Presentation and History
The presenting clinical signs in acute abdomen cases vary enormously and depend on underlying pathology, the duration of the process and the temperament of the patient. Some cases will present with vague, non-specific symptoms such as anorexia, lethargy and vomiting. In some instances, such as rapid intra-abdominal bleeds, the first sign the owner notices may simply be collapse. Other cases may have more obviously specific signs such as abdominal enlargement due to gas distension, or accumulation of fluid effusions.
The history of any acute abdomen case is very important. Start by gaining information on the signalment of the animal, ask about the age, sex, whether neutered and the breed. This information may make some differential diagnoses more likely than others; pancreatitis is more common in some breeds of dogs, parvovirus is more likely in young unvaccinated puppies and pyometra can only occur in unneutered females.
The triaging nurse should ask about vaccination status, worming, existing medical problems and current medication, possible foreign body ingestion and access to toxins or human medication.
Clinical Examination
On initial presentation a rapid primary examination should be performed, targeting the major body systems, as for any emergency patient. The examination should focus on the respiratory system, the cardiovascular system and neurological deficits before moving on to an examination of the abdomen.
The initial examination of the emergency patient is covered in Chapter 1, but points to consider in the acute abdomen patient are as follows.
Respiratory System
Animals may have tachypnoea due to pain, or in some acute abdomen cases, distended organs or large abdominal effusions may press on the diaphragm causing respiratory compromise. Bear in mind that vomiting animals are also at risk of aspiration pneumonia.
Cardiovascular System
Assessment of perfusion parameters (heart rate, pulse quality, capillary refill time [CRT], mucous membrane colour) will identify patients that are hypovolaemic (see Chapter 4). Hypovolaemia is common in patients with abdominal crises. Large amounts of fluid may be lost in vomit and diarrhoea. Fluid may also be sequested into distended or strangulated intestines. If peritonitis is present, then the inflammation of the serosal surfaces of the peritoneum leads to much fluid leaking from vessels into the abdomen.
Patients may present with signs of distributive shock, or systemic inflammatory response syndrome (SIRS) due to a inflammatory stimulus such as septic peritonitis, or severe pancreatitis. In these patients, mucous membranes appears injected (or ‘brick red’), CRT is rapid and tachycardia is present.
Neurological Deficits
In addition to assessment of mentation, a quick appraisal of gait, posture and proprioception helps to prevent cases of spinal pain or trauma from being confused with abdominal crises.
Abdominal Examination
Abdominal examination may give an indication of intra-abdominal pathology:
- Visual assessment for distension, asymmetry, subcutaneous swelling or bruising
- Percussion to detect tympany from gas distension, or a fluid ‘thrill’ or ripple effect
- Palpation is useful to detect the presence of diffuse or localised pain. In some instances palpation may reveal an intestinal foreign body, intussusceptions, etc.
Stabilisation
Before moving on to diagnostic evaluation to determine the exact cause of the acute abdomen, it is important that initial stabilisation of the patient is initiated. Many patients will have evidence of hypovolaemic shock, others may have distributive shock. It is important suitable intravenous fluid therapy is administered as soon as these syndromes are identified to minimise the effects of hypoperfusion on tissues, and to stabilise the animal prior to anaesthesia should it become necessary. Shock rate boluses of balanced istonic crystalloids are indicated; dose rates being dictated by the degree of hypoperfusion present (see Figure 11.3). Initial stabilisation can be started and continue during further work-up.
Figure 11.3 A patient with gastric dilation and volvulus (GDV) receiving isotonic crystalloids at shock rates. To enable this rapid administration of fluids, two IV lines have been placed, one in each forelimb, using wide-bore catheters.
Even if hypovolaemia due to abdominal bleeding is suspected, unless blood products are readily available, crystalloids are indicated. The risk of anaemia due to haemodilution is less of a risk than the effects of continued hypoperfusion due to reduced circulating volume.
If septic peritonitis is suspected, broad spectrum antibiotics should be administered intravenously (see Figure 11.4).
Figure 11.4 Potentiated amoxicillin is commonly used to provide broad spectrum antibacterial cover in suspected septic peritonitis cases. The addition of metronidazole gives greater cover of anaerobes.
If the animal is in pain, analgesia can be started. Non-steroidal anti-inflammatory drugs should be avoided where hypovolaemia is present or intestinal damage is suspected – this probably means most acute abdomen cases at presentation; for this reason, opioids are preferred.
Diagnostic Techniques
The focus of diagnostic evaluation of the acute abdomen must be on identifying those patients that require surgical management from those cases where medical management is possible.
Clinical Pathology
Blood samples and, if possible, urine samples should be obtained. As well as giving information on possible aetiology, this also provides a benchmark of the current metabolic and haematological status, helping to guide stabilisation and judge the effectiveness of fluid resuscitation based on serial samples. A minimum database recommended from blood is: packed cell volume (PCV), total solids by refractometer (TS), blood urea levels, blood glucose levels and, where possible, electrolyte analysis. A specific gravity measured from the urine sample is useful to assess renal perfusion and concentrating ability.
If possible, a full biochemistry and haematology profile should be obtained. The biochemistry in particular may point towards more specific causes of acute abdomen.
A coagulation profile is useful in patients where abdominal surgery is indicated; this may highlight an increased risk of intra-operative bleeding and allow planning for provision of blood products where necessary.
Radiography
Orthogonal radiographs of the abdomen should be inspected closely for any free abdominal gas, abnormal soft tissue masses, dilated portions of the gastrointestinal tract and intestinal obstruction (see Figure 11.5). Foreign bodies may be visible, or if they are not radio-opaque, then there may be associated signs of gut dilation and obstruction. Large peritoneal effusions may reduce contrast and make interpretation difficult (see Figure 11.6).
Figure 11.5 (a) Visible gastric foreign bodies, in this case fragments of a rubber ball. (b) Distended loops of small intestine caused by a radiolucent foreign body (a sock) lodged in the jejunum.
Figure 11.6 Abdominal effusion leading to loss of serosal detail, and a generalised ‘ground glass’ appearance.
Occasionally, contrast studies may be required, especially in animals with a partial gastrointestinal obstruction. Barium contrast agents are used for gastrointestinal studies, either as a liquid or in impregnated beads (see Figure 11.7). Water-soluble iodine contrast agents are recommended in some texts where gastrointestinal perforation is suspected (as barium is irritant to the peritoneum). In practice, if perforation is suspected, then exploratory surgery should be performed as soon as the patient is stable enough to undergo anaesthesia.
Figure 11.7 Contrast radiography of a suspected partial intestinal obstruction, using barium impregnated spheres. The larger spheres have failed to leave the pylorus. A duodenal partial obstruction was found at exploratory surgery.
Ultrasound Examination
Ultrasound examination of the abdomen is useful in detecting even small amounts of peritoneal effusion (see Figure 11.8). Focused assessment with sonography for trauma (FAST) is a technique originally described in human medicine which is equally useful in animals to assess for the presence of peritoneal effusions (see Practical techniques at the end of the chapter). FAST is a simple, rapid technique that can be performed by clinicians with minimal ultrasound experience.
Abdominocentesis
Abdominocentesis is a quick and easy technique to obtain samples of free abdominal fluid for analysis, something that can be vital to establish the cause of an acute abdomen (see Practical techniques at the end of the chapter). There are few contraindications (e.g. coagulopathy, distension of a viscus), and perforation of organs is rare. A single point can be tapped, or a four quadrant tap can be carried out (see Figure 11.9). If only small amounts of fluid are present, diagnostic peritoneal lavage can be performed (see Practical techniques at the end of the chapter). This increases the volume by dilution, so during analysis of the fluid this must be taken into account.
Figure 11.9 Performing abdominocentesis on the patient seen in Figure 11.8; ultrasonography had confirmed the presence of an effusion, abdominocentesis will allow analysis to determine the source of effusion.
Once a fluid sample has been obtained, there is much valuable information that can be gained from it:
- The fluid is visually examined to assess turbidity.
- The PCV of the fluid can be measured to assess any abdominal haemorrhage.
- The total protein levels of the fluid can indicate if the effusion is a transudate or an exudate (see Figure 11.10).
- Microscopic examination of a Diff-Quik stained smear will reveal cytology. The presence of toxic neutrophils with intracellular bacteria indicates septic peritonitis. Bilirubin crystals are visible in cases of bile peritonitis. Faecal material and food fibres may be present in cases of bowel rupture.
- Biochemical testing may be required. This can be performed with in-house biochemistry analysers. Fluid with bilirubin levels higher than blood levels indicates bile leakage. Similarly, fluid with creatinine levels higher than blood levels indicates urine leakage.
- A very quick and easy test for septic peritonitis is to measure glucose levels of the effusion with a hand-held glucometer. If a septic exudates is present, bacteria and white blood cells will be metabolising glucose in the effusion, resulting in a lowered glucose levels. So, if effusion glucose levels are low, septic peritonitis is suspected. If effusion glucose levels are normal, but significantly lower than concurrent blood glucose levels, again septic peritonitis is almost certain to be established (see Figure 11.11).
Figure 11.10 Measuring total protein content of an abdominal effusion using a refractometer.
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