Is ammonia in patients with hepatic encephalopathy dialysable?

Is Ammonia Dialysable in Hepatic Encephalopathy?

Yes, ammonia is dialysable, and continuous modes of hemodialysis should be used when needed in patients with acute liver failure and hepatic encephalopathy, particularly when renal failure is present. 1

Evidence for Dialysis in Hepatic Encephalopathy

Acute Liver Failure Context

The AASLD position paper on acute liver failure management explicitly recommends continuous modes of hemodialysis when needed for patients with hemodynamic instability and renal failure. 1 This recommendation appears in the context of managing patients with Grade III/IV encephalopathy, where ammonia plays a pathogenic role in cerebral edema development. 1

Rationale for Ammonia Removal

• Ammonia is strongly associated with cerebral herniation when arterial levels exceed 200 µg/dL in acute liver failure patients. 1
• Ammonia causes brain edema through direct neurotoxic effects, as demonstrated in animal models where ammonia infusion produces cerebral edema. 1
• In hyper-acute ALF with sustained arterial ammonia >150 mMol/L, patients face increased risk of cerebral edema and intracranial hypertension. 1

Technical Considerations

Continuous renal replacement therapy (CRRT) is preferred over intermittent hemodialysis in the acute liver failure setting because: 1

• Patients often have hemodynamic instability requiring pressor support (dopamine, epinephrine, norepinephrine). 1
• Continuous modes provide more stable ammonia clearance without rapid fluid shifts that could worsen intracranial pressure. 1
• These patients require intensive monitoring of metabolic parameters (glucose, potassium, magnesium, phosphate) that CRRT facilitates. 1

Important Clinical Caveats

When Dialysis Is NOT the Primary Intervention

In chronic liver disease with hepatic encephalopathy, dialysis is not a standard treatment approach. 1 The management focuses on:

• Lactulose for ammonia reduction through gut mechanisms. 1
• Rifaximin and other gut-directed therapies. 2
• Treatment of precipitating factors (infection, GI bleeding, constipation). 1

Monitoring During Dialysis

• Arterial ammonia should be monitored when implementing any ammonia-lowering strategy, including dialysis. 1
• However, ammonia levels alone do not guide treatment decisions or predict outcomes in chronic liver disease patients. 1, 3
• A normal ammonia level during treatment should prompt reevaluation for alternative causes of altered mental status. 4, 5

Clinical Algorithm for Dialysis Decision

Initiate continuous hemodialysis when:

1. Acute liver failure with Grade III/IV encephalopathy AND renal failure is present. 1
2. Arterial ammonia levels are severely elevated (>150-200 µmol/L) with risk of cerebral herniation. 1
3. Hemodynamic instability requires continuous renal support rather than intermittent dialysis. 1

Do NOT use dialysis as primary ammonia-lowering therapy when:

1. Patient has chronic liver disease with standard hepatic encephalopathy (use lactulose/rifaximin instead). 1
2. Renal function is preserved and gut-directed therapies are feasible. 1
3. The goal is solely ammonia reduction without concurrent renal failure indication. 1

Common Pitfall to Avoid

Do not initiate dialysis based solely on elevated ammonia levels. 1, 3 The decision must be driven by clinical indications (renal failure, severe metabolic derangements, acute liver failure with cerebral edema risk), not by ammonia values alone, as ammonia levels do not correlate reliably with encephalopathy severity or treatment response in chronic liver disease. 1, 3