The Burden

• Hyperammonemia develops in ~30-50% of patients with acute liver failure (ALF)
• Hepatic encephalopathy (HE) affects ~60-80% of ALF patients
• Cerebral edema from severe hyperammonemia is a leading cause of death in ALF
• Time-sensitive condition: Hours matter — delays in RRT initiation correlate with worse neurological outcomes

Clinical Scenarios You’ll See

1. Acute liver failure from acetaminophen overdose, viral hepatitis, mushroom toxicity
2. Acute-on-chronic liver failure (ACLF) in a cirrhotic patient with infection or GI bleed
3. Severe hepatitis with rising ammonia levels despite lactulose/rifaximin
4. Urea cycle disorders in neonates/children (out of scope here but similar dialysis principles)

Normal Ammonia Metabolism

The liver normally detoxifies ammonia via the urea cycle: 1. Ammonia (NH3) from protein metabolism enters hepatocytes 2. Reacts with carbamoyl phosphate → Citrulline → Arginine → Urea 3. Urea excreted by kidneys 4. Normal blood ammonia: 11-35 μmol/L (varies by lab)

In Liver Failure, This Pathway Collapses

• Loss of hepatic synthetic capacity → Cannot convert ammonia to urea
• Portosystemic shunting → Blood bypasses liver; ammonia-laden portal blood reaches systemic circulation
• Result: Ammonia accumulates systemically → Neurotoxicity

How Ammonia Damages the Brain

Subtle Early Signs (Grade 1-2 Encephalopathy)

• Sleep disturbance (inverted sleep-wake cycle)
• Personality changes, anxiety
• Mild confusion, difficulty concentrating
• Tremor (asterixis — “flapping tremor”)

Moderate Signs (Grade 3 Encephalopathy)

• Somnolence, easily aroused
• Disorientation to time/place
• Inappropriate behavior
• Asterixis present

Severe Signs (Grade 4 Encephalopathy, Often With Severe Hyperammonemia)

• Deep coma, unresponsive
• No asterixis (because patient cannot extend wrists)
• Signs of cerebral edema: Papilledema, decerebrate posturing
• Prognosis grave: Without emergency intervention, death from herniation

Ammonia Level Correlation

• Mild elevation (100-150 μmol/L): May be asymptomatic or mild HE
• Moderate (150-250 μmol/L): Often grade 2-3 HE; consider RRT
• Severe (>300 μmol/L): Almost always grade 3-4 HE; RRT urgently needed
• Very severe (>400 μmol/L): Medical emergency; high mortality without intervention

Normal Kidneys

• Don’t eliminate ammonia effectively
• Kidney clearance of ammonia is slow (~0.5-1 mL/min)
• Ammonia is primarily handled by the liver (urea cycle)

Dialysis Can Remove Ammonia Much Faster

Key Studies & Findings

Ammonia Level Thresholds (Evidence-Based Recommendations)

Special Populations

Pediatric/Neonates (Urea Cycle Disorders): - Lower thresholds: RRT considered at 100-150 μmol/L - Higher neurotoxicity risk in children - Earlier intervention prevents permanent neurological damage

Acute Liver Failure (ALF): - More aggressive approach: RRT often started at 150 μmol/L - Rationale: ALF progresses rapidly; neurotoxicity risk is high - Delay of hours can lead to herniation

Cirrhosis with Acute Decompensation: - Threshold ~200-250 μmol/L (slightly higher tolerance) - Chronic hyperammonemia may be partially tolerated - But acute rises still warrant urgent intervention

Hemodialysis (Intermittent, 3-4 Hours) — When to Use

Best for: - Acute, severe hyperammonemia (>300 μmol/L) requiring rapid reduction - Stable patients hemodynamically - Need for quick initial ammonia drop before CRRT is running

Prescriptions for Ammonia Removal: - Blood flow: 400-500 mL/min (higher = better ammonia clearance) - Dialysate flow: 500-600 mL/min - Dialyzer: High-flux preferred (higher middle-molecule clearance) - Duration: 3-4 hours; may repeat daily if ammonia remains >250

Caution: - Risk of rebound hyperammonemia 4-6 hours post-dialysis - Intradialytic hypotension can occur; monitor closely - Not ideal for hemodynamically unstable patients

Continuous Renal Replacement Therapy (CRRT) — When to Use

Best for: - Hemodynamically unstable patients (septic shock, on vasopressors) - Need for sustained ammonia control without rebound - Concurrent acute kidney injury requiring RRT anyway - Patients on mechanical ventilation where dialysis sessions interrupt care

Prescriptions for Ammonia Removal: - Mode: CVVH (continuous venovenous hemofiltration) or CVVHD - Blood flow: 200-300 mL/min - Effluent rate: 25-35 mL/kg/hr (higher clearance for ammonia) - Duration: Continuous (24/7) until ammonia levels controlled

Advantage: - Smooth, gradual ammonia reduction - No rebound hyperammonemia - Compatible with vasopressor support and sedation

Hybrid Approach

• Day 1-2: Intermittent HD (rapid ammonia drop) in stable patient
• Day 3 onwards: Transition to CRRT if unstable, need sustained control, or rebound occurs
• Albumin dialysis: Consider if available and persistent high ammonia despite standard RRT

The Evidence on Early vs. Late RRT

Cho et al. (2022, Neurological Outcomes Study): - Every hour of delay in initiating RRT for severe hyperammonemia (>300 μmol/L): - Increased risk of permanent neurological deficits - Increased risk of cerebral edema and herniation - Patients with RRT initiated within 2 hours of ammonia >300: better outcomes - Patients with RRT initiated >6 hours after crossing 300: significantly worse prognosis

Practical Implication

• If ammonia >300, start dialysis TODAY/NOW, not tomorrow
• Don’t wait for “one more lab,” or for patient to deteriorate further
• Early RRT is essentially never harmful; delay can be catastrophic

Step 1: Recognize Hyperammonemia Risk

• Any patient with ALF: get baseline ammonia
• Any cirrhotic patient with acute decompensation + encephalopathy: check ammonia
• Any patient with unexplained altered mental status + liver disease: check ammonia

Step 2: Check Ammonia Level (Proper Technique)

• Blood tube: Use iced tube (ammonia very labile)
• Send immediately to lab (ammonia rises ~20% per hour if not iced)
• Note the time — ammonia fluctuates throughout the day
• Repeat in 4-6 hours if initial level elevated; watch trend

Step 3: Consult Nephrology Early (Before Crisis)

• Ammonia >150 μmol/L + symptoms → Nephrology consult
• Discuss: Ammonia trajectory, likely need for RRT, best modality for this patient
• Prepare vascular access (central line if not already present)
• Optimize medical therapy while decision is being made

Step 4: Initiate RRT Per Protocol

• Ammonia 150-250 μmol/L: Monitor closely; prepare for RRT; optimize medical Rx
• Ammonia 250-300 μmol/L: Initiate RRT (CRRT preferred if patient unstable)
• Ammonia >300 μmol/L: START RRT EMERGENTLY — don’t delay

Step 5: Monitor During RRT

• First 4 hours: Check ammonia; expect 30-40% reduction with HD
• Ongoing: Serial ammonia levels q4-6h initially, then daily
• Watch for: Rebound hyperammonemia (4-6 hours post-HD); signs of cerebral edema
• Goal: Ammonia <100 μmol/L; once stable, can transition to less aggressive RRT

Step 6: Concurrent Medical Therapy

Dialysis is NOT the only approach; use synergistic medications: - Lactulose: 15-30 mL 2-3× daily (produces osmotic diarrhea; acidifies colon → traps ammonia) - Rifaximin: 550 mg 2-3× daily (non-absorbed antibiotic; reduces urease-producing bacteria) - L-Ornithine L-Aspartate (LOLA): 10-20 g/day IV or PO (enhances urea cycle) - Zinc supplementation: 100-200 mg/day (cofactor for urea cycle enzymes) - Branched-chain amino acids (BCAA): 50-100 g/day (substrate for urea cycle; reduces ammonia)

Managing AKI in Cirrhotic Patients on Dialysis

If your dialysis patient develops concurrent acute liver failure:

1. Continue dialysis — they still need RRT for kidney function
2. Add ammonia monitoring — check baseline; repeat if symptoms develop
3. Modality choice: CRRT preferred (more forgiving; better hemodynamic stability)
4. Intensify treatment: Higher effluent rates; longer hours
5. Medical Rx: Maximize lactulose, rifaximin, LOLA
6. Watch for complications: Hepatic encephalopathy can mask uremia; difficult to assess

Peritoneal Dialysis in Liver Disease

• Contraindicated in presence of ascites (common in cirrhosis)
• May worsen ascites; difficult to instill/drain
• Risk of peritonitis (contaminated peritoneum from SBP history)
• Avoid in acute liver failure with hyperammonemia

Question 1: Case Presentation

A 48-year-old man with alcoholic cirrhosis is admitted with fever and confusion. Labs: ammonia 285 μmol/L, INR 3.2, bilirubin 6.5 mg/dL, creatinine 1.8 (baseline 1.1). He’s on lactulose and rifaximin. Mental status is worsening (now Grade 3 encephalopathy).

What is the most appropriate next step?

A. Increase lactulose dose to q2h; recheck ammonia in 8 hours B. Initiate continuous renal replacement therapy (CRRT) C. Wait for ammonia to rise above 300 before starting dialysis D. Start high-dose furosemide to increase urine ammonia clearance

Answer: B. This patient has ammonia 285 μmol/L (approaching 300) with worsening encephalopathy and rising trend. He needs CRRT now, not later. At this ammonia level with declining mental status, further delay risks cerebral edema and herniation. CRRT is chosen over intermittent HD because he has concurrent AKI requiring dialysis and likely hemodynamic stress from cirrhosis. Increasing lactulose alone is insufficient; he needs RRT. Furosemide won’t help remove ammonia.

Question 2: Pathophysiology Question

A patient with acute liver failure has ammonia 350 μmol/L and Grade 4 encephalopathy. After 3 hours of hemodialysis (high-flux, 450 mL/min blood flow), ammonia improves to 185 μmol/L. However, 6 hours after dialysis ends, repeat ammonia is 265 μmol/L.

What is the most likely explanation for this rebound?

A. Dialysis machine malfunction B. Inadequate lactulose dosing C. Rebound hyperammonemia — ongoing ammonia production by muscles/GI tract; no dialysis ongoing to remove it; ammonia redistributes from intracellular to serum D. Worsening liver function

Answer: C. This is classic rebound hyperammonemia post-intermittent HD. During dialysis, ammonia is rapidly cleared from serum, but ammonia continues to be produced by muscle and GI tract. Once dialysis stops, ammonia redistributes from tissue to serum, causing rebound. This is exactly why CRRT is often preferred for sustained ammonia control — continuous removal prevents rebound. Solution: Transition to CRRT or repeat HD sooner.

Question 3: Clinical Decision Question

A 72-year-old with ESRD on hemodialysis develops acute hepatitis (likely viral), with ammonia 190 μmol/L and Grade 2 encephalopathy. He is hemodynamically stable. Nephrologist asks: Should we keep him on standard 3×/week HD, or switch to something else?

What is the best approach?

A. Continue 3×/week HD; it’s adequate B. Switch to CRRT or increase HD frequency (e.g., 5-6×/week) to remove ammonia continuously or more frequently C. Hold dialysis until ammonia improves D. Switch to peritoneal dialysis

Answer: B. This patient needs more aggressive RRT given hyperammonemia. Standard 3×/week HD creates a “feast/famine” pattern — he accumulates uremia and now ammonia between sessions. Options: (1) Increase to 5-6× weekly HD, or (2) Switch to CRRT for continuous ammonia removal. Holding dialysis is dangerous (will accumulate uremia). Peritoneal dialysis is not practical for dialysis patients. More frequent/aggressive dialysis is the answer.