Aim: Current cardiopulmonary bypass (CPB) procedures use non-hematic fluids to prime bypass circuits, often resulting in marked hemodilution. Patients' total blood volume (TBV) is estimated prior to hemodilution. We aimed to evaluate differences between calculation of TBV by Nadler's formula, a classic reference book method, and an established formula calculated by the authors.
Methods: A total of 285 patients of Asian origin received primary cardiac surgery between September 2010 and October 2011 in our institution. Patients' total blood volume was estimated by: 1) standard Nadler formula: TBV (men) =0.417H3+0.045TBM-0.030L TBM (total body mass, Kg); TBV (women) =0.414H3+0.0328 TBM-0.030L; 2) classic reference book method: patient's weight in kilograms times 7% (women) or 7.5% (men); and 3) our practical calculation: TBV=HCT2*(CPB prime volume + intravenous fluids before CPB - urine volume before CPB)/(HCT1- HCT2).
Results: Bland-Altman plotting revealed no mean differences between Nadler formula and reference book TBV measurements (Figure 1A). Differences in means (95% limit of agreement) for reference book/Nadler formulas was 0.52 (-0.21, 1.24, N.=285). Comparing authors' results with those of reference book/Nadler, TBV yielded divergent results. TBV correlated positively to patient's height (P=0.001) and body surface area (P<0.01), and correlated positively to height after controlling for age and gender (β=87.3, SE=42.9, P=0.043).
Conclusion: Total blood volume of Asian patients calculated by the authors differs markedly from that estimated by Nadler and classic reference book formulas, which suggests that more accurate calculation of TBV is needed for Asian cardiac patients requiring CPB, especially patients with valvular disease.