Acute Pancreatitis

Definition & Epidemiology

Etiology

• Gallstones: 40-70%
• Chronic alcohol use: 25-35%

Pathophysiology

1. Autodigestion of acinar cells and surrounding tissue
2. Release of inflammatory mediators (cytokines, phospholipase A2, elastase)
3. Local inflammation → increased microvascular permeability → third-spacing of fluid
4. Systemic inflammatory response (SIRS) → potential multiorgan failure

Classification (2012 Revised Atlanta Classification)

• Interstitial edematous pancreatitis: Diffuse enlargement with edema, no necrosis - the majority (~90-95%)
• Necrotizing pancreatitis: ~5-10% of patients; involves parenchymal and/or peripancreatic necrosis; increased morbidity when infected

Clinical Features

• Persistent epigastric or LUQ pain radiating to the back, chest, or flanks
• Pain severity does not correlate with clinical severity
• Nausea, vomiting, anorexia; oral intake worsens pain
• Pain may be relieved by sitting forward or leaning forward

• Vital signs may be normal in mild/early disease
• Tachycardia, fever, tachypnea with progressive disease
• Jaundice suggests biliary obstruction
• Epigastric tenderness ± guarding
• Cullen sign (periumbilical bluish discoloration) and Grey Turner sign (flank reddish-brown discoloration) indicate retroperitoneal hemorrhage - rare, neither sensitive nor specific, but suggest poor prognosis
• Diminished bowel sounds if ileus is present
• Pleural effusions in up to 50% of patients - more commonly left-sided
• Rosen's Emergency Medicine, p. 1265-1266

Diagnosis

1. Abdominal pain characteristic of AP
2. Serum lipase or amylase >3× upper limit of normal
3. Characteristic findings on abdominal imaging

Biochemical Tests

• Testing both lipase AND amylase does not improve diagnostic sensitivity or specificity
• Degree of enzyme elevation does NOT correlate with severity

Imaging

1. Diagnostic uncertainty or normal enzyme levels with high clinical suspicion
2. Need to exclude other serious pathology (e.g., aortic aneurysm, bowel obstruction)
3. Failure to improve after 48-72 hours of appropriate therapy

• Rosen's Emergency Medicine, p. 1267

CT Imaging: Interstitial Edematous Pancreatitis

CT showing acute interstitial pancreatitis with mild peripancreatic fluid and fat stranding (Rosen's Emergency Medicine, Fig. 77.2)

CT Imaging: Necrotizing Pancreatitis

CT showing necrotizing pancreatitis with decreased enhancement of pancreatic parenchyma (Rosen's Emergency Medicine, Fig. 77.3)

Severity Scoring Systems

Local Complications

In Interstitial Edematous Pancreatitis:

• Acute peripancreatic fluid collection (APFC): Homogeneous fluid adjacent to pancreas, <4 weeks from onset; most resolve spontaneously
• Pancreatic pseudocyst: Encapsulated fluid collection with well-defined wall, >4 weeks from onset; contains no significant solid debris; forms from ductal leak

In Necrotizing Pancreatitis:

• Acute necrotic collection (ANC): Heterogeneous fluid + necrosis, <4 weeks
• Walled-off necrosis (WON): Heterogeneous fluid + necrosis with well-defined wall, >4 weeks; sterile or infected

Vascular Complications:

• Splenic or portal vein thrombosis
• Pseudoaneurysm (splenic, hepatic, gastroduodenal arteries)
• GI bleeding, gastric outlet obstruction

Management

1. Fluid Resuscitation (Most Important Early Intervention)

• IAP/APA goal-directed approach: 5-10 mL/kg/h, targeting:
  • HR <120/min
  • MAP 65-85 mmHg
  • Urine output >0.5-1 mL/kg/h
• ACG recommendation: 250-500 mL/h initially
• Preferred fluid: Lactated Ringer's (LR) over normal saline - LR is thought to provide anti-inflammatory benefits and avoids the hyperchloremic metabolic acidosis of large-volume NS (acidosis activates trypsinogen, worsening disease)
• Colloids are NOT generally recommended; may be considered if hematocrit <24% or albumin <2 g/dL
• Monitor with hematocrit, BUN, creatinine as surrogates

2. Pain Management

• IV opioids for moderate-to-severe pain; hydromorphone and morphine are commonly used
• NSAIDs as adjuncts

3. Nutrition

• Mild AP: Early oral feeding tolerated (even with elevated enzymes) - begin when nausea/vomiting controlled
• Severe AP: Early enteral nutrition is preferred over TPN - associated with fewer infectious complications and lower cost
• NG feeding is as effective as nasojejunal feeding; nasojejunal tubes preferred if gastric retention occurs
• NPO is no longer standard for all cases; prolonged fasting provides no benefit

4. Antibiotics

• Prophylactic antibiotics are NOT indicated in AP
• Antibiotics ARE indicated in:
  • Confirmed or suspected infected pancreatic necrosis
  • Other clear evidence of sepsis/infection
  • Concomitant cholangitis

5. ERCP

• Concomitant cholangitis
• Confirmed biliary obstruction (elevated bilirubin + clinical evidence)
• NOT indicated routinely in biliary pancreatitis without obstruction
• MRCP and EUS can identify bile duct stones and select patients for ERCP before proceeding

6. Surgery/Intervention for Complications

• Cholecystectomy: Standard of care for gallstone pancreatitis - laparoscopic cholecystectomy within 3 days in mild biliary pancreatitis improves outcomes and reduces need for ERCP
• Infected necrosis: Requires drainage/debridement - endoscopic transmural drainage (for WON abutting stomach/duodenum), minimally invasive surgical necrosectomy, or percutaneous drainage
• Drainage of pseudocysts: When symptomatic, infected, or enlarging; endoscopic ultrasound-guided transmural drainage preferred for those abutting GI wall
• Rosen's Emergency Medicine, p. 1268-1270; Sleisenger & Fordtran's (Endoscopy section), p. 2783-2787

Differential Diagnosis

• Peptic ulcer disease / perforation
• Acute cholecystitis / cholangitis / choledocholithiasis
• Gastritis / gastroenteritis
• Mesenteric ischemia / bowel obstruction
• Myocardial infarction (inferior MI can mimic epigastric pain with radiation to back)
• Pneumonia
• Aortic dissection/aneurysm
• Ectopic pregnancy
• Diabetic ketoacidosis
• Sickle cell crisis

Summary Table: Key Points