Presented at the Neonatal Society 2006 Spring Meeting.
Deshpande S
Royal Shrewsbury Hospital, Shrewsbury SY3 8XQ, UK
Background: Early identification of infants at risk of serious brain injury following perinatal asphyxia is of utmost importance for targeting neuroprotective therapies.
Aim: To assess the ability of early postnatal blood lactate concentrations to predict short-term outcome (death or moderate to severe neonatal encephalopathy) in babies with perinatal asphyxia.
Methods: I reviewed the case records of all consecutive babies of >36 weeks gestation with 5- minute Apgar score of <6 and needing positive pressure ventilation for resuscitation and admission to the neonatal unit between 1999 and 2003. Babies with major congenital malformations and chromosomal abnormalities were excluded. Neonatal encephalopathy staged using the Sarnat and Sarnat classification. Mann-Whitney U test was used for comparison of continuous data whilst receiver operating characteristic (ROC) curves were used to determine the sensitivity, specificity, and positive and negative predictive values for prediction of the adverse outcome.
Results: Blood lactate concentrations during the first 3 hours after birth were available for 84/116 (72%) of eligible infants. Their mean (SD) gestational age and birth weight were 39.7 (1.4) weeks and 3483 (568) g, respectively. Their median (IQR) 1 and 5 minute Apgar scores were 2 (1-3) and 5 (4-6) respectively with median (IQR) age at onset of regular respirations being 10 (6-15) minutes. Severe acidosis (pH <7.0 and/or base excess ≤-16 mmol/l in cord or first postnatal blood gas) was found in 41 (49%) of infants. Moderate to severe encephalopathy developed in 28 (33%); 10 (11.9%) infants, all with severe encephalopathy, died.
First postnatal blood lactate concentrations, measured at a median (IQR) age of 65 (38-119) min, ranged from 0.5 to 42.7mmol/l. All infants with first lactate <12 mmol/l survived but 24% of those with values above this died. Median (IQR) first postnatal blood lactate concentration was significantly higher among infants with moderate to severe encephalopathy than among those with no or mild encephalopathy {19 (14.6-22) vs 8.4 (5.217-12.5), p<0.0001}. Blood lactate concentration showed significantly greater discriminating ability for prediction of moderate to severe encephalopathy than the first postnatal pH or base excess {0.881 (SE 0.04) vs 0.782 (SE 0.06) and 0.822 (SE 0.06)}. The sensitivity, specificity, positive and negative predictive values of first postnatal blood lactate concentration ≥12 mmol/l for moderate to severe encephalopathy were 92%, 67%, 58% and 95%, respectively, the corresponding values for a composite predictor (5-min Apgar score ≤5, or pH <7.0, or base excess ≤-16 mmol/l) being 93%, 39%, 43% and 92% respectively. Lactate concentration of ≥12mmol/l correctly classified 75% of infants compared to 57% when the composite predictor was present.
Conclusions: Elevated blood lactate concentration during first 3 hours after birth is a significant predictor of moderate to severe encephalopathy.