Ischemic hepatitis

Epidemiology & Risk Factors

• ICU Prevalence: Accounts for up to 10% of critically ill patients.
• Pathophysiology: The liver’s dual blood supply (hepatic artery & portal vein) typically protects it from ischemia. Injury occurs via a “two-hit” mechanism:
  • Pre-existing passive hepatic congestion (typically from right-sided heart failure) reduces hepatic outflow.
  • Acute systemic hypoperfusion (shock) leads to severe centrilobular (Zone 3) hepatocyte necrosis, which has the lowest baseline oxygen tension.
• Risk Factors:
  • Cardiogenic shock (e.g., acute MI, severe CHF, cardiac arrest, arrhythmias).
  • Septic shock or systemic inflammatory response syndrome (SIRS).
  • Hypovolemic shock (e.g., severe hemorrhage, profound dehydration).
  • Severe hypoxemia (e.g., COPD exacerbation, acute respiratory failure).

---

Clinical Features

• History: Recent event causing profound hypotension, shock, or cardiorespiratory failure.
• Symptoms:
  • Often asymptomatic, identified incidentally on lab work.
  • RUQ pain or discomfort due to hepatic capsular stretch.
  • Nausea, vomiting, and mental confusion (often secondary to global cerebral hypoperfusion rather than hepatic encephalopathy).
• Physical Exam:
  • Hepatomegaly (tender, smooth, and firm liver edge).
  • Signs of systemic shock (hypotension, tachycardia, cool extremities).
  • Signs of right-sided heart failure (JVD, positive hepatojugular reflux, peripheral edema).
  • Jaundice is typically absent or mild early in the course.

---

Diagnosis

• Key Labs (Initial):
  • Transaminases (AST & ALT): Massive, rapid increase (>1,000 U/L, often >25–250x ULN). Typically peaks within 24–72 hours of the inciting ischemic event. c
  • Lactate Dehydrogenase (LDH): Exceedingly elevated. An AST/ALT to LDH ratio < 1.5 strongly suggests ischemic hepatitis over viral/autoimmune causes.
  • Coagulation Panel: Rapid increase in PT/INR due to impaired hepatic synthesis.
  • Bilirubin & ALP: Mild-to-moderate elevation, occurring late in the course.
• Confirmatory (Diagnostic Trend):
  • Rapid normalization of transaminases: Levels typically drop by >50% within 72 hours of restoring perfusion and return to baseline in 1–2 weeks.
• Imaging:
  • RUQ Doppler Ultrasound: To rule out biliary obstruction or acute hepatic vein thrombosis (Budd-Chiari). May show IVC dilation or passive hepatic congestion.
• Biopsy:
  • Rarely indicated; reserved for diagnostic dilemmas. Shows centrilobular (Zone 3) necrosis.

---

Differential Diagnostics

• Acute Viral Hepatitis:
  • Differentiating features: Viral prodrome (fever, malaise), prominent jaundice, AST/ALT to LDH ratio > 1.5, and transaminases decline slowly over weeks (vs. days in ischemic). Confirmed with viral serology.
• Acetaminophen (APAP) Toxicity:
  • Differentiating features: High transaminases, but lacks preceding shock/hypotension history. Confirmed with serum APAP level.
• Budd-Chiari Syndrome:
  • Differentiating features: Classic triad of acute RUQ pain, hepatomegaly, and ascites. Does not self-resolve rapidly. Doppler US shows hepatic vein thrombosis/obstruction.
• Autoimmune Hepatitis:
  • Differentiating features: Subacute or chronic presentation, elevated IgG, positive ANA/ASMA, and interface hepatitis on biopsy.

---

Management

• 1. Hemodynamic Optimization (First-line):
  • Correct the underlying cause of shock/hypoperfusion (e.g., IV Fluids for hypovolemic/septic shock; inotropes/pressors for cardiogenic shock).
  • Optimize cardiac output (e.g., treat underlying arrhythmia, acute MI).
  • Provide supplemental oxygen or mechanical ventilation if hypoxemic.
• 2. Monitoring & Supportive Care (Second-line):
  • Serial LFTs, PT/INR, and BMP (monitoring for concurrent AKI/shock kidney).
  • Avoid hepatotoxic agents and adjust doses of hepatically/renally cleared drugs.
• 3. Management of Acute Liver Failure (Refractory):
  • If progression to acute liver failure (ALF) (defined as INR ≥ 1.5 + encephalopathy in a patient without cirrhosis):
    • Transfer immediately to a liver transplant center.
    • Initiate hepatic encephalopathy protocols (e.g., lactulose, monitoring ammonia) and manage cerebral edema.

---

Complications

• Acute Liver Failure (ALF): Occurs in cases of severe, prolonged hypoperfusion.
• Acute Kidney Injury (AKI): Commonly co-occurs (“shock kidney”) due to concurrent renal hypoperfusion.
• Coagulopathy & Hemorrhage: Secondary to impaired synthesis of clotting factors.
• Hepatic Encephalopathy: Caused by accumulation of neurotoxins (ammonia) in setting of liver failure.