi mask (24-28% FiO2) is preferred to prevent worsening hypercapnia by suppressing hypoxic r…