Managing the acute abdomen (Part 1): evaluation, diagnosis, and decision making (Proceedings)

Acute abdomen is the acute onset of abdominal pain that requires prompt diagnosis and immediate intervention to prevent patient deterioration. The decision to operate depends on efficient diagnostic evaluation, and the timing of the surgery should be based on what will maximize survival and minimize morbidity.

Clinical Signs, Initial Patient Management, Signalment, History, and Physical Examination

Abdominal pain may be noted as peculiar posture, reluctance to move, stilted ambulation, avoidance reaction, vocalization, guarding ("splinting"), or hypersalivation (pain-induced nausea). Other clinical signs are dictated by the underlying cause. A primary survey is performed to set diagnostic and therapeutic priorities. Signalment and history help develop the appropriate differential diagnoses. Complete physical examination is performed as soon as the patient's status allows. The abdomen is examined by visual inspection, auscultation, percussion, ballottement, superficial and deep palpation, and digital rectal palpation.

Clinical Pathology and Diagnostic Imaging

Blood and urine testing characterizes the patient's hematologic and metabolic status, and may aid in reaching a definitive diagnosis. When waiting on laboratory tests is potentially detrimental to the patient's well-being, an emergency minimum data base is performed, and the remaining tests are done later on pretreatment samples. Some testing may aid in establishing a quick prognosis. One example is blood lactate. Lack of tissue perfusion results in elevation of blood lactate, and higher elevations seem to correlate with more severe ischemia. Dogs with gastric dilatation-volvulus that have blood lactate less than 6 mmol/L have much greater chance of survival (99%) than those with lactate greater than this concentration (58%).

Abdominal radiography, ultrasonography, and contrast studies provide valuable direction for patient management. Notable radiographic findings include fluid (abdominal effusion), gas-distended intestines (obstruction or ileus), free abdominal air (ruptured viscus), masses, organomegaly, foreign bodies, urinary calculi, and signs of pancreatitis (loss of detail in the right cranial quadrant and lateral displacement of a gas-filled descending duodenum). Abdominal radiographs may be omitted in cases of evisceration, penetrating trauma, postoperative peritonitis confirmed on abdominocentesis, and suspected gastric dilatation-volvulus in which the patient is unstable. Abdominal ultrasonography is helpful in defining masses, enlarged organs, and fluid-filled lesions (such as abscesses). Contrast radiography of the gastrointestinal and urinary systems is sometimes necessary after survey radiographs fail to define a suspected abnormality.

Abdominocentesis/Diagnostic Peritoneal Lavage

When other diagnostic techniques fail to clearly define the diagnosis and course of therapy, abdominocentesis is aseptically performed. Traditionally, a four-quadrant tap is performed with hypodermic needles or catheters. When possible, the author prefers to use a multiholed catheter to perform a single abdominocentesis just to the right of the umbilicus and, if insufficient fluid is obtained, progress directly to diagnostic peritoneal lavage.

Diagnostic peritoneal lavage is performed with a multiholed catheter such as a commercially available dialysis catheter, a standard intravenous catheter modified by adding side holes (taking care to avoid breakage at the holes and resultant intraperitoneal foreign body), or a commercially available thoracocentesis catheter that has a protected needle/stylet and four offset side holes. The catheter is inserted just to the right of the umbilicus to avoid fat associated with the falciform ligament and median ligament of the bladder. The right side is used to minimize the chance of iatrogenic damage to the spleen and descending colon. A subcutaneous bleb of local anesthetic (9:1 solution of 2% lidocaine:sodium bicarbonate) is placed at the proposed entry site and a tiny stab incision is made in the skin with a number 11 scalpel blade. The catheter is advanced through the skin stab and into the abdomen, and gentle aspiration is applied with a syringe. In the absence of an adequate sample, 22 ml/kg of warm sterile isotonic saline is infused. After completing the infusion the patient is gently rolled from side to side and the abdomen is gently balloted to disperse the saline. Then, careful slow aspiration with a syringe is performed to collect a 10 to 20 ml sample.

Abdominal fluid is evaluated for color, packed cell volume, white blood cell count, and cytology. Occasionally, bacterial cultures and chemistries should be performed. The most useful chemistry evaluation for abdominal fluid is creatinine. Diagnostic peritoneal lavage creatinine that is (two or more times) greater than serum creatinine indicates uroabdomen. Potassium concentrations can also be used to detect uroabdomen. A ratio of abdominal fluid potassium to peripheral blood potassium greater than 1.4:1 indicates uroabdomen. Glucose concentration may be used to diagnosis septic peritonitis. Abdominal fluid glucose concentration that is more than 20 mg/dl lower than simultaneously measured blood glucose indicates that the animal has septic peritonitis.

Exploratory Celiotomy

A complete systematic exploratory celiotomy to detect and correct all significant abnormalities is performed as soon as the need is determined. Delaying surgery is justified only when the delay will decrease morbidity or chance of mortality. Occasionally during emergent celiotomy life-threatening problems (such as ongoing hemorrhage) will require immediate attention; systematic exploration can be performed later in the procedure. Only rarely should systematic exploration be abandoned altogether (for instance, in cases judged to be at risk of death or severe disability if not soon recovered from anesthesia).

Analgesic Medication

Analgesic therapy is important because abdominal pain is present at some point in each case of acute abdomen, and definitive therapy will not necessarily immediately resolve the pain. Most patients can be managed with either buprenorphine (dogs and cats) if the major source of pain is visceral (such as a distended organ), or morphine (dogs) if the major source of pain is musculoskeletal (such as abdominal wall trauma). Although morphine would likely be effective for visceral pain, potential side effects (nausea, emesis, urine retention, constipation, and greater chance of respiratory depression than buprenorphine) make morphine a less desirable analgesic for most acute abdomen cases. Currently, the most common postoperative analgesic protocol used by the author is buprenorphine given as a constant rate IV infusion (0.04 mg/kg/day) for the first 12 to 36 hours until a switch can be made to an oral opioid (or nonsteroidal anti-inflammatory drug if there are no gastrointestinal concerns). When used, morphine is most commonly given as a constant rate IV infusion (0.1 mg/kg/hr). As an adjunct to opioid analgesia, or to minimize the amount of opioids used, lidocaine (20 mcg/kg/min) may be used (dogs only) as a constant rate IV infusion for the first 12 to 24 hours. When given together for infusion, buprenorphine (or morphine) and lidocaine may be mixed in the same bag of fluids, typically normal saline or the maintenance crystalloid solution being used for fluid therapy.

Analgesics should be given as early in the course of treatment as possible, usually as soon as the physical examination is complete. Withholding analgesics for fear of masking important clinical signs should be the exception rather than the rule. Analgesics are not immediately given to animals in shock, but should be begun soon after the shock state is reversed using the same guidelines discussed above. The duration of analgesic administration may vary with the individual animal, but should be at least 24 hours in both postoperative and nonsurgical patients.

References

Mann FA. "Acute Abdomen: Evaluation and Emergency Treatment", in Kirk's Current Veterinary Therapy XIV, Bonagura JD, ed. St. Louis, Saunders Elsevier, 2009:67-72.

de Papp E, Drobatz KJ, Hughes D. Plasma lactate concentration as a predictor of gastric necrosis and survival among dogs with gastric dilatation-volvulus: 102 cases (1995–1998). J Am Vet Med Assoc 1999;215:49–52.

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;32:161-6.