Residency · Residency · Gastroenterology

Acute Pancreatitis

Definition and Diagnosis

Revised Atlanta Classification (2012)

The diagnosis of acute pancreatitis according to the Revised Atlanta Classification requires the presence of at least 2 of 3 criteria: abdominal pain consistent with pancreatitis, characterized by acute onset, severe intensity, epigastric location, and radiation to the back; serum lipase (or amylase) elevated to 3 or more times the upper limit of normal; and characteristic findings on cross-sectional imaging, whether CT, MRI, or ultrasonography. Lipase is preferred over amylase for diagnosis due to its higher sensitivity and specificity and because it remains elevated for a longer duration. Importantly, imaging is not needed for diagnosis when the first two criteria are both satisfied.

Severity Classification (Revised Atlanta)

The Revised Atlanta Classification defines three severity categories. Mild acute pancreatitis, which accounts for 80% of cases, is characterized by the absence of organ failure and local complications, with a mortality below 1%. Moderately severe pancreatitis is defined by transient organ failure lasting less than 48 hours and/or the presence of local complications. Severe pancreatitis is characterized by persistent organ failure exceeding 48 hours, carrying a mortality of 20 to 40%. Organ failure is defined using the modified Marshall score across three systems: cardiovascular (systolic blood pressure less than 90 mmHg despite fluid resuscitation), renal (creatinine greater than 1.9 mg/dL), and respiratory (PaO2/FiO2 ratio less than 300).

Etiology

Common Causes (80-90%)

Gallstones account for 40 to 50% of acute pancreatitis cases. The mechanism involves transient ampullary obstruction, and risk factors include small stones less than 5 mm in diameter and a wide cystic duct. Alcohol is responsible for 25 to 35% of cases and typically requires more than 5 years of heavy use exceeding 50 grams per day. The first episode may represent an acute exacerbation of underlying chronic pancreatitis.

Hypertriglyceridemia causes 2 to 5% of acute pancreatitis, usually when triglyceride levels exceed 1000 mg/dL. The mechanism involves the generation of toxic free fatty acids through lipase-mediated triglyceride hydrolysis. Post-ERCP pancreatitis occurs in 3 to 15% of ERCP procedures, with risk factors including female sex, prior post-ERCP pancreatitis, sphincter of Oddi dysfunction, difficult cannulation, and pancreatic duct injection. Prevention strategies include rectal indomethacin 100 mg administered before or immediately after the procedure and prophylactic pancreatic duct stent placement.

Less Common Causes

Less common etiologies include medications such as azathioprine and 6-mercaptopurine, valproic acid, didanosine, mesalamine, ACE inhibitors, and rarely statins. Autoimmune pancreatitis may be type 1 (IgG4-related) or type 2 (granulocytic). Anatomic variants including pancreas divisum (prevalence 3 to 7%, with clinical significance debated) and annular pancreas may predispose to pancreatitis. Sphincter of Oddi dysfunction is another recognized cause. Genetic causes include PRSS1 mutations (hereditary pancreatitis, autosomal dominant), as well as SPINK1, CFTR, CTRC, and CPA1 mutations. Additional etiologies encompass trauma, ischemia, infections (mumps, CMV, HIV), scorpion envenomation, pancreatic neoplasms (IPMN or adenocarcinoma obstructing the duct), and hypercalcemia from hyperparathyroidism.

Idiopathic (10-30%)

Idiopathic pancreatitis accounts for 10 to 30% of cases after thorough initial evaluation. Many of these cases are ultimately found to have microlithiasis, sphincter of Oddi dysfunction, or a genetic predisposition. Endoscopic ultrasonography identifies occult biliary disease including sludge and microlithiasis in 30 to 70% of cases initially classified as idiopathic. MRCP with secretin stimulation evaluates ductal anatomy to identify pancreas divisum and strictures. Genetic testing should be considered in cases of recurrent idiopathic pancreatitis, a positive family history, or young age of presentation.

Prognostic Assessment

Scoring Systems

The Bedside Index for Severity in Acute Pancreatitis (BISAP) incorporates five variables: BUN greater than 25 mg/dL, impaired mental status, the presence of systemic inflammatory response syndrome, age greater than 60, and pleural effusion. A BISAP score of 3 or higher predicts severe disease, and its simplicity and availability at admission make it clinically practical. APACHE-II is a more complex scoring system using 12 variables; a score of 8 or higher at admission predicts severe disease. The Ranson criteria use 11 variables assessed at admission and at 48 hours but have been largely supplanted by BISAP and APACHE-II. The Harmless Acute Pancreatitis Score (HAPS) identifies patients with mild disease at presentation based on three features: absence of rebound tenderness or guarding, normal hematocrit, and normal creatinine. When all three are present, the positive predictive value for a non-severe course is 98%.

Individual Markers

Among individual prognostic markers, a rising BUN in the first 24 hours is the strongest predictor of mortality, as demonstrated in the Wu study. Hemoconcentration with a hematocrit greater than 44% at admission is associated with increased risk of pancreatic necrosis. C-reactive protein greater than 150 mg/L at 48 hours predicts severe disease, though its clinical utility is limited by a delayed rise that peaks at 48 to 72 hours. Persistent systemic inflammatory response syndrome at 48 hours is predictive of organ failure and mortality.

Initial Management

Fluid Resuscitation

Goal-directed fluid therapy is preferred over aggressive, high-volume intravenous fluid administration. The WATERFALL trial, published in 2022, compared aggressive fluids (a 20 mL/kg bolus followed by 3 mL/kg/hr of lactated Ringer solution) with moderate fluids (1.5 mL/kg/hr of lactated Ringer with a bolus administered only if the patient was hypovolemic). The aggressive fluid strategy was associated with more fluid overload complications without demonstrable benefit. Lactated Ringer solution is preferred over normal saline based on its anti-inflammatory properties and reduced incidence of SIRS. Clinical targets for adequate resuscitation include a urine output of 0.5 mL/kg/hr or greater, decreasing BUN, and decreasing hematocrit. Fluid status should be reassessed every 6 to 8 hours, and overhydration must be avoided given the risks of pulmonary edema and abdominal compartment syndrome.

Pain Management

Opioids are first-line for moderate-to-severe pain. The historical concern that morphine worsens pancreatitis through sphincter of Oddi spasm is not supported by evidence. Hydromorphone or fentanyl are often preferred for their shorter-acting profiles. A multimodal approach incorporating intravenous or oral acetaminophen, NSAIDs (ketorolac, indomethacin), and patient-controlled analgesia when needed can optimize pain control while minimizing opioid exposure. Meperidine should be avoided due to seizure risk and the absence of any benefit over other opioids.

Nutrition

Early oral feeding, initiated as soon as the patient can tolerate it, is the current standard. A low-fat solid diet can be started within 24 hours if pain permits, without the need to wait for complete pain resolution or normalization of pancreatic enzymes. Enteral nutrition via nasogastric or nasojejunal tube should be instituted if the patient is unable to eat by day 3 to 5; both routes have been shown to be equally effective, and a standard polymeric formula is acceptable. Parenteral nutrition should be used only when enteral nutrition is not tolerated or is contraindicated, as it is associated with more infections and complications. Prolonged NPO status is harmful, increasing infection risk and delaying recovery.

ERCP in Gallstone Pancreatitis

Urgent ERCP within 24 hours is indicated only for concomitant acute cholangitis. Early ERCP within 72 hours should be considered for persistent biliary obstruction as evidenced by rising or persistent bilirubin and a dilated common bile duct without cholangitis. ERCP is not indicated for predicted mild gallstone pancreatitis with improving liver function tests and no cholangitis, as stones pass spontaneously in the majority of cases. Same-admission cholecystectomy should be performed for mild gallstone pancreatitis, as this approach reduces the recurrence rate from 30 to 40% to less than 5%. For severe disease, cholecystectomy should be delayed approximately 6 weeks after resolution.

<image>A timeline infographic for acute pancreatitis management. Horizontal timeline from Day 0 to Day 28+. Day 0-1: "Diagnosis (2 of 3 Atlanta criteria), Severity assessment (BISAP, SIRS), Goal-directed fluid resuscitation (LR preferred, moderate rate per WATERFALL trial), Pain management (multimodal), NPO -> early oral feeding when tolerated, ERCP only if cholangitis." Day 1-3: "Reassess severity, Monitor for organ failure (modified Marshall score), Oral diet advancement, Start enteral nutrition if not tolerating oral by day 3-5." Day 3-7: "Monitor for local complications (CT only if not improving or clinical concern), Identify etiology (if unclear: EUS for occult biliary disease, lipid panel, calcium, medication review)." Day 7-14: "Local complications management: Peripancreatic fluid collection (observation), Walled-off necrosis developing (observe unless infected)." Day 14-28+: "Infected necrosis: step-up approach (percutaneous drain -> endoscopic necrosectomy -> minimally invasive surgery)." Across the bottom, show a "Cholecystectomy timing" bar: "Same admission for mild; delay 6 weeks for severe." Use color-coded segments: blue for supportive care, orange for interventional decisions, red for complications management.</image>

Local Complications

Early (<4 weeks)

Acute peripancreatic fluid collections are homogeneous collections without a defined wall that arise in the setting of interstitial pancreatitis. They usually resolve spontaneously and do not require intervention. Acute necrotic collections are heterogeneous collections containing necrotic tissue that develop in necrotizing pancreatitis. They also lack a defined wall and appear within the first 4 weeks.

Late (>4 weeks)

Pseudocysts are encapsulated fluid collections with a well-defined wall that contain no solid debris and are complications of interstitial pancreatitis. Drainage is indicated only when they are symptomatic (causing pain, obstruction, or infection) or measure greater than 6 cm and are enlarging. Drainage options include EUS-guided cystogastrostomy (preferred), percutaneous drainage, and surgical drainage. Walled-off necrosis is an encapsulated collection containing solid necrotic debris with a defined wall that complicates necrotizing pancreatitis and develops at 4 weeks or later.

Necrotizing Pancreatitis

Necrotizing pancreatitis occurs in 15 to 20% of acute pancreatitis cases. Sterile necrosis is managed with supportive care, and intervention is indicated only if symptomatic complications such as gastric outlet obstruction or failure to thrive develop. Infected necrosis should be suspected when clinical deterioration occurs after initial improvement, manifesting as fever, leukocytosis, and sepsis, typically at 2 to 4 weeks. Gas within the necrotic collection on CT is pathognomonic for infection. CT-guided fine-needle aspiration for Gram stain and culture was previously the standard approach but is now often bypassed in favor of empiric intervention when the clinical picture is clear. Prophylactic antibiotics are not recommended, as multiple randomized controlled trials have shown no benefit in preventing infection of necrosis.

Step-Up Approach for Infected Necrosis

The PANTER trial, published in 2010, established the step-up approach as superior to primary open surgical necrosectomy. Step 1 involves percutaneous catheter drainage or endoscopic transmural drainage with a lumen-apposing metal stent, which resolves approximately 35 to 50% of cases without further intervention. Step 2, performed if no improvement occurs within 72 hours, consists of endoscopic necrosectomy (direct endoscopic necrosectomy via a transgastric or transduodenal route) or video-assisted retroperitoneal debridement. Step 3, reserved as a last resort, is open surgical necrosectomy, which carries a morbidity of 40 to 95%.

The TENSION trial demonstrated that the endoscopic step-up approach was non-inferior to the surgical step-up approach, with lower rates of major complications including pancreatic fistula and new-onset organ failure. Whenever clinically safe, intervention should be delayed to 4 weeks or later to allow walled-off necrosis to mature, providing better encapsulation and safer drainage.

<image>A CT imaging comparison panel showing the four major local complications of acute pancreatitis according to the Revised Atlanta Classification. Four panels with axial CT images (contrast-enhanced). Panel 1 "APFC (Acute Peripancreatic Fluid Collection)": homogeneous fluid density surrounding the pancreas without a defined wall, occurring within 4 weeks; the pancreas shows normal enhancement (interstitial pancreatitis). Panel 2 "ANC (Acute Necrotic Collection)": heterogeneous collection with non-liquid density areas representing necrosis, no defined wall, pancreatic and/or peripancreatic non-enhancement; within 4 weeks. Panel 3 "Pseudocyst": well-defined, round, encapsulated homogeneous fluid collection with a distinct enhancing wall; no solid component; after 4 weeks. Panel 4 "WON (Walled-Off Necrosis)": encapsulated heterogeneous collection with solid debris and fluid, well-defined enhancing wall; after 4 weeks; may show gas bubbles indicating infection. Label each panel with: name, contents, wall presence, timing, and recommended management (observe vs. drain). Use arrows pointing to key features. Include a timeline bar at the bottom showing the 4-week demarcation between early and late complications.</image>

Other Complications

Vascular

Splenic vein thrombosis complicates 5 to 20% of cases and leads to sinistral (left-sided) portal hypertension with the development of gastric varices. Splenectomy is indicated if variceal bleeding occurs. Pseudoaneurysms may involve the splenic, gastroduodenal, or pancreaticoduodenal arteries and carry a risk of rupture, making angiographic embolization the preferred treatment. Portal and mesenteric vein thrombosis should be treated with anticoagulation when symptomatic or extensive.

Pancreatic Duct Disruption

Downstream duct disruption leads to pseudocyst formation, which can be managed with internal drainage. Disconnected pancreatic duct syndrome occurs when necrosis causes complete duct disruption, isolating the viable upstream pancreas. This condition is associated with a high recurrence of fluid collections and may require transmural stenting or distal pancreatectomy for definitive management.

Abdominal Compartment Syndrome

Abdominal compartment syndrome is defined by an intra-abdominal pressure exceeding 20 mmHg with new organ dysfunction. Risk factors include aggressive fluid resuscitation and severe pancreatitis. Management strategies include nasogastric decompression, rectal drainage, sedation and paralysis, percutaneous drainage of ascites, and decompressive laparotomy for refractory cases.

Special Considerations

Hypertriglyceridemic Pancreatitis

Pancreatitis from hypertriglyceridemia typically occurs at triglyceride levels exceeding 1000 mg/dL, with levels above 2000 mg/dL most commonly associated with clinical disease. Treatment includes an insulin drip at 5 to 10 units per hour with glucose monitoring to activate lipoprotein lipase, heparin (which enhances lipoprotein lipase activity but may deplete it), and plasmapheresis for severe cases with triglycerides above 2000 and severe pancreatitis. The target is to reduce triglycerides below 500 mg/dL. Long-term prevention is achieved with fibrate therapy.

Recurrent Acute Pancreatitis

Recurrent acute pancreatitis is defined as 2 or more well-documented episodes with complete symptom resolution between attacks. Etiologic considerations include microlithiasis (for which EUS is the investigation of choice), sphincter of Oddi dysfunction, genetic mutations (PRSS1, SPINK1, CFTR), autoimmune pancreatitis, and anatomic variants. Cholecystectomy should be considered if a biliary cause is suspected, even in the absence of stones on imaging.

Pregnancy

Gallstones are the most common cause of pancreatitis in pregnancy, and hypertriglyceridemia may contribute as triglyceride levels rise physiologically during gestation. MRI without gadolinium is preferred over CT for imaging. Cholecystectomy is safe during the second trimester if clinically indicated.

Key Clinical Pearls

• Lipase >= 3x ULN is diagnostic; imaging is NOT needed for diagnosis if pain + elevated lipase criteria are met
• The WATERFALL trial (2022) showed that aggressive IV fluids are NOT superior to moderate fluids and may cause harm — goal-directed, moderate-rate LR is the current standard
• Early oral feeding (within 24 hours) is safe and preferred; prolonged NPO is harmful
• ERCP is indicated in gallstone pancreatitis ONLY for concurrent cholangitis or persistent biliary obstruction — NOT for predicted mild disease
• Same-admission cholecystectomy for mild gallstone pancreatitis prevents 30-40% recurrence rate
• Prophylactic antibiotics do NOT reduce infected necrosis and are NOT recommended
• Step-up approach (PCD/endoscopic drainage -> necrosectomy) is superior to primary open surgery for infected necrosis (PANTER, TENSION trials)
• Delay intervention for infected necrosis to >= 4 weeks when clinically safe to allow WON maturation
• Rising BUN in the first 24 hours is the single strongest predictor of mortality

References

1. Tenner S, et al. ACG Clinical Guideline: Management of Acute Pancreatitis. Am J Gastroenterol. 2024;119(3):419-437.
2. de-Madaria E, et al. Aggressive or moderate fluid resuscitation in acute pancreatitis (WATERFALL). N Engl J Med. 2022;387(11):989-1000.
3. van Santvoort HC, et al. A step-up approach or open necrosectomy for necrotizing pancreatitis (PANTER). N Engl J Med. 2010;362(16):1491-1502.
4. van Brunschot S, et al. Endoscopic or surgical step-up approach for infected necrotising pancreatitis: a multicentre randomised trial (TENSION). Lancet. 2018;391(10115):51-58.
5. Banks PA, et al. Classification of acute pancreatitis — 2012: revision of the Atlanta classification. Gut. 2013;62(1):102-111.

Read this lecture as Markdown