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Acute Abdomen: Clinical Approach

Acute Abdomen: Clinical Approach
Adam R. Lancaster, DVM, DACVECC

A patient with an acute abdomen can typically be identified by the presence of acute abdominal pain. Other signs such as vomiting and diarrhea may also be present. General causes of abdominal pain include distention of a hollow viscus or organ capsule, ischemia, traction and inflammation. Any of these causes may progress to necrosis and loss of organ function. There are numerous causes of acute abdominal pain including intestinal obstruction, septic peritonitis, hemoabdomen, pancreatitis, uroabdomen, gallbladder disease or rupture, GDV and ileus. This is not an exhaustive list but rather some of the more common causes.

Once a patient has been identified as having acute abdominal pain, a primary survey of the patient should be completed. At this point, it is important to recognize and treat shock and other concurrent injuries quickly. Following initial stabilization, a thorough diagnostic evaluation should be performed to identify the underlying cause of the abdominal pain. A full physical examination should be performed and a careful and detailed abdominal palpation may occasionally locate the specific area of pain, such as a loop of intestine, the prostate, kidney or an abdominal mass. Frequently a specific area cannot be identified and additional diagnostics may need to be performed.

In-clinic diagnostics may include PCV/TS, BUN, blood smear, venous blood gas and electrolyte levels, abdominal radiographs, abdominal ultrasound, and abdominal fluid analysis and cytology. PCV/TS should be performed on all patients with acute abdomen. Increases in PCV/TS suggest dehydration. A high PCV with low or normal TS may indicate hemorrhagic gastroenteritis. Patients with bleeding into the abdomen may have low PCV, TS or both. In acute hemorrhage, the TS will often decrease before the PCV due to splenic contraction. If a patient is found to have a bloody fluid in the abdomen, the fluid PCV/TS should be compared to a peripheral sample.

Hypoglycemia is often associated with sepsis or non-septic systemic inflammatory response syndrome (SIRS). Identification of hypoglycemia warrants immediate treatment as well as an aggressive diagnostic plan to identify the underlying cause. A venous blood gas may reveal acidosis or electrolyte abnormalities. Many cases of acidosis are from lactic acidosis from hypoperfusion and are best treated with fluid resuscitation. The presence of hyperkalemia may indicate kidney dysfunction or bladder rupture among other things.

Abdominal radiographs are indicated for any animal with abdominal pain. Any number of radiographic abnormalities may be presented based on the underlying cause. Specific abnormalities to look for include evidence of peritoneal or retroperitoneal effusion, free gas in the abdomen, a mass effect or GI distention (either generalized or segmental). Peritoneal effusion typically causes a loss of serosal detail or may be more of a “ground glass” appearance, especially in the cranial abdomen associated with pancreatitis. Retroperitoneal effusion may occur secondary to inflammatory diseases of the kidney or bleeding of renal or adrenal masses. Retroperitoneal effusion occurs as “streaky” areas typically just caudal to the kidneys in the retroperitoneum. Free gas in the abdomen can be identified by pockets of gas that do not coincide with a gas-containing structure. This is most easily seen between the stomach or liver and the diaphragm. You may also see two walls of the stomach indicating gas on the inside and outside of the stomach. The presence of free gas indicates rupture of a hollow viscus or the presence of gas-producing bacteria within the abdomen. The presence of free gas in the abdomen is a clear indication for abdominal exploratory.

Segmental gaseous or fluid distention of the small bowel suggests intestinal obstruction. Generalized small bowel distention suggests small intestinal ileus or a distal GI obstruction. Localized small bowel distention is not a definitive finding for obstruction but should prompt further investigation if an obvious foreign body is not evident. This may include repeat radiographs, abdominal ultrasound or an upper GI contrast study.

An abdominal focused assessment with sonography for trauma (AFAST) is a useful diagnostic tool for all patients with severe abdominal pain. It allows for rapid identification of peritoneal effusion and increases the sensitivity of abdominocentesis for fluid evaluation. If fluid is identified an attempt to obtain a sample for analysis and cytology should be made. Generally speaking, effusions can be grouped into one of three categories:

Fluid Type Protein level Cell Count Common Causes
Transudate TP <2.5 g/dl <500 cells/µl Hypoalbuminemia, portal venous obstruction
Modified transudate TP 2.5-5.0 g/dl 300-5500 cells/µl Many including CHF, liver disease, neoplasia
Exudate TP >3 g/dl 5000-7000 cells/µl Septic peritonitis, pancreatitis, bile peritonitis

Other specific types of effusion may also be diagnosed based on various chemistries that can be performed on the fluid. These include septic peritonitis, bile peritonitis and uroabdomen. The chart below summarizes some of these findings:

Type Tests Other
Septic peritonitis Fluid Lactate >2 mmol/L higher than bloodFluid glucose >20 mg/dl lower than blood Caution: very inflammatory exudates may mimic septic peritonitisConfirm via presence of intracellular bacteria on cytology
Uroabdomen Fluid creatinine >2x the blood creatinineFluid potassium >1.4x the blood potassium
Bile peritonitis Fluid bilirubin >2x the blood bilirubin May also see bile crystals or intracellular bile on cytology

Cytology should also be performed on all samples to look for evidence of bacteria or neoplastic cells.

Treatment

Generally speaking treatment will be based on the underlying condition and may be medical or surgical management. Surgical management is required in cases with confirmed (or highly suspected) septic peritonitis, bile peritonitis, GDV, mesenteric torsion, persistent abdominal hemorrhage or small intestinal obstruction. Uroperitoneum is often managed surgically but may be medically managed in some cases. Fluid therapy, pain medications, antibiotics and supportive care and monitoring make up the bulk of management of these cases.