Objective: To investigate the prognostic significance of early lactate clearance rate for severe acute respiratory failure patients on extracorporeal membrane oxygenation (ECMO).
Methods: Forty-three patients with severe acute respiratory failure supported by venous-venous (v-v) ECMO were enrolled from January 2007 to January 2013. Arterial blood lactate at pre-ECMO support(0 h) and at post-ECMO 6 hours (6 h) were measured and then 6 h lactate clearance rate was calculated. The acute physiology and chronic health evaluation II (APACHEII) score was evaluated on the first day of ECMO support. Survival at 90 d after admission was the study endpoint. Patients were divided into the survival group (n = 24) and the death group (n = 19) . The 0 h blood lactate, 6 h lactate clearance rate and APACHE II score were compared between groups. The value of 0 h blood lactate, 6 h lactate clearance rate and APACHE II score for predicting death was evaluated by receiver operating characteristic (ROC) curves. The surviving curve was drawn using the Kaplan-Meier method, and the survival of the patients was analyzed by the Log-rank test. Factors influencing the prognosis were analyzed by the multiple logistic regression analysis.
Results: (1) The 0 h blood lactate and APACHE II score were lower in survivors than in nonsurvivors [(3.8 ± 2.1) mmol/L vs. (5.9 ± 2.3) mmol/L, (18 ± 7) vs. (25 ± 7) , t = 7.924, 8.446, respectively, both P < 0.05], while the 6 h lactate clearance rate was higher in survivors than in nonsurvivors [(35.7 ± 20.4) % vs. (10.7 ± 18.2) %, t = 8.607, P < 0.05]. (2) The areas under the ROC curve of 0 h blood lactate, 6 h lactate clearance rate and APACHE II score for predicting death were 0.699 ± 0.083 (95%CI:0.567∼0.892, P < 0.05) , 0.871 ± 0.119 (95%CI:0.724∼0.980, P < 0.05) and 0.836 ± 0.063 (95%CI: 0.713∼0.958, P < 0.05) . The best cutoff point was 17.5% for 6 h lactate clearance with a sensitivity of 87.5% and specificity of 84.2%. (3) Kaplan-Meier survival analysis showed that 90 d survival rate of the high lactate clearance rate group and the low lactate clearance rate group were 78.3% and 30%, with significant difference between the two groups (χ² = 10.103, P < 0.05). (4) Multivariate logistic regression analysis showed that 0 h blood lactate (OR = 1.318, 95%CI:1.159∼6.882, P < 0.05) , 6 h lactate clearance rate (OR = 6.921, 95%CI:4.469∼15.036, P < 0.05) and APACHEII score (OR = 4.417, 95%CI:3.058∼10.356, P < 0.05) were independent risk factors associated with mortality of patients on ECMO.
Conclusion: Early lactate clearance rate could be used as an important variable for evaluating the prognosis of severe acute respiratory failure patients on ECMO.