Lactate level as prognostic factor of mortality in patients after cardiac surgery

Objectives: This study was performed to examine lactate-levels as prognostic factor of mortality in patients after cardiac surgery and its usefulness as a screening tool in postoperative intensive care.

Methods: Retrospective data on 733 patients after cardiac surgery were obtained. Peak lactate-level was measured and perioperative data recorded. Receiver operating characteristic curve was generated. Optimal cut-off-value for peak-lactate was calculated to determine the value for the best predictor of in-hospital mortality. Therefore patients were separated in low-risk (LRG) and high-risk-group (HRG). Mann-Whitney-U-test and fisher's exact test were used to detect differences between LRG and HRG for perioperative data.

Results: Area under the curve was 0.852. For lactate the optimal cut-off-value was 3.95mmol/l. This value led to a sensitivity of 73.9% and a specificity of 87.3% for mortality. Mortality in LRG was 0.96% versus 15.89% in HRG (p<0.001). Postoperative complications in HRG were 30.84%, in LRG 6.55% (p<0.001). ICU-stay was significant longer in HRG than in LRG 4.24±7.41d vs. 2.83±2.11d (p<0.001). In HRG mean peak-lactate was 8.92±6.14mml/l versus 1.61±0.76mmol/l (p<0.001), central venous oxygen saturation was 69.48±12.34% in HRG and 65.29±9.77% (p<0.001) in LRG.

Conclusion: The measurement of lactate-level is useful to predict outcome in patients after cardiac surgery. This could be useful to identify patients with high risk for mortality after cardiac surgery. A threshold of 3.95mmol/L is able to identify this high risk population.