Serum lactate as a predictor of mortality after paediatric cardiac surgery

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Abstract
OBJECTIVE To assess the value of sequential lactate measurement in predicting postoperative mortality after surgery for complex congenital heart disease in children. DESIGN Prospective observational study. SETTING Sixteen bedded paediatric intensive care unit (PICU). SUBJECTS Ninety nine children ( 90 survivors, nine non-survivors). MEASUREMENTS Serum lactate and base deficit were measured on admission and every six hours thereafter. Data were analysed by Mann-Whitney and Fisher’s exact tests. RESULTS There was considerable overlap in initial lactate values between the survivor and non-survivor groups. Initial lactate was significantly raised in non-survivors (median 8.7, range 1.9–17.6 mmol/l) compared with survivors (median 2.4, range 0.6–13.6 mmol/l) (p = 0.0002). Twenty one patients (21.1%) with initial lactate concentrations greater than 4.5 mmol/l survived to PICU discharge. Using receiver operating characteristic analysis an initial lactate of 6 mmol/l had the optimum predictive value for mortality. Initial postoperative serum lactate >6 mmol/l predicted mortality with sensitivity 78%, specificity 83%, and positive predictive value of only 32%. CONCLUSION Initial lactate concentrations have poor positive predictive value for mortality. The routine measurement of lactate for this purpose cannot be justified in clinical practice.