Effects Of Temperature On Cerebral Oxygen Balance In Pediatric Cardiac Surgery During Cardiopulmonary Bypass

IntroductionRecovery rate of some cardiac diseases, which were needed to be operated in the past, has been raised recently accompanying with the development of medical science and the improvement of medical instruments. Nevertheless, the neuropsychological complication after cardiopulmonary bypass(CPB)is an important issue. Especially, the high incidence of the cerebral functional disorder postoperatively has also been occured in the severe patients, such as the severe valvular heart disease, aortic aneurysm and the complicated pediatric congenital heart disease. The previous studies suggested that these symptoms may be related to the imbalance of cerebral oxygen supply and demand during the operation.The hypothermia can inhibit all biochemistry reaction in vivo and reduce the consumption of the high energy phosphate and decrease the cerebral metabolism rate obviously. Therefore, the hypothermal cardiopulmonary bypass is used to protect neurofunction. But the changes of temperature during CPB still resulted in the disorder of cerebral?metabolism and the dysfunction of the central nervous system. CPB can destroy the balance of the cerebral oxygen supply and demand, and then lead to the cerebral impairment. The clinical major indexes reflecting the balance of the cerebral oxygen supply and demand include the jugular bulb venous oxygen saturation (SjvO), the oxygen content of artery (CaO), the arteriovenous oxygen difference (AVDO), the cerebral extraction of oxygen (CEO), lactic acid content of arterial blood (LA), lactic acid content of jugular bulb venous blood (LV), arterial blood glucose content (GA), jugular bulb venous blood glucose content (GV) and the difference of lactic acid content between artery and jugular bulb venous blood (AVDL). Up to now, most studies have concerned in the hypothermic influence on adult cerebral oxygen balance during CPB. There has been no previous study investigating whether hypothermic cardiopulmonary bypass disrupts cerebral oxygen balance in children. The purpose of this study was to investigate the effects of the changes of body temperature on the cerebral oxygen balance in pediatric patients of VSD undergoing cardiac surgery with hypothermic CPB. We attempted to find the characteristic of this influence and to assess the experimental proofs for cerebral protection of the cardiac surgery in children during hypothermic CPB.Materials1．Instrument: Hayer anaesthesia machine (Germany); Datex versatile anaesthesia monitor (Finland); Jostra cardiopulmonary bypass unit (Germany); membrane oxyg-enato (Japan); Bayer 865 blood gas analyzer (USA); microamount blood glucose meter (USA); 722 spectrophotometer (Fujian); TGL-16C centrifuger (Shanghai); K-8D thermostatic waterbath (Shanghai).2．Reagent: the lactic acid kit of whole blood (Nanjing).3．Drugs: atropine; dolantine; ketamine; sulfentanyl; propofol; pipecuronium; isoflurane studied fifteen children(nine boys and six girls), ASA(?), aged 4-9 years old, 13-24 kilograms in weight, requiring CPB for repairing VSD. Patients with the stenosis of internal carotid artery, hypertension, diabetes, abnormal hepatorenal function were excluded. Patients had no diseases of nervous system before surgery, such as the transient cerebral ischemic episode, the cerebral hemorrhage, the cerebral infarction, the cerebral trauma and the cerebral tumor.2．Anaesthesia methodThe premedications were atropine (0．01mg/kg) and dolantine (1mg/kg). The patients were injected with i.m. ketamine (6mg/kg) after entering the operation room immediately. When the patients fall asleep, the radial artery puncture was performed, and the pressure transducer was connected to the Datex versatile anaesthesia monitor. The mean artery pressure (MAP), the heart rate (HR), the electrocardiogram (ECG), the saturation of pulse oxygen (SpO), the central venous pressure (CVP), the nasopharynx temperature (NPT) were recorded at different times during anaesthesia and operation. Anaesthesia was induced with i.v. sulfentanyl (1(?)g/kg), propofol (2．5 mg/kg) and pipecuronium (0．1mg/kg). Anaesthesia was maintained with propofol (6mg/kg(?)h), isoflurane (0(?)1．5%) inhalation and intermittent i.v. sulfentanyl and pipecuronium. Catheter was placed in the right jugular bulb by retrograde jugular vein approach until the tip was felt to about on the base of the skull after tracheal intubation.3．GroupBlood samples were collected at eight time points: T (baseline): NTP is at 36(?) before initiation of CPB; T: during cooling at 33(?); T: during cooling at 30(?); T: during cooling at 26(?); T: during rewarming at 30(?); T: during rewarming at 33(?); T: during rewarming at 36(?); T: one hour after rewarming at 36(?).4．Measuremental index(1) The balance of cerebral oxygen supply and demand. 0．5ml blood samples were collected from the radial artery and jugular bulb respectively at these specific points for blood gas analysis. According to Fick formula: Oxygen content of artery (CaO)=Hba(?) 1．36(?)SaO+0．0031(?)PaO Jugular bulb venous oxygen content (CjvO)=Hbv(?)1．36(?)SjvO+0．0031(?)PjvO The arterio-venous oxygen content difference (AVDO)=CaO-CjvO Cerebral extraction rate of oxygen (CEO)=(CaO-CjvO)/CaO(2) Lactic acids metabolismBlood samples were collected from the radial artery and jugular bulb respectively at these specific points and measured by lactic acids kit of whole blood, and then the lactic acid content of arterial blood (LA) and lactic acid content of jugular bulb venous blood (LV) and the difference of lactic acid content between artery and jugular bulb venous blood (AVDL=LV-LA) were calculated.(3) Blood glucoseBlood samples were collected from the radial artery and jugular bulb respectively at these specific points and measured by the microamount blood glucose meter, and the difference of blood glucose content between artery and jugular bulb venous blood (AVDG=GV-GA) were calculated.5(?)Statistical analysisData were expressed as mean (?) SD. Statistical comparision between different time points with ANOVA. Associations between temperature and SjvO at each time point were determined using Pearson 's rank correlation coefficients for all patients. In all analysis, p < 0．05 was considered statistically significant.ResultsCompared with baseline (T), SjvO were significantly higher at T, T, T and were significantly lower at T, T, T (p<0．05) . CaO, AVDO and CEO were significantly lower at T, T and T (p<0．01) and AVDO, CEO were significantly higher at T, T, T (p<0．05) . Compared with T, SjvO were significantly lower at T, T, T (p<0．05) and AVDO, CEO were significantly higher at T, T, T(p<0．01) . At T, CaO, SjvO, AVDO and CEO return to the baseline.Compared with baseline (T), LA, LV, GA and GV at different points increased progressively (p<0．05) . AVDL showed a significant difference between the baseline (T) and T, T (p<0．05) . There were no significant differences in AVDG at all points (p>0．05) .SjvO showed a significant negative correlation with the temperature during cooling (r=-0．820, p<0．01) . The value of SjvO increased gradually accompanying with the decreasing of temperature. But there was a significant positive correlation between SjvO and the temperature during rewarming (r=0．808, p<0．01) . The value of SjvO increased gradually accompanying with the increasing of temperature.DiscussionIn recent years, the neuropsychological dysfunction after CPB has been considered gradually, and it is related to the balance of cerebral oxygen supply and demand. Hypothermia is considered to be the most important treatment for cerebral protection during CPB. But during the hypothermal CPB, the changes of temperature still resulted in the disorder of cerebral metabolism and the dysfunction of the central nervous system. The duty of anesthetist is to maintain the cerebral oxygen balance and the stability of cerebral function during hypothermal CPB.The clinical major index reflecting the balance of the cerebral oxygen supply and demand include SjvO, AVDO, CEO, LA, LV and AVDL. The reference value of SjvO is from 54 % to 75 %. When SjvO is higher than 75 %, it indicates that cerebral blood flow (CBF) is superior to cerebral metabolic rate for oxygen (CMRO). When SjvO < 50%, it reflects inadequate CBF in proportion to CMRO and this is called cerebral desaturation. Cerebral anoxia will occur when SjvO < 40%. Therefore, the monitoring of SjvO during hypothermal CPB is extremely important to prevent the occurrence of cerebral ischemia and cerebral hypoxemia. The present study showed that SjvO altered accompanying with alteration of temperature during hypothermal CPB. SjvO increased accompanying with decrease of temperature during cooling period, and then it decreased accompanying with increase of temperature during rewarming period. It suggests that the hypothermia may result in the decrease of CBF. But compared with the decrease of CBF, the decrease of cerebral oxygen consu-mption was more obviously, and so the cerebral oxygen balance can be maintained during cooling period. After the beginning of rewarming, SjvO was lower than baseline, and cerebral oxygen supply was stable and cerebral oxygen consumption increased, and so the imbalance of cerebral oxygen supply and demand occured easily.AVDO and CEO is not affected by hemoglobin, and they can reflect the alteration between cerebral oxygen supply and demand. If AVDO and CEO increase, cerebral extraction of oxygen will increase. There is inadequate CBF in proportion of the cerebral oxygen consumption. If AVDO and CEO decrease, cerebral extraction of oxygen will decrease. There is adequate CBF in proportion of the cerebral oxygen consumption. In the present study, CaO, AVDO and CEO decreased accompanied with body temperature decrease after the beginning of CPB. After rewarming, AVDO and CEO were higher than those during cooling, and the imbalance of cerebral oxygen supply and demand might occure.Lactic acid is the specific product of anaerobic glycolysis. Increasing of blood lactic acid can be a sensitive index measuring the balance of cerebral oxygen supply and demand. Hypothermia can lead to increase of blood lactic acid. Other factors including the increasing of oxygen consumption, inadequate oxygen supply, dys-utilization of oxygen and anaerobic metabolism will result in increasing of blood lactic acid. Glucose is the origion of energy of cell. Hyperglycemia may enhance the effects of ischemia, especially in the brain. Stress reaction resulting from anesthesia and surgery can lead to hyperglycemia.AVDL may reflect the cerebral infusion. There is inadequate cerebral oxygen supply in proportion to cerebral oxygen metabolism if AVDL increase. In the present study, the level of AVDL at times T and T decreased obviously compared with that at T. It suggests that the level of anaerobic glycolysis in brain may decrease during cooling period.All patients were the children survived of VSD in our investigation. It was excluded that the index of cerebral oxygen metabolism was influenced by the different kinds of disease. Our investigation suggested that the body temperature may be the important factor impacting on the balance of cerebral oxygen supply and demand during CPB in the pediatric congenital heart disease. During hypothermia, the supply of cerebral oxygen is sufficient and superior to the demand of cerebral oxygen. The imb-alance of cerebral oxygen supply and demand may occurre easily during rewarming, and the essential measures should be taken, such as the protection of drug, to prevent the postoperative complication of central nerve system resulted from the imbalance of cerebral oxygen supply and demand.Conclusion1．Temperature is an important factor reflecting the balance of cerebral oxygen supply and demand during CPB in the pediatric patient underlying the cardiac surgery. The cerebral oxygen supply is adequate for cerebral oxygen demand during hypo-thermic phase of CPB. The imbalance of cerebral oxygen supply and demand might occur easily during rewarming phase.2．Variances of SjvO, AVDO, CEO and AVDL in children during CPB are similar to that of adult.