The Effects Of Hypothermic Cardiopulmonary Bypass On Oxygen/Glucose Uptake And Their Relationship In The Brain

[Background] Advances in myocardial protection and operative technique have dramatically reduced mortality resulting from cardiac surgery undergoing cardiopulmonary bypass (CPB), but the incidence and fatality of postoperative neurologic complications grow relatively. Because of those, attention is increasingly focusing on the CPB-related cerebral injury and protection. The mechanism of cerebral injury hasn' t been most clear, and may be associated with multifactorial etiology. The common factor leading to neurologic complications is the imbalance of cerebral energy metabolism, which plays a very important role in the pathogenesis of CPB-related cerebral injury. To make a further understanding of cerebral metabolic alterations will contribute to improvement of cerebral protection and reduction of neurologic complications.[Objectives] In this study, we will test and verify the hypothermic CPB effects and their extents on the balance of oxygen/glucose supply and demand in the brain, and analyze the alterations of arteriojugular differences for oxygen, glucose, and lactate or oxygen/glucose index obtained before, during, and after bypass. Then preliminarily go furtherinto the hypothermic CPB effects on oxygen/glucose uptake and their relationship in the brain, hoping to make a further understanding of cerebral metabolic changes and finding out the optimal conditions which clinically could protect brain from damages.[Methods] Eleven screened adults (range 28~55 years) undergoing cardiac surgical procedures of valves with the use of hypothermic CPB were studied. Before steraotomy, a catheter was inserted retrogradely into the right internal jugular vein, the tip of which reached the jugular bulb. Once simultaneous, paired blood samples were withdrawn at six points before, during, and after moderate hypothermic CPB, oxygen partial tension, hemoglobin, hemoglobin saturation, lactate and glucose were analyzed immediately. Arteriojugular differences for oxygen (AJDOi), glucose (AJDgluc), and lactate (AJDL) were calculated. On the basis of the predictable stoichiometric relationship for the oxidation of glucose, the oxygen/glucose index (OGI) was also calculated to express relationship of substrates uptake.[Results] All adults survived with no obvious neurologic complications. With the initiation of CPB, during cooling and at the temperature nadir on CPB, AJDO2 and OGI fell significantly from prebypass (P<0.01). During rewarming, AJDO2 and AJDgluc increasedsignificantly as compared with the former two points (P<0.01), and there was a tendency of slight growth in OGI without statistical significance. After rewarming but on or off CPB, AJDO2 and OGI continued rising while AJDgluc decreased from rewarming(P<0.01), and these 3 parameters had nonsignificant difference compared with prebypass (P>0.05). The levels of glucose and lactate were on the increase throughout the operation , but AJDL always approximated to 0 without significant difference between points (P>0.05). Correlation analysis showed that there is evident positive linear correlation between OGI and temperature (r-0.828, P<0.01).[Conclusions] Hypothermic cardiopulmonary bypass obviously alters the relationship between oxygen and glucose uptake in the adult brain. We observed that positive linear correlation exists between OGI and temperature, suggesting uncoupling of substrates uptake in hypothermia and probably more glucose metabolism via shunt than normothermia. And we also noticed no signs of anaerobic metabolism in the brain throughout CPB. Cooling and rewarming are the most hazardous phases during hypothermic CPB. The alterations of body temperature disturb the balance of cerebral metabolism during CPB. Therefore, measures must be taken to maintain cerebral flow-metabolism coupling close tophysiological status, contributing to realize clinically cerebralprotection.