Nitric oxide release during hypothermic versus normothermic cardiopulmonary bypass

Cardiopulmonary bypass (CPB) produces hemodynamic and inflammatory disorders involving changes in vascular permeability and regional blood flow and alterations of coagulation and complement systems. It has been reported that an abnormal release of vasoactive substances during CPB, like bradykinin or nitric oxide, could play a role. The aim of this study was to investigate the changes in nitric oxide (NO) release occurring in patients undergoing CPB, under both hypothermic and normothermic conditions. Forty patients (mean age 61.4 +/- 8.4 years) undergoing coronary bypass surgery were studied. In 20 patients (group A) systemic hypothermic CPB and antegrade cold intermittent crystalloid cardioplegia were used. The remaining 20 cases (group B) underwent surgery under systemic normothermic CPB and with antegrade warm blood intermittent cardioplegia. Nitric oxide was measured as the nitrite plasma level (NPL) by the Gries reaction. The time course of changes in NPL were obtained by collecting five whole blood samples: before CPB, 10 and 30 min after the start of CPB, and 10 and 60 min after the end of CPB. Although there were no significant variations of NPL shortly after the start of CPB (10 min after), values measured 30 min after CPB commencement and 10 min after the end of CPB showed a significant increase (P < 0.0001) in both groups. Considering the two groups separately, NPL changes seemed to be similar, so independent of temperature; however, in group B higher values of NPL were measured during (30 min) and after (60 min) CPB (P < 0.0001). In conclusion, during CPB there is a progressive increase, independent of temperature in NO release.