Acceptable hematocrit levels in surgical patients

The ready availability of blood and blood components has resulted in a liberal use of blood transfusions; however, the transfusion of blood is still associated with significant risks for the recipient. The appearance of the acquired immunodeficiency syndrome and the evidence that homologous blood can induce immunosuppression and thereby impair the host resistance of surgical patients has led to a reconsideration of the indications for blood transfusions. It has also fostered application of alternative methods with the aim of reducing the number of homologous blood transfusions. Based on the data available from studies on intentional perioperative hemodilution in patients undergoing elective surgery, and data from patients in intensive care, a hematocrit level of about 30% is acceptable for surgical patients, provided oxygen transport is not impaired by the reduced saturation of arterial blood or inadequate perfusion. The basic mechanism that compensates for the reduced oxygen capacity of the blood is a rise in cardiac output and stroke volume, both depending on adequate venous return and myocardial function. The hematocrit setpoint has to be determined for the individual patient with regard to the history of the underlying disease, circulating blood volume, and actual oxygen needs. By accepting a perioperative hematocrit level of 30% for patients without respiratory and cardiac disease or increased oxygen demand, respectively, the number of transfusions of homologous blood can be reduced and dangerous side effects can be avoided.