Hyperammonaemia in Neonatal Transport: A Retrospective Statewide Review of Neonates Retrieved With Elevated Ammonia

To characterise the aetiology, retrieval characteristics and outcomes of neonatal hyperammonaemia in a statewide neonatal retrieval service.

Retrospective chart review of all neonates (aged ≤ 8 weeks) retrieved by the statewide Paediatric Infant Perinatal Emergency Retrieval (PIPER) service to the Royal Children's Hospital (RCH), Melbourne, Australia, between April 2016 and February 2025, with a pre-transport plasma ammonia > 100 μmol/L.

Twenty-one neonates met inclusion criteria. Median gestation was 38 weeks (IQR: 38-39) and median age at retrieval referral was 59 h (IQR: 48-84). A confirmed inborn error of metabolism (IEM) was identified in 16 of 21 neonates (76%), with urea cycle disorders accounting for 12 of the 16 confirmed IEMs (75%). Twelve patients (57%) required continuous veno-venous haemofiltration (CVVHF). Compared with those managed without haemofiltration, the CVVHF group had higher peak ammonia (median 854 vs. 378 μmol/L) and a higher rate of confirmed IEM (92% vs. 56%). Twelve retrievals (57%) were classified as time-critical, and metabolic medication was administered during transport in nine cases (43%). Median time from decision to retrieve to team dispatch was 20 min (IQR: 13-26) and to specialist hospital arrival 152 min (IQR: 97-229). Seventeen neonates (81%) survived to hospital discharge.

Neonatal hyperammonaemia requiring retrieval is predominantly caused by an IEM and frequently requires CVVHF, with low occurrence of spurious elevation. These findings support early retrieval to a quaternary centre with haemofiltration capability and provide benchmarking data for retrieval services managing this rare, high-acuity condition.