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The purpose of this study was to investigate retrospectively what factors contribute to the development of the type of hyperlactatemia which may follow cardiopulmonary bypass despite well-maintained oxygen delivery and a normal perioperative course.The medical records of 124 patients undergoing elective cardiac surgery using cardiopulmonary bypass were reviewed. The patients were divided into a hyperlactatemia group (n =34), where the serum lactate concentration was > 5.0 mmol L−1 perioperatively, and a normal lactatemia group (n =90), which comprised the remaining patients.The duration of cardiopulmonary bypass in the hyperlactatemia group was significantly longer than for the normal lactatemia group. Significant differences of lactate concentrations between the groups, and significant elevations of serum lactate had been observed after the start of cardiopulmonary bypass. Oxygen extraction rates were significantly reduced during the period of cardiopulmonary bypass but, on the contrary, increased in the hyperlactatemia group after surgery. The area under the curve of mean arterial pressure consisted of 5-min interval plots during the initial period of cardiopulmonary bypass in the hyperlactatemia group. This was significantly smaller than for the normal lactatemia group. Weakly significant correlations between maximal lactate and duration of cardiopulmonary bypass, and especially the area under the curve, were observed.It is suggested that the pathophysiology observed is based on impairment of tissue oxygen utilization. The duration of cardiopulmonary bypass and especially the occurrence of hypotension at the start of the bypass period appears to be related to the development of lactic acidosis.