Abstract
Purpose of study– Transient hyperammonemia of the newborn can lead to an overwhelming and potentially fatal illness. The etiology of this condition is obscure although hypoxia, immature urea cycle and inadequate hepatic blood flow have all been implicated. We hypothesized that preterm infants with hypoxia would have elevated ammonia levels after birth that normalize within 3–4 weeks. The study aim was to measure serial plasma ammonia levels in preterm infants with hyaline membrane disease (HMD) or perinatal asphyxia to elucidate the role of hypoxia in the pathogenesis of hyperammonemia.
Methods– Infants 24–37 weeks gestation with severe HMD or perinatal asphyxia who had indwelling umbilical catheters and parental consent were enrolled. Hyperalimentation with 10% trophamine was initiated at 24–48 hours of life. Blood samples were drawn at 24 hours, 48 hours and weekly until ammonia levels normalized. Plasma ammonia was analyzed using Vitros AMON Slide Analyzer. A level ≥ 50 umol/l was considered elevated. Pregnancy and neonatal data were collected. Repeated measures ANOVA was employed to examine mean differences in serial plasma levels in each group. All analyses were conducted using SPSS Version 11.5.
Results– The study sample consisted of 20 neonates in the HMD and 6 in the asphyxia group. Infants with asphyxia had significantly lower apgar scores, cord pH and higher ALT levels. In the HMD group, mean plasma ammonia level decreased from 100.68±28.35 umol/l at 24 hours to 88.42±23.61umol/l at 48 hours (p=0.003) and 56.84±18.42 umol/l at week 2 (p<0.001). In the perinatal asphyxia group, mean ammonia levels decreased from 97.67±10.78 umol/l at 24 hours to 88.67±9.02 umol/l at 48 hours (p=0.003) and 56.83±7.12 umol/l at week 2 (p<0.001). No significant between group differences were seen in mean plasma ammonia. Ammonia levels correlated significantly with pH (neg), pO2(neg) and FiO2 (pos). Multiple regression analyses revealed that both pO2 and pH accounted for ∼73% variance of plasma ammonia levels (p<0.001) and pO2 alone accounted for ∼52% variance.
Conclusions– Ammonia levels decreased significantly from 24 hours to week 2 in both groups. No significant correlation of plasma ammonia levels was seen with birth weight, gestational age, apgar scores, glucose, calcium, bilirubin, ALT levels and total caloric and protein intake. Hyperammonemia was not associated with neurologic dysfunction. PO2 and pH significantly predicted ammonia levels. Thus, hypoxic state associated with HMD and perinatal asphyxia is associated with transient hyperammonemia that lasts for 2–3 weeks.
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Brar, G., Thomas, R., Bawle, E. et al. Transient Hyperammonemia in Preterm Infants With Hypoxia.. Pediatr Res 56, 671 (2004). https://doi.org/10.1203/00006450-200410000-00052
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DOI: https://doi.org/10.1203/00006450-200410000-00052