Decision Making in Emergency Critical Care

SECTION 7 - Gastrointestinal and Hematological Critical Care

26
Pancreatitis

Susan Y. Quan and Walter G. Park

BACKGROUND

The pancreas is approximately 6 to 10 inches long, is located directly behind the stomach, and has distinct endocrine and exocrine functions. The endocrine portion of the pancreas is composed of islets of Langerhans cells that constitute about 2% of the organ. These cells produce and secrete hormones including insulin, glucagon, and somatostatin. The exocrine portion of the pancreas is composed of acinar cells (80% of the organ) and ductal cells (18% of the organ). Acinar cells produce digestive enzymes that are sequestered until physiologic impulses stimulate their release into the pancreatic ductal system where they are transported to the small intestine. The digestive enzymes are enzymatically inert until activated in the small intestine by various peptides. Disruption of this physiologic process, by any of a variety of etiologies, is the basis for our current understanding of acute and chronic pancreatitis. This chapter primarily focuses on acute pancreatitis, which is more commonly seen in emergency care. Pertinent aspects of chronic pancreatitis are also addressed.

ACUTE PANCREATITIS

The incidence of acute pancreatitis is estimated to be as high as 38 per 100,000 patients and accounts for more than 220,000 hospital admissions in the United States annually.1 Most cases are clinically mild and self-limited; a minority of cases are severe and are associated with critical illness, prolonged hospitalization, infection, organ failure, and death.

Acute pancreatitis occurs from premature activation of digestive enzymes within the pancreatic parenchyma leading to an autodigestive and inflammatory process. Evolution into a life-threatening systemic process begins when acinar cell injury leads to expression of endothelial adhesion molecules that further potentiates the inflammatory response. Local microcirculatory failure and ischemia–reperfusion injury ensue, with some patients developing systemic complications such as systemic inflammatory response syndrome (SIRS), acute respiratory distress syndrome, and multiorgan failure.

The most common causes of acute pancreatitis are gallstones and excess alcohol ingestion. These account for about 45% and 35% of cases, respectively.2,3 Hypertriglyceridemia accounts for up to 5% of cases. Other causes include hypercalcemia, autoimmune diseases, infections, medications, trauma, and complications after endoscopic retrograde cholangiopancreatography (ERCP) (Table 26.1). Controversial etiologies include pancreatic divisum and sphincter of Oddi dysfunction. Idiopathic pancreatitis occurs in up to 20% of patients, and by definition, the cause is not established by history, physical exam, routine laboratory tests, or imaging.

TABLE 26.1 Causes of Acute Pancreatitis

History and Physical Exam

The typical presentation includes a constant (as opposed to waxing and waning) upper abdominal pain located primarily in the epigastric area with radiation to the back. The onset of pain is rapid and typically reaches maximum intensity within 10 to 20 minutes. Pain that lasts only a few hours is unlikely to be pancreatitis. About 90% of patients will also complain of nausea and vomiting.

Mild pancreatitis may involve minimal abdominal tenderness without guarding. In severe disease, abdominal tenderness can be elicited with superficial palpation. Abdominal distention and reduced bowel sounds can occur secondary to ileus. Extravasation of hemorrhagic pancreatic exudate can lead to ecchymosis in one or both flanks (Turner sign) or the periumbilical regions (Cullen sign). Severe disease should be suspected with abnormal vital signs that can include fever, tachycardia, tachypnea, and hypotension. These signs represent a transition from localized retroperitoneal inflammation to one of systemic inflammation. Pleural effusions and mental status changes are also hallmarks of severe disease. The presence of jaundice may suggest an underlying alcoholism or choledocholithiasis.

Diagnostic Evaluation

Acute pancreatitis is diagnosed when two of the following three criteria are met: (1) characteristic abdominal pain, (2) serum amylase or lipase greater than three times the upper limit of normal, and, if needed, (3) radiologic imaging consistent with the diagnosis.4 Amylase and lipase are the most frequently used serum-based tests for pancreatitis. The most common source of amylase is not the pancreas, but salivary glands. In contrast, 90% of lipase is made from the pancreas, making it a more specific marker. Amylase rises within 6 to 24 hours of acute pancreatitis and peaks in 48 hours, normalizing in 3 to 7 days. Lipase has a longer half-life than amylase, with levels increasing within 4 to 8 hours, peaking at 24 hours, and falling over 8 to 14 days.5 The degree of elevation is not a marker of disease severity, and mild elevation of these serum markers—less than three times the upper limit of normal—is not specific for pancreatitis.

The use of computed tomography (CT) or magnetic resonance imaging (MRI) should only be considered when the first two diagnostic criteria are not met and (1) the pretest probability for pancreatitis remains high or (2) there is a high pretest probability for another abdominal process. Otherwise, CT and MRI have no role and may exacerbate renal injury from use of intravenous contrast.6 Such imaging can be considered 7 days later should the diagnosis remain uncertain or to assess disease severity and identify complications related to severe pancreatitis. Following clinical and laboratory parameters allows adequate initial assessment of disease severity. For patients with an established history of chronic pancreatitis or recent acute pancreatitis, imaging may be considered as part of the initial emergency department assessment for specific treatable complications of pancreatitis including, but not limited to, enlarging pseudocysts, arterial pseudoaneurysms, and/or new common bile stones.

Differential Diagnosis

The differential diagnosis includes biliary colic, acute cholecystitis, acute cholangitis, biliary dyskinesia, peptic ulcer disease, dyspepsia, acute mesenteric ischemic, and bowel obstruction. Nongastrointestinal disorders, including acute myocardial infarction, aortic dissection, pulmonary embolism, acute spinal disorders, and renal calculi, should also be considered.

Complications

The majority of cases (80% to 90%) of pancreatitis are mild and self-limiting; 10% of cases, however, develop severe disease, defined as the presence of significant fluid collections, infectious complications including abscess formation, infected necrosis, and/or extrapancreatic organ failure. These patients typically exhibit SIRS or sepsis physiology.

Fluid collections around the pancreas affect over half of patients. Most will resolve, but for those that persist, a fibrogenic anti-inflammatory response will lead to containment of these fluid collections, resulting in the formation of a pseudocyst. A pancreatic pseudocyst is a fluid collection that persists beyond 4 weeks. Other complications include infections (arising from pancreatic necrosis or within pseudocysts), thrombosis (splenic, superior mesenteric, and/or portal vein), arterial pseudoaneurysms, and gastrointestinal bleeding. The mortality rate for patients with severe pancreatitis is approximately 30%. Death within the first 2 weeks of illness is usually due to multiorgan failure. Death after 2 weeks typically stems from infection.

Management Guidelines

Once a diagnosis of acute pancreatitis is made, a risk stratification calculation should be performed. Clinical risk scoring systems, such as Ranson's and APACHE II, have traditionally been used. However, both are cumbersome and require 48 hours before a meaningful interpretation can be made. The Bedside Index for Severity in Acute Pancreatitis (BISAP) score is a newer validated scoring system that requires five data points of collection in the emergency room.7,8 This includes a blood urea nitrogen (BUN) >25 mg/dL, impaired mental status, SIRS, age >60, and the presence of a pleural effusion (Table26.2). The presence of three or more features at admission is associated with a 7- to 12-fold increase in organ failure. Such patients should be managed in the intensive care unit.

TABLE 26.2 Risk Stratification Scoring System for Severity of Acute Pancreatitis

Initial treatment is primarily supportive and includes adequate fluid resuscitation, pain control, and bowel rest.6 Fluid resuscitation is necessary to replace intravascular volume depletion that occurs from third-space losses. The amount of fluid should be calibrated to a urine output of 0.5 mL/kg/h. Initial resuscitation may begin with 1 to 2 L of normal saline within the first several hours of presentation. Early resuscitation appears to be clinically important in reducing downstream complications. In a large retrospective analysis of 434 patients with acute pancreatitis, early compared to late resuscitation was associated with less organ failure at 72 hours (5% vs. 10%), a lower rate of admission to the intensive care unit (6% vs. 17%), and a reduced length of hospital stay (8 vs. 11 days).9 After early initial bolus treatment of intravenous fluids, maintenance fluids should be titrated (up or down) to urine output. In severe disease, aggressive fluid resuscitation is important to maintain adequate vascular volume in the setting of SIRS or sepsis physiology.9 Pain can be controlled with intravenous short-acting narcotic pain medications. Nausea and vomiting can be controlled with antiemetic medications as needed.

Acute pancreatitis is a hypercatabolic state, and initiating nutrition at 48 hours from onset is important. In mild disease, patients can be started on an oral diet. For those with severe disease, enteral nutrition by nasojejunal feeding should be started. The current rationale for nasojejunal feeding is that bypassing the duodenum minimizes pancreatic stimulation. Enteral nutrition is superior to parenteral nutrition because it carries a lower risk for infectious complications and mortality.10

Documented infections associated with pancreatitis require prompt treatment with carbapenem-based antibiotics to ensure optimal penetration. Antibiotic prophylaxis, however, is not indicated.11,12Endoscopy is indicated for removing common bile duct stones and secondary cholangitis, and cholecystectomy should be planned during hospitalization for those with gallstone-related pancreatitis identified by right upper quadrant ultrasound.

For some patients who have no clinical or laboratory evidence to suggest severe disease (i.e., a BISAP score of 0, no other laboratory abnormalities), discharge from the emergency room can be considered. These patients should also have mild enough pain to be managed with PO pain medications, have the ability to consume liquids without vomiting, and be considered adequately competent and compliant to follow instructions to return to the emergency room for worsening signs and/or symptoms.

CHRONIC PANCREATITIS

Chronic pancreatitis is characterized by chronic inflammation and fibrosis with destruction of exocrine and endocrine cells. The incidence is estimated to be 6 cases per 100,000 people, and it affects about 0.04% of the US population.13 Although relatively uncommon, chronic pancreatitis is associated with a high level of morbidity and use of health care resources.14 In the United States, the most common cause is chronic alcohol use, accounting for nearly 70% of cases. It should be noted that only approximately 10% of heavy drinkers ever develop pancreatitis, suggesting an underlying genetic predisposition. In up to 20% of patients, the etiology is idiopathic. The remaining 10% are due to obstructive causes, metabolic derangements, autoimmune diseases, and hereditary disorders.15

History and Physical Exam

The most common complaint is chronic abdominal pain that is often associated with nausea and vomiting. In advanced disease, maldigestion develops from pancreatic exocrine insufficiency and presents as chronic diarrhea with unintentional weight loss. The stool is particularly odorous as most is maldigested fat (also known as steatorrhea). Other late findings include symptoms and signs of diabetes.

Mild abdominal tenderness with palpation may be elicited. An abdominal mass may represent a pseudocyst or splenomegaly. Splenomegaly occurs in the setting of splenic vein thrombosis—the result of chronic (or recurrent acute) pancreatic inflammation in proximity to the splenic vein—and can compromise venous return from the spleen with subsequent splenic engorgement and splenomegaly. As alcohol is the most common precipitating cause of pancreatitis, findings of liver disease including hepatomegaly, jaundice, ascites, and hepatic encephalopathy may also be observed. Because of chronic maldigestion of fat, these patients can be fat-soluble vitamin deficient (vitamins A, D, E, and K), and this can lead to related examination findings including peripheral neuropathy, fatigue, and signs of easy bruising and bleeding.

Diagnostic Evaluation

Diagnosis begins with an assessment of clinical symptoms, signs, and risk factors for chronic pancreatitis. CT can be used for diagnosing structural features associated with advanced disease including calcifications, atrophy, pancreatic duct dilation, and/or strictures. CT may also show common complications including pseudocysts, splenic vein thromboses, and inflammatory masses. Magnetic resonance cholangiopancreatography may be used to evaluate the pancreatic and biliary ducts without requiring ERCP. Endoscopic ultrasound currently offers the most sensitive imaging for diagnosis of chronic pancreatitis. Functional diagnostic tests for chronic pancreatitis include stool elastase, 72-hour fecal fat, and secretin stimulation test.

Differential Diagnosis

The differential diagnosis for chronic pancreatitis includes gastritis, dyspepsia, small bowel bacterial overgrowth, intestinal obstruction, neoplasms, mesenteric ischemia, biliary obstruction, celiac disease, inflammatory bowel disease, Zollinger-Ellison syndrome, and functional gut disorders such as irritable bowel syndrome.

Complications

Chronic pancreatitis is associated with a nearly fourfold increase in standardized mortality rate, which stems mostly from continued alcohol and tobacco abuse.16 Common complications include pseudocysts, gastrointestinal bleeding, bile duct obstruction, duodenal obstruction, and pancreatic fistula formation.

Management Guidelines

Management of suspected chronic pancreatitis with increased abdominal pain should include prompt and adequate analgesia (often requiring narcotic pain medications) and assessment of hydration and nutrition status.17 Evaluation of acute complications of chronic pancreatitis and nonpancreatic abdominal emergencies should also occur though with judicious use of imaging. When imaging suggests a main duct stricture, pancreatic ductal stones, and/or pseudocysts, an endoscopic intervention may be appropriate. During evaluation, patients should be counseled on smoking and alcohol cessation when applicable. Management of chronic pain and nutritional deficiencies from long-standing pancreatitis is primarily an outpatient issue, and a referral to gastroenterology is indicated.

CONCLUSION

Pancreatitis is a common presenting illness in the emergency department. Initial management centers on early aggressive fluid resuscitation, pain control, and bowel rest. All patients should be risk-stratified using a validated scoring system such as the BISAP to help direct appropriate disposition, including intensive care services. Advanced imaging, although generally not required, should be used when there is diagnostic uncertainty or when there is concern for the presence of associated complications including pseudocysts, arterial pseudoaneurysms, or common bile stones.

LITERATURE TABLE

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