Inborn errors of metabolism and decompensation — Rapid

Synopsis

Recognise metabolic decompensation in a newborn or child with encephalopathy, hypoglycaemia, acidosis, hyperammonaemia or organ failure, stop catabolism immediately and obtain time-critical diagnostic samples while specialist detoxification and dialysis are mobilised.

Suspect an inborn error when a previously well newborn deteriorates after feeding, illness causes disproportionate encephalopathy or a child has recurrent fasting collapse, unexplained acidosis, hyperammonaemia, hypoglycaemia or liver dysfunction.
Metabolic and infectious emergencies coexist in the differential: use ABCDE, treat sepsis when indicated and contact the regional paediatric metabolic service and intensive care immediately.
First-line emergency tests are bedside glucose, blood gas, lactate, electrolytes, liver tests, coagulation, ketones and an urgently handled plasma ammonia; repeat an unexpected ammonia promptly from a clean free-flowing sample without delaying action.
Before treatment changes the pattern, save plasma amino acids, acylcarnitine profile, free fatty acids, insulin and C-peptide during hypoglycaemia and urine organic acids and ketones, but never postpone resuscitation to complete sampling.
Reverse catabolism with the child's current BIMDG emergency regimen or intravenous glucose when oral or nasogastric intake is unsafe; a normal glucose at presentation does not mean catabolism is controlled.
Hypoglycaemia with few or no ketones suggests fatty-acid oxidation disease or inappropriate insulin action, while marked ketosis and acidosis suggests organic acid, glycogen or fasting-related mechanisms.
Hyperammonaemia with respiratory alkalosis and little acidosis suggests a urea-cycle defect; organic acidaemia often has metabolic acidosis, ketosis, raised lactate and secondary ammonia elevation.
Temporarily stop natural protein when hyperammonaemia, maple-syrup urine disease or organic acidaemia is suspected, but use metabolic-team direction and reintroduce essential protein promptly to avoid further catabolism.
Severe or rising ammonia, cerebral oedema, refractory acidosis or toxic metabolites requires immediate ammonia-scavenger or disease-specific therapy and early haemofiltration or haemodialysis planning; do not wait until coma.
Known patients must bring their emergency letter, diagnosis-specific medicines, maximum safe fasting time and glucose-polymer recipe; follow that document rather than a generic fluid plan.

Key red flags

Any raised ammonia with neurological deterioration requires urgent repeat sampling and immediate metabolic specialist discussion.

Respiratory alkalosis in an encephalopathic newborn is a classic warning for a urea-cycle defect.

Hypoglycaemia with absent or minimal ketones is not normal fasting adaptation and suggests fat-oxidation failure or hyperinsulinism.

High-anion-gap acidosis with ketosis, lactate or unusual odour can signal an organic acidaemia.

Cardiomyopathy, arrhythmia or rhabdomyolysis during fasting illness suggests an energy-production disorder.

A normal newborn blood-spot result cannot exclude the many metabolic conditions outside the panel or a false-negative screened condition.

Failure to improve after glucose and sepsis treatment requires renewed toxin-removal and metabolic assessment, not diagnostic closure.

Severe metabolic decompensation

Coma, refractory acidosis, rising ammonia, cerebral signs or multiorgan failure requires immediate metabolic intensive care and dialysis planning.

Investigation priorities

First-line glucose, gas and lactateFirst stepFirst line

Detect immediately treatable hypoglycaemia and define respiratory alkalosis, metabolic acidosis and tissue stress.

Management branches

Unknown metabolic collapseSample rapidly and stop catabolism

A newborn or child has unexplained encephalopathy, acidosis, hypoglycaemia, ammonia elevation or organ failure.

Use ABCDE and treat sepsis and hypoglycaemia while contacting metabolic and intensive-care teams and retrieving family history.
Send urgent ammonia, glucose, gas, lactate, organ tests and saved plasma and urine metabolic samples without delaying resuscitation.
Begin IV glucose or the age-appropriate BIMDG high-energy regimen and withhold natural protein briefly when the biochemical mechanism supports it.

Key medicines

Intravenous glucose for anti-catabolic therapyTreat documented hypoglycaemia with 10% glucose at the current paediatric emergency bolus dose, then use the age- and weight-specific BIMDG glucose infusion rate needed to suppress catabolism, adding insulin only under metabolic critical-care direction when hyperglycaemia limits delivery.Monitor glucose, sodium, potassium, lactate and fluid balance closely; maintenance fluid alone may provide inadequate energy and excess free water can worsen cerebral oedema.

Glucose-polymer emergency regimenGive the child's prescribed age-specific concentration and volume frequently by mouth or nasogastric tube when airway and gut are safe; use the current BIMDG recipe and switch to intravenous energy if the target intake is not achieved.Do not improvise concentration, delay hospital transfer for persistent vomiting or drowsiness, or use enteral feeds when aspiration or ileus is likely.

Open full textbook →Answer 2 questions