What factors are associated with hyperlactatemia after cardiac surgery characterized by well-maintained oxygen delivery and a normal postoperative course? A retrospective study

Background and objective The purpose of this study was to investigate retro spectively what factors contribute to the development of the type of hyperl actatemia which may follow cardiopulmonary bypass despite well-maintained o xygen delivery and a normal perioperative course. Methods The medical records of 124 patients undergoing elective cardiac sur gery using cardiopulmonary bypass were reviewed. The patients were divided into a hyperlactatemia group (n = 34), where the serum lactate concentratio n was >5.0 mmol L-1 perioperatively, and a normal lactatemia group (n = 90) , which comprised the remaining patients. Results 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 cardiopulm onary bypass. Oxygen extraction rates were significantly reduced during the period of cardiopulmonary bypass but, on the contrary, increased in the hy perlactatemia group after surgery. The area under the curve of mean arteria l pressure consisted of 5-min interval plots during the initial period of c ardiopulmonary bypass in the hyperlactatemia group. This was significantly smaller than for the normal lactatemia group. Weakly significant correlatio ns between maximal lactate and duration of cardiopulmonary bypass, and espe cially the area under the curve, were observed. Conclusions It is suggested that the pathophysiology observed is based on i mpairment of tissue oxygen utilization. The duration of cardiopulmonary byp ass and especially the occurrence of hypotension at the start of the bypass period appears to be related to the development of lactic acidosis.