Background and Goal: Increased endothelial permeability following cardiopulmonary bypass (CPB) is thought to be an important contributor to microcirculatory perfusion disturbances and postoperative organ dysfunction. We therefore hypothesised that microcirculatory perfusion disturbances remain altered after surgery and are paralleled by prolonged impairment of endothelial barrier function.
Materials and Methods: Microcirculatory perfusion was assessed in 17 patients undergoing cardiac surgery with CPB using sublingual sidestream dark-field imaging and the percentage of perfused vessels was calculated. Plasma was obtained before connection to CPB (pre-CPB), during CPB, after weaning from CPB and 72 hours following CPB. Using electric cell–substrate impedance sensing of human endothelial cells, the effect of plasma exposure for 3 hours on in vitro endothelial barrier was measured. Plasma heparan sulphate and syndecan-1 levels were studied with ELISA as marker for glycocalyx degradation. 
Results and Discussion: Patients, aging 68±7 years, underwent 103±18 minutes of CPB. Microcirculatory proportion of perfused vessels immediately decreased from 92±6 to 69±9 % (P<0.001) after onset of CPB and did not restore in the first 72 postoperative hours (71±5 vs 92±6 %, P<0.001). Using an in vitro endothelial barrier assay, plasma obtained after CPB decreased endothelial resistance with 17% compared to pre-CPB plasma (1.2±0.05 vs 0.9±0.08, P=0.01). The reduction in endothelial resistance was still present when exposed to plasma obtained 72 hours after CPB (1.2±0.05 vs 1.0±0.05, P=0.009). Moreover, CPB was associated with increased plasma levels of heparan sulphate (24±8 vs 14±2 ng/ml, P=0.0008) and syndecan-1 (61±9 vs 10±5 ng/ml, P<0.0001).
Conclusion: Microcirculatory perfusion disturbances in patients undergoing cardiac surgery with CPB persist in the first postoperative days and are paralleled by prolonged endothelial hyperpermeability and shedding of endothelial glycocalyx constituents. Future research should reveal whether targeting endothelial barrier could preserve microcirculatory perfusion and organ function in patients undergoing cardiac surgery with CPB.

Funding N.A.M.D. is financially supported by the Dutch Heart Foundation [Grant number 2016T064]. C.E.v.d.B. is financially supported by the European Society of Anaesthesiology [Research Project Grant 2016].

03 / Microcirculatory perfusion disturbances and endothelial hyperpermeability following cardiopulmonary bypass persist in the early postoperative period