Impact of body mass index on postoperative bleeding in cardiopulmonary bypass

Introduction

Body mass index (BMI) has been described as a risk factor for coronary artery disease, but association with postoperative bleeding after cardiopulmonary bypass (CPB) has been found in several studies recently. Nevertheless the strong relationship between a low BMI and excessive bleeding remains unexplained. We sought to investigate the BMI role on postoperative bleeding and its relationship with leptin levels, coagulation, fibrinolysis and complement parameters.

Methods

We performed a nested case–control study of 26 patients, who did not receive antifibrinolytic prophylaxis. We used Bray's classification for BMI: lower than 27 kg/m²; 27–30 kg/m²; higher than 30 kg/m². Variables were collected preoperatively, at ICU admission (0 hours), and at 4 and 24 hours after surgery. Excessive bleeding was defined as blood loss higher than 1 l in the first 24 hours after intervention. The associations of BMI with demographic factors, leptin levels, coagulation, fibrinolysis and complement parameters were analyzed. Pearson's chi-squared test and Fisher's exact test were used, the Student t test for independent groups and the Mann–Whitney U test for nonparametric variables.

Results

In total, 61.5% of patients showed BMI >27 kg/m² (median 28 kg/m², range 25.2–30.7 kg/m²). Patients with BMI lower than 26.4 kg/m² (25–28 kg/m²) presented excessive bleeding (P = 0.026). Leptin levels after adjusting by BMI were significantly associated with excessive bleeding at all postoperative time points (P < 0.001, P < 0.001 and P = 0.004, respectively) (Figure 1). BMI presented a direct correlation with leptins, fibrinogen and plasminogen activator inhibitor-1 (PAI-1) on arrival, meanwhile 24-hour bleeding showed an inverse correlation with the same parameters and BMI (Table 1). Patients with BMI < 27 kg/m² had significantly greater coagulation, fibrinolysis and complement activation. Therefore these patients required significantly greater hemoderivatives.

Figure 1

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Table 1 abstract P257)

Conclusion

Lower BMI was associated with higher postoperative bleeding and lower procoagulant factor levels.