An acute abdomen, from a surgeons point of view, should be divided into problems that need to go to surgery immediately to save an animals life, problems that need to be treated with surgery once the animal is stable enough to go through anesthesia and problems in which surgery should be avoided if possible. The decision making in a case of acute abdominal pain includes therefore two things: 1) Identify that the dog is painful from an abdominal origin; and 2) decide as soon as possible whether surgery is indicated. The following list is helpful for a student during the preparation of exams, but proves to be useless for the practicing veterinarian. The experienced emergency veterinarian will try to identify certain clinical patterns and decide from there on to treat the patient with a very limited amount of options, e.g., surgery versus medical therapy.

A list of non traumatic problems leading to an acute abdomen includes the following:

The clinical patterns would therefore be

1.  Patients with acute abdominal pain concurrent with trauma

2.  Generalized peritonitis

3.  Local peritonitis

4.  Intestinal obstruction

5.  Hemoabdomen

6.  Other important medical hemoabdomen

This lecture will concentrate on diagnostic possibilities of these clinical patterns.

Optimizing a patient

The preparation of a patient for surgery is as important as surgery itself. It is of outmost importance to try to correct initially fluid volume deficits, because patients with a fluid volume deficit have a tendency not to withstand well anesthesia and surgery. A systemic vasodilation is induced on anesthesia induction which inhibits compensatory mechanisms in early shock. The intraabdominal pressure decreases instantly on opening of the abdomen leading to venous stasis and decreased cardiac output which are other reasons for preoperative fluid therapy.

Emergency laparotomies have two major indications: Control of hypovolemia and prevention or treatment of sepsis. The goal of optimization is to increased/normalize oxygen delivery to intraabdominal tissues. Optimization includes therefore 100% oxygen application, an adequate fluid volume and enough oxygen carriers to reach the goal of adequate preparation for surgery.

Diagnostic principles

Diagnostic principles can be grouped according to the clinical patterns that need to be identified.

1. Localized or generalized peritonitis

To identify intraabdominal infection diagnostic procedures include clinical examination, blood values, diagnostic imaging with focused abdominal ultrasound examination, abdominocentesis and exploratory laparotomy.

Clinical signs of peritonitis are non-specific, ranging from mild to severe signs of an acute abdomen. Vomiting and a painful abdomen are commonly seen. Clinical signs of shock can be present. A hypermetabolic stage of shock with elevated heart rate, red mucous membranes and strong pulses is an indication of acute sepsis. Decreased heart rate and signs of decompensation are also possible.

Abdominal size can be increased especially with uroabdomen or with bile peritonitis. Bile is relatively hypertonic and attracts free fluid into the abdominal cavity more than other forms of peritonitis.

Especially in trauma related peritonitis cases, it is very hard to correlate the onset of visible clinical signs with the initial event that leads to bacterial contamination. Ranging from animals with a perforating trauma and concurrent gastrointestinal rupture that usually show signs of an acute abdomen within 2-3 days to animals with a bile peritonitis that can be free of clinical symptoms for more that 5 days.

Complete blood cell count and serum chemistry changes are of limited value to help to make the decision to go to surgery. The neutrophil count may be elevated, normal or low and a left shift does not have to be present at all. Chemistry changes can be helpful to diagnose the source of abdominal infection. Liver enzymes and total bilirubin concentrations are usually elevated in cases of bile peritonitis. Blood urea nitrogen, creatinine and potassium are elevated in cases of uroabdomen. Serum chemistry values become an important tool for the diagnosis if they are evaluated in the context of biochemical values from abdominal fluid.

Radiology has only a limited role the peritonitis case. Loss of detail from an effusion is the most common signs on the radiograph. Sometimes free abdominal air can be seen. Abdominocentesis or surgical exploration prior to the radiological examination have to be excluded in the case of free peritoneal air. Gas forming bacteria, penetrating trauma and gastrointestinal perforations are reasons for free abdominal air.

Ultrasound examination has an important role in the peritonitis diagnosis. Structures of organs, masses and fluid accumulation can be identified with ultrasound. Since it is possible to do ultrasound guided local fluid aspiration, ultrasound has replaced the diagnostic peritoneal lavage (DPL) procedure in our hospital. It has been reported that 5-6ml/kg of fluid was necessary to obtain a positive result in abdominocentesis and if a negative result was present DPL was the next logical step to perform. Even small local fluid pockets can be easily identified with ultrasound and aspirated under controlled circumstances.

Abdominocentesis is by far the most useful diagnostic step for peritonitis patients. Fluid is retrieved with a single tap in the umbilical region. A local anesthesia is only necessary if a large peritoneal catheter is introduced for temporary fluid drainage. Usual 20G catheter taps do not need anesthetic pretreatment. A needle is slowly advanced into the peritoneal cavity. This will allow intestinal structures to be pushed away and diminish the risk of intestinal perforation. This risk is higher with increased intraabdominal pressure and with organomegaly. Splenic puncture is the most common iatrogenic problem but is usually not followed by serious consequences. Splenic or vascular perforation can be diagnosed by observing clotting of the retrieved sample. Free blood from the abdomen tends not to form clots due to protective fibrinolytic properties of the peritoneal surface.

After the fluid is retrieved, it should be saved for culture and sensitivity and an immediate cytological evaluation performed. The presence of intracellular bacteria and degenerate neutrophils indicates septic peritonitis and an immediate exploratory is warranted. A large number of extracellular bacteria without neutrophils indicate that the needle penetrated the GI tract during abdominocentesis. Unfortunately, abdominal fluid cytology has only been reported to be accurate in the diagnosis of septic peritonitis in 57-87% of cases. A recent comparison of patients with septic peritonitis and non septic effusions showed that an abdominal fluid glucose concentration <50 mg/dl was 100% specific for a septic effusion; however, sensitivity was only 71%. The Animal Medical Center in New York recently completed a study comparing the abdominal fluid glucose and lactate concentrations to serum concentrations. Dogs with septic effusions had peritoneal fluid glucose concentration always lower than the blood glucose concentration. When the difference between the blood and fluid glucose concentrations was calculated, either a glucose difference >20 mg/dl or a lactate difference <-2.0 were 100% sensitive and specific for the diagnosis of septic peritonitis. Similar results were seen in cats. Comparing abdominal fluid concentrations to blood concentrations are also helpful in diagnosing other forms of peritonitis. The bilirubin concentration of the effusion in patients with bile peritonitis is consistently higher than the serum concentration, and has been shown to be the most effective test in diagnosing bile leakage prior to surgical intervention. In cases of uroabdomen, the fluid potassium and creatinine concentrations should also be higher than serum concentrations.

Table 1. Laboratory evaluation of peritoneal fluid

2. Intestinal Obstructions

Diagnosis of intestinal obstruction is performed using clinical exam, blood parameters, diagnostic imaging including focused abdominal ultrasound. Vomiting/ retching and abdominal pain are main indicators of gastrointestinal obstruction. However obstructions in the distal gut could be present without concurring vomiting. The radiological picture of an obstruction can be summarized as follows:

1.  Focal or generalized dilated intestinal loops (gas and fluid filled)

2.  Radioopaque/dense foreign bodies

3.  Tubular structures

4.  Fixed, rigid intestinal loops

Gastric dilation/volvulus can usually be diagnosed by clinical exam but also have a classical radiological picture.

3. Hemoabdomen

Nontraumatic hemoabdomen includes clear nonsurgical cases and clear surgical indications. Coagulation abnormalities need obviously a non surgical approach versus tumor induced abdominal bleeding that ultimately will need a surgical exploration.

There are no true laboratory tests for diagnosing acute severe hemorrhage, or estimating the amount of fluid lost. A minimum data base should include immediate determination of PCV/TS. Although a decreasing PCV may not be observed for several hours after hemorrhage, obtaining a baseline value is essential for monitoring ongoing bleeding and response to treatment. Compared to the PCV, plasma total solids will be disproportionately low as a result of splenic contraction. Splenic contraction is not routinely observed in the cat. Coagulation tests are necessary for non-trauma related bleeding, or persistent bleeding despite attempts at hemostasis. Minimal testing for activated clotting time, platelet count or estimate, and buccal mucosal bleeding time can be performed in most clinics. Submitting additional lab results for prothrombin, partial thromboplastin time, and antithrombin may also be necessary.

Using PCV values from the abdominocentesis and concurrently taken PCV values from peripheral blood can help to make decisions if a hemoabdomen is under control or has an ongoing bleed. If the PCV of the fluid is getting similar to the venous PCV an ongoing hemorrhage has to be suspected.

Ultrasound examination is indicated for any cause of hemoabdomen. A single tumor or multiple masses can be detected. Thoracic radiographs should be performed to evaluate for possible metastasis and evidence of cardiac tamponade as animals with abdominal hemangiosarcoma can have concurrent right atrial tumors.

4. Medical causes

Again the decision to operate or not has to be asked very early in the course of these problems.

Hematology, abdominocentesis and diagnostic imaging play the most important role in the diagnosis of medical acute abdominal problems. Diagnostic procedures are also used to separate initial surgical from non-surgical cases.

Treatment patterns

Treatment for an acute abdomen follows again a typical pattern, which includes controlling of the source of the problem (e.g., derotation of the stomach, enterotomy and foreign body removal or drainage of an prostatic abscess) and concurrent support and anticipation/prevention of possible complications of the patient until a stable situation is reached. This treatment is governed by control of cardiovascular status and prevention or treatment of sepsis. Helpful guidelines have been established to optimize the treatment of critically ill patients (see ref).

References

1.  Purvis D, Kirby R. Systemic Inflammatory Response Syndrome: Septic Shock In The Veterinary Clinics of North America, Small Animal Practice; Emergency Medicine . Philadelphia, Saunders, 1994, p 1225.

2.  Kirby R: Septic Shock. In Bonagura JD (ed): Current Veterinary Therapy XII. Philadelphia, Saunders, 1995, p 139.