Presented at the Neonatal Society 2005 Autumn Meeting.
Deshpande S
Royal Shrewsbury Hospital, Shrewsbury SY3 8XQ, UK
Background: Illness severity scores estimate the probability of hospital mortality for ill neonates. Elevated blood lactate (BL) concentrations too have been shown to relate to poor outcomes in neonates but have not been directly compared with illness severity scores.
Aim: To compare the performance of the neonatal illness severity scores (CRIB, CRIB II and SNAPPE-II) and BL for prediction of mortality among very low birth weight infants.
Methods: Babies of <32 weeks’ gestation and/or birth weight <1500 g admitted to the neonatal unit between 1999 and 2003 were included in the analysis. Babies with inevitably lethal malformations, those given comfort care only, early (<2 h of age) neonatal deaths, and those in whom BL levels were not available for the first 6 hours of life were excluded. The outcome of interest was in-hospital mortality. The discriminatory ability of the scores and BL was assessed by calculating the area under the receiver operating characteristic curves (AUC). Hosmer-Lemeshow (HL) test was used to measure the goodness of fit of the models. The study was approved by the Shropshire local research ethics committee.
Results: Of the 312 eligible infants, BL was measured during the first 6 hours in 269 (86.2%). Their mean (SD) gestation and birth weight were 29 (2.5) weeks, and 1205 (373) g, respectively. 98% were inborn, 77% had received antenatal steroids, 47% were born by caesarean section, and 59% required ventilation for a median (IQR) duration of 3 (1-9) days. There were 41 (15.2%) in-hospital deaths.
The lowest BL concentrations during first 6 hours were significantly higher among non-survivors than survivors (median (IQR) – 4.8 (2.7-9.1) vs 1.8 (0.99-3) mmol/l, p<0.0001). Higher BL during first 6 hours was associated with increasing mortality [lowest BL<2.5 mmol/l (n=155) – mortality 4.5%, BL 2.5-4.9 mmol/l (n=64) – 22%, BL 5 -9.9 mmol/l (n=33) – 33%, and BL≥10 mmol/l (n=17) – 53%]. Compared to survivors, non-survivors had significantly higher median (IQR) illness severity scores [9 (7-12) vs 1 (1-3) for CRIB, 12 (9-16) vs 5 (3-8) for CRIB II, and 56 (32-63) vs 8 (0-23.5) for SNAPPE II; p<0.0001 for all]. The illness severity scores showed significantly greater discrimination for mortality than the lowest 6-h BL concentrations [AUC (SE): CRIB – 0.92 (0.023), CRIB II – 0.91 (0.022), SNAPPE II – 0.89 (0.026) vs BL – 0.78 (0.041), p=0.003)]. Indeed, the Draper grid of gestation and birth weight was similar to the illness severity scores [AUC (SE) 0.86 (0.036), p=0.12]. All the scores and BL showed good calibration (HL: CRIB – p= 0.37, CRIB II – 0.60, SNAPPE II – 0.65, and BL – 0.39).
Conclusions: Elevated BL during early hours after birth is associated with increased in-hospital mortality. However, CRIB, CRIB II and SNAPPE II discriminate better between survivors and non-survivors than the BL levels. Indeed, gestation and birth weight appear to be as reliable measures of mortality risk in very low birth weight infants as the scores of illness severity.