Clinical Scenario:
A 2-week-old male infant, born at term, presents with a 24-hour history of poor feeding, vomiting, lethargy, and tachypnea. Examination shows hypotonia and depressed consciousness. Investigations reveal blood glucose of 45 mg/dL, arterial blood gas with pH 7.52, pCO₂ 25 mmHg, HCO₃⁻ 20 mEq/L, plasma ammonia 180 µmol/L, and urine negative for ketones. Based on the most likely diagnosis of a neonatal-onset urea cycle disorder, which of the following is the most appropriate acute management?
A) High-protein feeding
B) IV glucose + nitrogen scavengers
C) IV bicarbonate therapy
D) Lactulose and neomycin
E) Insulin infusion
Correct answer & Explanation:
Correct Answer: B) IV glucose + nitrogen scavengers
Explanation
This infant has a urea cycle disorder (UCD) presenting with hyperammonemia. The typical findings include poor feeding, vomiting, lethargy, hypotonia, encephalopathy, elevated ammonia, respiratory alkalosis, and absence of urinary ketones.
The immediate goals in an acute UCD crisis are:
- Stop catabolism by providing high-calorie glucose infusion (usually IV 10% dextrose) to suppress protein breakdown.
- Remove excess nitrogen using ammonia-scavenging agents such as sodium benzoate and sodium phenylacetate/phenylbutyrate.
Why other options are incorrect:
- A) High-protein feeding: Increases nitrogen load and worsens hyperammonemia.
- C) IV bicarbonate therapy: Does not remove ammonia and is not the primary treatment.
- D) Lactulose and neomycin: Used mainly for hepatic encephalopathy; not effective for inherited urea cycle defects.
- E) Insulin infusion: May worsen hypoglycemia and does not treat hyperammonemia.
Key point: In neonatal hyperammonemia due to UCD, the emergency treatment is IV glucose to prevent catabolism plus nitrogen-scavenging therapy, with dialysis considered if ammonia remains severely elevated or neurological status deteriorates.
