Original ContributionPreoperative blood volume deficit influences blood transfusion requirements in females and males undergoing coronary bypass graft surgery
Introduction
Females are known to receive more blood transfusion than males during coronary artery bypass graft (CABG) surgery.1, 2, 3, 4 The reason for such a gender difference in the requirement for blood transfusion is not fully understood. Previous studies have reported that blood transfusion in CABG patients was significantly influenced by age, gender, weight, body surface area (BSA), preoperative hematocrit (Hct), previous CABG, coagulation defects, insulin-dependent diabetes mellitus, and severe clinical complications.4, 5, 6, 7, 8 Low Hct, which is characteristic of females, was suggested to be a major reason for the greater need for blood transfusion in females.8 However, gender difference in transfusion need was persistent even when male and female CABG patients with similar preoperative Hct levels were compared.4, 9 Our previous studies further showed that differences in age, weight, and duration of surgery could not account for the gender difference in transfusion need, but gender by itself was an independent determining factor.9
The present study was aimed at understanding the characteristics by which gender can have an influencing role in determining the blood transfusion for CABG surgery. Calculations based on Hct and total body mass show that females have lower blood volume and red blood cell (RBC) mass than males.2, 10 Although these factors theoretically may account for the gender difference in the need for blood transfusion during CABG surgery, no direct measurements were made to establish such a relationship. In the present study, the volumes of total blood, RBC, and plasma were measured in female and male patients before CABG surgery, and their relationship to the transfusion of blood received by them was evaluated. The role of blood loss during the operation as a possible contributing factor to this gender difference in transfusion was also evaluated by measuring the blood volumes in some patients before and after CABG surgery.
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Materials and methods
After obtaining Maimonides Medical Center Institutional Review Board approval, 57 consenting patients undergoing CABG surgery were prospectively studied from June 1999 to March 2001. The patients included 21 females and 36 males. Pregnant women and patients who had multiple procedures or repeat operations were not included in this study.
Preoperatively, aspirin was stopped 10 days before elective surgery, and those patients taking coumadin were switched to heparin. Standardized anesthesia
Clinical features
Among the female and male CABG patients studied, there was no significant difference in the mean age, weight, and duration of surgery (Table 1). Mean BSA was 1.73 m2 in females and 1.93 m2 in males, and it was significantly lower (p < 0.001) in females than in males (Table 1). Mean preoperative hematocrit was 33.5% in females and 37.8% in males, and it was significantly lower (p < 0.01) in females than in males. There was no significant difference in discharge hematocrit between females and
Discussion
In the present study, we employed the “gold standard” radioactive tracer dilution method11, 12, 13 to determine experimentally the preoperative blood volume, and we evaluated its relationship to the blood transfusion received by female and male CABG patients. This study clearly showed that among patients scheduled for CABG surgery, preoperative volumes of total blood, RBCs, and plasma were significantly lower in females than in males (Figure 1). This finding is consistent with the lower RBC
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