Reduction in prime volume attenuates the hyperdynamic response after cardiopulmonary bypass

A hyperdynamic response to cardiopulmonary bypass is characteristically observed in the post-operative course. To determine the effect of prime volume on the hemodynamic response, a database study was performed on patients who underwent elective coronary artery bypass grafting with an extracorporeal circuit with either a large prime volume (2,350-mL prime, n = 20) or a small prime volume (1,400-mL prime, n = 20).

Measurements were carried out at fixed time points before and after cardiopulmonary bypass (until 18 hours postoperatively) and include hematocrit, colloid oncotic pressure, fluid balance, and hemodynamic profile (mean of three measurements).

The lower colloid oncotic pressure in the large prime group (16.2 +/- 0.6 mm Hg versus 19.1 +/- 1.1 mm Hg, p = 0.0002) was associated with a highly positive fluid balance (5.5 +/- 0.9 L versus 2.8 +/- 0.7 L, p = 0.0001). With the on-bypass hematocrit aimed at 22% to 23%, autologous blood was predonated by 16 patients in the small prime group but by none in the large prime group. Reinfusion of autologous blood resulted in a reduction in blood bank requirements (p = 0.03). Mean arterial pressure was 83 +/- 4 mm Hg for small prime versus 76 +/- 4 mm Hg for large prime (p = 0.01). Cardiac index was 2.9 +/- 0.2 L.min-1.m-2 for small prime versus 3.8 +/- 0.3 L.min-1.m-2 for large prime (p = 0.0001). Pulmonary vascular resistance index was 281 +/- 40 dyne.s.cm5.m-2 for small prime versus 188 +/- 22 dyne.s.cm5.m-2 for large prime (p = 0.0009). Oxygen delivery was 42 +/- 5 mL.min-1.m-2 for small prime versus 51 +/- 3 mL.min-1.m-2 for large prime (p = 0.004). Vasoactive medication was not different among groups.

Reduction in prime volume attenuates the hyperdynamic response after cardiopulmonary bypass. Furthermore, an important reduction in blood bank products can be obtained with small prime volumes.