Consider hyperammonaemia in the differential diagnosis of any sick neonate
The neurological outcome of affected neonates is directly related to the duration of hyperammonaemic coma
Contact the Emergency Department Consultant urgently if the patient is unwell
Assessment
History
Clinical signs of hyperammonaemia are non specific but can include tachypnoea, seizures and encephalopathy
Investigations
Ammonia (x2)
Free flowing, consider arterial sample if difficult. Place on ice and transport urgently to lab.
Venous blood gas
Respiratory alkalosis in Urea Cycle Defects, metabolic acidosis in Organic Acideamias
Lactate
Raised in Organic Acideamias, Fatty Acid Oxidation defects and Urea Cycle defects with circulatory collapse
Liver Function
Deranged in liver failure, Organic Acideamias and Fatty Acid Oxidation defects
Clotting
Deranged in liver failure, Organic Acideamias and Fatty Acid Oxidation defects
Urine Ketones (dipstick)
Low in Fatty Acid Oxidation defects and Urea Cycle defects. Raised in Organic Acidaemias.
Plasma Amino Acids
Urine Amino Acids
Urine Organic Acids
Plasma Acylcarnitines
Can also be done on the Guthrie card
Differential diagnoses
Spurious
Sample haemolysed, not collected on ice, or delayed separation
Hepatic liver failure/impairment
Metabolic
Urea Cycle defects (UCD)
Organic Acidaemias (OA)
Fatty Acid Oxidation defects (Fatox)
Transient hyperammonaemia of the newborn (due to open ductus venosus)
Management
Elevated plasma ammonia is a medical emergency
Do not delay treatment whilst awaiting results of further investigations
Initial management
Stop all enteral feeds
Promote anabolism :
Start intravenous 10% Dextrose to ensure glucose infusion of 8-10mg/kg/minute, aiming for a blood glucose level of 4-8 mmol/L
Add Insulin infusion of 0.05U/kg/hr if blood glucose > 15mmol/L. Do not turn down the rate of 10% Dextrose (remember the aim is to stop catabolism and this can only be done by giving lots of calories).
If ammonia > 150 μmol/L, commence:
Sodium Benzoate 250mg/kg/day as a continuous IV infusion and
Carnitine 100mg/kg/day as a continuous IV infusion
These products are now available as concentrated solutions in ampoules in the hyperammonia kit on 6B (Neonatal Unit)
If ammonia > 300μmol/L
Need to prepare for probable haemodiafiltration
Contact PICU Consultant to discuss admission and further management
Remember: It can take some time to get appropriate central venous access and commence haemodiafiltration so ALL other measures to lower plasma ammonia must be initiated as soon as possible.
In addition, consider arginine 350/kg/day as a continuous infusion
If boluses of fluid are required:
Use 0.9% saline
Remember: 4.5% Human Albumin solution and Fresh Frozen Plasma contain protein
In the event of imminent death, an antemortem liver biopsy and a skin biopsy should be obtained, to assist with diagnosis
Contact the biochemistry laboratory to arrange
2mls EDTA whole blood should also be collected for potential genetic studies
Finally, consider carefully whether to perform a post-mortem, even if liver and skin biopsies have been taken
x
Give feedback here