Size makes a difference: use of a low-prime cardiopulmonary bypass circuit and autologous priming in small adults

Low hematocrit (Hct < 20) during cardiopulmonary bypass (CPB) is associated with higher mortality and other adverse outcomes. More frequently low Hct is encountered in patients with small body size and women patients. This prompted us to take an aggressive approach in our care of these patients, involving a strategy for predicting patients at risk of low Hct, with the aid of an electronic worksheet that accurately predicts CPB Hct, and two prevention strategies: use of a low-prime CPB circuit (LP) for all adult patients with a body surface area (BSA) <1.7 m(2) and use of autologous circuit priming (AP), in addition to the low-circuit volume in some patients. The two cohorts of patients in whom these techniques were employed were compared to a group matched for body size where our standard adult circuit (STD) was used. There were 233 patients in the standard group, 139 in the LP group, and 68 in the LP/AP group. The CPB circuit prime volume was 1710 mi for the STD group and 1110 mi for the LP group. Use of autologous priming techniques further reduced the prime volume by 545 +/- 139 mi. The incidence of low Hct (<20%) during CPB was thus reduced from 70% to 15% (p = 0.001) when using both techniques together without increasing red blood cell (RBC) transfusions. These changes in perfusion management resulted in a reduction in the incidence of renal complications (STD = 9.4%, LP = 6.5% (ns) and LP/AP = 0%, p = 0.008) and a decrease in hospital mortality (STD = 9.8%, LP = 4.3 p = 0.05 and LP/AP = 0%, p =. 007). Matching the CPB circuit to the patient's size and use of other prime-reduction strategies can increase Hct levels during CPB and improve outcomes in smaller patients, who are susceptible to increased risk.