The relationship between blood lactate concentration, the Paediatric Index of Mortality 2 (PIM2) and mortality in paediatric intensive care.

INTRODUCTION: Blood lactate concentration predicts mortality in neonates, infants, children and adults, with evidence that it has better predictive power than other markers of acid-base status such as absolute base excess or pH.
OBJECTIVE: To investigate whether blood lactate concentration on admission predicts mortality in paediatric intensive care and if its addition can improve the performance of the Paediatric Index of Mortality 2 (PIM2) mortality prediction score. DESIGN AND
SETTING: Retrospective cohort study in one 20-bed UK paediatric intensive care unit (PICU) using data from the PICU clinical and blood gas analyser databases between 2006 and 2010. Only cases with a blood lactate concentration measured at the same time as the PIM2 variables were included. Logistic regression was used to assess if blood lactate concentration predicted mortality independently of PIM2, adjusting for potential confounders, and if it could replace absolute base excess in the PIM2 model.
RESULTS: There were 155 deaths amongst 2,380 admissions (6.5 %). Admission lactate in non-survivors was higher than in survivors (mean [standard deviation, SD]) 6.6 [5.6] versus 3.0 [2.5] mmol/l, had a positive association with mortality [adjusted odds ratio (OR) for death per unit (mmol/l)] increase 1.11 [95 % confidence interval (CI) 1.06-1.16; p < 0.001] and significantly improved the model fit of PIM2 when it replaced absolute base excess (p < 0.001).
CONCLUSIONS: PICU admission blood lactate concentration predicts mortality independently of PIM2. Given the limitations of this study, a prospective multi-centre evaluation is required to establish whether it should be added to the PIM2 model with or without replacement of base excess.