Speed of blood withdrawal and accurate measurement of oxygen content in mixed venous blood.

Background: Measurement of mixed venous oxygen saturation helps determine whether cardiac output and oxygen delivery are sufficient for metabolic needs. As recommended by the American Association of Critical-Care Nurses guideline, blood samples for determining mixed venous oxygen saturation are obtained by slowly, in 1 to 2 minutes, withdrawing 1.5 mL of blood from the distal port of the pulmonary artery catheter.