Is nephrology consultation necessary for a patient with hyperammonemia?

Nephrology Consultation for Ammonia Level of 239 μmol/L

Yes, nephrology should be consulted immediately for an ammonia level of 239 μmol/L (approximately 407 μg/dl), as this level exceeds the threshold where kidney replacement therapy (KRT) should be strongly considered, particularly if there are any signs of encephalopathy or neurological deterioration. 1, 2

Clinical Context and Urgency

An ammonia level of 239 μmol/L represents significant hyperammonemia that warrants aggressive intervention:

• Normal ammonia levels are defined as <50 μmol/L (85 μg/dl) in term infants, children, and adolescents, and <100 μmol/L (170 μg/dl) in neonates 3
• Your patient's level of 239 μmol/L is approximately 4-5 times the upper limit of normal, placing them in a high-risk category for neurological complications 3, 4
• The duration of hyperammonemic coma and plasma ammonia levels are the two primary determinants of neurological damage prognosis 3

When to Involve Nephrology

Nephrology consultation is indicated when:

• Ammonia levels exceed 150 μmol/L (255 μg/dl) with any signs of moderate to severe encephalopathy or seizures 3
• Ammonia levels reach 200-300 μmol/L despite medical management with nitrogen scavengers 1, 2
• The patient shows clinical deterioration including lethargy, altered mental status, hyperventilation, hypotonia, ataxia, disorientation, or seizures 3
• Ammonia levels are 3-4 times the upper limit of normal (>150-200 μmol/L), which applies to your patient 4

Immediate Medical Management While Preparing for Nephrology Consultation

Before nephrology arrives, initiate the following:

• Stop all protein intake immediately to prevent further ammonia production 1, 2
• Provide adequate calories (≥100 kcal/kg daily) as intravenous glucose at 8-10 mg/kg/min and lipids (0.5 g/kg daily, up to 3 g/kg daily) to prevent catabolism 1, 2
• Administer nitrogen-scavenging agents while preparing for potential dialysis:
  • Intravenous sodium benzoate: 250 mg/kg if <20 kg or 5.5 g/m² if >20 kg 1, 2
  • Intravenous sodium phenylacetate: 250 mg/kg if <20 kg or 5.5 g/m² if >20 kg 1, 2
  • Intravenous L-arginine hydrochloride (dose depends on specific urea cycle disorder if known) 1, 2

Kidney Replacement Therapy Considerations

The nephrology team will likely recommend KRT based on:

• High-dose continuous venovenous hemodialysis (CVVHD) is the first-line treatment for severe hyperammonemia when available, with blood flow rate 30-50 ml/min and dialysate flow rate/blood flow rate >1.5 1, 2
• Intermittent hemodialysis is more effective than CKRT for rapidly reducing blood ammonia levels, showing a 50% reduction within 1-3 hours 1, 2
• At your patient's ammonia level of 239 μmol/L, KRT should be considered especially if there is evidence of encephalopathy or if levels continue to rise despite medical management 1, 2

Critical Monitoring Requirements

Once nephrology is involved, ensure:

• Check plasma ammonia levels every 3-4 hours until normalized 1, 2
• Samples must be collected from free-flowing venous or arterial blood, transported on ice, and processed within 15 minutes to avoid false elevations 1, 2
• Assess neurological status regularly using Glasgow Coma Scale for signs of encephalopathy 2
• Monitor electrolytes, especially during CKRT 1

Common Pitfalls to Avoid

• Do not delay nephrology consultation while waiting to see if medical management alone will work—at this ammonia level, the risk of irreversible neurological damage increases with every hour of delay 3, 1
• Do not prolong protein restriction beyond 48 hours—gradually reintroduce protein (by 0.25 g/kg daily, up to 1.5 g/kg daily) within 48 hours when ammonia levels return to 80-100 μmol/L to prevent catabolism 1, 2
• Do not rely solely on ammonia levels—the patient's evolving clinical status should be the primary determinant of treatment intensity 3
• Adverse prognostic factors include hyperammonemic coma lasting >3 days, increased intracranial pressure, and plasma ammonia level >1,000 μmol/l (1,703 μg/dl) 3

Decision Algorithm

For ammonia 239 μmol/L:

1. Assess neurological status immediately 3
2. If any encephalopathy present → Consult nephrology immediately for KRT 1, 2
3. If no encephalopathy → Initiate medical management AND consult nephrology for standby/monitoring 1, 2
4. Recheck ammonia in 2-3 hours 1
5. If rising or not improving → Proceed with KRT 3, 1

The decision to initiate KRT should be made jointly by pediatric/internal medicine, nephrology, metabolism, and critical care teams as appropriate 3