Retrospective cohort study on the correlation between high value of lactic acid and risk of death in 127 patients with extensive burn during shock stage

Objective To analyze the relationship between serum lactic acid value and risk of death in patients with extensive burn during shock stage and the related influencing factors. Methods Clinical data of 127 patients (111 males and 16 females) with extensive burn admitted to Institute of Burn Research of the First Affiliated Hospital of Army Medical University from January 2009 to December 2013 and Department of Plastic Surgery and Burns of the Affiliated Hospital of Southwest Medical University from January 2016 to December 2018, who met the admission criteria, were retrospectively analyzed. The patients aged 21 to 62 years, with total burn area more than 50% total body surface area. All patients were treated with antishock therapy after admission. (1) According to the treatment outcome, the patients were divided into survival group (n=98) and death group (n=29). The gender, age, total burn area, partial-thickness burn area, full-thickness burn area, abbreviated burn severity index (ABSI), admission time after injury, number of patients with inhalation injury, number of patients with acute renal failure, and serum lactic acid values on admission and at post admission hour (PAH) 12, 24, 36, and 48 were recorded. (2) According to the optimal positive cut-off value of serum lactic acid 48 hours after admission, the patients were divided into high lactic acid group and normal lactic acid group. Age, gender, total burn area, indexes at PAH 48 including urea nitrogen, creatinine, alanine aminotransferase (ALT), aspartate aminotransferase (AST), total serum bilirubin, alkaline phosphatase (ALP), albumin, white blood cell count, platelet count, lymphocyte count, prothrombin time (PT), hematocrit value, oxygenation index, respiratory index (RI), the alveolar-arterial oxygen partial pressure difference, mean arterial pressure (MAP) at PAH 48, the average urine volume within 48 hours after admission, the total volume of intravenous fluid infusion within 48 hours after admission, the volume of fluid infusion per kilogram of body mass within the first 24 hours after admission, the volume of fluid infusion per one percent of body surface area per kilogram of body mass within the first 24 hours after admission, the volume of urine per kilogram of body mass per hour within the first 24 hours after admission, and the percentage of hospital death were recorded. Data were processed with t test, chi-square test, and Fisher′s exact probability test. Cox regression analysis was used to screen independent risk factors affecting the prognosis of patients. Receiver operating characteristic curve (ROC) of serum lactic acid value at PAH 48 of 127 patients was drawn to predict patients′ death and determine the optimal positive cut-off value. Multivariate logistic regression analysis was used to screen independent risk factors causing increase of serum lactic acid. Results (1) There were significantly statistical differences in total burn area, full-thickness burn area, and ABSI of patients between survival group and death group (t=6.257, 4.476, 5.727, P<0.01), while other indexes between the two groups were close. (2) The serum values of lactic acid of patients in death group on admission and at PAH 12, 24, 36, and 48 were (4.00±0.28), (4.50±0.26), (4.02±0.31), (3.48±0.22), (3.40±0.19) mmol/L, respectively, which were significantly higher than those in survival group [(3.30±0.21), (3.20±0.19), (2.33±0.17), (1.85±0.18), (1.50±0.09) mmol/L, t=14.552, 29.603, 38.133, 40.648, 74.973, P<0.05 or P<0.01]. (3) Cox regression analysis showed that the serum value of lactic acid at PAH 48 was the independent risk factor affecting the prognosis of patients, with risk ratio of 1.853 and 95% confidence interval of 1.342-2.559, P<0.01. (4) The total area under ROC of serum value of lactic acid at PAH 48 to predict death of 127 patients was 0.811, with 95% confidence interval of 0.699-0.924, P<0.01. The optimal positive cut-off value of serum value of lactic acid was 1.75 mmol/L, with sensitivity of 75.0% and specificity of 79.5% for predicting death. (5) There were significantly statistical differences in total burn area, ALT, AST, ALP, PT, total serum bilirubin, total volume of intravenous fluid infusion within 48 hours after admission, volume of fluid infusion per kilogram of body mass within the first 24 hours after admission, and percentage of hospital deaths of patients between high lactic acid group (n=34) and normal lactic acid group (n=93), t=3.592, 6.797, 10.367, 2.089, 2.880, 4.517, 2.984, 4.044, χ²=58.498, P<0.05 or P<0.01, while other indexes were close between the two groups. (6) Multivariate logistic regression analysis showed that AST and total serum bilirubin were independent risk factors for increase of serum lactic acid, with odds ratios of 1.021 and 1.064 and 95% confidence intervals of 1.001-1.040 and 1.001-1.132, P<0.05. Conclusions Serum value of lactic acid at PAH 48 can independently predict the death of patients with extensive burns. Liver injury is an important risk factor causing hyperlacticemia during burn shock stage. Widespread increase of vascular permeability and large amount of fluid resuscitation are the core factors leading to aggravation of abdominal organ injury.