Approach to the acute abdomen (Proceedings)

The acute abdomen is a common presenting complaint in veterinary medicine emergency rooms. The acute abdomen implies an otherwise normal animal that has developed a recent and acute onset of signs that stem from the abdominal region in general or often specifically the gastrointestinal tract. The animals do not necessarily have to be previously completely healthy, as acute changes can occur in the more debilitated animals such as those with neoplasia or chronic diseases. It does imply that whatever the current state of the patient, this presentation represents an acute and abrupt change. The major role of the emergency clinician is to determine if the specific patient is in need of an exploratory surgery of not.

Included in the program are discussions of GDV, mesenteric torsion (rarity), gastrointestinal bleeding, urogenital emergencies, abdominal surgeries, septic peritonitis and pancreatitis. The history, signalment, physical examination, in addition to results of preliminary blood tests and imaging such as survey radiography and ultrasound, all form the foundation for assessment, stabilization and decision-making that is mandatory for the patient presenting with an acute abdomen.

The signalment alone alerts the clinician to potential genito-urinary tract disease that may present as gastrointestinal disease: pyometra is common in the middle aged to older unspayed female, and prostatitis or prostatic abscess can occur in the older, noncastrated male. A ruptured pyometra or acute prostatitis can manifest as peritonitis, and the animal may be weak, painful, or even cardiovascularly collapsed. A young cat or dog may have severe viral disease, or intususception, or gastrointestinal obstruction from ingested foreign materials. A young to middle aged dog may have metabolic disease such as Addison's disease. Also known as the "great imposter", these dogs commonly present with severe gastrointestinal signs, collapse and painful abdomen. Cancer resulting in intrabdominal masses (liver, pancreas, kidney) that may be necrotic and result in abdominal sepsis , or gastrointestinal masses resulting in obstruction and or perforation, have to be considered in middle-aged to older cats and dogs.

Medical history:

Dogs with prior abdominal surgeries can develop adhesions and bowel can be entrapped or strangulated and represent with ischemic bowel injury or even perforation. Animals on prednisone or anticonvulsant may in particular eat foreign objects or be more likely to get into the garage. Owners may tell you there is a missing article of clothing or toy. Also, make sure to include diet in the history taking portion of the exam. For example is the animal eating a raw food diet, this may make you consider Salmonella in your differential lists. Was vomiting acute in its onset or chronic. Is the dog retching or regurgitating, where animals that vomit tend to have digested food versus undigested food with regurgitation, and vomiting is more active, while regurugitation tends to be passive in nature. Is there bile or blood associated with the vomit. Is the diarrhea large-bowel or small. Is this episode following a Thanks Giving turkey dinner, then pancreatitis maybe added to the differential list (Phenobarbital and KBr therapy have been know to cause pancreatitis). Is it a deep-chested dog that was fed 6 hours ago and has been retching for 3 hours and the abdomen is taught and distended, GDV should be suspected. Always remember dogs with back pain can present with abdominal pain signs. In the case of cats with acute onset of vomiting, it is imperative that you look under the tongue, because linear foreign bodies can be easily missed in the initial exam process. If ever in doubt light sedation to do a complete and through oral exam may go a long way to help rule out a string under the tongue. These are just a few examples of where history is an important part of the exam process.

After the initial history and physical exam, we then move onto move onto the appropriate diagnostics and imagining modalities required to make an accurate diagnosis, when appropriate (therapy may need to come first with critical cases). These tests will vary with the stable versus the unstable patients. A minimum database to include CBC, chemistry, UA, abdominal radiographs, may be the appropriate tests for the stable patients. In the unstable emergent patient then PCV, TS, AZO, BG, blood gas, abdominal radiographs and ultrasound maybe more appropriate to obtain diagnosis while the other tests are pending at the laboratory.

Dogs with GDV tend to be deep chested large breeds (ie. Great Danes, Akitas, Hounds, Standard poodles). Any large breed deep chested dog with an acute onset of non-productive retching, with a distended abdomen and signs of shock, such as increased heart rate, weak rapid pulses, pale mucous membranes, and increased lactate, should be suspected of having a gastric dilation and volvulus. These are emergent cases that require rapid diagnosis and surgical correction. Predisposing factors include, male gender, being underweight, eating one meal per day, eating rapidly, a deeper thorax to width ratio, and a fearful/anxious temperament. Prior to diagnosis, treatment of the cardiovascular shock should be the main focus. Two large bore IV catheters should be placed to obtain minimum database and lactate if available. Shock doses of IV crystalloids (90 ml/kg) maybe warranted, but I tend to give a third to quarter shock doses of fluids and then monitor the response to therapy and repeat as necessary. An IV catheter (two cephalic) should be placed prior to obtaining abdominal radiographs, in which the standard right lateral abdominal radiograph is the view of choice to make the diagnosis. Once diagnosis is made, decompression with an oral gastric tube under heavy sedation with an inflated endotracheal tube should be completed prior to surgical correction. If unable, then transcutaneous trocarization with a large bore (16 or 18 gauge over the needle catheter) can be performed prior to passing the oral gastric stomach tube. There are numerous surgical corrections of GDV, which are beyond the scope of the talk.

Dogs with mesenteric torsion tend to present with severe signs of cardiovascular shock, that tend not to be very responsive to fluid therapy resuscitation. The abdominal radiographs reveal diffusely dilated small intestinal loops. These are also cases which require immediate surgical correction, or the outcome is grave. These tend to be large breed (usually German shepards) with severe signs of shock (tachycardia, hypotension {<80 mmHg systolic}, pallor, and thready if the pulses are even palpable). Exocrine pancreatic insufficiency has been discussed as a predisposing factor. If a young to middle age GSD dog presents with collapse and shock, which is unresponsive to fluid resuscitation, surgical exploration should be considered. The prognosis is very guarded.

Dogs and cats with gastrointestinal bleeding may present in severe shock or with minimal clinical signs depending on the duration and extent of the bleeding. A minimum database including coagulation times (PT, aPTT), and platelet counts should be performed in the initial work up. Dogs and cats with an acute (several days) bleed may tend to be more regenerative, then ones with chronic or peracute disease as the cause of bleeding. The patient with GIT bleeding are pale, often tachycardic unless compensated, and may have melena on rectal exam (always do a rectal on anemic patients unless there is another obvious source of loss) if from the upper small intestine. Depending on the source and cause, GIT bleeding maybe surgical or medical when it comes to what appropriate treatment to institute. Immune-mediated thrombocytopenia is a common cause of severe GI bleeding, and is not surgical. A single or several small ulcers or masses maybe able to be resected surgically, but diffuses ulcers in the stomach or duodenum tend to be best managed medically. Medical treatment would require the use of GIT protectants such as H2 blockers and carafate, but more effective in dogs is proton pump inhibitors and carafate based on the available research. Supportive care may also include IV fluids, pRBC, frozen platelets concentrates (MidwestAnimal Blood Services, 517-851-8244), whole blood if indicated, and possibly fresh frozen plasma if a coagulopathy (elevated PT or aPTT) is suspected. In dogs receiving pRBC for GIT bleeding, intestinal pathology (primary or secondary) was the main cause for the bleeding, while dogs with ITP required more transfusions than non-immune mediated causes.

Small animals may present with signs of acute abdomen but caused by disease in systems other than the gastrointestinal tract, such as the genitourinary system. Trauma, infection and ureteral obstruction are common causes of acute signs. Fever, weakness or collapse in an intact male or female should alert the clinician to the potential for infections of the uterus or prostate. The most common bacteria implicated in pyometra and prostatic infections is E. coli. Dogs can present with signs of apparent acute abdominal pain with intrabdominal or retained testicular torsions, as well as within the scrotum. Renal diseases can result in stretching of the renal capsule such as pyelonephritis or renoliths can cause pain. Acute ureteral obstruction in the cat should be considered for acute onset of vomiting, lethargy and painful walking. Unilateral ureteral obstruction will not cause the development of azotemia provided the opposite kidney has adequate function. Trauma can result in rupture of the urinary bladder, or if severe enough, body wall hernia with entrapped urinary bladder or detached ureters and free urine in the abdomen. Rupture of the urinary bladder tends to be more common in males then females due to long narrow urethra. While it's important to obtain urine for analysis and culture and the beginning of treatment, cystocentesis should be performed cautiously and judiciously in animals suspected of having intrabdominal abscessation-as with pyometra or prostatitis, or metastatic neoplasias. Diagnosis of uroabdomen can be made from chemical exam of free abdominal fluid obtained from abdominocentesis. Abdominal fluid creatinine to blood creatinine ratio of >2:1 was diagnostic, and an abdominal fluid potassium to blood potassium ration of >1.4:1 was diagnostic in dogs, and in cats the ratio has been reported to be >1.9:1.

Animals with recent abdominal surgery that present with acute onset abdominal pain could have an incisional infection, septic or aseptic (pancreatitis) peritonitis, dehiscence of the enterotomy or R/A site, or pancreatitis. All, except the diagnosis of pancreatitis would encourage abdominal re-exploratory. If there is purulent material from the incision the incision and possibly the abdomen should be re-explored. If ultrasound is available then the abdomen and the incision should be evaluated for free fluid, and if present should be aspirated. Looking for free fluid just caudal to the xyphoid, both paralumbar areas, and in the area of the bladder are good places to start. Cytology with intracellular bacteria is diagnostic for septic peritonitis, but is operator dependent with no time to wait for an off site pathologist interpretation. In the last decade the use of abdominal fluid glucose and lactate compared to blood glucose and lactate, have helped to bridge this gap in dogs and cats. If the abdominal fluid glucose is less then blood glucose with a difference of greater than 20 mg/dl this was shown to be diagnostic. Also, the abdominal lactate concentration greater than 2 mmol/L then the blood lactate was also shown to be diagnostic for septic peritonitis. Poor prognostic indicators for dehiscence of an R/A site included having two or more of the following; presence of a foreign body at the R/A site, evidence of preoperative peritonitis, and an albumin concentration of < 2.5 g/dL. Cats with septic peritonitis tend to present bradycardic, hypothermic, and may have lack of abdominal pain.

Diagnosis of pancreatitis may be more challenging then the others. Nonspecific blood work abnormalities include nonregenerative anemia, an increased/decreased WBC count, an increased or decreased potassium or glucose concentration, a decreased calcium or albumin concentration, and an increased bilirubin, cholesterol, alanine aminotransferase, alkaline phosphatase, blood urea nitrogen, or creatinine concentration. Abnormalities in leukocytes, calcium, and potassium are associated with a poorer prognosis, especially in cats with hypocalcemia.

Although amylase and lipase serum values have been used as a diagnostic tool, they are not sensitive or specific. Values may be increased with renal disease, glucocorticoid use, GI disease, peritonitis, and dehydration. The diagnostic utility of measuring amylase and lipase may be increased when serum values are compared with those in abdominal fluid. Recently, there has been increased interest in using both the trypsin-like immunoreactivity (TLI) and pancreatic lipase immunoreactivity (PLI) tests to evaluate potential pancreatitis cases. Increased TLI is associated with pancreatitis in dogs but less so in cats because it is compromised by azotemia and GI disease. Positive PLI test results are associated with disease in both dogs and cats, and the PLI test is now considered the blood test of choice.

The sensitivity of radiography is very poor (i.e., 24%), and ultrasound has better sensitivity (i.e., 68%) for detecting pancreatic abnormalities; allows evaluation of concurrent disease. Ultrasonographic signs include of pancreatitis include a hypoechoic pancreas, a hypoechoic focus in the pancreas, a hyperechoic mesentery, and excessive corrugation of the duodenum.

In conclusion differentiate between the sick and not sick acute abdomen, and as soon as possible determine if the patient is a surgical candidate. A negative exploratory is never a waste of time, and biopsies with aerobic and anaerobic cultures should be obtained. These cases tend to require intensive monitoring and 24 hour supervision.

References

Heeren V, Edwards L, Mazzaferro EM. Acute Abdomen: Diagnosis. Compend Contin Educ Pract Vet. 2004. 26[5]: 350-363.

Heeren V, Edwards L, Mazzaferro EM. Acute Abdomen: Treatment. Compend Contin Educ Pract Vet. 2004. 26[5]: 366-373.

Bonczynski JJ, Ludwig LL, Barton LJ, et al. Comparison of peritoneal fluid and peripheral blood pH, bicarbonate, glucose, and lactate concentration as a diagnostic tool for septic peritonitis in dogs and cats. Vet Surg. 2003 Mar-Apr;32(2):161-166.