A 66-Year-Old Man with Poorly Controlled Type 2 Diabetes Is

A 66-year-old man with poorly controlled type 2 diabetes is admitted to the hospital due to a 2-day history of fever and confusion.  Blood pressure is 110/50 mm Hg.  Pulse oximetry shows an oxygen saturation of 97% on room air.  Examination reveals warm extremities with full peripheral pulses, an infected neuropathic foot ulcer with surrounding cellulitis, and normal lung sounds.  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

Correct Answer:

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