The term "acute abdomen" is commonly used to refer to patients presenting with a rapid onset of acute abdominal pain. However, a more encompassing definition that includes any intraabdominal disease process leading to an acute onset of severe clinical signs is preferable as not all life threatening intraabdominal conditions are painful. Also, the demonstration of clinical signs associated with abdominal pain such as postural changes or vocalization may not occur in a depressed or obtunded patient. Cats are less likely than dogs to show clinical signs that are associated with abdominal discomfort.

There are a large number of causes of an acute abdomen many of which need urgent surgical intervention. The patient presenting with an acute abdomen will often also be showing systemic (often cardiovascular or metabolic) abnormalities associated with the underlying disease process.

Therefore the approach to these patients has to combine two main areas:

 Stabilisation of the patient with identification and treatment of secondary systemic abnormalities - this should be started as soon as possible after admission of the animal to the clinic.

 Diagnostic evaluation to identify the primary cause and most especially whether it is a problem that requires urgent surgery following initial stabilization to provide the best chance of a successful outcome.

As with all patients, evaluation should start with a history and full physical examination focussing first on the major body systems (cardiovascular, respiratory and neurological). An IV catheter should be placed and blood should be obtained for a basic database.

Once this has occurred and any immediately life threatening problems such as hypovolaemia are being addressed, further diagnostic evaluation can continue.

History

The history of a patient presenting with an acute abdomen is often vague with the owners reporting nonspecific signs such as lethargy, inappetence, vomiting or diarrhoea. In many cases the animal is simply found in a collapsed state. However sometimes, historical information may be extremely suggestive of the underlying cause for example witnessed ingestion of a foreign body.

Physical Examination (PE)

Cardiovascular system: Many patients with acute abdomen will have signs of cardiovascular instability secondary to hypovolaemic or distributive shock. This should be addressed immediately whilst the rest of the diagnostic evaluation continues. Discordant findings such as an inappropriately slow heart rate may also be helpful diagnostically by prompting a search for an underlying cause such as hyperkalaemia.

Respiratory system: Many animals with acute abdomen are tachypnoeic secondary to pain or as compensation for a metabolic acidosis. Also, animals that are depressed and vomiting are at risk of developing aspiration pneumonia which may be detected commonly as crackles audible in the cranioventral lung fields. If in doubt as to the significance of any findings related to the respiratory tract, oxygen supplementation is warranted until it is safe for the animal to undergo imaging of the chest.

Neurological system: Some animals with acute abdomen are profoundly depressed and the only stimulus they respond to is palpation of their abdomen. This degree of depression may well be consistent with the severity of the underlying problem. However, other factors such as the presence of hypoglycaemia should be assessed as correction of these may improve the animal's mentation. Abdominal pain may be easily confused with spinal pain by both owners and vets - however animals with spinal disease rarely have serious abnormalities of the other major body systems.

Temperature

Animals presenting with acute abdomen may have low, normal or high temperatures and unfortunately this is not helpful diagnostically. Cats with septic abdomens particularly are commonly markedly hypothermic.

Examination of the Abdomen

This should be performed after the rest of the examination so any pain/distress caused does not interfere with the rest of the assessment. The following should be included:

 External assessment for any generalized or localized distension or deformity that may be associated with herniation/local masses, etc.

 If abdominal distension is present, percussion of the abdomen to detect a fluid thrill or tympany.

 Gentle superficial palpation.

 If permitted, deeper palpation to localize the source of pain. This may help with prioritizing the differential list, e.g., cranial abdominal pain may be associated with pancreatitis.

Intravenous Catheter Placement and Emergency Blood Database

Almost invariably, patients with an acute abdomen will require some form of fluid therapy or intravenous drug administration, thus intravenous access should be obtained as soon as possible. This also has the advantage that a small amount of blood can be easily obtained for an emergency database. The initial blood tests performed will be variable depending on the facilities available but it is recommended that they should include packed cell volume and total solids, blood glucose and evaluation for blood urea nitrogen. If available, electrolyte and venous blood gas analysis should also be performed. These values are important as a baseline prior to fluid therapy. They also may be helpful diagnostically for example revealing hypoglycaemia in septic patients or hyperkalaemia in patients with a uroabdomen.

Further Diagnostic Tests

Once stabilization is underway, further diagnostic tests can be carried out with the aim of identifying the underlying cause so definitive therapy can be instituted. In some cases it is not possible to make a definitive diagnosis without advanced imaging techniques and it is more important in these patients to determine if urgent exploratory laparotomy is necessary. Cases where urgent surgery is indicated whether or not a complete diagnosis has been reached include septic peritonitis, uroabdomen and bile peritonitis.

Clinical Pathology

Haematology and particularly blood smear examination may be useful in suggesting a diagnosis (e.g., haemoabdomen with anaemia and septic abdomen with neutrophil changes). Along with clotting tests it can also be helpful in identifying DIC (disseminated intravascular coagulation). Biochemistry panels may again help with diagnosis (for example azotaemia with uroabdomen) but is rarely diagnostic. Use of pancreatic specific lipase tests may aid the diagnosis of pancreatitis although it is worth remembering that any cause of generalised peritonitis (including septic peritonitis) will commonly lead to secondary pancreatic inflammation.

Diagnostic Imaging

Abdominal imaging should be performed in most cases of acute abdomen as soon as the patient is sufficiently stable.

Plain Radiography

As the most familiar and readily available technique, plain radiographs are often the most common modality employed. Two orthogonal views should be taken in most cases except where to do so may place the animal at risk (e.g., concurrent respiratory compromise). Plain radiography is the technique of choice for the identification of small intestinal obstruction. It is less useful in patients with large volumes of intraabdominal fluid due to the loss of intraabdominal contrast. It is also important to assess for the presence of free gas (often seen just caudal to the diaphragm) as this is an indication for urgent surgery.

Contrast Radiography

This may be necessary to obtain a diagnosis in patients with partial gastrointestinal obstructions. Even if gastrointestinal perforation is a concern, I would still recommend the use of barium as the contrast agent due to the superior nature of the studies - if leakage into the peritoneal cavity occurs, it is an indication for urgent surgery and the peritoneal cavity can be lavaged. Occasionally contrast studies of the urinary tract may be necessary if a uroabdomen is suspected.

Ultrasound

Skilled operators can determine a tremendous amount of information from an abdominal ultrasound examination. However, ultrasound is still useful in the evaluation of the acute abdomen even in the hands of a relatively unskilled operator. Its prime role in this situation is to allow the identification and retrieval of abdominal fluid even if only relatively small quantities are present. The best places to look for fluid are around the liver lobes and at the cranial pole of the bladder.

Abdominal Fluid Analysis

Analysis of any free abdominal fluid is arguably the most important part of the diagnostic evaluation of the patient with an acute abdomen. In many instances, notably septic peritonitis, it can provide confirmatory evidence that urgent surgery is needed.

In patients with large volumes of fluid, blind abdominocentesis can be performed. Insertion of the needle into the right cranial quadrant is recommended as this minimizes the chance of puncture of the spleen or urinary bladder. If small volumes of fluid are present, ultrasound guidance can be used to help obtain the fluid or a diagnostic peritoneal lavage (DPL) can be carried out.

Although full analysis and characterization of the abdominal fluid (cell count, protein levels, cytological analysis) is ideal, this often requires that the fluid is sent to an outside laboratory. In an emergency patient, the delay in receiving the results may make the difference between a successful and unsuccessful outcome. Many decisions as to whether the patient needs urgent surgery can be made using equipment available in most practices. In house evaluation should include measurement of PCV (if fluid appears haemorrhagic), cytological evaluation and occasionally measurement of fluid glucose (to aid in diagnosing septic peritonitis), BUN/creatinine/potassium (to diagnose uroabdomen) and/or bilirubin (to diagnose bile peritonitis).

References

1.  Bonczynski JJ, Ludwig LL, Barton LJ, Loar A, Peterson ME. Comparison of peritoneal fluid and peripheral blood pH, bicarbonate, glucose and lactate concentration as a diagnostic tool for septic peritonitis in dogs and cats. Veterinary Surgery. 2003;32:161–166.

2.  Connally HE. Cytology and fluid analysis of the acute abdomen. Clinical Techniques in Small Animal Practice. 2003;18:39–44.

3.  Crowe DT. Diagnostic abdominal paracentesis techniques: clinical evaluation in 129 dogs and cats. Journal of the American Animal Hospital Association. 1984;20:223–230.

4.  King LG. Postoperative complications and prognostic indicators in dogs and cats with septic peritonitis: 23 cases (1989–1992). Journal of the American Veterinary Medical Association. 1994;204:407–414.