A physiologic basis for red blood cell transfusion decisions.

Identification of a universal "transfusion trigger" has eluded surgeons for years. Optimization of cardiopulmonary hemodynamics should precede the decision to transfuse red blood cells. Red blood cell transfusion should be considered when global oxygen delivery falls below a critical point with increasing oxygen extraction and lactate levels. At present, these parameters must be monitored with invasive techniques. This article addresses some aspects of global oxygen delivery physiology that appear to correlate with cardiac function, metabolism, and tissue perfusion.