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Portocaval (Portosystemic) Anastomosis Sites

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Diagram

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The 4 Main Anastomotic Sites

1. Gastro-oesophageal Junction (Lower Oesophagus / Gastric Cardia)

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2. Umbilicus / Anterior Abdominal Wall

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3. Anorectal Junction (Lower Rectum / Anal Canal)

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4. Retroperitoneal / Bare Area Collaterals (Veins of Retzius and Sappey)

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Summary Table

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Key Clinical Points

• Portal hypertension threshold for collateral development is ~8-10 mmHg (HVPG). Clinically significant portal hypertension = HVPG >10 mmHg.
• The coronary (left gastric) vein is the main feeder of oesophagogastric varices and is the primary target in surgical shunt procedures.
• Caput medusae specifically indicates left portal vein hypertension; its presence points to left lobe congestion.
• In isolated splenic vein thrombosis (e.g., from pancreatitis), the left gastroepiploic vein becomes a major collateral and gastric (rather than oesophageal) varices predominate - this is "left-sided portal hypertension" and is cured by splenectomy alone.
• Intraoperative bleeding from retroperitoneal collaterals is a major hazard during abdominal surgery in cirrhotic patients.

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Pulmonary Complications of Liver Failure and Portal Hypertension

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1. Hepatopulmonary Syndrome (HPS)
2. Portopulmonary Hypertension (POPH)
3. Hepatic Hydrothorax
4. General Pulmonary Function Disturbances

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1. Hepatopulmonary Syndrome (HPS)

Definition

1. Intrapulmonary vasodilation (IPVD)
2. Abnormal arterial oxygenation - alveolar-arterial PO₂ gradient (A-a)PO₂ ≥15 mmHg (or >20 mmHg if age >64 years) in the absence of another cause of hypoxemia
3. Advanced liver disease (cirrhotic or non-cirrhotic portal hypertension)

Epidemiology

• Occurs in 5-35% of patients with cirrhosis evaluated for liver transplantation
• Also described in non-cirrhotic portal hypertension and chronic hepatitis without confirmed cirrhosis

Pathogenesis

• Ventilation-perfusion (V/Q) mismatch - dilated vessels perfuse alveoli that are ventilated but cannot oxygenate blood efficiently
• Right-to-left shunting through dilated vessels
• Diffusion-perfusion impairment in severe cases - blood transits so quickly through widened capillaries that haemoglobin cannot equilibrate with alveolar O₂

• The injured liver releases endothelin-1 (ET-1), which paradoxically stimulates pulmonary microvascular endothelin-B receptors to upregulate eNOS (endothelial nitric oxide synthase) → excess nitric oxide (NO) production
• Monocyte adhesion in pulmonary vasculature activates iNOS, heme oxygenase-1 (HO-1, producing vasodilatory CO), and VEGF-mediated angiogenesis
• Gut bacterial translocation and endotoxemia drive the inflammatory cascade (TNF-α, TGF-β)
• The result: vasodilatation + angiogenesis → hypoxemia

Clinical Features

Grading of Severity (Task Force consensus)

Diagnosis

• Contrast echocardiography (bubble echo): most sensitive test - microbubbles appear in the left-sided chambers after 3-5 cardiac cycles (late appearance = intrapulmonary shunting, vs. early appearance = intracardiac shunt). This confirms IPVD.
• ABG: elevated (A-a)PO₂; hypoxemia in moderate-severe cases
• CT chest: dilated peripheral pulmonary arteries in the lung bases

Treatment & Prognosis

• Definitive treatment: liver transplantation - resolves hypoxemia in most patients
• MELD exception points are allocated for advanced HPS to expedite transplantation
• Patients with pretransplant PaO₂ ≤44 mmHg have worse post-transplant survival
• No effective medical therapy; supplemental O₂ for palliation

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2. Portopulmonary Hypertension (POPH)

Definition

• Mean pulmonary arterial pressure (mPAP) >20 mmHg at rest
• Pulmonary artery wedge pressure (PAWP) ≤15 mmHg
• Pulmonary vascular resistance (PVR) ≥240 dynes·sec·cm⁻⁵ (normal <130)

Epidemiology

• Prevalence: ~5-6% of patients evaluated for liver transplantation
• More common in women and patients with autoimmune hepatitis
• Hepatitis C is associated with a decreased risk

Pathogenesis (Robbins / Murray & Nadel)

• The mechanism is not fully understood. Unlike HPS (which causes vasodilation), POPH involves excessive pulmonary vasoconstriction and vascular remodeling.
• Portosystemic shunting allows vasoactive substances (thromboxanes, serotonin, neuropeptide Y, endothelin-1) that are normally cleared by the healthy liver to reach the pulmonary vasculature, causing vasoconstriction.
• Elevated macrophage migration inhibitory factor (proinflammatory), reduced bone morphogenetic protein 9 (endothelial quiescence factor), and altered estrogen metabolism have been implicated.
• Histopathology is identical to idiopathic PAH: intimal thickening, smooth muscle proliferation, plexogenic pulmonary arteriopathy, and in situ thrombosis - all contributing to elevated PVR. (Robbins)

Clinical Features

Comparison: HPS vs. POPH

Treatment

• PAH-targeted vasodilator therapy: epoprostenol, treprostinil, sildenafil, tadalafil, bosentan, ambrisentan, macitentan (used similarly to idiopathic PAH)
• Calcium channel blockers: CONTRAINDICATED - worsen splanchnic vasodilation
• Beta-blockers: avoid if possible - worsen cardiac output and exercise capacity in POPH
• Liver transplantation: safe in selected patients with mPAP <35-45 mmHg and preserved RV function; liver Tx is contraindicated if mPAP >45-50 mmHg due to high perioperative mortality

Prognosis

• Without treatment: 5-year survival ~14%
• Modern PAH therapy era: 5-year survival ~40% (worse than idiopathic PAH despite better hemodynamics at baseline)
• Liver transplantation 1-year survival in selected POPH patients: 77-85%; highest risk in first 6 months

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3. Hepatic Hydrothorax

Definition

Epidemiology

• Affects 5-10% of patients with cirrhosis

Pathophysiology

• Ascitic fluid passes from the peritoneal cavity into the pleural space through small diaphragmatic defects (<1 mm), usually in the tendinous portion of the right hemidiaphragm.
• The pressure gradient (positive intra-abdominal → negative intrapleural) drives unidirectional flow.
• Laterality:
  • Right-sided: 80% (thinner right hemidiaphragm is more prone to defects)
  • Left-sided: 18%
  • Bilateral: 2%
• Up to 20% of patients have no detectable ascites (all ascitic fluid is decompressed into the chest), but residual ascites is visible on ultrasound/CT in the large majority.

Clinical Features

• Ranges from asymptomatic to severe dyspnea and cough
• Rarely, rapid rupture into the pleural space can cause respiratory failure
• Thoracentesis: transudative in 94% (by Light's criteria; note Light's criteria can misclassify ~18% as exudates - use pleural/serum albumin ratio <0.6 as a more reliable marker in cirrhotics)

Management

• Sodium restriction + diuretics (mirrors ascites management)
• Repeated thoracentesis for symptom palliation (high recurrence risk)
• TIPS: reduces portal pressure, achieves response in 70-80% initially; limited by shunt occlusion, hepatic encephalopathy
• Chest tube drainage: NOT recommended - unacceptably high complication rate (protein/electrolyte loss, infection, renal failure)
• Video-assisted thoracoscopic surgery (VATS): diaphragmatic defect repair ± pleurodesis for refractory cases
• Indwelling pleural catheters (IPC): bridge to transplantation; empyema is the most common complication
• Liver transplantation: definitive - hepatic hydrothorax typically resolves; post-transplant outcomes are not inferior to those without hepatic hydrothorax

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4. General Pulmonary Function Disturbances

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Summary Overview

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Acute-on-Chronic Liver Failure (ACLF)

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Definition

• Harrison's (2025): "Acutely decompensating cirrhosis with associated failure of one or more organ systems - liver, kidneys, brain, lung, circulatory system, and coagulation - analogous to sepsis syndrome."
• Sleisenger & Fordtran: "A condition in patients with underlying chronic liver disease with or without cirrhosis that is associated with mortality within 3 months in the absence of treatment of the underlying liver disease, liver support, or liver transplantation."
• Robbins: "Some individuals with stable but well-compensated, advanced chronic liver disease suddenly develop signs of acute liver failure...short-term mortality is around 50%."

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Classification by Underlying Liver Disease (Sleisenger & Fordtran, Type A/B/C)

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Epidemiology

• 5% of all hospitalizations in patients with cirrhosis are for ACLF, and incidence is rising

• Over two-thirds of hospitalized ACLF patients have an active infection
• In-hospital mortality ~50%
• ACLF mortality exceeds that of acute liver failure (ALF) after 1 week of hospitalization; unlike ALF, the high mortality risk in ACLF persists rather than returning to baseline at ~3 weeks
• ~50% of ACLF patients listed for liver transplantation are delisted or dead within 6 months

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Pathophysiology

Core Mechanism: Systemic Inflammation + Immune Dysregulation

1. Gut bacterial translocation → pathogen-associated molecular patterns (PAMPs) enter the circulation
2. Marked systemic inflammatory response - more pronounced than in simple decompensated cirrhosis; levels of markers of cell death are also markedly elevated
3. Sterile inflammation from hepatocyte death (e.g., alcohol-induced) superimposed on infection-driven inflammation
4. Innate immune suppression: patients develop significant suppression of the innate immune system, representing "failed immune tolerance"
5. Compensatory anti-inflammatory response (CARS): immunosuppression with enhanced susceptibility to secondary infections → organ failure cascade

• East: HBV reactivation, HEV superinfection in chronic liver disease, alcoholic hepatitis dominate
• West: Bacterial infection and alcoholic hepatitis dominate

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Precipitating Factors (Harrison's 2025)

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Clinical Features

• Fever, tachycardia, tachypnea, leukocytosis

Organ Failure Manifestations in ACLF (Sleisenger & Fordtran, Table 74.2)

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Prognosis - Organ Failure Scoring (Sleisenger & Fordtran)

• CLIF-C ACLF score (European/CANONIC study) - based on organ failure grading
• SOFA (Sequential Organ Failure Assessment) - more accurately reflects ICU prognosis than Child-Pugh or MELD scores in the ICU setting (Sleisenger & Fordtran)
• NACSELD score (North American)

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Management (Harrison's 2025 + Sleisenger & Fordtran)

General Principles

• Managed by a multidisciplinary team with critical care and liver transplantation expertise
• Search for and treat all precipitating causes
• Determine if ICU care is needed
• Immediate referral for liver transplantation evaluation

Specific Interventions (Table 74.3, Sleisenger & Fordtran)

Key Notes on Specific Treatments

• Hepatorenal syndrome (HRS-1): poor response to terlipressin in advanced ACLF
• Liver support devices (MARS, Prometheus): bioartificial liver support has not been proven effective in ACLF-specific trials; no demonstrated mortality benefit
• Granulocyte-colony stimulating factor (G-CSF) + erythropoietin: combination shown to decrease mortality risk in decompensated cirrhosis; hepatic regenerative therapy is a promising direction
• Routine prophylactic antibiotics in all cirrhotics are not currently recommended

Transition to Palliative Care (Harrison's 2025)

• If after 3-7 days of ICU support, there are 4 or more organ failures and liver transplantation is not an option, transition to palliative care should be considered

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Liver Transplantation in ACLF

• LT offers the only hope of long-term survival (Sleisenger & Fordtran)
• Patients with multiple organ failures may be too sick for transplantation
• In selected patients with alcohol-associated hepatitis who undergo LT, long-term results have been good
• Na-MELD score ≥15 is used to identify patients likely to benefit from transplantation
• ACLF patients may receive special MELD exception points for expedited listing

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Summary

Stable chronic liver disease (cirrhosis)
         ↓  Precipitant (infection, alcohol, viral, drugs)
Acute decompensation
         ↓  Systemic inflammation + immune dysregulation
Multiorgan failure
         ↓
ACLF (28-day mortality 20-70% depending on organ failure count)
         ↓
Treatment: Remove precipitant + organ support + LT (if eligible)

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Drug- and Toxin-Induced Liver Injury (DILI / TILI)

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Overview

• Drugs account for >50% of cases of ALF referred to specialist units in the USA
• 10% of patients with DILI die or require liver transplantation
• 17% develop chronic liver disease
• Drugs account for 43% of severe hepatitis in patients aged >50 years
• Herbal and dietary supplements account for >25% of DILI in some countries (e.g., South Korea)

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Hepatic Drug Metabolism - Why the Liver is Vulnerable

• CYP2E1 (localised in acinar zone 3 - centrilobular hepatocytes) catalyses oxidation of acetaminophen to NAPQI (N-acetyl-p-benzoquinone imine) - a highly reactive electrophilic and oxidising metabolite
• Under normal doses, NAPQI is rapidly conjugated and detoxified by glutathione
• At high doses or with glutathione depletion, free NAPQI covalently binds hepatocyte proteins and mitochondrial enzymes → zone 3 (centrilobular) necrosis
• CYP2E1 is concentrated in zone 3, explaining why acetaminophen toxicity is always centrilobular

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Classification of DILI: Predictable vs. Idiosyncratic

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Mechanisms of Hepatocellular Injury

1. Direct / Intrinsic Toxicity

• Drug or its reactive metabolite directly injures the hepatocyte
• Mitochondrial injury is a primary target: NAPQI (acetaminophen) directly damages mitochondrial enzymes; mitochondrial permeability transition releases Ca²⁺, activates JNK and GSK-3β signalling → further mitochondrial dysfunction
• Necrosis pathway: Drug injury de-energises mitochondria → ATP depletion → cell swelling → membrane rupture → necrosis (when ATP is absent) or apoptosis (when ATP is preserved)
• Reactive oxygen species (ROS) generate oxidative stress and trigger cell death

2. Immune-Mediated (Hypersensitivity) Idiosyncrasy

• Drug or its metabolite acts as a hapten, covalently binding to cellular proteins → creates new immunogen
• Triggers CD8+ cytotoxic T-cell response and antibody formation against hepatocytes
• Features: fever, rash, eosinophilia, arthralgia (DRESS syndrome), positive rechallenge
• Prototype: halothane hepatitis (fatal immune hepatitis after repeated exposure)

3. Metabolic Idiosyncrasy

• Drug is converted by an unusual metabolic pathway in a genetically susceptible individual to a toxic metabolite
• No overt immune features
• Prototype: isoniazid - slow acetylators (NAT2 variant) accumulate toxic acetylhydrazine metabolites → hepatitis

4. Mitochondrial Toxicity

• Direct impairment of mitochondrial oxidative phosphorylation → microvesicular steatosis (fatty change with small cytoplasmic fat droplets = Reye-like picture)
• Drugs: valproic acid, tetracycline, zidovudine, didanosine, zalcitabine, fialuridine
• Results from impaired β-oxidation of fatty acids with fat accumulation in small vacuoles

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Patterns of Morphological Injury

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Prototype Drug: Acetaminophen (Paracetamol) - Direct Hepatotoxin

Mechanism

Acetaminophen
    ↓ (CYP2E1, CYP3A4 - concentrated in zone 3)
NAPQI (N-acetyl-p-benzoquinone imine)
    ↓ (normal dose)     ↓ (overdose / glutathione depleted)
Conjugated with     →  Free NAPQI
glutathione (safe)         ↓
                    Covalently binds hepatocyte proteins
                    + Mitochondrial enzyme damage
                    + JNK / GSK-3β activation
                          ↓
                    Zone 3 (centrilobular) NECROSIS

• Fasting (depletes glutathione)
• Chronic alcohol use (induces CYP2E1 + depletes glutathione) - alcoholics develop toxicity at therapeutic doses
• Enzyme inducers (rifampicin, phenytoin, isoniazid)

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Prototype Drug: Isoniazid (INH) - Metabolic Idiosyncratic Hepatotoxin

• CYP and NAT2 metabolise INH → acetylhydrazine and other reactive metabolites
• Slow acetylators (NAT2 variant): accumulate toxic acetylhydrazine → hepatotoxicity
• Fast acetylators: may generate more hydrazine (alternative toxic metabolite)
• Hepatitis develops in ~1% of patients; rarely fulminant (preventable deaths still occur)
• Enzyme inducers (rifampicin, phenytoin, alcohol) increase risk
• Concomitant rifampicin accelerates INH metabolism to hydrazine

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Prototype Drug: Halothane - Immune-Mediated Hepatotoxin

• Minor halothane metabolism by CYP2E1 generates trifluoroacetyl chloride (TFA) → covalently binds liver proteins → neoantigens
• Prior sensitisation required: fatal hepatitis classically occurs on repeated exposure
• Characterised by fever, eosinophilia, elevated LFTs appearing 1-2 weeks post-anaesthesia
• Mostly replaced by sevoflurane and desflurane (much lower metabolic rate)

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Risk Factors for DILI (Sleisenger & Fordtran, Table 88.2)

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Diagnosis

1. Temporal association: Drug exposure precedes onset; liver injury resolves (usually) on drug withdrawal
2. Exclusion of other causes: Viral hepatitis (including HEV), autoimmune hepatitis, biliary obstruction, vascular disorders
3. Hy's Rule (FDA guideline): ALT ≥3× ULN + bilirubin ≥2× ULN (without ALP elevation >2× ULN) predicts ~10% risk of ALF in the exposed population - signals a drug's potential to cause serious hepatotoxicity
   • R ratio = (ALT/ULN) ÷ (ALP/ULN): R >5 = hepatocellular pattern; R <2 = cholestatic; R 2-5 = mixed
4. RUCAM (Roussel-Uclaf Causality Assessment Method) / RECAM: Standardised causality scoring tool
5. Rechallenge: Positive if ALT or ALP rises ≥2-fold on re-exposure (deliberate rechallenge rarely justified)
6. Extrahepatic features: Rash, fever, eosinophilia, lymphadenopathy support immune mechanism (DRESS syndrome)
7. Liver biopsy: When diagnosis is uncertain or drug-induced chronic hepatitis/cholestasis is suspected
8. LiverTox database (livertox.nih.gov): NIH resource for drug-specific hepatotoxicity profiles

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Management

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Summary of Key DILI Examples by Pattern