Lactate clearance is the rate of fall in lactate after resuscitation is started. This has shown more promise in predicting mortality. Two studies in adult patients with shock showed that lactate clearance of <10% was related to mortality [5,6]. There are no pediatric studies looking at lactate clearance and mortality although Hatheril, et al. [7] showed that persistent hyper-lactatemia at 24 hours (>2 mmol/dL) was associated with mortality. We investigated whether lactate clearance in the early period of resuscitation (first 6 hours of hospitalization) could help predict mortality in pediatric patients.

Admissions to the PICU (aged >1 month and <13 years) were studied between May 2012 and June 2013 after obtaining informed written consent from parents. Children with inborn error of metabolism and trauma were excluded. The study was approved by the hospital ethics committee. As a pilot study, a convenience sample of 45 patients admitted consecutively was enrolled. Heparinized syringe was used to collect venous blood. Lactate estimation was done by Radiometer Copenhagen ABL 555 blood gas analyzer.

Lactate levels were estimated at admission and after six hours of admission and the clearance was calculated as follows: Lactate clearance = [Initial Lactate - Current Lactate) × 100 / Initial Lactate].

A positive value denotes clearance of lactate, whereas a negative value denotes an increase in lactate after intervention. Routine ICU care and investigations were performed and Pediatric Risk of Mortality (PRISM) score was calculated. In-hospital mortality was the primary outcome of interest.

Survivors and non-survivors were compared by the Mann-Whitney test for continuous variables and by Fisher’s exact test for categorical variables. For non-parametric data, pair-wise comparisons were made using Wilcoxon’s signed-rank test. For continuous variable, we used t-test. A P value <0.05 was taken as statistically significant. SPSS version 16.0 was used.

Out of 45 children (mean age 40.15, range 1-144 months, M:F ratio 1.5:1), twelve died. The initial lactate was not significantly different between those who died and those who survived [8.44 (3.27) vs 7.29 (3.31), P=0.18], but clearance at 6 hours was significantly lower in those who died (-4.01%) than those who survived (55.53) (P<0.001). The mean (SD) PRISM score was also higher in those who died compared with those who survived [43.6 (7.27) vs. 21.7 (9.2), P<0.001].

Where lactate clearance was <30% at 6 hours, nine out of ten died. In those with clearance >30% only three out of thirty-five died. ROC curve analysis for mortality prediction was 0.97 (P< 0.001) (Fig. 1). Three children died within 24 hours. Mean (SD) duration of hospital stay in those with lactate clearance >30% was 18.5 (8.44) d (range 3-40), against 3.1 (2.61) d (range 1-9) in those with clearance <30%.

Area under curve = 0.97%

Fig. 1 ROC curve for lactate clearance at 6 hours in relation to mortality prediction.

An inverse relationship was observed between lactate clearance and PRISM score (Table I). Lactate clearance <30% at six hours predicted mortality with sensitivity of 75%, specificity of 97%, PPV 90%, NPV 91.42%. Observed and expected mortality was almost similar in those having PRISM score of >30.

TABLE I	Correlation of PRISM Score with Lactate Clearance in Relation to Observed and expected Mortality

Lactate clearance at 6 hours was significantly associated with mortality as was a PRISM score >35. The ROC curve shows mortality prediction of lactate clearance was 0.977.

The duration of stay was longer in those with good clearance because of early mortality in the ones with poor clearance. There were very few survivors among those with poor clearance to allow us to compare duration of stay in survivors in the two groups.

Acknowledgement: Dr DK Shukla for data analysis.

Contributors: AM: Design, Manuscript writing, Data-Collection and Data Interpretation; NK: Concept, Design, Manuscript drafting and guarantor of the study; RSB: Manuscript writing and JMP: Manuscript Drafting and Design of the study.

Funding: None; Competing interest: None stated.

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