A nomogram has been prepared that depicts relationships between cardiac output (Q), oxygen consumption Vo2), hemoglobin concentration (Hb) the position of the oxygen-hemoglobin dissociation curve, the oxygen saturation of arterial blood (Sao2), and the partial pressure of oxygen in the mixed venous blood (Pvo2). Examples are provided to illustrate how this nomogram may be employed to facilitate decisions regarding the need for blood transfusions in patients in whom oxygen delivery may be impaired.