Mortality and the nature of metabolic acidosis in children with shock.

HYPOTHESIS: Mortality in children with shock is more closely related to the nature, rather than the magnitude (base deficit/excess), of a metabolic acidosis.

OBJECTIVE: To examine the relationship between base excess (BE), hyperlactataemia, hyperchloraemia, 'unmeasured' strong anions, and mortality.

DESIGN: Prospective observational study set in a multi-disciplinary Paediatric Intensive Care Unit (PICU).

PATIENTS: Forty-six children, median age 6 months (1.5-14.4), median weight 5 kg (3.2-8.8), admitted to PICU with shock.

INTERVENTIONS: Predicted mortality was calculated from the paediatric index of mortality (PIM) score. The pH, base excess, serum lactate, corrected chloride, and 'unmeasured' strong anions (Strong Ion Gap) were measured or calculated at admission and 24 h.

MEASUREMENTS AND RESULTS: Observed mortality ( n=16) was 35%, with a standardised mortality ratio (SMR) of 1.03 (95% CI 0.71-1.35). There was no significant difference in admission pH or BE between survivors and nonsurvivors. There was no association between elevation of 'unmeasured' anions and mortality, although there was a trend towards hyperchloraemia in survivors ( P=0.08). Admission lactate was higher in nonsurvivors (median 11.6 vs 3.3 mmol/l; P=0.0003). Area under the mortality receiver operating characteristic curve for lactate was 0.83 (955 CI 0.70-0.95), compared to 0.71 (95% CI 0.53-0.88) for the PIM score. Admission lactate level >5 mmol/l had maximum diagnostic efficiency for mortality, with a likelihood ratio of 2.0.

CONCLUSION: There is no association between the magnitude of metabolic acidosis, quantified by the base excess, and mortality in children with shock. Hyperlactataemia, but not elevation of 'unmeasured' anions, is predictive of a poor outcome.