Chapter 112 - Acute Abdominal Pain PDF

PART XII INTRAABDOMINAL DISORDERS CHAPTER 112 ACUTE ABDOMINAL PAIN Kenneth J. Drobatz, DVM, MSCE, DACVIM, DACVECC KEY POINTS The principles of emergency and critical care should be applied initially to any patient with a painful abdomen (stabilize respiratory and cardiovascular systems). Any portion...

PART XII INTRAABDOMINAL DISORDERS CHAPTER 112 ACUTE ABDOMINAL PAIN Kenneth J. Drobatz, DVM, MSCE, DACVIM, DACVECC KEY POINTS The principles of emergency and critical care should be applied initially to any patient with a painful abdomen (stabilize respiratory and cardiovascular systems). Any portion of the abdomen or lumbar and sacral spine could be a source of apparent abdominal pain. The general causes of abdominal pain include distention of a hollow viscus or organ capsule, ischemia, traction, and inflammation secondary to a variety of causes. If the underlying cause of abdominal pain can be identified quickly and treated, the occurrence of more serious complications such as septic peritonitis or systemic inflammatory response syndrome and multiorgan dysfunction syndrome can be minimized. Animals with an acute condition of the abdomen are characterized primarily as having abdominal pain. Vomiting and/or diarrhea often accompany this abdominal pain. As with any patient suffering from an emergent condition, the basic principles of stabilization of the four most important body systems (respiratory, cardiovascular, neurologic, and renal systems) should be applied when initially assessing and stabilizing these patients (see Chapter 1). After initial stabilization, a thorough diagnostic evaluation should be performed to determine the underlying cause as soon as possible so that definitive care can be provided. The general causes of abdominal pain include distention of a hollow viscus or organ capsule, ischemia, traction, and inflammation secondary to a variety of causes. If left untreated, any of these causes could result in necrosis of tissue and loss of function; therefore the underlying cause must be identified quickly. Prompt identification and treatment of the underlying abnormality minimize the occurrence of more serious complications, such as septic peritonitis or systemic inflammatory response syndrome and multiorgan dysfunction syndrome. DIAGNOSTIC EVALUATION The diagnostic evaluation of animals with abdominal pain begins with signalment, medical history, and physical examination, followed by a complete blood count, biochemical profile, urinalysis, radiographs, abdominal ultrasound, radiographic contrast studies, abdominocentesis, peritoneal lavage, response to treatment, and/or exploratory laparotomy. The list of specific causes of abdominal pain is extensive because any portion of the abdomen could be a source of pain. Intervertebral disk disease also may simulate a painful abdomen, but direct palpation of the area of spinal pain usually elicits a more diagnostic response. Signalment and History Signalment can be a clue to the cause of abdominal pain or vomiting. For example, young animals commonly swallow foreign bodies or contract infectious diseases. An older, intact male dog may have a painful prostate. Abdominal pain in an intact female dog with a pyometra should raise concern of a possible uterine rupture and septic peritonitis. Young adult German Shepherd Dogs with pancreatic exocrine insufficiency are predisposed to mesenteric volvulus. String foreign bodies are common in cats. Acute pancreatitis commonly occurs in middle-aged, obese female dogs. An accurate history may be the most important diagnostic clue in the assessment of animals with acute abdominal pain. Questions should include the potential for exposure to toxins or dietary indiscretion. In addition, is ingestion of a foreign body a possibility? Are any other animals affected? Has the animal had any major medical problems in the past? Is the patient currently receiving any medications, including over-the-counter drugs such as aspirin or other nonsteroidal antiinflammatory medications? Is there a possibility of trauma? Could the patient have been exposed to any other animals? Is the patient current on all vaccinations? The clinician should determine when the animal’s condition was last normal, what the first abnormal sign was, and how clinical signs have progressed since the problem began. The progression of the clinical signs also can help determine the urgency of diagnosing the underlying cause. Chronic abdominal pain that has remained relatively static in its progression is not usually an emergency, although the problem could become an emergency at any time. An animal that has a chronic problem and deteriorates rapidly, or an animal with an acute problem that is or is not deteriorating rapidly, warrants a more aggressive and expedient approach to define the underlying cause of the painful abdomen. Physical Examination A full physical examination should be performed, with initial attention given to the cardiovascular, respiratory, central nervous, and renal systems, as for any critically ill patient. More specifically for the animal with acute abdominal pain, a careful and detailed abdominal palpation occasionally may locate the specific area of pain (e.g., a loop of intestine, the prostate, or the kidneys), and this may help in the diagnostic approach. Many times, a specific area cannot be identified and diagnosing the underlying cause requires assimilation of information from a variety of diagnostic tests; these include 597 598 PART XII INTRAABDOMINAL DISORDERS clinical pathology, abdominal imaging, abdominocentesis, diagnostic peritoneal lavage (see Chapter 200), response to treatment, and/or exploratory laparotomy. Emergency Clinical Pathology An extended database that includes a packed cell volume (PCV), total solids (TS), glucose, dipstick blood urea nitrogen (BUN), blood smear, venous blood gas, and electrolyte levels (including sodium, potassium, chloride, and ionized calcium) helps to provide rapidly a relatively well-rounded metabolic assessment of the patient and sometimes can point toward the underlying cause. The PCV and TS always should be assessed together. Parallel increases in both (hemoconcentration) suggest dehydration. A normal or increased PCV with a normal to low TS indicates protein loss from the vasculature. In animals with an acute condition of the abdomen, this clinicopathologic picture often is associated with protein loss from peritonitis. Hemorrhagic gastroenteritis (HGE) is associated with a high PCV (60% to 90%) and normal or low TS in dogs presenting with an acute onset of vomiting and bloody diarrhea. Hemorrhage most commonly results in a parallel decrease in the PCV and TS, although in animals with acute hemorrhage these changes may not be recognized initially until intravenous fluid therapy has been provided. Acute hemorrhage in dogs can lead to a normal or increased PCV and normal or decreased TS. Splenic contraction in dogs makes TS a more sensitive indicator of acute blood loss than PCV. The most common causes of hemorrhage in dogs with acute conditions of the abdomen are splenic rupture (usually secondary to neoplasia) and severe hemorrhage from gastrointestinal (GI) ulceration. The most common causes of hemoabdomen in cats are nonneoplastic conditions (54%) and abdominal neoplasia (46%). Blood glucose measurement is obtained easily and rapidly by dipstick methods and a glucometer. Increased blood glucose in a dog with an acute condition of the abdomen may be caused by diabetes or transient diabetes associated with severe pancreatitis. Blood glucose is rarely more than 200 mg/dl in dogs with extreme hypovolemia secondary to severe abdominal or GI hemorrhage, presumably a result of the effects of catecholamines on glycogenolysis and gluconeogenesis. Physical examination findings of extremely poor tissue perfusion are evident, and the animal may die imminently if the hypovolemia is not corrected rapidly. Increased blood glucose levels in cats may be associated with stress or diabetes; therefore hyperglycemia in cats is not as useful diagnostically as it is in dogs. Decreased blood glucose often is associated with sepsis and warrants an aggressive approach to find the underlying cause of the acute abdominal pain, particularly if septic peritonitis may be present. Rarely, extremely low blood glucose levels may occur as a result of sepsis, but more typically it falls in the 40 to 60 mg/dl range. Hypoadrenocorticism also may be a cause of low blood glucose levels (see Chapter 66). Dipstick BUN provides an estimate of azotemia in an animal with an acute condition of the abdomen. Increased BUN may be due to prerenal, renal, or postrenal causes. Increased BUN also may be noted in animals with acute abdominal pain caused by pyelonephritis or ureteral or urethral obstruction. Disproportionately high BUN compared with creatinine levels should prompt the clinician to rule out GI hemorrhage. Reliable assessment of a blood smear depends on a good-quality sample. All cell lines should be evaluated systematically, including the red blood cells, white blood cells, and platelets. The average number of platelets per monolayer field under oil immersion should be estimated (see Chapter 196). The smear first should be screened at low power to search for platelet clumps that may result in a falsely low platelet estimate before evaluating the counting area under oil immersion. In normal dogs and cats, there are 8 to 15 platelets per oil immersion field (100×); each platelet in a monolayer field is equivalent to approximately 15,000 platelets/µl. If there are more than two to three platelets per field, it is unlikely that the bleeding is strictly the result of thrombocytopenia. Most patients with spontaneous bleeding resulting from thrombocytopenia have less than two platelets per oil immersion field. A decreased number of platelets is one of the most consistent findings in animals with disseminated intravascular coagulation (DIC). Animals with acute conditions of the abdomen may have DIC secondary to systemic inflammation or massive peritoneal inflammation. Red blood cell morphology should be examined. Anisocytosis, macrocytosis, and polychromasia indicate regeneration. Schistocytes or fragments of red blood cells suggest DIC. Heinz bodies often are seen in systemically ill cats. The smear should be scanned at lower power to get an estimate of the number of white blood cells and then at higher power to assess the character of the white blood cells. Leukocytosis with a mature neutrophilia suggests an inflammatory or infectious process, although excessive numbers of any cell line may indicate neoplasia. Band cells indicate a more severe inflammatory or infectious process. The absence of a leukocytosis or a left shift does not rule out an inflammatory or infectious process. Leukopenia can be due to decreased production or sequestration of white blood cells, a viral infection such as parvovirus, or immunosuppressive drugs. A venous blood gas provides an evaluation of the metabolic acid-base status. Animals that have severe vomiting because of GI foreign bodies may have a hypochloremic metabolic alkalosis as well as hypokalemia and hyponatremia.1 Often, a metabolic acidosis is also present because of severe diarrhea or lactic acidosis from hypoperfusion.1 Abdominal Radiographs A full description of all radiographic and ultrasonographic findings in an animal with acute abdominal pain is beyond the scope of this chapter, but specific points regarding plain abdominal radiographs are provided. Abdominal radiographs should be obtained in any animal with abdominal pain. A systematic and detailed review of all abdominal and extraabdominal structures should be performed. All organs in the abdominal cavity should be evaluated for density, shape, size, and location. Abnormalities in any organ may help localize the cause of the abdominal pain. Extraabdominal structures should be examined for completeness of evaluation and further diagnostic clues. The retroperitoneal space should be assessed as well. Loss of detail of the kidneys, a “streaky” appearance, or distention of the retroperitoneal space suggests fluid accumulation, a space-occupying mass, or sublumbar lymphadenopathy. The structures that make up the abdominal compartment “walls” should be assessed carefully for integrity to rule out herniation or rupture. Evidence of free gas in the peritoneum without prior abdominocentesis or recent abdominal surgery suggests intestinal perforation or the presence of gas-forming organisms within the abdominal cavity. Free gas is detected most commonly between the stomach or liver and the diaphragm on the lateral radiograph. A horizontal beam radiograph with the animal in left lateral recumbency and focused at the least dependent area can increase the sensitivity for identifying free gas in the peritoneal space. A large volume of free gas in the peritoneum often is associated with pneumocystography of a ruptured urinary bladder, a ruptured vagina, recent abdominal surgery, ruptured gastric dilatation-volvulus, pneumoperitoneography, or extension of a pneumomediastinum. Pneumomediastinum is CHAPTER 112 associated most often with pneumoretroperitoneum, although on rare occasions, pneumoperitoneum can occur. A small volume of free gas in the peritoneal space is associated most often with rupture of the GI tract or infection with a gas-forming organism. Gas in the gallbladder wall, liver, or spleen is associated most often with a Clostridia spp. infection. Segmental gaseous or fluid distention of the small bowel suggests an intestinal obstruction. The normal diameter of the small intestine in the dog is approximately two to three times the width of a rib, or less than the width of an intercostal space. In addition, all of the small bowel loops should have a similar diameter, and it is abnormal for one segment to be 50% larger than other portions. Feline small intestines should not exceed twice the height of the central portion of L4 vertebral body, or 12 mm.2 Generalized small bowel distention suggests generalized small bowel ileus or a distal GI obstruction. Localized small bowel distention is not always a definitive finding for intestinal obstruction but should prompt further investigation if an obvious foreign body is not evident. One option is to repeat plain radiographs 3 hours later. If the bowel remains distended in the same area, this suggests a bowel obstruction. A more definitive diagnosis for intestinal obstruction can be obtained by performing an upper GI positive contrast study with barium. Severe intraperitoneal inflammation and granuloma formation can occur if barium leakage occurs as a result of a bowel rupture. This problem can be minimized if abdominal surgery with peritoneal lavage is done immediately, as indicated after the diagnosis of small bowel rupture. Therefore upper GI contrast study with barium is not contraindicated if the clinician is attempting to diagnose GI perforation. Abdominal ultrasound by an experienced, trained ultrasonographer is becoming the standard for ruling out GI obstruction and has been found to be more sensitive and specific than abdominal radiography.3 Loss of abdominal detail on plain abdominal radiographs may be due to lack of fat in the abdomen (puppies or very thin animals), free abdominal fluid, pancreatitis, large mass(es), or carcinomatosis. Abdominal Fluid Analysis Obtaining free abdominal fluid for analysis is important if it is present in an animal with a painful abdomen. Abdominal fluid analysis can help rule out septic peritonitis and also may provide a diagnosis or help direct further diagnostic investigation. Fluid may be obtained by abdominocentesis (blindly or by ultrasound guidance). If fluid cannot be obtained but still is suspected to be present, a diagnostic peritoneal lavage is indicated (see Chapter 200). Free abdominal fluid should be analyzed for creatinine and/or potassium and compared with peripheral blood concentrations if urinary tract leakage is suspected (see Chapter 122). Creatinine and potassium are higher in the abdominal fluid if a uroperitoneum is present.4,5 Measurement of fluid glucose and lactate concentrations may be helpful in diagnosing a bacterial peritonitis. These measurements can be compared with simultaneously collected peripheral blood glucose and lactate concentrations. A glucose gradient greater than 20 mg/dl of peripheral blood to abdominal fluid was 100% sensitive and 100% specific in diagnosing septic peritonitis in dogs (86% sensitive and 100% specific in cats) in one study. In addition, Acute Abdominal Pain a blood-to-abdominal fluid lactate gradient of 2 mmol/L or more was also 100% sensitive and 100% specific in diagnosing septic peritonitis in dogs.6 If bile peritonitis is suspected, abdominal bilirubin concentration often is higher than simultaneously collected blood bilirubin concentration.7 A pure transudate is grossly clear and is characterized by a total protein less than 2.5 g/dl and low cell count (fewer than 500 cells/µl). Of the few cells present, most are either nondegenerate neutrophils or reactive mesothelial cells. The most common causes of a pure transudate in the abdomen include hypoalbuminemia and portal venous obstruction. A modified transudate is usually serous to serosanguineous, with a total protein level between 2.5 and 5 g/dl and a moderate total cell count (300 to 5500 cells/µl). Depending on the cause, there may be variable numbers of red blood cells, nondegenerate neutrophils, mesothelial cells, macrophages, and lymphocytes. This type of effusion often is due to passive congestion of the liver and viscera and impaired drainage of the lymphatic vessels. The most common causes include right-sided heart failure, dirofilariasis, neoplasia, and liver disease. An exudate is often cloudy and has a total protein concentration greater than 3 g/dl and a cell count greater than 5000 to 7000 cells/µl. The predominant cell type is usually the neutrophil, although numerous other cells may be present as well. This is the most common type of free abdominal fluid associated with acute abdominal pain. Exudates can be septic or nonseptic, but making this classification can be challenging at times. Septic exudates are characterized by the presence of intracellular and extracellular bacteria. In most animals with septic peritonitis, cytologic evidence of bacteria can be found, particularly if the clinician has patience and explores numerous microscopic fields and examines the cytology of the sediment of the abdominal fluid. Rarely, septic peritonitis can be present despite the absence of cytologic evidence of bacteria in the fluid. Table 112-1 summarizes some objective diagnostics in the patient with an acute abdomen. SURGICAL VERSUS MEDICAL MANAGEMENT One of the most challenging decisions regarding animals with acute abdominal pain is deciding whether immediate surgery is indicated. Clear indications for immediate surgery include abdominal wall perforation, septic peritonitis, persistent abdominal hemorrhage, intestinal obstruction, intestinal foreign body causing pain or bowel obstruction, uroperitoneum, free abdominal gas (not associated with previous surgery, pneumomediastinum, or invasive procedures), abdominal abscess, ischemic bowel, gastric dilation volvulus, mesenteric volvulus, and bile peritonitis. Without these clear indications, the clinician must use all information that can be obtained quickly to determine if exploratory surgery is warranted, including signalment, history, physical examination, clinicopathology, imaging modalities, response to medical therapy, informed discussion with the owner, and clinical intuition. Using all this information, the clinician can make the correct decision whether to perform exploratory surgery. 599 600 PART XII INTRAABDOMINAL DISORDERS Table 112-1 Summary of Some Objective Diagnostics Used in the Approach to the Acute Abdomen* Test Diagnostic Criteria Sensitivity Specificity Blood glucose minus peritoneal glucose for diagnosis of septic peritonitis >20 mg/dl Dogs: 100% Cats: 86% Dogs: 100% Cats: 100% Peritoneal fluid lactate minus blood lactate for diagnosis of septic peritonitis >2.0 mmol/L Dogs: 100% Cats: not reported Dogs: 100% Cats: not reported Dogs abdominal ultrasound: small intestinal lumen dilation Jejunal luminal diameter of >1.5 cm with normal wall layering Not reported but should aggressively investigate for intestinal obstruction Not reported but luminal diameter not dilated then intestinal obstruction not likely Fluid to blood potassium ratio for diagnosis of uroabdomen Dogs: ratio of 1.4 : 1 Cats: ratio 1.9 : 1 Dogs: 100% Cats: unknown Not reported but considered diagnostic for uroabdomen Fluid to blood creatinine ratio for diagnosis of uroabdomen Dogs: ratio 2 : 1 Cats: ratio 2 : 1 Dogs: 86% Cats: unknown Dogs: 100% Cats: unknown Fluid to blood bilirubin ratio for diagnosis of bile peritonitis (also may see bile pigment/crystals in abdominal fluid) >2 : 1 Dogs: 100% Cats: unknown Not reported Dogs: ratio of maximal small intestinal diameter to the narrowest width of L5 on lateral radiograph Ratio > 1.6 Not reported but suggestive of small intestinal obstruction. Not reported but suggestive of small intestinal obstruction Cats: ratio of maximal small intestinal diameter to the height of cranial endplate of L2 Ratio > 2.0 Not reported but suggestive of small intestinal obstruction. Not reported but suggestive of small intestinal obstruction Specific cPLI (serum) for diagnosis of pancreatitis 400 mcg/L: pancreatitis likely 82% with severe pancreatitis, 63.6% with less severe pancreatitis 96.8% Specific fPLI (serum) for diagnosis of pancreatitis 5.3 mcg/L: pancreatitis likely 67% in all cats with pancreatitis and 100% in cats with moderate to severe pancreatitis 100% SNAP cPLI (serum) for diagnosis of pancreatitis Spot intensity test 92%-94% 71%-78% SNAP fPLI (serum) for diagnosis of pancreatitis Spot intensity test 79% 80% *Confidence intervals for the diagnostic characteristics (sensitivity and specificity) have not been reported. Therefore the numbers are point estimates and should be considered to have some degree of variation. REFERENCES 1. Boag AK, Coe RJ, Martinez TA, et al: Acid-base and electrolyte abnormalities in dogs with gastrointestinal foreign bodies, J Vet Intern Med 19:816, 2005. 2. Owens JM, Biery DN: Radiographic interpretation for the small animal clinician, ed 2, Media, Penn, 1999, Williams & Wilkins. 3. Sharma A, Thompson S, Scrivani PV, et al: Comparison of radiography and ultrasonography for diagnosing small-intestinal mechanical obstruction in vomiting dogs, Vet Radiol Ultras 52(3):248-255, 2011. 4. Schmiedt C, Tobias KM, Otto CM: Evaluation of abdominal fluid: peripheral blood creatinine and potassium ratios for diagnosis of uroperitoneum in dogs, J Vet Emerg Crit Care 11:4, 275, 2001. 5. Aumann M, Worth LT, Drobatz KJ: Uroperitoneum in cats: 26 cases (19861995), J Am Anim Hosp Assoc 34:315, 1998. 6. Bonczynski JJ, Ludwig LL, Barton BJ, et al: Comparison of peritoneal fluid and peripheral blood pH, bicarbonate, glucose, and lactate concentration as a diagnostic tool for septic peritonitis in dogs and cats, Vet Surg 32:161, 2003. 7. Ludwig LL, McLoughlin MA, Graves TK, et al: Surgical treatment of bile peritonitis in 24 dogs and 2 cats: a retrospective study (1987-1994), Vet Surg 26:90, 1997.