3.8 Acute Pancreatitis

Pancreatic and biliary disorders frequently appear on the ABIM examination as acute emergencies, complex diagnostic algorithms, or chronic malabsorptive syndromes. Precision regarding fluid management, intervention timing, and autoimmune diagnostic markers is essential.

1. Acute Pancreatitis

Revised Atlanta Diagnostic Criteria

Diagnosis requires at least 2 of the following 3 criteria:

1. Characteristic Abdominal Pain: Acute onset of severe, persistent epigastric pain often radiating straight through to the back, partially relieved by sitting forward.
2. Serum Lipase or Amylase Elevation: $\ge 3\times\text{ the upper limit of normal (ULN)}$. (Lipase is preferred over amylase due to higher sensitivity, specificity, and prolonged elevation up to 8–14 days).
3. Characteristic Imaging Findings: Contrast-enhanced computed tomography (CECT), MRI, or transabdominal ultrasound demonstrating peripancreatic inflammation.

[!NOTE] If a patient presents with classic epigastric pain and lipase $\ge 3\times\text{ ULN}$, diagnostic CT imaging is NOT required on admission and should be avoided to prevent unnecessary contrast-induced nephrotoxicity. CT is indicated only when the diagnosis is uncertain or if clinical deterioration occurs after 48–72 hours.

Common Etiologies

1. Gallstones (40–45%): Most common cause. Gallstone transiently impacts the ampulla of Vater. Check RUQ ultrasound and liver function tests (ALT $>150\text{ U/L}$ has a 95% positive predictive value for biliary etiology).
2. Alcohol (30–35%): Second most common cause (usually requires $\ge 4-5\text{ drinks/day}$ over $\ge 5$ years).
3. Hypertriglyceridemia (2–5%): Typically occurs when serum Triglycerides $> 1,000\text{ mg/dL}$. Managed with IV regular insulin infusion (activates lipoprotein lipase, accelerating triglyceride clearance) plus 5% dextrose infusion to maintain euglycemia; therapeutic plasma exchange (plasmapheresis) for severe cases.
4. Post-ERCP Pancreatitis (3–5%): Prevent with rectal Indomethacin (100 mg PR immediately post-procedure) and temporary pancreatic duct stenting in high-risk patients.
5. Medications: Azathioprine, 6-MP, didanosine, valproic acid, thiazides, furosemide, DPP-4 inhibitors.
6. Autoimmune Pancreatitis (AIP): Type 1 (IgG4-related systemic disease, "sausage-shaped" pancreas, elevated serum IgG4); Type 2 (duct-centric, associated with IBD). Both exhibit dramatic response to oral corticosteroids.

Severity Stratification & Early Resuscitation

• Severity Classification:
  • Mild: No organ failure, no local or systemic complications.
  • Moderately Severe: Transient organ failure ($<48\text{ hours}$) or local/systemic complications.
  • Severe: Persistent organ failure ($>48\text{ hours}$) involving cardiovascular (shock), pulmonary ($\text{PaO}_2/\text{FiO}_2 \le 300$), or renal ($\text{Cr} \ge 1.9\text{ mg/dL}$) systems.
• Early Predictors of Severity: Admission Hematocrit $>44%$, rising BUN at 24 hours ($>20\text{ mg/dL}$), and BISAP score $\ge 3$.
• Goal-Directed Fluid Resuscitation:
  • Fluid of Choice: Lactated Ringer's (LR) solution (preferred over normal saline; LR reduces systemic acidosis and decreases SIRS incidence).
  • Administration Rate: Moderate goal-directed rate of $200-250\text{ mL/hour}$ (or $5-10\text{ mL/kg/hr}$ initially if hypovolemic), titrated to clinical targets: urine output $>0.5-1.0\text{ mL/kg/hour}$, normalization of BUN and creatinine, and MAP $\ge 65\text{ mmHg}$.
  • Avoid Fluid Overload: Aggressive fluid loading ($>3.5-4.0\text{ L}$ in first 24h) increases pulmonary edema, abdominal compartment syndrome, and mortality.
• Early Nutrition: Initiate early oral feeding with a low-fat solid or liquid diet as soon as abdominal pain improves, ileus resolves, and nausea subsides (typically within 24–48 hours). If oral intake is not tolerated, enteral tube feeding (nasogastric or nasojejunal) is superior to total parenteral nutrition (TPN).
• Prophylactic Antibiotics: Routine prophylactic antibiotics are NOT recommended for mild, severe, or sterile necrotizing pancreatitis.

Atlanta Classification of Local Pancreatic Complications

The "Step-Up Approach" for Infected Pancreatic Necrosis

• Clinical Suspicion: Suspected when a patient develops recurrent fever, leukocytosis, and clinical deterioration 7 to 14+ days after admission. CECT demonstrates gas bubbles within the necrotic retroperitoneal bed.
• Algorithmic Step-Up Protocol:
  1. Systemic Antibiotics: Initiate IV broad-spectrum antibiotics with proven pancreatic tissue penetration: IV Carbapenem (Meropenem 1 g IV q8h).
  2. Delayed Intervention: Postpone invasive intervention for $\ge 4\text{ weeks}$ to allow encapsulation into mature WOPN.
  3. Minimally Invasive Drainage: If sepsis persists, perform CT-guided Percutaneous Catheter Drainage or Endoscopic Transluminal Transgastric Drainage.
  4. Minimally Invasive Necrosectomy: If no improvement after drainage, perform Video-Assisted Retroperitoneal Debridement (VARD) or endoscopic necrosectomy.