Is ammonia dialyzable?

Ammonia is Highly Dialyzable and Dialysis is Recommended for Severe Hyperammonemia

Yes, ammonia is highly dialyzable and both hemodialysis and continuous kidney replacement therapy (CKRT) are effective methods for rapidly reducing blood ammonia levels in hyperammonemic patients. 1, 2

Ammonia Clearance Through Dialysis

Ammonia is a small molecule that is effectively removed through various dialysis modalities:

• Hemodialysis (HD): Can decrease blood ammonia by 75% within 3-4 hours 2

  • Provides the most rapid ammonia clearance
  • Flow-dependent clearance (higher blood and dialysate flow rates improve clearance) 3
  • Can achieve extraction rates of more than 80% with high dialysate flow rates 3

• Continuous Kidney Replacement Therapy (CKRT):

  • Specifically, high-dose CVVHD (continuous venovenous hemodialysis) is recommended as first-line treatment 1
  • Provides more stable clearance with less rebound hyperammonemia compared to HD 1
  • Recommended clearance rates ≥2,500 ml/1.73 m²/h for high-dose CKRT 2

• Peritoneal Dialysis (PD):

  • Less effective than HD or CKRT but can still reduce ammonia levels 1
  • May be used when vascular access is difficult

Indications for Dialysis in Hyperammonemia

Dialysis is indicated in the following scenarios:

Condition	Blood Ammonia Level	Treatment
Rapidly deteriorating neurological status	>150 μmol/L	Initiate CKRT
Coma or cerebral edema	>150 μmol/L	Initiate CKRT
Moderate/severe encephalopathy	Any level	Consider treatment
Persistently high levels	>400 μmol/L	Initiate CKRT if refractory to medical management
Rapid rise in levels	>300 μmol/L	Initiate CKRT if uncontrolled by medical therapy
Very high levels	>1,000 μmol/L	High-dose CKRT with Qb 30-50 ml/min, Qd/Qb >1.5

Optimal Dialysis Strategy for Hyperammonemia

For optimal ammonia clearance:

1. Initial Approach:

   • For severe hyperammonemia (>1,000 μmol/L), start with HD for rapid reduction 2
   • For levels >400 μmol/L refractory to medical management, initiate CKRT 1

2. Dialysis Prescription:

   • HD: Maximize blood flow and dialysate flow rates 3
   • CKRT: Use high-dose CVVHD with blood flow (Qb) 30-50 ml/min and dialysate flow/blood flow ratio (Qd/Qb) >1.5 1
   • High-dose CRRT using dialysis/replacement flow rates of 8,000 mL/h/1.73 m² has been shown to rapidly decrease ammonia levels 4

3. Transition Strategy:

   • Switch from HD to CKRT once ammonia levels are <200 μmol/L on two consecutive hourly measurements 1
   • Continue nitrogen-scavenging agents during dialysis to prevent rebound hyperammonemia 2, 5

Preventing Rebound Hyperammonemia

Rebound hyperammonemia is a common complication after intermittent HD:

• Continue nitrogen-scavenging agents (sodium benzoate, sodium phenylacetate) during dialysis 2, 5
• Consider hybrid therapy (HD followed by CKRT) 2
• CKRT is associated with less rebound compared to HD due to its continuous nature 1

Clinical Pearls and Pitfalls

• Timing is Critical: Early initiation of dialysis is crucial - the duration of hyperammonemic coma is a key prognostic factor 1
• Monitoring: Check ammonia levels hourly during initial treatment 2
• Complementary Therapy: Dialysis should be used alongside nitrogen-scavenging agents and dietary protein restriction 5
• Vascular Access: CKRT requires vascular access, which may be challenging in neonates 1
• Hemodynamic Stability: CKRT provides better hemodynamic stability than HD, especially important in critically ill patients 1
• Warming the Dialysate: Helps maintain hemodynamic stability, particularly in neonates 1

Ammonia clearance through dialysis is a life-saving intervention in severe hyperammonemia, with the choice of modality depending on the clinical situation, available resources, and patient stability.