Management of dogs and cats with septic peritonitis (Proceedings)

Introduction:

The dog or cat with septic peritonitis may display evidence of sepsis, severe sepsis, septic shock, and frequently, multiple organ dysfunction. Septic peritonitis is a rapidly progressive clinical syndrome with an array of underlying etiologies. Early recognition accompanied by rapid medical stabilization, early surgical intervention, and diligent postoperative care is crucial to optimize the likelihood of a positive outcome.

Etiology and Presenting Complaints in Small Animals with Septic Peritonitis:

Septic peritonitis most commonly results from disruption of the gastrointestinal tract, however, ruptured uterus or prostatic abscess, penetrating injury, urinary tract disruption, bile leakage, hepatic or splenic abscesses, and sepsis can all result in this immediately life-threatening condition. Common presenting complaints include vomiting, lethargy, anorexia, diarrhea, and collapse.¹ Septic peritonitis should also be on the list of differential diagnoses for any patient that has recently undergone abdominal surgery.

Diagnosis of Septic Peritonitis

Physical examination findings are centered on acute abdominal pain, dehydration, fever, and shock (likely a combination of hypovolemic and septic/distributive). Cytologic evaluation of abdominal fluid samples has been the diagnostic test of choice for the acute diagnosis of septic peritonitis in dogs and cats. Cytologic evaluation alone is considered to be 57-87% accurate in making the diagnosis. Samples can be collected via abdominocentesis, four quadrant abdominocentesis, paracentesis with a peritoneal lavage catheter, and diagnostic peritoneal lavage (DPL). DPL is recognized to be superior to other methods for the acute diagnosis of significant intraperitoneal disease or injury.⁵ Samples collected by DPL should be centrifuged prior to evaluation in order to concentrate the cellular material for analysis. Samples collected for cytologic and biochemical evaluation should also be saved for aerobic and anaerobic culture. Early gram-stain procedures will help direct empirical antibiotic therapy while culture is pending.

A recent study evaluated the utility of blood glucose gradients between the abdominal fluid and the blood in an effort to find a highly sensitive and specific mechanism for the rapid diagnosis of septic peritonitis. Biochemical tests such as glucose determination must be performed on samples acquired directly from the peritoneum rather than from DPL samples. The authors concluded that a gradient of >20mg/dL between the blood and the abdominal fluid (the abdominal fluid will be less than the blood) was 100% sensitive and specific in dogs for the diagnosis of septic peritonitis. In cats, the same gradient was 86% sensitive and 100% specific for the diagnosis of septic peritonitis. This study should be interpreted with some caution due to small sample size and decreased sample heterogeneity. Of particular concern was the fact that the low glucose in the abdominal fluid samples may have been a reflection of the increased cellularity of the septic samples compared to the non-septic samples, rather than the presence of bacteria.

Suggestive historical and physical examination findings supported by cytologic and biochemical evidence should prompt surgical intervention as soon as patient stability is achieved. Aggressive fluid therapy (isotonic crystalloid and colloid therapy) and early antibiotic therapy are cornerstones of stabilization. Normalization of blood pressure, blood glucose, and other physiologic abnormalities should be attempted prior to anesthetic induction.

Antibiotic Therapy:

Antibiotic therapy for dogs and cats with septic peritonitis is empirical pending culture. However, cytologic characteristics, gram stain results, and the underlying cause (if known) may help direct initial antibiotic therapy. In one retrospective study of septic peritonitis, a high rate of bacterial resistance was found to ampicillin, cefazolin, and flouroquinolones. Lower rates of resistance were found to aminoglycosides and third generation cephalosporins.¹ Recently, the author has completed a microbiological survey of isolates from dogs with septic peritonitis. E. coli and Enterococcus sp. were the most common isolates. Combination therapy with Ampicillin / Aminoglycoside / Metronidazole or Ampicillin / Baytril / Metronidazole provide very appropriate empirical antibiotic choices in cases of community acquired septic peritonitis. Caution must be exercised when using aminoglycosides in animals with poor perfusion as they may potentiate acute renal failure; a condition already recognized as a complication of septic peritonitis in domestic animals. The addition of antibiotics with a strong anaerobic spectrum is appropriate (metronidazole).The author also identified that appropriate empirical antibiotic therapy (antibiotic therapy that was appropriate for all bacteria later isolated) resulted in improved survival compared to inappropriate antibiotic therapy (antibiotic therapy that did not adequately provide coverage against all isolated bacteria). In addition, the author also identified that among survivors of septic peritonitis, those that received appropriate empirical antibiotic therapy (as defined above) had a significantly shorter duration of hospitalization than those that did not receive appropriate empirical antibiotic therapy. It should be recognized that although antibiotic therapy is important, establishment of effective peritoneal drainage is also critical to maximize the likelihood of a positive outcome.

Surgical Goals:

Surgical intervention should be performed as soon as patient stability allows. In most cases, surgical intervention should be able to occur within 3-4 hours of arrival at the hospital. Goals of surgical intervention in dogs and cats with septic peritonitis include elimination of / correction of the source of the contamination, vigorous lavage of the peritoneal cavity using isotonic saline warmed to body temperature, and provision of abdominal drainage when appropriate.

Abdominal Drainage Techniques:

The decision of whether or not to provide postoperative abdominal drainage for animals with septic peritonitis is one that has been debated in the veterinary community for over 20 years without conclusive evidence to support primary closure (PC) over the various methods of peritoneal drainage or vice versa. Until a prospective, randomized clinical trial is performed in which patients are matched according to disease severity and cause, the answer to this question will go unanswered. However, it is the author's contention that providing appropriate abdominal drainage optimizes the likelihood of a positive outcome in dogs with septic peritonitis. Currently, providing appropriate peritoneal drainage in septic peritonitis is considered "standard-of-care".

At the present time, open peritoneal drainage (OPD) is recommended in dogs and cats with septic peritonitis and severe peritoneal contamination that cannot be adequately resolved during the operative period (ex. food within the peritoneum due to gastrostomy tube dislodgement). OPD is performed by placing a continuous monofilament suture pattern in the linea and not tightening it such that a 2-3cm gap remains to allow for drainage, while preventing evisceration. The abdomen is then bandaged with highly absorbent, sterile bandage material. Some surgeons prefer to lavage the peritoneum in the operating room daily when using this method and others merely perform bandage changes every 12-24 hours. Disadvantages of open peritoneal drainage include risk of evisceration, nosocomial infection, and labor intensity necessary to perform bandage changes.

A second method of abdominal drainage that has received recent attention involves utilization of closed suction drains placed within the abdominal cavity (one placed in the cranial abdomen and one placed caudally, both exiting paramedian.¹ These drains are then connected to reservoirs that generate gentle, continuous, negative pressure. The reservoirs are then emptied as necessary. A sterile bandage should be placed to cover the exit sites for the closed suction drains. This bandage should be changed daily. The author prefers to use closed suction drainage techniques when there is generalized peritonitis, but contamination has been well controlled and the source has been resolved. Closed suction drains are likely appropriate for all degrees of severity of septic peritonitis. Disadvantages of closed suction drainage include a low risk of ascending nosocomial infection. Obstruction of drain sites / tubes is rare.

When one of the methods of abdominal drainage is chosen for management of the septic peritonitis case, cytologic examination of the effusion will provide guidelines for when drainage techniques can safely cease. Closure should be considered or closed suction drains removed when cytologic evidence of bacterial contamination (phagocytosed bacteria and degenerate neutrophils) has resolved and volume of the effusion has decreased to <10mL/Kg/day.

Primary closure (PC) is ONLY recommended when contamination is completely controlled and there is only mild evidence of localized peritonitis. Eliminating bacterial infection from a body cavity is difficult without appropriate drainage techniques. The choice to attempt PC accepts this difficulty and the possibility that the patient will effuse further into the peritoneal space.

Postoperative Care:

Postoperative care of the dog or cat with septic peritonitis should include but not be limited to the following key therapeutics.

Optimize blood volume and hydration through fluid therapy with isotonic crystalloids (LRS, Normosol-R, and 0.9% saline) and synthetic colloids (6% Hetastarch). Plasma should only be utilized to control coagulopathy. Central venous pressure can help direct fluid therapy and should be maintained between 5-10cm H2O (above normal). Systolic arterial blood pressure should be maintained at or above 100mmHg and mean arterial pressure should be at least 70-80mmHg. Positive inotropes and pressor therapy may be necessary in dogs and cats with persistent hypotension (after volume loading) due to septic / distributive shock. Hydration should be maintained by calculating maintenance requirements, ongoing losses (discharge volume from closed suction drains or bandage weight), and deficits. Interstitial edema and imbalance between ins and outs is expected in animals with septic peritonitis.

Optimize oxygenation and blood oxygen content. Maintain SpO₂ above 95% and PCV >25% (dogs) and 20% (cats).

Provide nutritional support within 24hrs postoperatively. Combinations of enteral (oral, nasogastric, gastric, or jejunostomy tube feeding) and parenteral (TPN) feedings can be used to meet caloric requirements and prevent protein catabolism. Ideally, all calories are provided enterally, however, enteral feedings are sometimes not well tolerated. The author is currently utilizing a fluoroscopically-guided nasojejunal or esophagojejunal tube placement technique to facilitate enteral nutritional support. Oral force-feeding of critically-ill animals is not indicated in a time when feeding tubes can make enteral nutritional support less stressful. Some patients may need anti-emetics and promotility agents to tolerate enteral feeding.

Optimize electrolyte and acid-base status. Monitor venous or arterial blood gas and electrolyte concentrations 1-2x daily along with blood glucose. Albumin concentration or colloid oncotic pressure (COP) should be assessed once daily. Dogs with septic peritonitis are prone to severe hypoalbuminemia and peripheral edema. Synthetic colloids (6% Hetastarch delivered at 20ml/Kg/day) can be used to provide oncotic support. It is very difficult (and expensive) to transfuse significant amounts of albumin in the form of fresh frozen plasma to medium to large breed dogs. Fresh frozen plasma should be administered to help manage clinical coagulation abnormalities (DIC).

Provide good nursing care. Frequent turning (Q2hr) if the patient is immobile along with range of motion, standing, and even short walks are excellent for the prevention of pulmonary atelectasis. Catheter insertion sites should be assessed daily and rewrapped at that time. Gloves should be worn at all times when handling critically-ill patients.

Provide a mechanism for gastric decompression. Frequently, dogs and cats with septic peritonitis have decreased gastric motility. Accumulation of gastric secretions can result in vomiting or regurgitation, both of which are risk factors for aspiration pneumonia and even vagal arrest. The author uses a nasogastric or gastrostomy tube (placed during surgery) for this purpose in dogs.

Pain / anxiety control. The postoperative patient with septic peritonitis is likely to be severely painful and anxious. Due to frequent hemodynamic instability associated with the postoperative period, cardiovascularly sparing analgesic choices are important. The author prefers a Fentanyl CRI at 3-5mg/Kg/hr because it is short acting, reversible, and provides a steady state of analgesic support. Intermittent bolus therapy with 0.05-0.1mg/Kg Oxymorphone or 0.05-0.2mg/Kg Hydromorphone are also acceptable choices. If additional sedation is necessary above and beyond the sedation that the analgesics will supply, a benzodiazepine may be effective (Midazolam 0.2mg/Kg IV Q2-4hrs).

Conclusion:

A high index of suspicion, early recognition through abdominal fluid sampling, and cardiovascular stabilization will make the dog or cat with septic peritonitis a good anesthetic candidate. Goals of surgery are to eliminate the source of the contamination, to remove the contamination, and provide appropriate abdominal drainage through closed suction or OPD techniques. In the postoperative period, supportive measures directed at existing and emerging problems will help maximize the likelihood of a positive outcome.

Significant portions of these proceedings were previously published for various veterinary continuing education conferences.

Footnotes

Blake Drain Kit. Johnson & Johnson Medical, Somerville, NJ

J-Vac. Johnson & Johnson Medical, Somerville, NJ.

References

1. Mueller MG, Ludwig LL, Barton LJ. Use of closed-suction drains to treat generalized peritonitis in dogs and cats: 40 cases (1997-1999). J Am Vet Med Assoc 2001;219:789-794.

2. Lanz OI, Wllison GW, Bellah, JR et al. Surgical treatment of septic peritonitis without abdominal drainage in 28 dogs. J Am Anim Hosp Assoc 2001;37:87-92.

3. Hardie EM, Rawlings CA, Calvert CA. Severe sepsis in selected small animal surgical patients. J Am Anim Hops Assoc 1986;22:33-41.

4. 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;32:161-166.

5. Crowe DT. Diagnostic abdominal paracentesis techniques: clinical evaluation in 129 dogs and cats. J Amer Anim Hosp Assoc 1984;20:223-230

6. Staatz AJ, Monnet E, Seim HB. Open peritoneal drainage versus primary closure for the treatment of septic peritonitis in dogs and cats: 42 cases (1993-1999). Vet Surg 2002;31:174-180.