Introduction. The amount of blood loss during surgery that requires transfusion is frequently estimated with a linear formula (1) using blood volume--calculated on a volume per weight basis--, preoperative hemoglobin concentration, and an established minimum hemoglobin concentration. This formula, however, underestimates allowable pretransfusion blood loss, because it implies that all blood lost contains the initial hemoglobin concentration. In addition, hemodilution
by infusion therapy prior to surgery is usually not taken into consideration. Methods. In order to estimate allowable pretransfusion blood loss more accurately and conveniently, a program was developed for a programmable pocket computer. This program calculates (number of equation in parenthesis): blood volume (2a, 2b) expansion of blood volume prior to surgery (3) hemodilution prior to surgery (4) allowable blood loss during isovolemic hemodilution (5). The applicability of the program to the situation during orthopedic operations was tested in a study in which allowable pretransfusion blood loss was estimated for one group of patients and was calculated with the computer program for another group of patients. Eighty patients undergoing major orthopedic surgery were studied. After preoperative evaluation the attending anesthetist established a minimum hemoglobin concentration and the type of cardiocirculatory monitoring to be used. Patients were divided at random into two groups: for one group blood volume was estimated on a volume per weight basis and allowable blood loss was calculated using equation (1); for the second group allowable blood loss was calculated with the computer program. During the evaluation of the data the computer calculations were also carrier out for group 1.(ABSTRACT TRUNCATED AT 250 WORDS)
