Clear prime for infant cardiopulmonary bypass: a miniaturized circuit

The extracorporeal circuit used clinically to perform cardiopulmonary bypass (CPB) in small infants is relatively large requiring blood to prime the circuit to reduce hemodilution. To study the merits of clear prime also in infants, we did experiments in rabbits with two extracorporeal circuits: one employing traditional venous gravity drainage (priming volume 330 ml) and the other employing vacuum drainage (priming volume 90 ml). The first circuit still had to be primed with blood, whereas the second circuit could be primed with a clear solution. Both circuits were automatically controlled to lighten the task of the perfusionist to operate the CPB safely and accurately. We demonstrated that the clear priming solution in the second circuit eliminates the hemodynamic deterioration caused by blood prime in the first circuit. Studying the effect of various modes of regulation, we showed that automatic control of CPB based on venous return is similar to autoregulation of the heart according to Starling's law, and maintains not only normal hemodynamics, but also an optimal microcirculation.