Effect of normothermic versus hypothermic cardiopulmonary bypass on cytokine production and platelet function

Proinflammatory cytokines and platelets play a key role in the systemic inflammatory response associated with cardiopulmonary bypass (CPB). The aim of this study was to evaluate the effects of both hypothermic and normothermic CPB on platelet activation, cytokine production, as well as their possible correlations.

Twenty patients who underwent CABG were randomly assigned into two groups receiving hypothermic and normothermic CPB. Blood samples were obtained through a venous catheter at 6 time points. The following parameters were measured: in vitro platelet aggregation, in vivo platelet activation, complete and differential blood cell counts, plasma soluble P-selectin levels, plasma IL-6, IL-1beta and TNFalpha levels.

The results demonstrated that platelet abnormalities could be observed to a greater extent during hypothermic rather than normothermic CPB. The occurrence of in vivo platelet activation was suggested by the presence of a significantly increased percentage of platelets expressing CD62P on their surface, as well as by a decreased in vitro platelet aggregation induced by different agonists. Complete and differential blood cell counts showed no substantial decrease in platelet number without differences between groups. The results obtained also showed the presence of a significant release of sP-selectin during CPB, as well as a more pronounced increase of plasma sP-selectin levels in patients undergoing hypothermic compared to normothermic CPB. A comparison of cytokine levels demonstrated a significant elevation of plasma IL-6 levels during either hypothermic or normothenmic CPB, paralleling the neutrophil rise, while no differences were observed for TNF-alpha levels. Conversely, plasma IL-1beta levels were significantly elevated during hypothermic, but not during normothermic CPB.

Hypothermic CPB is responsible for a greater platelet activation and endothelial dysfunction than normothermic CPB, leading to more profound changes in the hemostatic and inflammatory systems, which, in turn, might be responsible for the higher incidence of postoperative complications reported during hypothermic CPB.