Introduction: Many efforts have been made in cardiac surgery to avoid allogeneic RBC transfusion. However blood product transfusion after cardiopulmonary bypass (CPB) is a common event. Its cause is multifactorial but the haemodilution effect of the extracorporeal circuit on blood volume has been implicated as one of the major contributions for the need of transfusion. Nevertheless a low haematocrit (hct) during CPB has been associated with increased difficulty of weaning from CPB and with an increased postoperative morbidity and mortality .
The objective of the current study was to identify the clinical and demographic variables that let us determine patients at risk of having a critically low hct during CPB.
Method: We prospectively followed up all patients undergoing cardiac surgery under CPB in a 1 year period (334 patients). The CPB prime volume in all cases was 1450 mL. We determined the hct decrease after CPB haemodilution by measuring hct just before cannulation, and just after beginning CPB. We evaluated in a multivariate analysis, using a multiple linear regression model, which factors other than the haemodilution would contribute to the hct decrease, such as age, sex (0 = men,1 = women), body surface area (BSA), body mass index, ejection fraction, kind of surgery (0 = coronary, 1 = valvular, 2 = mixed, 3 = other), medical history of hypertension or diabetes, and previous administration of beta-blocking agents, calcium channel blockers, nitrates, diuretics, angiotensin-converting enzyme inhibitors and inotropes (0 = no, 1 = yes).
Results: We obtained a statistically significant predictive model that includes female sex, low BSA, low previous hct, β blockers and coronary surgery as risk factors implicated in hct decrease on CPB.
Hct on CPB = −11.1 + 0.7 × hct + 5.8 × BSA −0.7 × β block − 0.8 × sex + 0.3 × surgery. (r2 = 0.802 and P < 0.001).
The cross-validation with 20% of the cases got a r2 of 0.788 that means a shrinkage of 1.3%.
Discussion: The applicability of our model in predicting the hct decrease is highly accurate and it led us to identify patients at risk in order to use more aggressive measures to minimize intraoperative haemodilution and to prevent critically low hct during CPB.
1 R.C. Groom. High or low hematocrits during cardiopulmonary bypass for patients undergoing coronary artery bypass graft surgery? An evidence-based approach to the question. Perfusion