A 52-Year-Old Woman Comes to the Emergency Department Because of a 2-Day

A 52-year-old woman comes to the emergency department because of a 2-day history of worsening fever, chills, malaise, productive cough, and difficulty breathing. She has type 2 diabetes mellitus, hypertension, and varicose veins. Her current medications include metformin, lisinopril, and atorvastatin. Her temperature is 39.4°C (102.9°F) , pulse is 102/min, respirations are 31/min, and blood pressure is 88/59 mm Hg. Pulse oximetry on 2 L of oxygen via nasal cannula shows an oxygen saturation of 94%.   A central venous catheter terminating in the superior vena cava is placed.  Blood aspirated from the catheter appears red.  Blood gas analysis of this venous sample reveals an oxygen saturation of 87% (normal: 65%-70%) , and lactate is moderately elevated.  Which of the following is the most likely cause of this patient's abnormal blood gas findings?

A) Decreased cardiac output to the vital organs
B) Impaired mitochondrial oxidative respiration in the vital organs
C) Large-vessel thrombosis throughout the vital organs
D) Poor uptake of oxygen in the lungs
E) Stronger oxygen-hemoglobin binding in peripheral tissues