Plasma ammonia concentrations in extremely low birthweight infants in the first week after birth: secondary analysis from the ProVIDe randomized clinical trial

Barbara E Cormack,Michael Hewson,Jane E Harding,Caroline A Crowther,Roland Broadbent,Arun Nair,Mike Meyer,Emma Glamuzina,Frank H Bloomfield,Adrienne Lynn,Yannan Jiang,Bryony Ryder,Dianne Webster

doi:10.1038/s41390-019-0730-z

Abstract

BackgroundLittle is known about normative ammonia concentrations in extremely low birthweight (ELBW) babies and whether these vary with birth characteristics. We aimed to determine ammonia concentrations in ELBW babies in the first week after birth and relationships with neonatal characteristics and protein intake.MethodsArterial blood samples for the measurement of plasma ammonia concentration were collected within 7 days of birth from ProVIDe trial participants in six New Zealand neonatal intensive care units.ResultsThree hundred and twenty-two babies were included. Median (range) gestational age was 25.7 (22.7–31.6) weeks. Median (interquartile range (IQR)) ammonia concentration was 102 (80–131) µg/dL. There were no statistically significant associations between ammonia concentrations and birthweight or sex. Ammonia concentrations were weakly correlated with mean total (Spearman’s rs = 0.11, P = 0.047) and intravenous (rs = 0.13, P = 0.02) protein intake from birth, gestational age at birth (rs = −0.13, P = 0.02) and postnatal age (rs = −0.13, P = 0.02).ConclusionsPlasma ammonia concentrations in ELBW babies are similar to those of larger and more mature babies and only weakly correlated with protein intake. Currently, recommended thresholds for investigation of hyperammonaemia are appropriate for ELBW babies. Protein intake should not be limited by concerns about potential hyperammonaemia.

Highlights

Ammonia is a normal constituent of body fluids, but at high concentrations it is a known neurotoxin.[1]
Our aim was to determine whether plasma ammonia concentrations in extremely low birthweight (ELBW) babies in the first week after birth differ from those previously published for moderately preterm and term neonates and to investigate: 1. The relationships between plasma ammonia concentrations and gestational age at birth, birthweight, sex of the baby, smallness for gestational age (SGA), postnatal age and protein intake
More babies who did not have a sample for ammonia concentration died (27.6% vs. 16.1%, p = 0.02), but there was no difference in gestational age, SGA status or sex between babies who did not have an ammonia sample compared with those who did

Summary

Introduction

Ammonia is a normal constituent of body fluids, but at high concentrations it is a known neurotoxin.[1]. Little is known about normative ammonia concentrations in extremely low birthweight (ELBW) babies and whether these vary with birth characteristics. We aimed to determine ammonia concentrations in ELBW babies in the first week after birth and relationships with neonatal characteristics and protein intake. CONCLUSIONS: Plasma ammonia concentrations in ELBW babies are similar to those of larger and more mature babies and only weakly correlated with protein intake. Protein intake should not be limited by concerns about potential hyperammonaemia

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