The Transfusion Trigger –The Search For A Quantitative Holy Grail

The decision to transfuse blood before or during an operation has begun to be called the “transfusion trigger.” For many years, a fixed value of blood hemoglobin concentration was used as the main “trigger” (usually 10 g/dl) in a pre-operative patient. It was based on little scientific data and took little account of the patient’s condition. Further, Belk and Sunderman [1] and others showed that assays of blood hemoglobin were unstandardized and the results were often inaccurate. In 1988, an NIH Consensus Conference reconsidered the de facto standard criterion for perioperative blood transfusions and added a consideration of the patient’s clinical condition [2], but even this recommendation was based on limited data. The revised guidelines state that most patients will not need preoperative blood transfusion if the blood hemoglobin level is ≥10g/dl, but probably will require transfusion if the level is ≥7g/dl. The guidelines stress that the decision to transfuse also depends on clinical criteria such as the duration of anemia, the patient’s intravascular volume, the probable extent and continuation of blood loss, the probability of massive blood loss, and various coexisting medical factors. These factors must be balanced against the small but real hazards of receiving blood. Only after these conditions have been considered can a decision be reached as to if, how much, and when the blood should be given. When a person has been injured and has lost a significant amount of blood, there is little question that sooner or later the patient will need to be transfused. However, the decision to transfuse can be complicated by the clinical condition of the patient. A clinical decision is required to determine if blood is to be transfused, when it is to be given, how much to give, the patient’s response to the blood loss, and the anticipation of further loss of blood and its quantity, weighing the need for blood against the small hazards of blood transfusion. Blood transfusion has only one goal–to increase the oxygen carrying capacity of the body. As Weiskopf [3] states, “We transfuse red cells to treat or prevent imminent inadequate delivery of oxygen to tissues, with consequent tissue hypoxia.” Three types of clinical decisions exist with a surgical patient. The first is preor peri-operative transfusion, ie, getting the patient in the best possible condition for surgery. This is dependent on the condition of the patient prior to surgery both medically and surgically. The second is intra-operative transfusion, ie, maintaining the patient’s condition during surgery. This depends on the amount of blood lost during surgery, the other fluids and drugs that are given, and the patient’s response to the anesthetic and the surgery. The last is post-operative transfusion, ie, keeping the patient stable after surgery. This is dependent on the condition of the patient at the end of surgery, the loss of blood from oozing after surgery, and the other fluids that are given. Each of these conditions involves a somewhat different set of criteria to assess the need for transfusion. In this commentary, we shall deal only with the first decision—pre-operative transfusion. One of the most pervasive rules in transfusion medicine has been (and to a certain extent still is)