A 72-year-old man with diabetes, renal insufficiency, and coronary aery disease presents in septic shock from emphysematous cholecystitis. His oxygen saturation is 100% on 6-L nasal cannula and his hemoglobin is 7.2 mg/dL. His mixed venous oxygen saturation is 58%. Which of the following treatment options will improve his oxygen delivery the most?

Transfusion of 2 units of packed red blood cells will increase the patient's oxygen delivery the most. Mixed venous oxygen saturation reflects the difference between the oxygen delivered to the tissues and the oxygen taken up by the tissues. Oxygen delivery is the product of cardiac index and oxygen content of blood (CaO2 ), the latter of which is determined primarily by hemoglobin (Hb) concentration. Oxygen saturation (SaO2 ) and the paial pressure of oxygen (PaO2 ) contribute much less. The formula for oxygen content (CaO2 ) can be expressed as CaO2=1.36*Hb*SaO2/100+0.0031*PaO2. Since the patient's oxygen saturation is 100%, increasing his inspired oxygen concentration is unlikely to increase his oxygen delivery. Since the contribution of PaO2 is so low, hyperbaric oxygen is also not the treatment of choice. Fuhermore, transpoing unstable patients to the hyperbaric chamber can be dangerous. Correction of the patient's anemia by the most expeditious manner, that is, transfusion of blood, is the treatment of choice.