Acute Abdomen

Introduction

Acute abdomen generally refers to rapid onset of abdominal pain. However a number of causes of abdominal conditions are not necessarily painful and it may therefore better be defined as ‘any situation involving an acute onset of clinical signs referable to intra-abdominal pathology’. It has a variety of causes, often requiring surgery as definitive treatment.

Causes include but are not limited to:

Gastrointestinal (GI) – gastroenteritis, foreign bodies, gastric dilatation and volvulus, perforations, intussusception, neoplasia, hernias, vascular compromise (e.g. mesenteric torsion), mesenteric artery thrombosis

Pancreatic – pancreatitis, abscess, ischaemia, neoplasia

Hepatic – rapid hepatomegaly, gallbladder obstruction/necrosis/rupture, hepatic abscess, portal vein thrombosis, acute hepatitis/cholangiohepatitis, liver lobe torsion, cholecystitis

Splenic – torsion, ruptured mass, abscess, infarction, neoplasia

Urinary – obstruction due to tumours/calculi/urethritis, bladder rupture, urethral tear, pyelonephritis, nephroliths, ureteroliths, acute renal failure, renal ischaemia, nephritis, uroabdomen

Genital – prostatitis, prostatic abscess, pyometra, uterine/ovarian torsion, testicular torsion, ovarian cyst/neoplasia, uterine rupture, uterine/prostatic neoplasia

Abdominal Wall - strangulating hernias, abdominal wall rupture

Lymph nodes – lymphadenitis, reactive lymphadenopathy, neoplastic infiltrate

Peritonitis – septic or non-septic

Other - e.g. haemoabdomen, feline infectious peritonitis (FIP), migrating foreign bodies, pansteatitis

Signalment

Cats present with fewer clinical signs of abdominal pain than dogs. Parvovirus and intussusception are more common in younger dogs, or in the case of parvovirus, those which are unvaccinated. Pancreatitis is more common in middle aged miniature schnauzers. Any entire female should be checked for pyometra, and entire males for prostatic disease. Recent use of NSAIDs may increase the likelihood of ulceration. Gastric dilatation and volvulus is more common in large breed deep-chested dogs. Male cats are more likely to present with urinary tract obstruction.

Clinical Signs

Often non-specific, though some can present severely depressed and collapsed. Signs include anorexia, vomiting, diarrhoea. Some animals may present in the typical ‘praying position’ associated with abdominal pain (the cause is often in the cranial abdomen). If this is seen it is often considered to be a specific sign of abdominal pain. A thorough history should be taken to help identify the cause e.g. foreign body ingestion, dysuria/pollakiuria etc.

The mouth should be examined for signs of ingestion of foreign bodies/material, as linear foreign bodies can often attach under the tongue. Lymph nodes should be palpated, as if lymphadenopathy is present this may indicate the presence of lymphoma or generalised infection.

Animals often present with signs of shock (usually either distributive or hypovolemic); an elevated heart rate, poor pulse quality, reduced CRT and pale mucous membranes. If a severe inflammatory process is occurring (e.g. septic peritonitis or severe acute pancreatitis), signs of hyperdynamic systemic inflammatory response syndrome (SIRS) may be present (injected mucous membranes, rapid CRT, strong, short pulses, tachycardia, pyrexia) with or without those of hypovolemia.

Tachypnoea secondary to pain is likely to be present, though every animal that has a history of vomiting should be checked for signs of aspiration pneumonia or any concurrent pleural space disease.

Gentle abdominal palpation should be performed last during the clinical examination to avoid the pain from abdominal palpation interfering with the rest of the findings. Abdominal distension may be present and can indicate gastric dilation, effusion, abdominal masses, hernias or cellulitis. Percussion is useful to identify free fluid or air accumulation. If gas is present in the stomach, this will be tympanic, whereas pneumoperitoneum is not. A fluid thrill will be present with effusions, though there can also be non-pathogenic causes of an abdominal thrill such as intrabdominal fat.

Cranial abdominal pain is often associated with pancreatitis and caudal pain with prostatic disease. Intestinal foreign bodies, cholecystitis, tumours will cause focal areas of pain. Septic peritonitis usually causes diffuse abdominal pain and often severe depression - often the animal will only react to abdominal palpation. Some causes (e.g. uroabdomen, pyometra) may not cause abdominal pain.

Rectal examination should be performed especially in intact male dogs to assess for the presence of prostatic disease, and the vulva should be examined in intact female dogs for signs of discharge etc., which may indicate a pyometra. Rectal examination can also reveal the presence of melena indicating upper GI bleeding or may reveal acholic faeces indicating a biliary obstruction. If bile peritonitis is present animals will often appear jaundiced unless the biliary tract rupture is very recent. Pancreatitis can also cause biliary obstruction and hence jaundice.

Neurological examination should also be carried out as pain due to intervertebral disk disease can often mimic the signs of abdominal pain.

Diagnosis

Blood and urine samples should be taken, both to assess the stability of the animal and to aid in diagnosis. This should (ideally) be done before fluid therapy has begun in order to avoid false results. Gastric obstructions will cause metabolic alkalosis, electrolyte abnormalities and dehydration. Acute renal failure will cause hyperkalaemia. Azotaemia will often be present due to either pre, post or renal causes which urine specific gravity measurement will help to differentiate. Urine samples can also be used to detect the presence of any infection.

Low total solids (TS) and normal packed cell volume (PCV) on blood results can be indicative of either acute haemorrhage or severe vasculitis (e.g. due to septic peritonitis). Vasculitis will also cause hypoproteinemia due to loss of protein into the peritoneal cavity. Thrombocytopenia may be an early warning sign of disseminated intravascular coagulation, which can be caused by many of the conditions associated with acute abdomen. Hypoglycaemia will be present in sepsis or pancreatic/hepatic neoplasia. Clotting times are also useful to rule out the presence of a coagulopathy e.g. in cases of haemoabdomen. Uroperitoneum will raise the blood urea nitrogen, creatinine, potassium and phosphorus. Bile peritonitis will raise the total bilirubin, alanine transaminase and alkaline phosphatase. Increased amylase and lipase can indicate pancreatitis but this is not diagnostic as it is associated with other conditions and not present in all cases. Trypsin-like immunoreactivity (TLI) tests can be useful in diagnosing feline pancreatitis and canine pancreatic lipase immunoreactvity (PLI) can be used in dogs.

Faecal analysis should be performed especially in younger animals to look for the presence of parvovirus or parasites.

Abdominal radiographs (ideally lateral and ventrodorsal views) should be taken. This can be useful in detecting obstructions due to foreign bodies where loops of distended intestine proximal to the obstruction will be present. Free gas present in the abdomen is a surgical emergency as it indicates rupture of the GI tract or the presence of gas producing bacteria (unless it is iatrogenic due to abdominocentesis or recent surgery). If large volumes of fluid are present in the abdomen then ultrasound is the diagnostic method of choice due to the loss of contrast on radiographs. Contrast radiography may be used in partial intestinal obstructions or if foreign material is present within the gastrointestinal tract but not obstructing passage. Water soluble contrast should be used if perforation of the GI tract is suspected.

IV urography or retrograde urethrocystography should be performed in cases where disorders of the urinary tract are suspected.

Abdominal ultrasound is useful to detect small amounts of peritoneal fluid and assisting in aspirating fluid for analysis, especially in cases of septic peritonitis (though the absence of fluid does not rule it out). Fluid can usually be seen collecting at the apex of the bladder or between the liver lobes if only small amounts are present. Abdominocentesis should be performed within the ventral aspect of the right cranial abdominal quadrant to start with. If this is unsuccessful then one of the other four quadrants can be used (taking care with the left cranial quadrant due to the presence of the spleen). Peritoneal lavage can be used to aid fluid aspiration if the volumes are too small to easily aspirate, though this should be performed after radiographs have been taken due to the introduction of fluid to the abdomen. Lavage has the advantage over abdominocentesis in that, due to the introduction of fluid, all surfaces are covered so it will obtain a more representative sample and can be used to rule out the presence of septic peritonitis.

If blood is present in the aspirate and it clots, this indicates the blood is from within a vessel/organ. If it doesn’t clot then the blood is from within the abdominal cavity. Cytology of the aspirate will help determine whether emergency surgery is needed (e.g. intracellular bacteria and toxic degenerate neutrophils in septic peritonitis). If antibiotics have previously been given then this can make it hard to distinguish between septic peritonitis and severe acute pancreatitis. Measuring glucose and lactate levels within the aspirate and comparing them to blood levels can be useful, with fluid glucose levels being lower in septic peritonitis (abdominal fluid glucose : serum glucose concentration gradient over 20mg/dL). Amylase and lipase concentrations in the aspirate may be elevated in the case of pancreatitis, though pancreatitis can often be found alongside septic peritonitis. Fluid obtained should also be cultured.

If a uroabdomen is present then (initially) creatinine and potassium levels will be higher in the abdominal fluid than blood serum (creatinine - gradient over 2.0mg/dL; potassium - gradient over 1.4mg/dL in dogs and over 1.9mg/dL in cats). Over time the difference will decrease (though creatinine equilibrates more slowly) and if fluids have been administered this can lead to misdiagnosis.

Abdominal fluid obtained in the presence of a biliary rupture or necrotising cholecystitis will be green in colour with the presence of bilirubin crystals and has a higher total bilirubin concentration than serum ( gradient over 2.0mg/dL). Bile may also be seen phagocytosed within neutrophils.

Ultrasound can also be used to identify masses, abscesses, pancreatitis, pyometra, and to assess blood flow within the abdominal organs.

Abdominal paracentesis can be used to obtain samples of fluid if abdominocentesis is unsuccessful. This can be done in left lateral or dorsal recumbency under sedation. Lidocaine is used as a local anaesthetic caudal to the umbilicus and an incision made through the skin and linea alba into the abdomen. A catheter is placed through the incision in a dorsocaudal direction and negative pressure applied to obtain the sample.3

Treatment

If in hypovolemic or distributive shock, fluid therapy should be administered using crystalloids taking into account the severity of the shock. Initially fluid boluses may be required. Hypoproteinemic animals such as those with vasculitis may require colloids. If there is evidence of haemorrhage then blood products should be used, though if unavailable crystalloids should be given. If fluid therapy is not effective to restore normal parameters catecholamines may be required in addition to fluids.

Broad spectrum antibiotics should be used in cases where a bacterial component is suspected or in cases where contamination is possible (e.g. foreign body). Intravenous antibiotic use has been shown to be more effective when dealing with septic peritonitis.

Analgesia should be given, though NSAIDs should be avoided if hypoperfusion is present, renal function is poor or GI ulceration is present.

Conditions causing acute abdomen that require immediate surgery include: gastric dilatation-volvulus, septic peritonitis, intra-abdominal haemorrhage, ruptured pancreatic/prostatic abscess, pyometra, urethral obstruction that cannot be catheterised, intestinal foreign body, intussusception, upper gastrointestinal obstruction, intestinal perforation, abdominal perforation, biliary rupture splenic/testicular torsion, mesenteric torsion.

Gastric foreign bodies may be removable via endoscopy. Uroperitoneum can be treated by draining the fluid from the abdomen and placement of a transurethral catheter. If the uroperitoneum is caused by trauma or is secondary to urethral obstruction then surgery will be required.

Septic peritonitis can be managed by identification of the cause, peritoneal lavage and either open peritoneal drainage or the placement of peritoneal drains. If available animals should be given fresh frozen plasma to increase plasma proteins as well as increase blood volume. Administration of antibiotic treatment within 1hr of presentation has been shown to increase survival.Studies have shown that the use of heparin in dogs with septic peritonitis may increase survival due to the reduction in disseminated intravascular coagulation and improved bacterial clearance.

Prognosis

Largely dependent on underlying causes and the speed at which the animal is stabilised and the underlying cause identified. The provision of enteral support (through the placement of feeding tubes if necessary) is paramount to the recovery of animals with acute abdomen.

References

Boag, A., Hughes, D. (2004), Emergency management of the acute abdomen in dogs and cats: 1. Investigation and initial stabilisation, In Practice; 26: 476-483

Dye, Teresa (Feb 2003), The acute abdomen: A surgeon's approach to diagnosis and treatment, Clinical Techniques in Small Animal Practice, Volume 18, Issue 1, Pages 53-65

Mazzaferro, Elisa M. (Feb 2003), Triage and approach to the acute abdomen, Clinical Techniques in Small Animal Practice, Volume 18, Issue 1, Pages 1-6

Cruz-Arámbulo , Robert, Wrigley, Robert (Feb 2003), Ultrasonography of the acute abdomen, Clinical Techniques in Small Animal Practice, Volume 18, Issue 1, Pages 20-31

Nelson, Richard W., Couto, C. Guillermo (2005) Manual of Small Animal Internal Medicine (Second Edition) Mosby