The Use of Vacuum-Assisted Closure in the Management of Septic Peritonitis in Six Dogs

Introduction

Septic peritonitis is a complicated disease process that may result from perforated bowel, penetrating wounds, urogenital infections with perforation or rupture, neoplastic processes, hepatobiliary and pancreatic disease, or hematogenous spread. Intraperitoneal sepsis incites a systemic inflammatory cascade that results in a number of physiologic derangements (defined as systemic inflammatory response) that often include cardiovascular dysfunction, shock, subsequent multiple organ dysfunction syndrome, and disseminated intravascular coagulopathy. All of these can contribute to increased patient morbidity or death.^1,2

The treatment of septic peritonitis is challenging, and although studies have shown a dramatic increase in the costs and complexity of treatment, there has been little change in survival rates in either human or veterinary patients.^1–9 Aggressive initial stabilization prior to anesthesia, surgical intervention, abdominal drainage, and appropriate empirical antibiotic therapy are the mainstays of treatment of septic peritonitis in veterinary medicine. Death is a common sequel to septic peritonitis despite aggressive intervention, with mortality rates of 11–48% in veterinary and 23–48% in human patients.^1–8 Treatment requires not only emergent anesthetic and surgical intervention in a systemically unstable patient, but also intense postoperative supportive care. Exploratory laparotomy is indicated for removal of the source of infection, for debridement and lavage of the peritoneal cavity, and for establishment of drainage (if necessary). To date, no objective criteria have been established to determine the need for postoperative drainage, and no standard of care has been established.^{1,3–6,10–12} Several techniques have been reported for achieving postoperative drainage; however, the most effective form of drainage has yet to be established. Reported techniques include placement of closed suction drains, open peritoneal drainage (“open abdomen”), placement of Penrose sump drains, and primary closure that may be followed by a planned second laparotomy for further debridement and lavage.^{3–6,11,13,14} There has been no objective or subjective scoring system used in veterinary medicine to stratify patients, which is commonly used in human medicine.^15,16

In human patients, open abdominal techniques are used in: patients who may benefit from planned re-exploration to re-evaluate organ viability and tenuous closure of perforated bowel; in cases with inadequate initial debridement due to patient instability (“damage control surgery”) or severe contamination; and for patients in which primary closure may lead to unacceptable abdominal wall tension.^{7–9,17–19} In the veterinary literature, open abdomen techniques have been advocated to treat septic peritonitis in grossly contaminated abdomens due to increased survival rates in human and experimental animal studies.^3,6,10,12 One advantage of open abdomen techniques over closed-suction drains is the ability for continuous effective drainage of the entire abdominal cavity.³ Potential disadvantages include the need for a secondary surgical procedure, increased postoperative nursing care, and loss of intra-abdominal fluid, including protein and electrolytes. In the veterinary literature, Lanz et al. (2001) reported similar outcomes with primary closure compared with historical data of open peritoneal drainage following surgery for septic peritonitis in dogs and concluded that primary closure is an acceptable alternative to open drainage.⁵

Mueller et al. (2001) evaluated the use of closed-suction drains in dogs and cats and reported a 30% mortality rate, which is similar to reports using open drainage. Mueller et al. (2001) concluded that closed-suction drainage may provide adequate drainage without the potential complications associated with open peritoneal drainage; however, the amount of drainage was neither quantified nor compared with an open drainage technique.⁴ Multiple studies have illustrated that the presence of the omentum precludes effective drainage through a closed suction drain.^13,14 In other types of peritoneal drainage that require effective egress, such as the use of peritoneal dialysis catheters, problems associated with the omentum are avoided by performing either a partial or total omentectomy at the time of catheter placement.^13,14 However, omentectomy is not advocated in cases of septic peritonitis as it provides an early fibrin seal, as well as a source of immune cells and progenitor cells for injured tissues.¹⁶ In human patients, closed-suction or passive intra-abdominal drains are placed in cases of discrete abscesses, such as necrotizing pancreatitis, and even in those cases, are usually used in conjunction with continuous lavage or with underneath abdominal gauze packing.^9,19,20 Open abdominal drainage techniques remain one of the most common techniques for managing the peritoneal cavity with diffuse sepsis because of the ability for aggressive drainage, improvement in ventilation, and facilitation of re-exploration. Nonetheless, the techniques remain controversial.^17–23 Penrose sump drains are reportedly the most effective form of passive drainage; however, they are less effective in experimental studies than open drainage techniques.¹³ At the authors’ institution, drainage of the peritoneal cavity is implemented when complete removal of the septic nidus is not completely possible because of extensive contamination. Historically, the authors’ institution has used closed-suction drains.

Negative-pressure dressings have been successfully used in wound management in both human and veterinary studies. This technique increases local blood flow in animal wound models, which may also lead to an increased rate of angiogenesis.^24–26 The removal of fluid accumulation and edema (interstitial fluid) is also theorized to decrease many chemical mediators, such as metalloproteinases, associated with impaired healing.²⁴ The decrease in bacterial load (most likely due to the negative-pressure environment and the increased mechanical stress on the tissue, which increases granulation tissue formation), is important to successful wound healing.^25,26 In the human literature, vacuum-assisted laparostomy and temporary closure have been advocated as providing effective drainage of the peritoneal cavity with fewer complications than open drainage.^7,8 These studies have shown a significant reduction in morbidity and mortality associated with vacuum-assisted closure (VAC) compared with open abdominal techniques. Specifically, the mortality rate ranges from 23.9% to 25.9% for VAC compared with 36.6% for open techniques.^7,8 The advantages of vacuum-assisted laparostomy are reported to include the following: protection of the viscera from mechanical injury, prevention of internal organ desiccation, prevention of adherence of the bowel to the closure material or abdominal wall, prevention of external contamination of the peritoneal cavity, and continued effective egress of peritoneal fluid.⁷ The authors of the current study propose that the effects on angiogenesis, effective removal of fluid, and antibacterial properties will be beneficial in the treatment of septic peritonitis and may likewise decrease mortality in veterinary patients.

The goal of this pilot study was to describe the surgical technique, postoperative monitoring, and complications encountered with use of VAC for septic peritonitis. The hypotheses were that effective peritoneal drainage could be established with vacuum-assisted laparostomy and that the postoperative management of vacuum-assisted laparostomy is not subjectively different from the use of closed-suction drainage.

Materials and Methods

The study population included client-owned dogs of any breed, age, or weight >5 kg. Patients were initially diagnosed with septic peritonitis by identification of intracellular bacteria from either a blind or ultrasound-guided four quadrant abdominocentesis, biochemical analysis of abdominal fluid, and peripheral blood that was consistent with septic peritonitis. The reported blood-to-peritoneal fluid glucose difference in dogs is >20 mg/dL and blood-to-peritoneal fluid lactate difference is <−2.0 mmol/L in dogs with septic peritonitis.^27,28 Positive bacteriologic cultures obtained from the peritoneal cavity at the time of surgery were considered confirmatory. At the time of initial presentation, complete blood count and serum biochemistry testing were performed, and baseline parameters including indirect blood pressure by Doppler, temperature, heart rate, and respiratory rate were determined before and after initial stabilization with fluid and/or vasopressor therapy.

General anesthesia was induced in all patients according to standard protocols, depending on their American Society of Anesthesiologists physical status classification. Depending on the initial stability of the patient, induction of anesthesia was performed within the first 1–2 hr after initial diagnosis. The anesthetic protocol, including drugs, vasopressor support, and fluid therapy, was recorded. After routine celiotomy, surgical techniques used were dictated by the primary disease process and followed standard of care practices (i.e., isolation and elimination of infectious source, copious lavage, obtaining appropriate culture samples). After the appropriate surgical procedures were performed, the vacuum-assisted laparostomy was performed. The caudal two-thirds of the linea alba was sutured closed in three layers with appropriate-sized sutures using routine methods. The cranial one-third of the linea alba (i.e., the most dependent aspect) was sutured with a simple continuous pattern, leaving 0.8–1.2 cm between the edges and 1–1.5 cm between each pass of the needle to avoid any large gaps where bowel could become entrapped. A sterile 14 French red rubber catheter^a was inserted into a cut piece of sterile single cell polyethylene foam^b and placed over the laparostomy. Sterile suction tubing was connected to the red rubber catheter via a Christmas tree adapter^c, and a sterile sealant drape^d was placed over the ventral abdomen, incorporating the red rubber catheter and the polyethylene foam (Figure 1). The red rubber catheter was then connected to a continuous suction unit^e by sterile suction tubing^f and maintained at 125 mm Hg in the intensive care unit. Careful attention was paid to the seal after the vacuum was turned on to ensure there were no leaks in the system. A standard soft padded bandage (i.e., cast padding, elastic gauze, nonadhesive elastic dressing^g) was placed over the laparostomy and abdomen.

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Postoperatively, the patient was housed in the intensive care unit. Standard management included IV fluids (crystalloid with or without colloids), vasopressors (if necessary), antimicrobials, analgesia, abdominal fluid evaluation (for cytology and electrolytes) and quantification, nutritional support, urine output, daily monitoring of packed cell volume (PCV) and serum and abdominal protein levels, and monitoring of vital parameters (i.e., heart rate, respiratory rate, blood pressure, temperature). Bandages were evaluated at least q 12 hr daily for evidence of slippage, strike through, and loss of air seal. The decision for primary closure was at the discretion of the primary surgeon and was based on the absence of bacteria in the abdominal fluid collected daily, the extent of the initial infection, a significant decrease in the amount of fluid collected daily, and abdominal fluid and blood test results (i.e., albumin, lactate, glucose). Other variables involved in the decision to close involved necessity to re-evaluate internal organs and stability of the patient to undergo a second anesthetic procedure.

On the day of the final closure, the patient was moved to the operating room preparation area, and the soft padded bandage was removed, leaving the sterile sealant drape in place except for any shaving that was deemed necessary around the edges. The patient was moved into the operating room, and the sterile sealant drape and polyethylene foam were removed. The skin was prepared with saline and chlorhexidine scrub^h, carefully avoiding the open edges of the incision or abdominal contents with the chlorhexidine. The previous caudal incision was then opened, and a full exploratory was performed. If any pockets of fluid were encountered, they were drained, and copious lavage was performed, followed by routine abdominal closure. Time to closure (secondary procedure), postoperative complications, and survival to discharge were recorded.

Results

Six dogs met the inclusion criteria for the study (Table 1). Two were identified with jejunal perforations, two with colonic perforations, and one each with gastric necrosis and duodenal perforation at the time of the initial surgery. Patient ages ranged from 2.5 yr to 12 yr (median age was 7.25 yr). Body weights of the patients ranged from 5.5 kg to 39.3 kg (median weight was 23.4 kg). Four dogs weighed >17 kg, and the other two were <7 kg. There were variable heart rates, respiratory rates, and temperatures on admission in all six patients (Table 2). All dogs were considered to be in either compensated shock (evidenced by elevated hear rates, respiratory rates, normal to injected mucous membranes, normal to brisk capillary refill times) or decompensated shock, indicated by abnormal blood pressures that were poorly responsive to treatment with IV fluids, pale or dry mucous membranes with prolonged capillary refill times, decreased mental responsiveness, and biochemical (lactate, pH) derangements.

TABLE 1 Patient Information and Outcomes

SF, spayed female; M, male; MC, castrated male; G-tube, gastrostomy tube; G-J tube, gastrojejunostomy tube.

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TABLE 2 Patient Culture Results, Vital Parameters, and Fluid Quantification

BFG, blood-to-fluid glucose; BFL, blood-to-fluid lactate; PCV, packed cell volume; SpO₂, pulse oximeter oxygen saturation.

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TABLE 2 (Continued)

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Discussion

Septic peritonitis is a complex process initiated most commonly by a bacterial focus, causing damage and inflammation of the primary and surrounding organs and usually culminating in circulatory shock, multiorgan failure, and death. This process has been historically difficult to treat, with high mortality rates in both veterinary and human patients despite aggressive medical and surgical treatment. Due to the dismal outcomes seen in this patient group, alternate treatment techniques have been (and will continue to be) investigated. Although data suggesting one surgical closure method is superior are lacking, there has been no clear stratification of patients depending on the severity of their intraperitoneal disease.

VAC has been recommended in human medicine for cases of diffuse peritonitis and severe contamination and is especially helpful in cases where re-evaluation of the surgical site is desired.^8,9,17,18,21 This technique have many proposed advantages for treating severe peritoneal contamination, including effective ongoing drainage, decreased bacterial load due to a less favorable environment, and increased angiogenesis.^7,8 A survival advantage has been shown in human studies of VAC, but this is the first study to report on the feasibility of this technique in the veterinary population.⁸

The technique described herein for VAC was simple to perform in unstable patients and did not require any specialized equipment other than a portable suction unit and the open cell polyethylene foam. There is a commercially available systemⁱ that includes the suction unit, foam, and specially designed tubing, but in the authors’ experience, these items are not necessities. The theoretical effectiveness of the drainage was proven during the secondary procedure, as there was only small amounts (<5 mL) of fluid found within the peritoneal cavity. There was also a documented decrease in the amount of fluid production over the 2 days that the VAC was in place. The fluid suctioned off in the first few hours after surgery was most likely residual flush from surgery, but peritonitis and the suction mechanism from the VAC both could contribute to fluid production in the days following the initial procedure. The patients (subjectively) appeared comfortable with the VAC in place and did not require aggressive pain management (all patients were managed with either bolus injections of opioids or low rates of fentanyl infusions). A decrease in fluid production most likely leads to a decrease in stimulation of the many nerve endings lining the peritoneum; however, it is unknown how mechanical vacuum pressure may affect these peritoneal nerve endings in dogs.²⁹ In the veterinary reports of vacuum bandages for wounds, patients have tolerated the bandages quite well.^24,26 Decreasing peritoneal fluid accumulation should lead to a more comfortable patient, as well as decreasing the inhibitory effects of excessive fluid on the peritoneal immune system by diluting the circulating macrophages and monocytes.^13,29 There were no major complications with postoperative care of these bandages in the three patients that survived. The most common minor complication with the bandage included loss of suction from a leak in the seal, which was easily repaired by the technical staff. None of the patients had bandage sores or dermatitis at the wound edges or seemed uncomfortable when the suction was turned back on following visits from their owners or going for walks.

A potential disadvantage of the VAC technique is the secondary procedure that requires a subsequent anesthesia. All surviving dogs had uncomplicated anesthetic episodes for their closure procedure, and all three surviving dogs were considerably more stable at the time of the second surgery, requiring less intensive anesthesia. Although the cost of this additional procedure may be an important consideration, a comparison of historic patients at the authors’ hospital admitted for septic abdomen and treated with closed suction drainage revealed that VAC patients were sometimes hospitalized for shorter periods of time, and the cost was similar because of a decreased fee for the second procedure.

With regards to PCVs and protein changes seen in this small case series, there is unfortunately no ability to compare these results with previously reported studies on surgical treatment of septic abdomens. Interestingly, looking back to those reports, the discussion of protein loss is sparse and there is no discussion of changes in either peritoneal fluid or blood lactate levels, glucose, or PCV. Two of the three surviving dogs in the current study had low (but normal) albumin levels before surgery, and both of those patients experienced a decrease in postoperative albumin (Table 2). Albumin transfusions were performed in two dogs, and no obvious negative side effects were noted. Because of the lack of specific values discussed in the previous studies, it is impossible to compare the decrease in albumin levels noted in this study to other techniques. Additional studies are encouraged to determine whether this decrease in albumin was more rapid compared to other studies and whether it affects prognosis. Although the PCV did decrease in two of the three surviving patients, neither of those dogs required a blood transfusion.

A 50% mortality rate was observed in this case series, which is consistent with some of the previous reports of septic abdomen treatment techniques. Although this mortality rate is higher than some reports of open peritoneal drainage and closed suction techniques, there are other reports of primary closure and open peritoneal drainage that have reported consistent numbers to the current study.^3–6,12 Possible causes for the higher mortality rate in the current study may be attributable to the small case numbers compared with other reports and the extent of disease found in the dogs included in this study. When comparing methods of abdominal drainage with regards to determining outcome, it will be extremely important to stratify patients according to their systemic and peritoneal disease to establish a recommended drainage technique. Most likely, the deaths that occurred so quickly after surgery were related more to the severity of the systemic and peritoneal disease rather than the method of drainage chosen. Interestingly, the use of VAC in human medicine is most commonly indicated for the worst cases of peritoneal contamination.^7,8 Further study should be performed on a larger population to investigate whether this recommendation can be made for veterinary patients.

Conclusion

VAC is a feasible technique for managing septic peritonitis in the veterinary population and does not require a more strenuous postoperative management style than closed-suction drainage techniques in the hands of experienced staff. VAC may hold advantages over traditional methods due to increased efficacy of drainage, decreased bacterial load, and the ability for a “second look” investigation; however, prospective multicentered cohort studies are needed to compare VAC to other commonly used techniques.