Management of Hyperammonemia

Initial Management

• The American College of Nephrology recommends immediate investigations and treatment for elevated ammonia levels, without delaying, and discontinuing all oral feeds to reduce nitrogen load and providing adequate calories (≥100 kcal/kg daily) as intravenous glucose and lipids 1, 2
• Maintain a glucose infusion rate of 8-10 mg/kg/min and provide lipids (0.5 g/kg daily, up to 3 g/kg daily) to prevent protein catabolism driving further ammonia production 1, 2
• Gradually reintroduce protein (by 0.25 g/kg daily, up to 1.5 g/kg daily) within 48 hours to prevent protein catabolism driving further ammonia production 1, 2

Pharmacological Therapy

• Use nitrogen-scavenging agents such as sodium benzoate and sodium phenylacetate at recommended dosages, with intravenous sodium benzoate: body weight <20 kg, 250 mg/kg; body weight >20 kg, 5.5 g/m², and intravenous sodium phenylacetate: body weight <20 kg, 250 mg/kg; body weight >20 kg, 5.5 g/m² 1, 2
• Administer intravenous L-arginine hydrochloride based on specific urea cycle disorder, with dosages of 200 mg/kg for body weight <20 kg and 4 g/m² for weight >20 kg for OTC and CPS deficiencies, and 600 mg/kg for body weight <20 kg and 12 g/m² for weight >20 kg for ASS and ASL deficiencies 1, 2

Kidney Replacement Therapy (KRT)

• The American Society of Nephrology recommends high-dose continuous venovenous hemodialysis (CVVHD) as the first-line treatment for severe hyperammonemia when available, with a blood flow rate (Qb) 30-50 ml/min, aiming at dialysis fluid flow rate (Qd)/Qb >1.5 3, 4
• Consider intermittent hemodialysis (HD) for patients requiring rapid ammonia clearance, with HD being more effective than CKRT for rapidly reducing blood ammonia levels, showing a 50% reduction in ammonia levels within 3 hours 5, 6
• Combination of HD and CKRT (hybrid or sequential therapy) can gradually reduce ammonia levels while controlling rebound effect, and is recommended for neonates who are hemodynamically unstable 5, 6

Monitoring During Treatment

• Check plasma ammonia levels every 3-4 hours until normalized, and assess neurological status regularly for signs of encephalopathy 1
• Monitor electrolytes, especially during CKRT, to prevent complications 1

Common Pitfalls and Caveats

• Delayed recognition and treatment can lead to irreversible neurological damage, and ammonia samples must be collected from free-flowing venous or arterial blood, transported on ice, and processed within 15 minutes to avoid false elevations 3, 1
• The duration of hyperammonemic coma prior to the start of dialysis is the most important prognostic factor, not the rate of ammonia clearance 3

Management of Hyperammonemia

Initial Assessment and Treatment

• If ammonia levels remain elevated despite lactulose therapy or if neurological status deteriorates, the American Society of Nephrology recommends considering kidney replacement therapy 7
• For severe encephalopathy with high ammonia levels, the Society of Critical Care Medicine suggests considering initiating ammonia-scavenging agents while preparing for dialysis 8, 7

Escalation to Kidney Replacement Therapy (KRT)

• The National Kidney Foundation recommends considering continuous kidney replacement therapy (CKRT), specifically high-dose continuous venovenous hemodialysis (CVVHD), if the patient develops moderate to severe encephalopathy or if ammonia levels remain persistently high despite medical management 7
• The European Renal Association suggests that hemodialysis is the most effective method for rapidly reducing blood ammonia levels, showing a 50% reduction within 1-2 hours 9
• The American Society of Nephrology advises that the decision to initiate KRT should be based primarily on the patient's clinical status rather than rigid ammonia level thresholds 7

Management of Acute Hyperammonemia

Indications for Dialysis

• The National Kidney Foundation recommends urgent continuous kidney replacement therapy (CKRT) or hemodialysis for patients with ammonia levels >150 μmol/L and rapidly deteriorating neurological status, coma, or cerebral edema 10, 11
• The American Society of Nephrology suggests CKRT or hemodialysis for patients with ammonia levels persistently >400 μmol/L despite medical management 10, 11
• The European Renal Association recommends CKRT or hemodialysis for patients with a rapid rise to >300 μmol/L within hours uncontrolled by medications 10, 11
• The International Society of Nephrology advises CKRT or hemodialysis for patients with moderate to severe encephalopathy at any ammonia level 10, 11

Dialysis Modality

• The National Kidney Foundation recommends high-dose continuous venovenous hemodialysis (CVVHD) as the preferred modality for ammonia removal, with a blood flow rate of 30-50 ml/min and a dialysate flow rate to blood flow rate ratio >1.5 10, 11
• The American Society of Nephrology suggests using warmed dialysate to maintain hemodynamic stability during CVVHD 10, 11
• The European Renal Association recommends continuing CVVHD until ammonia levels are <200 μmol/L on two consecutive hourly measurements 10, 11

Alternative Dialysis Modality

• The International Society of Nephrology recommends intermittent hemodialysis as an alternative for rapid ammonia clearance, achieving a 50% reduction in ammonia within 1-2 hours, followed by transition to CKRT to prevent rebound 12

Neurological Monitoring

• The American Academy of Neurology recommends monitoring for signs of cerebral edema, including pupillary changes, posturing, and bradycardia, in patients with acute hyperammonemia 10, 12

Protein Reintroduction

• The European Society for Clinical Nutrition and Metabolism recommends not prolonging protein restriction beyond 48 hours in patients with acute hyperammonemia, as this can cause catabolism and worsen ammonia levels 13
• The American Society for Parenteral and Enteral Nutrition suggests reintroducing protein gradually at 0.25 g/kg daily increments, targeting 1.5 g/kg daily as tolerated, and beginning when ammonia levels are trending down toward 80-100 μmol/L 13

Management of Severe Hyperammonemia in Hepatic Encephalopathy

Indications for Initiating Kidney Replacement Therapy

• Initiate continuous kidney replacement therapy (CKRT) when a patient shows rapidly deteriorating neurological status, coma, or cerebral edema in the setting of ammonia concentrations > 150 µmol/L. 14
• Initiate CKRT for any patient with moderate or severe hepatic encephalopathy, regardless of the absolute ammonia value. Moderate encephalopathy is characterized by lethargy, distal flexion, reduced activity, hypotonia, weak suck, constricted pupils, or bradycardia; severe encephalopathy includes stupor or coma, absent activity, decerebrate posture, flaccid tone, absent reflexes, and non‑reactive pupils. 14

Dialysis Modality Selection

• High‑dose continuous venovenous hemodialysis (CVVHD) is the preferred first‑line modality when kidney replacement therapy is indicated, using a blood flow rate of 30–50 mL/min and a dialysate‑to‑blood‑flow ratio > 1.5. 14
• CVVHD provides superior ammonia clearance compared with continuous venovenous hemofiltration (CVVH) while preserving hemodynamic stability and minimizing rebound hyperammonemia. 14
• Employ warmed dialysate during CVVHD to further support hemodynamic stability. 14
• A hybrid approach—initial intermittent hemodialysis (HD) followed by CKRT—can be used to achieve rapid ammonia reduction while controlling the rebound effect. 15

Treatment Duration and Monitoring

• Continue CVVHD until ammonia concentrations fall below 200 µmol/L on two consecutive hourly measurements. 15

Prognostic Considerations

• The length of time a patient remains in hyperammonemic coma before dialysis initiation is the most critical prognostic factor for neurological outcome, outweighing the speed of ammonia clearance. 14

Guideline Recommendations for Initiating and Managing Dialysis in Hyperammonemia

When to Initiate Kidney Replacement Therapy (KRT)

• Urgent initiation of KRT is recommended when plasma ammonia exceeds 150 μmol/L (255 μg/dL) in the setting of rapidly worsening neurological status, coma, or cerebral edema. 16, 17
• If ammonia is 301–499 μmol/L (513–850 μg/dL) and the patient shows moderate to severe encephalopathy or seizures, nitrogen‑scavenging agents should be started immediately while dialysis is being prepared. 16
• When ammonia remains >300–400 μmol/L despite medical management (including nitrogen‑scavengers), continuous KRT (CKRT) should be considered. 17

Clinical Indicators Guiding Dialysis Decision

• The presence of seizure activity with consistent electroencephalographic (EEG) findings is an indication to start dialysis. 16
• Failure to achieve a clinical response to nitrogen‑scavenging therapy after 2 hours warrants initiation of dialysis. 16

Comparative Efficacy of Dialysis Modalities

Data derived from comparative studies of ammonia clearance across modalities. 16, 17

• CVVHD is the preferred first‑line modality for severe hyperammonemia when available, offering superior clearance while maintaining hemodynamic stability. (supported by the same clearance data) 16
• Peritoneal dialysis is not recommended as a first‑line therapy because its ammonia clearance is inferior to both CVVHD and intermittent HD. 16, 17

Treatment Targets After Initiating KRT

• Aim to reduce plasma ammonia to <200 μmol/L (≈280 μg/dL) on two consecutive hourly measurements before discontinuing dialysis. 16, 17