[Effect of lactic acid levels on the prognosis of critically ill patients after cardiac and non-cardiac surgery: an analysis of 549 cases].

OBJECTIVE: To compare the impact of mean lactate concentration and lactate variability on postoperative outcome after cardiac surgery and non-cardiac surgery in critical patients, and to explore the prognostic value of the first lactate and the highest lactate during the first 24 hours in intensive care unit (ICU).

METHODS: A retrospective study was conducted. The postoperative patients of cardiac surgery and non-cardiac surgery who were transferred to ICU immediately, and who were at least 18 years old and whose ICU lengths of stay were at least 1 day, and who were admitted to ICU of the First Affiliated Hospital of Zhengzhou University from September 2014 to September 2016 were enrolled. According to the mean lactate concentration, the patients were divided into normal lactate group (0-2 mmol/L), relatively high lactate group (2-4 mmol/L), and absolute high lactate group (> 4 mmol/L), and the relationship between the mean lactate concentration and the prognosis of patients was analyzed. According to the degree of lactate variability, the patients were divided into four groups, and multivariate regression models were used to assess the risk of death in three different lactate variability groups. The value of the first lactate value and the highest lactate value during the first 24 hours in ICU were evaluated to predict the prognosis by the receiver operating characteristic (ROC) curve.

RESULTS: 268 postoperative patients of cardiac surgery and 281 cases of non-cardiac surgery were selected, and the characteristic of the baseline data in the two groups was balanced. (1) Mean lactate concentration and mortality in ICU: in the normal lactate group (0-2 mmol/L), there was no significant difference in mortality between the post-cardiac operative group and post-non-cardiac operative group [7.9% (14/177) vs. 6.5% (14/217), odds ratio (OR) = 1.245, P = 0.694]. In the relatively high lactate group (2-4 mmol/L), there was no significant difference between the two groups, either [33.3% (12/36) vs. 23.7% (9/38), OR = 1.611, P = 0.442]. In the absolute high lactate group (> 4 mmol/L), ICU mortality in post-non-cardiac operative group was obviously higher than that of post-cardiac operative group [69.2% (18/26) vs. 43.6% (24/55), OR = 0.344, P = 0.036]. (2) The ranges of lactate variability per quartile (mmol×L-1 ×d-1 ) and ICU mortality risk: there was a linear relationship between lactate variability and ICU mortality in post-non-cardiac operative group, < 0.50 (reference), 0.50-0.85 (OR = 1.17, P = 0.87), 0.85-1.44 (OR = 4.86, P = 0.04), > 1.44 (OR = 22.66, P < 0.01) , and there was a significant difference between the two groups in the high degree of variability (0.85-1.44 and > 1.44). The risk of death after cardiac surgery tended to increase, < 0.55 (reference), 0.55-1.25 (OR = 0.61, P = 0.61), 1.25-2.43 (OR = 3.46, P = 0.10), > 2.43 (OR = 12.14, P < 0.01), and the risk of death only showed difference in the highest degree of variation (> 2.43). (3) ROC curve showed that the area under ROC curves (AUC) of the highest lactate in 24 hours were larger than that of the first lactate in both groups, with higher sensitivity and specificity. In the post-cardiac operative group and post-non-cardiac operative group, the AUC of the highest lactate in the first 24 hours were 0.877 and 0.875, the cut-off values were 5.35 mmol/L and 5.65 mmol/L, the sensitivity were 81.4% and 67.9%, and the specificity were 93.8% and 96.1%, respectively.

CONCLUSIONS: Patients with post-non-cardiac operation should be more active in controlling hyperlactatemia and lactate variability. The highest lactate in the first 24 hours maybe one of the indicator for the assessment of the prognosis of the postoperative patients.