Preoperative Hyperlactatemia and Early Mortality after Liver Transplantation: An Application of Random Survival Forest Analysis

Abstract

Background: Hyperlactatemia is a common finding in critically ill patients, including patient with septic shock, cardiogenic, hypovolemic shock, trauma and liver failure. In liver transplantation (LT) patients, postoperative lactate and lactate clearance rate are considered as good surrogate markers of early graft function and outcome. The objectives of this study are to identify variables that are most important for preoperative hyperlactatemia, to see if there are modifiable factors, and to examine the effect of preoperative hyperlactatemia on early mortality after LT using random forest method. Method: The data from Asan LT registry of all patients who underwent LT between January 2008 and February 2019 at the Asan Medical Center were analyzed. The most important variable for preoperative hyperlactatemia and the effect of preoperative hyperlactatemia on 30-day and 90-day mortality were identified by random forest method. Survival analysis for groups divided by preoperative lactate and modifiable factor was assessed and pairwise comparison between groups was calculated. Results: A total of 2036 patients were included in this study and median (interquartile range) of preoperative lactate level was 1.9 (1.4-2.4) mmol/L. The five most important variables for preoperative lactate level after comparing minimal depth and VIMP rankings were MELD, use of preoperative ventilator, hemoglobin, troponin I, and use of preoperative vasopressor. Mortality rate at 90 days and 30 days were 5.3% and 2.7%, respectively. Preoperative lactate level was important variables for predicting 30-day and 90-day mortality, and the 30-day mortality and 90-day mortality increased with increasing the concentration of lactate. Survival analysis for groups divided by preoperative lactate and hemoglobin levels revealed that the group with preoperative lactate ≥ 4.0 mmol/L and preoperative hemoglobin < 9.35 g/dL showed lower survival probability and higher cumulative hazard than other groups (p < 0.001). Conclusion: Preoperative hyperlactatemia is important factor to predict early mortality after LT. Among the important variables predicting this preoperative hyperlactatemia, hemoglobin is a modifiable factor. Considering lactate and hemoglobin together, high preoperative lactate and low preoperative hemoglobin are associated with higher early mortality after LT. Correcting low preoperative hemoglobin may play a role in preventing elevation of preoperative lactate level and lowering early mortality after LT.