3.1 First-Line Therapy: Lactulose

Lactulose remains the cornerstone of HE management. It acidifies the colon, traps ammonia as ammonium (NH₄⁺), and accelerates gastrointestinal transit to reduce systemic ammonia absorption.

Mechanism of Action

• A nonabsorbable disaccharide metabolized by colonic bacteria into lactic and acetic acids.
• This process lowers colonic pH, which promotes the conversion of absorbable ammonia (NH₃) to non-absorbable ammonium (NH₄⁺).
• Its osmotic cathartic effect clears ammonia-producing flora and reduces transit time.

Indications & Initiation

• Indicated for all grades of overt HE; should be initiated promptly in patients with West Haven Grade II–IV.
• The oral or enteral route is preferred if gut motility is intact. Rectal enemas (using a 20% solution) are an alternative in cases of ileus or inability to take oral medications.

Dosing & Titration

1. Loading: Administer 25 mL (approximately 16.7 g) orally or via nasogastric tube every 1–2 hours until the patient has their first bowel movement.
2. Maintenance: Adjust the dose to 20–30 mL orally 2–4 times daily to achieve and sustain the goal of 2–3 soft, formed stools per day.

Monitoring

• Efficacy: Stool frequency and consistency (target: 2–3 soft stools/day); mental status (West Haven grade) every 8–12 hours.
• Safety: Volume status, serum electrolytes (especially potassium and sodium), and acid–base balance.

3.2 Adjunctive Therapy: Rifaximin

Rifaximin is a minimally absorbed antibiotic that modulates gut flora to reduce ammonia production. It is typically added when lactulose alone is insufficient or for the secondary prevention of HE recurrence.

Mechanism of Action

• A broad-spectrum, non-absorbable rifamycin derivative that stays within the gastrointestinal tract.
• It suppresses ammonia-producing bacteria while largely preserving the beneficial commensal gut microbiome.

Indications

• Secondary prophylaxis in patients with two or more HE episodes in a 6-month period despite adequate lactulose therapy.
• As an add-on therapy in acute moderate-to-severe HE once the enteral route is available and the patient has not responded adequately to lactulose.

Dosing & Pharmacokinetics

• Standard Dose: 550 mg orally twice daily.
• Pharmacokinetics: Negligible systemic absorption (<0.4%) means no dose adjustment is required in hepatic or renal impairment.

3.3 Emerging & Adjunctive Agents

In cases of refractory HE or intolerance to first-line agents, several other therapies can be considered to target different pathophysiologic pathways.

L-Ornithine L-Aspartate (LOLA)

• Mechanism: Provides substrates for two key ammonia detoxification pathways: the urea cycle (ornithine) and glutamine synthesis in muscle and brain (glutamate).
• Dosing: IV infusion of 20 g over 4–6 hours daily for 3–5 days is used in the ICU setting for rapid ammonia reduction.
• Clinical Data: Evidence suggests it lowers ammonia levels and improves psychometric scores, primarily as an adjunctive therapy.

Zinc Supplementation

• Mechanism: Zinc is an essential cofactor for enzymes in the urea cycle (ornithine transcarbamylase) and glutamine synthesis. Deficiency is common in cirrhosis.
• Dosing: 50 mg of elemental zinc orally daily if a deficiency is documented or highly suspected.
• Monitoring: Monitor serum zinc and copper levels, as long-term zinc can induce copper deficiency.

Polyethylene Glycol (PEG) 3350

• Mechanism: An osmotic cathartic, similar to lactulose, that induces rapid bowel cleansing.
• Data: One major trial (HELP) showed that PEG led to faster resolution of HE and a shorter hospital stay compared to lactulose. It is a viable alternative in lactulose-intolerant patients.

Branched-Chain Amino Acids (BCAAs)

• Mechanism: Aims to restore the normal plasma amino acid ratio and support skeletal muscle ammonia detoxification.
• Effect: May improve HE symptoms and neurocognitive function but has not demonstrated a mortality benefit.

3.4 PK/PD & Renal Replacement Therapy Adjustments

Critical illness significantly alters pharmacokinetics (PK) and pharmacodynamics (PD). Adjustments for renal replacement therapy (RRT) are crucial for certain agents.

Critical Illness Alterations

• Volume of Distribution (Vd): Expands due to aggressive fluid resuscitation and capillary leak, potentially lowering peak drug concentrations.
• Protein Binding: Hypoalbuminemia is nearly universal in this population, increasing the free fraction of highly protein-bound drugs.

Continuous Renal Replacement Therapy (CRRT) Considerations

• Lactulose: Not systemically absorbed; no adjustment needed.
• Rifaximin: Minimal systemic absorption (<0.4%); no adjustment needed.
• IV LOLA & Zinc: Both have low molecular weights and are likely to be removed by CRRT. Consider post-filter supplementation or timing doses after RRT sessions.

3.5 Route of Administration & Delivery Devices

The choice of administration route depends on the patient’s gastrointestinal function, the severity of HE, and drug formulation.

Enteral/Oral

• This is the preferred route for lactulose and rifaximin when bowel motility is intact.
• For precise titration in the ICU, lactulose can be administered via a nasogastric (NG) or orogastric (OG) tube using an infusion pump.

Rectal

• Lactulose enemas (e.g., 300 mL of a 20% solution administered every 6 hours) are effective in patients with ileus, severe vomiting, or profound encephalopathy precluding safe oral intake.
• Placing the patient in the Trendelenburg position can improve retention of the enema.

Intravenous

• Available: L-Ornithine L-Aspartate (LOLA) is available as an IV infusion.
• Not Available: IV formulations of rifaximin or zinc are not commercially available in most regions and would require special compounding.

3.6 Monitoring Plan

A systematic monitoring framework is essential to ensure efficacy, maintain safety, and guide timely escalation or de-escalation of therapy.

Clinical Response

• Mental Status: Assess using the West Haven grading system every 8-12 hours. Key components include orientation, presence of asterixis, and changes in behavior.
• Minimal HE: In recovering patients, objective tools like the smartphone-based Stroop or inhibitory control tests can detect subtle residual deficits.

Laboratory Surveillance

• Daily Labs: Monitor electrolytes (Na⁺, K⁺), renal function (BUN, creatinine), and liver function tests.
• Ammonia Levels: Routine serial ammonia monitoring is not recommended. Reserve for diagnosing atypical presentations or in refractory cases where the diagnosis is uncertain.

Drug-Related Toxicities

• Lactulose: Monitor for excessive diarrhea, dehydration, hypernatremia, and hypokalemia.
• Rifaximin: Generally well-tolerated; monitor for GI upset. Risk of Clostridioides difficile is very low but not zero.

3.7 Pharmacoeconomic Comparison

Evaluating the total cost of care requires balancing drug acquisition costs against the financial benefits of preventing HE-related hospitalizations and reducing monitoring burdens.

3.8 Clinical Decision Points & Algorithm

A stepwise algorithm provides a clear framework for when to initiate, escalate, supplement, and de-escalate therapy for HE in the critically ill patient.