2 Nov 2016
Septic peritonitis is life-threatening if intervention is not rapid. Here, Andrew Linklater explains how guidelines from a human medicine campaign can help direct patient management.
Andrew Linklater
Job Title
Jejunal perforation.
Septic peritonitis is uncommon in veterinary medicine, but can be immediately life-threatening if treatment is not rapid and appropriate.
The sequence of common pathophysiological events that occur with any infectious or inflammatory disease can result in systemic inflammatory response syndrome (SIRS) which is hard to control once under way.
The consequences of SIRS include:
Alterations in production and distribution of proteins, specifically albumin, can be a major contributing factor and has been associated with poor prognosis.
The most common source of abdominal sepsis in veterinary patients results from an internally spreading bacteria, most commonly originating from the gastrointestinal (GI) tract. Other sources, such as abscessation (blood borne) or externally penetrating trauma may be causative factors as well.
Several types of diseases can lead to GI perforation:
Aggressive therapy is necessary for these patients to address and correct the source of the infection, or underlying problem, to limit the systemic consequences of SIRS.
The SIRS criteria for veterinary patients are quite sensitive (97%), but not very specific (64%). For a diagnosis of SIRS, a patient must meet two (dogs) or three (cats) of four criteria:
Dogs that met these criteria had an increased mortality in one study. Three of four of these criteria are changes that can be noted on a physical exam; these changes may be noted at the time of presentation, or during the course of hospitalisation.
Diagnosing sepsis involves meeting the definition of SIRS along with an identified, or suspected, infection. Suspected abdominal infection is often easily identified with imaging along with collection and analysis of fluid samples (glucose, cytology), or through surgical means (Figure 3). Two studies demonstrated a high sensitivity and specificity for abdominal sepsis when fluid glucose is more than 20mg/dl lower than blood glucose.
The Surviving Sepsis Campaign (SSC) has been put together in human medicine to define the roles of sepsis, note targets for intervention and, hopefully, cue increased research for future studies. Many aspects of the SCC have not been specifically examined in veterinary species, but the guidelines may direct patient management. The following is the author’s veterinary adaption of the SSC.
Patients should be screened early, based on history and physical exam, so appropriate therapy can be implemented early. Meeting the SIRS criteria, evidence of abnormal swelling and pain with or without heat should be immediately investigated.
Routine laboratory tests (complete blood count, serum biochemistry and lactate) and imaging (radiographs and ultrasound) can easily identify many septic patients.
Ultrasonography techniques, such as abdominal focused assessment with sonography for trauma (FAST) and thoracic FAST, are inexpensive and simple to perform. Any cavitary fluid should be collected via centesis for analysis.
Several studies support the use of paired blood and fluid glucose levels, and cytology, to assist diagnosis.
There should be minimal delay in definitive treatment if septic peritonitis is identified or suspected. Although it is ideal to wait until samples have been collected, there should be no delay in administration of antibiotics when a life-threatening infection is present.
In humans, each hour of delay in appropriate antibiotic administration is associated with increased mortality. A veterinary study demonstrated improved mortality when an emergency protocol for initiation of antibiotics was in place.
When antibiotics are administered, empirical therapy is initiated based on common aetiological agents, patient history, location of infection and in-house diagnostic tests (such as cytology or Gram staining). There is little margin for error when patients have a life-threatening infection, so four-quadrant antibiotic therapy is chosen initially while culture and susceptibility results are pending.
Tissue or fluid samples, when available, should always be sent to a laboratory to identify the aetiological agent and susceptibility pattern; this will ensure appropriate antibiotic therapy is administered.
One veterinary study has examined collection of culture material before and after abdominal cavity lavage, and did not demonstrate significant difference in positive culture samples.
Although broad-spectrum therapy is initiated early, this therapy should be de-escalated as soon as culture/susceptibility results are available. Rarely is it necessary for empirical therapy only to continue for more than three to five days.
Antibiotic therapy should be administered intravenously until oral absorption of medications can be relied on.
Due to the consequences of SIRS or the primary disease, poor GI motility, absorption and oedema are common in these patients and this results in unreliable antibiotic level when administered orally. What is considered appropriate antibiotic therapy is a widely controversial topic. Four-quadrant coverage includes:
Once the aetiological agent and susceptibility testing is known, coverage should be immediately de-escalated to the most appropriate antimicrobial agent. Antibiotics should not be excessive or insufficient.
In addition, one must consider the clinical response of the patient; an intact immune system should be able to eliminate causative bacteria and result in a resolution of clinical signs, even if empirical antimicrobial choice was not ideal.
Deterioration of the clinical condition may warrant a change in antimicrobial therapy or re-investigation of the aetiological agent, especially if four-quadrant coverage was not initiated.
The necessity for, and the spectrum of, antimicrobial therapy should be re-evaluated daily. Consideration should be given to narrowing the spectrum of antimicrobials used based on clinical improvement, and/or culture and susceptibility testing.
The goal of narrowing the spectrum of antimicrobials is to limit the development of multiple resistance patterns in bacterial populations; this “de-escalation” should be employed as soon as possible.
There is little to no evidence prolonged courses of inappropriate antibiotics improve outcome, even in septic patients.
Although one study demonstrated longer hospitalisation (by one day) for patients in whom de-escalation is employed, two studies have demonstrated an improved overall mortality rate when de-escalation was employed.
All three human studies came out after a 2013 Cochrane review when it was determined little evidence was available to support this practice.
Duration of antibiotics may also not need to be prolonged. Veterinarians tend to believe if the infection was “really bad”, it may require prolonged therapy; that’s not neccesarily the case.
Some evidence in human medicine shows a 7 to 10-day duration of antibiotics is often sufficient with appropriate source control. A recent review demonstrated as little as three to five days may be appropriate when source control is used and leukemoid response is monitored to guide therapy.
Investigating the use of biomarkers, such as procalcitonin, to help guide de-escalation and duration of antibiotics is ongoing in human medicine. Little evidence exists in veterinary medicine at this time for use of procalcitonin as a tool to guide antibiotic therapy.
A human study reported a decrease in duration of antibiotic use when procalcitonin was used as a guide; however, the study had small numbers.
One of the most important aspects of treatment is source control. Once a source of infection has been identified, it should be eliminated or minimised as soon as it is safe for the patient.
Source control has been demonstrated as an independent risk factor for mortality in humans with abdominal infections. When this involves an abdominal source, surgery to identify and remove, or minimise, the problem is initiated.
The most common sources of infection in the abdomen involve the GI tract; however, the urogenital or biliary system may also be involved. External penetrating injury, such as bite wounds or penetrating foreign objects, and blood-borne infection are less common.
Source control involves identifying the source of the infection, minimising further contamination, controlling and cleaning the infection area, and correcting the problem, such as with a resection and anastomosis.
Debate exists about the ideal postoperative management of septic peritonitis. Placement of a closed suction drain allows for daily cytological exam and quantification of fluid amount and character. Paired fluid and blood glucose is unreliable in the postoperative patient.
Open abdomen technique was used more commonly in the past; a potential increased risk of nosocomial infection is commonly cited for decreased use of this technique.
Placement of a vacuum-assisted suction device as an abdominal drain has been investigated and is considered an acceptable technique, although not widely used. Overall, little difference is seen between these techniques in outcome.
If a closed technique is used, re-exploration in three to five days may be a consideration. It is preferable to remove any medical devices (catheters, drains) as soon as possible to limit development of biofilms; they may contribute to development of bacterial resistance.
After the initial intervention, the patient must be monitored closely for:
Patient vital signs, complete blood count and fluid accumulation, or clinical signs of deterioration (pain, vomiting), may warrant re-exploration.
Preventing multiresistant bacteria is a multifaceted technique and involves most of the aforementioned steps – appropriate and timely antibiotic control with de-escalation, source control and removal of medical devices (Figure 4). Multi-drug resistance can complicate any infection.
It is important to not change the type of antibiotics without specific reason (lack of improvement, cytological exam or culture and susceptibility results).
Managing a critically ill patient involves addressing all organs and aspects that can be affected by critical illness. The author recommends using Kirby’s Rule of 20 to assess critically ill patients twice daily.
This will ensure the clinician is being proactive when monitoring and addressing all aspects of the patient’s needs, as many organs can be affected by systemic inflammation.
