Acute Pancreatitis - A Complete Guide

What Is It?

Quick Anatomy Reminder

Causes (Etiology)

Idiopathic cases exist - many are thought to be occult microlithiasis. Smoking and diabetes are independent risk factors.

Pathophysiology - How It Happens

Inciting event (gallstone / alcohol / drug)
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Duct obstruction OR direct acinar cell injury
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Disruption of normal membrane trafficking
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Premature activation of trypsinogen → TRYPSIN
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Trypsin activates MORE enzymes (lipase, elastase, phospholipase)
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AUTODIGESTION of pancreatic tissue
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Inflammatory cascade: macrophages + neutrophils recruited
Cytokine release → increased vascular permeability
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Edema, hemorrhage, necrosis (local effects)
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SIRS → Sepsis → Multiorgan failure (systemic effects)

Types of Acute Pancreatitis

Clinical Presentation

• Epigastric pain (constant, severe) radiating to the back - the hallmark
• Pain may radiate to the chest or flanks
• Nausea, vomiting, anorexia - eating makes it worse
• Pain is eased by leaning forward (classic)

• Epigastric tenderness ± guarding
• Diminished or absent bowel sounds (ileus)
• Jaundice if obstructive cause (gallstone)
• Fever, tachycardia, hypotension in severe disease

• Cullen's sign - bluish periumbilical discoloration
• Grey Turner's sign - reddish-brown flank discoloration

Both are rare, non-specific, but indicate severe disease when present.

Diagnosis

The "2 of 3" Rule (Revised Atlanta Criteria)

1. Characteristic abdominal pain
2. Serum lipase or amylase >3x upper limit of normal
3. Characteristic imaging findings

Labs

Elevation level does NOT correlate with severity - a mildly elevated lipase can still mean severe disease.

Imaging

• Ultrasound (first-line): Always do to look for gallstones/biliary dilation as cause
• CT scan with IV contrast: NOT routine - only for:
  1. Diagnostic uncertainty
  2. Rule out other pathology (AAA, obstruction)
  3. Assess complications after 48-72 hours of failed treatment
  • Best done 3-7 days after onset (necrosis not visible early)
  • Sensitivity >90% for AP when performed with contrast

Severity Classification (Revised Atlanta 2012)

Severity Scoring Systems

Ranson Criteria (admission + 48h)

• Age >55 years
• WBC >16,000/mm³
• Blood glucose >200 mg/dL
• LDH >350 IU/L
• AST >250 IU/L

• Hematocrit drop >10%
• BUN rise >5 mg/dL
• Calcium ≤8 mg/dL
• PaO₂ <60 mmHg
• Base deficit >4 mEq/L
• Fluid sequestration >600 mL

• 0-2 criteria: ~1% mortality
• 3-4 criteria: ~15% mortality
• 5-6 criteria: ~40% mortality
• 7-8 criteria: >50% mortality

BISAP Score (simpler, ED-friendly)

• BUN >25 mg/dL
• Impaired mental status
• SIRS criteria present
• Age >60 years
• Pleural effusion on imaging

CT Severity Index (Balthazar)

• Based on CT findings: pancreatic necrosis + extrapancreatic changes
• Score ≥5 = 15x higher mortality than score <5

Complications

Local Complications (usually after 1st week)

Systemic Complications

• Pulmonary: ARDS, pleural effusion (up to 50% of patients, usually left-sided), atelectasis
• Cardiovascular: Shock from third-spacing
• Renal: Acute kidney injury
• Coagulopathy: DIC
• Metabolic: Hypocalcemia, hyperglycemia

Management

The 3 Pillars of Treatment

Treatment is mainly supportive - there is no specific cure.

1. Fluid Resuscitation

• Patients are volume-depleted (vomiting + third-spacing)
• Lactated Ringer's preferred over Normal Saline - more physiologic, possible anti-inflammatory effect
• Inadequate fluid in first 24h → more necrosis, SIRS, organ failure
• Avoid over-resuscitation → abdominal compartment syndrome, ARDS

2. Pain Control

• IV opioids are the standard; no evidence favors one opioid over another
• Old myth that morphine causes sphincter of Oddi spasm and worsens AP - this is NOT clinically significant

3. Nutrition

• Mild AP: Resume oral feeding as soon as tolerated (no need to wait for enzymes to normalize)
• Severe AP: Early enteral feeding preferred over total parenteral nutrition (TPN)
  • Enteral nutrition maintains gut barrier, reduces bacterial translocation
  • Nasogastric (NG) feeds work as well as nasojejunal in most cases

What NOT to Do

• No prophylactic antibiotics - no benefit in sterile pancreatitis
• No routine CT early in the disease
• No routine ERCP - only if:
  • Cholangitis is present
  • Persistent biliary obstruction (elevated bilirubin + dilated bile ducts)

Gallstone Pancreatitis Specific Management

• Early laparoscopic cholecystectomy (within 3 days in mild disease) is standard of care - reduces risk of recurrence
• ERCP only if cholangitis or biliary obstruction is confirmed

Infected Necrosis

• IV antibiotics (carbapenems - penetrate pancreatic tissue well)
• Debridement/drainage - endoscopic (preferred), percutaneous, or surgical
• "Step-up approach" - start least invasive, escalate as needed

Summary Table

USMLE-Style Questions: Acute Pancreatitis

Question 1

• A) CT abdomen with IV contrast
• B) ERCP
• C) Abdominal ultrasound
• D) MRCP
• E) Serum amylase level

Question 2

• A) 5 criteria - 40% mortality
• B) 7 criteria - >50% mortality
• C) 3 criteria - 15% mortality
• D) 9 criteria - 100% mortality
• E) 4 criteria - 15% mortality

Question 3

• A) Normal saline - most isotonic and widely available
• B) Lactated Ringer's - more physiologic and may have anti-inflammatory effects
• C) D5W - provides caloric support during NPO status
• D) Albumin - corrects the oncotic pressure lost from third-spacing
• E) Hypertonic saline - reduces pancreatic edema

Question 4

• A) Start prophylactic antibiotics immediately
• B) IV imipenem and plan for necrosectomy if no improvement
• C) Increase IV fluids and observe for 48 more hours
• D) Immediate surgical debridement
• E) ERCP with pancreatic duct stenting

Question 5

• A) Hypertriglyceridemia - current level is diagnostic
• B) Occult microlithiasis
• C) Autoimmune pancreatitis
• D) Pancreas divisum
• E) Hereditary pancreatitis

Question 6

• A) Total parenteral nutrition (TPN) should be started immediately to rest the pancreas
• B) The patient should remain NPO until lipase normalizes
• C) Early enteral nutrition via nasogastric tube is preferred over TPN
• D) Nasojejunal feeding beyond the ligament of Treitz must be used to avoid stimulating the pancreas
• E) Oral feeding should not resume until CT shows resolution of inflammation

Question 7

• A) ERCP with biliary sphincterotomy before discharge
• B) Laparoscopic cholecystectomy within 3 days before discharge
• C) Interval cholecystectomy in 6-8 weeks after full recovery
• D) Conservative management - no surgery needed after first episode
• E) MRCP first to confirm absence of common bile duct stones before cholecystectomy

Question 8

• A) Necrotizing pancreatitis with >30% necrosis
• B) Interstitial edematous pancreatitis - Balthazar grade C
• C) Walled-off necrosis
• D) Pancreatic pseudocyst
• E) Pancreatic abscess

Question 9

• A) Lipase elevation in pregnancy is normal and not diagnostic
• B) Serum amylase, not lipase, should be used for diagnosis in pregnant women
• C) ERCP is absolutely contraindicated in pregnancy
• D) Gallstone pancreatitis is the most common cause of acute pancreatitis in pregnancy
• E) CT scan is the first-line imaging modality to avoid fetal risk from ultrasound

Question 10

• A) Superficial thrombophlebitis from IV access
• B) Retroperitoneal hemorrhage tracking to the periumbilical region via the falciform ligament
• C) Rupture of a pancreatic pseudocyst into the peritoneal cavity
• D) Mesenteric ischemia from splanchnic vasoconstriction
• E) Cutaneous manifestation of fat necrosis from circulating lipase

Quick High-Yield Summary for USMLE