Cardiopulmonary bypass with physiological flow and pressure curves: pulse is unnecessary!

Advocates of pulsatile flow postulate that the flow pattern during extracorporeal circulation (ECC) should be similar to the physiological one. However, the waveforms generated by clinically used pulsatile pumps are by far different from the physiological ones. Therefore, we constructed a new computer-controlled pulsator which can provide nearly physiological perfusion patterns during ECC. We compared its effect (group 1) with pulsatile (group 2) and non-pulsatile (group 3) perfusion generated by a conventional roller pump.

Thirty pigs (10 per group) underwent 180 min ECC with an aortic cross-clamp time of 120 min. Pulse pressure, peak aortic flow, dp/dt(max), pulsatility index and energy-equivalent pressure were measured online. Renal and intestinal blood flow was calculated by fluorescent microspheres. The inflammatory response was assessed by the level of interleukin 6/1ra, the haemolysis by the free haemoglobin, and the escape rate of plasma protein by the disappearance rate of Evans Blue dye.

When compared to the preoperative curves, pulsatile waveforms during ECC were similar in group 1 and severely damped in group 2. Inflammatory response increased without significant differences between the groups. There were no differences between groups in renal and bowel blood flow. Free haemoglobin after ECC was higher in the pulsatile groups (group 1=43+/-144 mg dl(-1), group 2=40+/-164 mg dl(-1), group 3=11+/-4mgdl(-1); group 1 vs 2 (ns); group 1 or 2 vs 3 (p<0.001)). The escape rate of Evans Blue increased after ECC in group 1 1.8-fold (p<0.05), in group 2 1.45-fold (p<0.05) and in group 3 1.27-fold (ns).

Even when using pulsatile flow patterns which mimic closely the physiological waveforms, there is no advantage concerning organ perfusion or inflammatory response. Moreover, the extent of haemolysis and capillary leak is higher compared to non-pulsatile perfusion. Efforts to optimise pulsatility are not justified.