| [Background] Children with congenital heart disease may appear hemodynamically stable after operations and then suddenly experience catastrophic decompensation, especially in infant children with complex cardiac deformity. Identification of the latent low cardiac output and relevant tissue malperfusion before the development of catastrophic change in cardiovascular status and early intervention might improve outcome. In the early postoperation period of cardiac operation under cardiopulmonary bypass (CPB), the relationship of system oxygen delivery (DOj) and oxygen consumption (VO2) takes on flow-dependent oxygen consumption, accompanied with relevant elevation of blood lactate levels. As the end product of the anaerobic metabolism of glucose, the degree of increase in blood lactate levels is proportional to the severity of tissue oxygen debt and hypoperfusion of microcirculation. Some studies have shown that hyperlactatemia following cardiac operations under CPB may be an early indicator for postoperation morbidity and mortality, but information linking lactate levels with outcome in infant children after open-heart surgery is limited.{Objective] The objective of this study was to discover the general regular change of the blood lactate levels within the initial 72 hours following heart surgery under CPB in pediatric patients less than 3 years old and evaluate its possible predictive value for patient's outcome. Through this study, we hope to find out an prompt > easy and reliable clinical marker which can signal impending circulatory failure and indicate the outcome. Taken advantage of this indicator, patients were probably to be given the lifesaving interventions that will improve the outcome. [Methods] we prospectively studied 119 children who were below 3 years of old and were undergoing open-heart surgery with CPB, and separated them into complexity categories. To all subjects, arterial blood lactate levels were recorded before operation, after CPB, on admission to the intensive care unit (ICU) and every 3 to 6 hours for the first 3 days; furthermore, arterial blood pFL bicarbonate and BE also be recorded on admission to the ICU. In order to evaluate the change in lactate levels during CPB, we choose 20 consecutive children receiving the procedure of ventricular septal defect (VSD) repair whose arterial blood lactate levels were additional measured before CPB and during CPB (cooling ^ nadir temperature and rewarming), moreover whose duration of CPB and aortic cross-clamp > duration of cooling and rewarming> nadir temperature, hematocrit value and the lowest mean arterial blood pressure were also recorded. A good outcome was defined as survival beyond postoperative day 3, and a poor outcome was defined as death. [Results] For children in CPB group, the largest increment in lactate levels occurred during CPB, and the mean lactate levels decreased progressively in theearly postoperative period which were within the normal range by 24 hours. There was an identical regular change in lactate levels among differential surgical complexity, but degree of change increased with increasing surgical complexity. For the 20 children chosen with VSD, arterial blood lactate concentrations were progressively increased during CPB, and significant increments in lactate levels occurred during cooling , rewarming, and the cessation of CPB. The duration of CPB and duration of aortic cross-clamp was positively correlated with a change in lactate during CPB, which was significantly negatively correlated with the smallest hematocrit value during CPB. For the 119 patients studied, 106 patients had a good outcome, and 13 patients had a poor outcome. The lactate levels progressively decreased in patients with a good outcome and were within the normal range by the first 24 hours after operations. In contrast, the patients who had a poor outcome exhibited significantly higher lactate levels at all time points. An elevated lactate concentration on admission to the ICU (initial lactate) of more than 5.35mmol/L had a 69.2% s...
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