Microvascular effects of pulsatile versus nonpulsatile perfusion during cardiopulmonary bypass

Introduction

While advantages of pulsatile perfusion (PP) during cardiopulmonary bypass (CPB) in terms of clinical outcome remain the subject of debate, possible benefits are generally thought to occur via improvements in microvascular flow [1]. However, this is currently not supported by human clinical data. Therefore we used real-time human microvascular imaging to test our hypothesis that pulsatile perfusion would enhance microvascular perfusion.

Methods

We used sidestream dark field imaging to record video clips of the human microcirculation in 16 patients undergoing routine CPB for cardiac surgery. Following administration of cardioplegia, CPB was continued in either pulsatile (PP, n = 8) or nonpulsatile (NP) mode. After 10 minutes, microvascular recordings were made. The perfusion mode was then switched from PP to NP or vice versa. Ten minutes later, a second series of microvascular video recordings were obtained. Global hemodynamic and laboratory data were recorded and the energy equivalent pressure (EEP) and pulse pressure (both mean ± SD) were calculated to quantify PP generated surplus energy. Microvascular analysis was performed both for smaller and larger microvessels with a diameter cut-off of 20 μm. Assessments included perfused vessel density (PVD) (mean ± SD, 95% confidence intervals of the difference between NP and PP (95% CID)) and the Microvascular Flow Index (MFI) (mean ± SD and interquartile range).

Results

Pulsatile perfusion resulted in higher pulse pressure (27 ± 6 vs 7 ± 2 mmHg, P < 0.0001) and CPB circuit EEP (184 ± 33 vs 150 ± 27 mmHg, P < 0.0001) as compared with NP while MAP was similar between these perfusion modes (52 ± 11 vs 56 ± 13 mmHg, P = 0.09). Both for small and larger microvessels, we found no differences in indices of microvascular perfusion between PP and NP. Small microvessel PVD was similar between PP and NP (6.65 ± 1.39 vs 6.83 ± 1.23/mm; 95% CID -0.50 to 0.87/mm, P = 0.58). The same was true for larger microvessel PVD (2.16 ± 0.64 vs 1.96 ± 0.48; 95% CID -0.50 to 0.11, P = 0.20). Similarly, the MFI did not differ between groups either for smaller (3.00 (2.83 to 3.00) vs 3.00 (2.75 to 3.0), P = 0.41) and larger microvessels (3.00 (2.75 to 3.00) 3.00 (3.00 to 3.00), P = 0.50).

Conclusions

PP during CPB does not alter human microvascular perfusion using standard equipment in routine cardiac surgery despite yielding higher CPB circuit energy equivalent pressure and patient pulse pressure.