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. Additionally, 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 the progression of clinical signs since the problem began.

The progression of the clinical signs can also 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 some point. An animal that has a chronic problem and has deteriorated 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 may occasionally locate the specific area of pain, (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 clinical pathology, abdominal imaging, abdominocentesis, diagnostic peritoneal lavage, 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 in rapidly providing a relatively well-rounded metabolic assessment of the patient and can sometimes point toward the underlying cause.

The PCV and TS should always be assessed together. Parallel increases in both 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 is often associated with protein loss from peritonitis. Hemorrhagic gastroenteritis (HGE) is associated with a very high PCV (60% to 90%) and normal or low TS. A dog with an acute onset of vomiting and bloody diarrhea and these changes in PCV and TS make HE the most likely diagnosis.

Hemorrhage most commonly results in a parallel decrease in the PCV and TS, although in animals with acute hemorrhage these changes may not initially be recognized until intravenous fluid therapy has been provided. Acute hemorrhage in dogs can sometimes be recognized by 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 acute hemorrhage in dogs with acute conditions of the abdomen are splenic rupture (usually secondary to neoplasia) and severe hemorrhage from gastrointestinal (GI) ulceration. In cats with an acute condition of the abdomen, the most common cause of acute hemorrhage is abdominal hemorrhage secondary to hepatic neoplasia.¹

Blood glucose measurement is easily and rapidly obtained by dipstick methods and a glucometer. Increased blood glucose in a dog with an acute condition of the abdomen may be associated with diabetes or transient diabetes associated with severe pancreatitis. Blood glucose is rarely quite high 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 it is clear that 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. Hyperglycemia in cats is not as useful diagnostically as it is in dogs.

Decreased blood glucose is often associated with sepsis and warrants an aggressive approach to find the underlying cause of the acute abdominal pain, particularly if septic peritonitis might 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 may also be a cause of low blood glucose levels.

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 may also 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 122, Blood Film Evaluation). The smear should first 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; each platelet in a monolayer field is equivalent to approximately 15,000 platelets/μl. If there are more than 4 to 5 platelets per field, it is unlikely that the bleeding is strictly due to thrombocytopenia. Most patients with spontaneous bleeding due to thrombocytopenia have less than 2 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 are often 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. 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 due to GI foreign bodies may have a hypochloremic metabolic alkalosis as well as hypokalemia and hyponatremia.² Often, a metabolic acidosis is also present due to severe diarrhea or lactic acidosis from hypoperfusion.²