Hepatic Failure Pathology

Quick Answer

CICM Exam Focus

Key Points

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Definition and Classification

Acute Liver Failure: Definition

Acute liver failure (ALF) is defined by the presence of (PMID: 21757548):

Temporal Classification (O'Grady Classification)

The O'Grady classification (1993) stratifies ALF by jaundice-to-encephalopathy interval (PMID: 8242296):

Alternative Classification: AASLD/ALFSG

The US Acute Liver Failure Study Group uses slightly different terminology (PMID: 21757548):

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Aetiology of Acute Liver Failure

Overview of Causes

Paracetamol (Acetaminophen) Hepatotoxicity

Paracetamol is the most common cause of ALF in Australia, UK, and USA (PMID: 18768945).

Single Acute Overdose vs Staggered Overdose

Risk Factors for Hepatotoxicity

Patient Factors (reduced glutathione):

• Chronic alcohol use (CYP2E1 induction, glutathione depletion)
• Malnutrition, fasting (depleted glycogen and glutathione)
• Enzyme-inducing medications (phenytoin, carbamazepine, rifampicin)
• Chronic liver disease

Dose Factors:

• Acute ingestion >150 mg/kg (adults) or >200 mg/kg (children) concerning

• 7.5 g in adults considered potentially hepatotoxic

• Therapeutic misadventure often involves multiple products containing paracetamol

Viral Hepatitis

Drug-Induced Liver Injury (DILI)

Common culprits in Australia (PMID: 20937949):

Wilson's Disease

An important cause of ALF in young patients (<40 years) (PMID: 18506894):

• Pathophysiology: ATP7B gene mutation → copper accumulation → oxidative damage, mitochondrial dysfunction
• Key features: Kayser-Fleischer rings (95% in neurological Wilson's), Coombs-negative haemolytic anaemia (copper release), low serum ceruloplasmin
• ALF presentation: Often presents with features suggesting haemolysis (low ceruloplasmin, high bilirubin:ALP ratio, Coombs-negative haemolysis)
• Prognostic scoring: Wilson's Disease Prognostic Index (bilirubin, AST, INR, albumin, WCC) - score ≥11 indicates need for transplant

Pregnancy-Related Causes

AFLP Pathophysiology: Often associated with long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency in fetus → accumulation of fatty acid metabolites → maternal hepatotoxicity (PMID: 10515901).

Other Causes

• massive AST/ALT elevation (thousands), rapid resolution if perfusion restored | | Budd-Chiari syndrome | Hepatic vein thrombosis; acute presentation can cause ALF | | Mushroom poisoning (Amanita phalloides) | α-amanitin inhibits RNA polymerase II; delayed GI symptoms → hepatic failure | | Autoimmune hepatitis | May present as ALF; responds to corticosteroids in some cases | | Heat stroke | Massive cytokine release, ischaemia, direct thermal injury | | Malignant infiltration | Lymphoma, metastatic breast cancer - rare cause |

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Hepatocyte Death Pathways

Overview

Hepatocyte death in ALF occurs through two major pathways: necrosis and apoptosis. The predominant pathway depends on the aetiology and severity of injury (PMID: 23720129).

Necrosis vs Apoptosis

Paracetamol-Induced Hepatocyte Death

NAPQI Formation and Toxicity

The mechanism of paracetamol hepatotoxicity is well-characterised (PMID: 23720129, PMID: 25033466):

Step 1: Metabolism

• 90% of paracetamol: glucuronidation (UGT) and sulfation (SULT) → non-toxic metabolites
• 5-10%: CYP450 oxidation (primarily CYP2E1, also CYP1A2, CYP3A4) → NAPQI

Step 2: Detoxification

• NAPQI normally conjugated with glutathione (GSH) → non-toxic mercapturic acid
• Requires adequate glutathione stores

Step 3: Toxicity (in overdose)

• Glutathione depleted (typically >70% depletion)
• Excess NAPQI binds covalently to cellular proteins (especially mitochondrial proteins)
• Protein adducts disrupt mitochondrial respiration

Step 4: Mitochondrial Dysfunction

• Inhibition of electron transport chain
• Decreased ATP production
• Increased reactive oxygen species (ROS) production
• Mitochondrial permeability transition pore (mPTP) opening

Step 5: Cell Death

• ATP depletion → necrosis
• Cytochrome c release → apoptosis (if ATP sufficient)
• Release of endonucleases → nuclear DNA fragmentation
• JNK (c-Jun N-terminal kinase) activation amplifies mitochondrial injury

The Role of JNK (c-Jun N-terminal Kinase)

JNK is a critical amplifier of paracetamol toxicity (PMID: 20673547):

1. Initial NAPQI-protein adducts cause mitochondrial dysfunction
2. ROS production activates JNK in cytoplasm
3. Activated JNK translocates to mitochondria
4. JNK amplifies ROS production and inhibits electron transport
5. This creates a positive feedback loop of mitochondrial injury

Zonality of Hepatic Injury

The liver acinus (functional unit) has three zones with different metabolic properties (PMID: 24905494):

Why Zone 3 is Most Susceptible to Paracetamol

1. Highest CYP2E1 concentration: More NAPQI generated per hepatocyte
2. Lowest oxygen tension: Impairs aerobic metabolism when stressed
3. Lowest glutathione: Less capacity to detoxify NAPQI
4. Lowest NADPH: Reduced regeneration of glutathione
5. Centrifugal blood flow: Toxins accumulate as blood flows centrally

Histopathology of Hepatocyte Death

Necrosis Patterns

Microscopic Features of ALF

• Hepatocyte dropout: Empty spaces where hepatocytes were
• Collapse of reticulin framework: Architecture destroyed
• Inflammatory infiltrate: Lymphocytes, macrophages, neutrophils
• Ductular reaction: Proliferation of biliary epithelium (regenerative response)
• Cholestasis: Bile plugs in canaliculi
• Mallory-Denk bodies: May be seen in alcoholic, NASH, some drug injury

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Coagulopathy in Acute Liver Failure

Synthesis Failure

The liver synthesises virtually all coagulation factors (except Factor VIII and von Willebrand factor) (PMID: 26070319):

Pro-coagulant Factors Affected

The Concept of "Rebalanced Haemostasis"

Traditional teaching suggested ALF patients have severe bleeding risk due to coagulopathy. However, modern understanding recognises a more complex picture (PMID: 26070319, PMID: 20947927):

Clinical Implications

1. INR does not predict bleeding: Standard INR correlates poorly with bleeding risk in ALF
2. Prophylactic FFP not recommended: Unless bleeding or invasive procedure planned
3. Thromboelastography (TEG/ROTEM): Better reflects global coagulation status
4. VTE prophylaxis: May be appropriate despite elevated INR (assess individually)
5. Avoid vitamin K deficiency: Give vitamin K but don't expect full INR correction

Additional Haemostatic Abnormalities

Disseminated Intravascular Coagulation

DIC may complicate ALF (PMID: 31327219):

• Incidence: 20-30% of severe ALF
• Triggers: Tissue factor release from necrotic hepatocytes, endotoxaemia, sepsis
• Features: Thrombocytopenia, elevated D-dimer, microangiopathic haemolysis (rare)
• Management: Treat underlying cause; blood products only for active bleeding

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Hepatic Encephalopathy

Definition and Grading

Hepatic encephalopathy (HE) is a spectrum of neuropsychiatric abnormalities in patients with liver dysfunction (PMID: 24866571):

Pathophysiology of Hepatic Encephalopathy

HE is multifactorial but ammonia is central to the pathophysiology (PMID: 25042402):

Ammonia Metabolism

Normal ammonia handling:

1. Sources: Gut bacteria (urease), enterocyte glutaminase, renal ammoniagenesis, muscle deamination
2. Absorption: Absorbed from colon into portal circulation
3. Hepatic clearance: Periportal hepatocytes convert NH₃ to urea (urea cycle) - 85% of ammonia clearance
4. Alternative pathway: Perivenous hepatocytes convert NH₃ to glutamine (glutamine synthetase)

In liver failure:

• Reduced hepatocyte mass → impaired urea cycle capacity
• Porto-systemic shunting → bypasses liver
• Arterial ammonia levels rise (normal <50 μmol/L; HE often >100 μmol/L)

The Ammonia-Glutamine-Astrocyte Swelling Pathway

This is the key mechanism linking hyperammonaemia to cerebral dysfunction (PMID: 25042402):

1. Ammonia crosses BBB: NH₃ (un-ionised) freely crosses blood-brain barrier
2. Astrocyte uptake: Ammonia enters astrocytes
3. Glutamine synthesis: Glutamine synthetase (in astrocytes) converts glutamate + NH₃ → glutamine
4. Osmotic effect: Glutamine is osmotically active → astrocyte swelling
5. Mitochondrial toxicity: Glutamine enters mitochondria → generates ammonia locally → mitochondrial dysfunction
6. Oxidative stress: ROS generation, impaired energy metabolism

Additional Mechanisms in HE

Precipitants of Hepatic Encephalopathy

In ALF, HE develops due to acute hepatocyte loss. In cirrhosis, precipitants should be sought:

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Cerebral Oedema in Acute Liver Failure

Epidemiology and Risk Factors

Cerebral oedema is a major cause of death in ALF, occurring in 20-30% of patients with Grade III-IV HE (PMID: 14714165):

Pathophysiology: Cytotoxic vs Vasogenic Oedema

Cerebral oedema in ALF is predominantly cytotoxic (intracellular), in contrast to many other causes of cerebral oedema (PMID: 25042402):

The "Trojan Horse" Hypothesis

Glutamine acts as a "Trojan horse" for ammonia toxicity (PMID: 17428996):

1. Ammonia is incorporated into glutamine in astrocyte cytoplasm
2. Glutamine is transported into mitochondria
3. Mitochondrial glutaminase cleaves glutamine → releases ammonia inside mitochondria
4. High intra-mitochondrial ammonia → mPTP opening → oxidative stress → mitochondrial dysfunction
5. This amplifies cellular energy failure and swelling

Intracranial Hypertension and Herniation

Monro-Kellie Doctrine

The skull is a rigid container; its contents (brain ~80%, blood ~10%, CSF ~10%) must remain constant. Cerebral oedema increases brain volume, initially compensated by CSF displacement and reduced venous blood. When compensation is exhausted, ICP rises exponentially.

Clinical Features of Raised ICP

Cerebral Perfusion Pressure

CPP = MAP - ICP

• Target CPP: >60 mmHg
• Target ICP: <25 mmHg (or <20 mmHg in severe cases)
• Autoregulation often impaired in ALF - CPP-dependent cerebral blood flow

Management of Cerebral Oedema in ALF

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Metabolic Derangements

Hypoglycaemia

Hypoglycaemia is a common and dangerous complication of ALF (PMID: 21757548):

Mechanisms

Clinical Implications

• May be severe, recurrent, and refractory
• Can cause or worsen encephalopathy
• Monitor blood glucose every 1-2 hours initially
• Continuous glucose infusion (10-20% dextrose) often required
• Target: Blood glucose 6-10 mmol/L

Lactate and Acid-Base Disturbances

Lactic Acidosis in ALF

Lactate elevation in ALF has multiple mechanisms (PMID: 20190714):

1. Impaired lactate clearance: Liver normally clears 70% of circulating lactate
2. Increased production: Tissue hypoxia (hyperdynamic shock), SIRS, anaerobic glycolysis
3. Hypoperfusion: Cardiogenic or distributive shock component

Prognostic significance:

• Lactate >3.5 mmol/L after resuscitation is a poor prognostic sign
• Included in modified King's College Criteria
• Lactate >3.0 mmol/L at 12 hours post-NAC initiation (paracetamol) predicts poor outcome (PMID: 20190714)

Acid-Base Patterns

Electrolyte Disturbances

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Haemodynamic Changes

Hyperdynamic Circulation

ALF produces a circulatory pattern remarkably similar to sepsis (PMID: 15671025):

Mechanisms of Vasodilation

Portal Hypertension in ALF

Unlike chronic liver disease, portal hypertension in ALF develops acutely (PMID: 21757548):

Mechanisms:

1. Sinusoidal obstruction: Hepatocyte swelling compresses sinusoids
2. Regenerative nodule formation: Disrupts normal architecture
3. Inflammatory infiltration: Adds to sinusoidal resistance
4. Microvascular thrombosis: DIC component

Consequences (often less pronounced than chronic portal hypertension):

• Ascites (usually mild)
• Gut oedema and ileus
• Contributes to bacterial translocation

Cardiac Dysfunction

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Hepatorenal Syndrome

Definition

Hepatorenal syndrome (HRS) is functional renal failure in patients with advanced liver disease, in the absence of intrinsic renal pathology (PMID: 26254576):

Diagnostic criteria (ICA 2015):

1. Cirrhosis with ascites OR acute liver failure
2. Diagnosis of AKI (increase in creatinine ≥26.5 μmol/L within 48 hours or ≥50% within 7 days)
3. No improvement after 2 days of diuretic withdrawal and albumin expansion (1 g/kg/day, max 100 g/day)
4. Absence of shock
5. No current or recent nephrotoxic drugs
6. No parenchymal kidney disease (proteinuria <500 mg/day, microhaematuria <50 RBCs/hpf, normal renal ultrasound)

Classification

Pathophysiology

The "arterial vasodilation hypothesis" explains HRS development (PMID: 15915323):

HRS in Acute Liver Failure (vs Cirrhosis)

HRS in ALF differs from cirrhotic HRS:

Differential Diagnosis of AKI in ALF

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SIRS and Sepsis in Acute Liver Failure

Immune Dysfunction in ALF

ALF causes a complex immune derangement with both hyperinflammation and immunodeficiency (PMID: 22972682):

Infection in ALF

Infection is common (50-80%) and is a major cause of morbidity and mortality (PMID: 22972682):

Common Organisms

Risk Factors for Infection

• Grade III-IV encephalopathy
• Prolonged ICU stay
• Multiple invasive devices (CVC, IDC, ETT)
• Renal replacement therapy
• Paracetamol aetiology (less immunocompromised than other causes)
• Need for vasopressors

Prophylactic Antibiotics

Sepsis Mimicry

ALF can mimic sepsis clinically, making infection diagnosis challenging:

Approach: High index of suspicion; low threshold for empiric antibiotics; repeat cultures.

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Hepatic Regeneration

Overview of Liver Regeneration

The liver has remarkable regenerative capacity, able to restore original mass after 70% hepatectomy within 2-3 weeks (PMID: 17245125):

Hepatocyte Proliferation

Initiation Phase (0-5 hours post-injury)

• makes hepatocytes competent to respond | | IL-6 | Kupffer cells, endothelium | Activates STAT3 → immediate early genes | | Complement (C3a, C5a) | Liver synthesis, activation | Promotes IL-6 release, NF-κB activation | | LPS | Gut (via portal vein) | TLR4 activation → TNF-α release |

Progression Phase (Growth Factors)

Termination Phase

Progenitor Cell (Oval Cell) Response

When hepatocyte proliferation is impaired (e.g., massive necrosis, chronic injury), hepatic progenitor cells are activated (PMID: 23392622):

Hepatic progenitor cells (HPCs):

• Location: Canals of Hering (junction of bile canaliculi and bile ducts)
• Bipotential: Can differentiate into hepatocytes OR cholangiocytes
• Also called "oval cells" (rodents), "reactive ductular cells" (humans)

Activation signals:

• Wnt/β-catenin pathway
• Notch signaling
• Hedgehog pathway
• FGF signaling

Ductular reaction: Proliferation of small ductular structures at portal margins - histological evidence of progenitor activation

Factors Affecting Regeneration in ALF

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Histopathology

Patterns of Hepatic Necrosis

The histopathological pattern provides aetiological and prognostic information (PMID: 24905494):

Microscopic Features

Acute Phase

Regenerative Phase

Specific Histopathological Patterns by Aetiology

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Prognostic Scoring

King's College Criteria (1989)

The most widely used criteria for transplant listing in ALF (PMID: 2490426):

Performance of King's College Criteria

Limitations:

• Developed in 1989; medical management has improved
• Does not account for aetiology-specific factors (e.g., Wilson's)
• May miss patients who would benefit from transplant

Modified King's College Criteria (with Lactate)

Addition of lactate improves sensitivity for paracetamol ALF (PMID: 20190714):

Lactate criteria:

• Arterial lactate >3.5 mmol/L after early fluid resuscitation (4 hours) OR
• Arterial lactate >3.0 mmol/L after full fluid resuscitation (12 hours)

MELD Score (Model for End-Stage Liver Disease)

Originally developed for cirrhosis, MELD is also used in ALF (PMID: 11172350):

MELD = 3.78 \times \ln(bilirubin) + 11.2 \times \ln(INR) + 9.57 \times \ln(creatinine) + 6.43

Bilirubin and creatinine in mg/dL; minimum values 1.0

In ALF: MELD may be comparable to King's criteria for prognosis; used for transplant allocation in many jurisdictions.

Other Prognostic Markers

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Australian/New Zealand Context

ALF Epidemiology in Australia

Paracetamol Overdose Patterns in Australia

Paracetamol poisoning has distinct patterns in Australia:

Demographics:

• Peak age: 15-35 years
• Female predominance (intentional overdose)
• Often associated with alcohol co-ingestion

Therapeutic misadventure:

• Significant proportion of ALF from staggered/therapeutic overdose
• Often involves multiple paracetamol-containing products
• Associated with chronic pain, poor health literacy

Combination products:

• Paracetamol combined with opioids (codeine, oxycodone)
• Paracetamol combined with antihistamines (cold preparations)
• Patients may not recognise paracetamol content

Retrieval and Transfer

Principles:

• Early contact with liver transplant unit (before meeting KCC)
• Transfer to transplant centre when Grade II+ HE or meeting KCC
• Retrieval services: NETS, CareFlight, Adult Retrieval Victoria, RFDS

Pre-transfer stabilisation:

• Secure airway if Grade III-IV HE
• Blood glucose management
• Coagulopathy correction only for active bleeding/procedures
• NAC continuation if paracetamol
• ICP management if cerebral oedema suspected

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Indigenous Health Considerations

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SAQ Practice Questions

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Viva Practice Scenarios

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MCQ Practice Questions

Question 1

A 28-year-old woman presents 18 hours after ingesting 40 paracetamol tablets. Which zone of the hepatic acinus is most susceptible to paracetamol-induced necrosis?

A. Zone 1 (periportal) B. Zone 2 (intermediate) C. Zone 3 (centrilobular) D. All zones equally affected E. Zone 1 and Zone 2 equally

Answer: C

Explanation: Zone 3 (centrilobular/perivenular) is most susceptible to paracetamol toxicity for several reasons: (1) Highest concentration of CYP2E1, the primary enzyme converting paracetamol to the toxic metabolite NAPQI; (2) Lowest oxygen tension as blood flows from portal (Zone 1) to central (Zone 3); (3) Lowest glutathione levels, reducing capacity to detoxify NAPQI. Histologically, paracetamol overdose shows centrilobular necrosis. Zone 1 is preferentially damaged by phosphorus poisoning. This zonality is a classic CICM First Part concept.

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Question 2

Which of the following statements about coagulopathy in acute liver failure is CORRECT?

A. INR accurately predicts bleeding risk in ALF B. Protein C levels are typically preserved while procoagulant factors decrease C. Prophylactic FFP should be given to all patients with INR >2.0 D. Thromboelastography provides better assessment of global haemostasis than INR E. VTE prophylaxis is contraindicated when INR >2.0

Answer: D

Explanation: Thromboelastography (TEG/ROTEM) provides a better assessment of global haemostasis in ALF because it measures the entire coagulation process, including the contribution of both procoagulant and anticoagulant factors. The concept of "rebalanced haemostasis" recognises that INR only measures procoagulant factor reduction, not the parallel reduction in Protein C, Protein S, and Antithrombin. Studies show INR does not accurately predict bleeding risk in liver failure. Routine prophylactic FFP is not recommended. VTE prophylaxis may be appropriate despite elevated INR as patients are not "auto-anticoagulated."

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Question 3

In the pathophysiology of hepatic encephalopathy, which cell type is primarily responsible for ammonia detoxification in the central nervous system?

A. Neurons B. Astrocytes C. Microglia D. Oligodendrocytes E. Ependymal cells

Answer: B

Explanation: Astrocytes are the only CNS cells that express glutamine synthetase, the enzyme that converts ammonia and glutamate to glutamine. This is the exclusive pathway for ammonia detoxification in the brain. The accumulation of glutamine within astrocytes creates osmotic stress, leading to astrocyte swelling - the hallmark of hepatic encephalopathy in ALF (cytotoxic oedema). Neurons do NOT have this enzyme and are not directly involved in ammonia metabolism. The "Trojan horse" hypothesis describes how glutamine subsequently enters mitochondria where it releases ammonia, causing further damage.

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Question 4

A patient with acute liver failure has Grade IV hepatic encephalopathy. CT brain shows cerebral oedema. Which type of cerebral oedema predominates in acute liver failure?

A. Vasogenic oedema B. Cytotoxic oedema C. Interstitial (hydrocephalic) oedema D. Osmotic oedema E. Mixed vasogenic and interstitial

Answer: B

Explanation: Cerebral oedema in ALF is predominantly CYTOTOXIC (intracellular), caused by astrocyte swelling from glutamine accumulation. The blood-brain barrier remains largely intact, at least initially. This differs from traumatic brain injury or tumours where vasogenic oedema (extracellular, BBB breakdown) predominates. On MRI, cytotoxic oedema shows restricted diffusion (DWI bright, ADC dark). This is why ALF patients are at high risk of cerebral oedema while chronic liver disease patients (who develop compensatory mechanisms) rarely develop significant oedema despite similar ammonia levels.

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Question 5

According to the King's College Criteria for paracetamol-induced acute liver failure, which single finding indicates poor prognosis and need for transplant assessment?

A. INR >3.5 B. Bilirubin >300 μmol/L C. pH <7.30 after adequate fluid resuscitation D. Creatinine >200 μmol/L E. Grade II hepatic encephalopathy

Answer: C

Explanation: For paracetamol-induced ALF, pH <7.30 ALONE (after adequate fluid resuscitation) meets King's College Criteria for poor prognosis. Alternatively, ALL THREE of the following are required: INR >6.5 (not 3.5) AND Creatinine >300 μmol/L (not 200) AND Grade III-IV encephalopathy (not Grade II). The pH <7.30 criterion has the strongest predictive value as it reflects severe metabolic acidosis from massive hepatocyte necrosis and lactate accumulation. INR >3.5 and bilirubin >300 are criteria for NON-paracetamol ALF, not paracetamol.