September 29, 2016Dr. Naeem Khan Consultant Surgeon | JPMC Karachi
Intra abdominal infections (IAI) represent diverse disease processes and therapies; however, earlier diagnosis with readily available CT imaging, advanced therapeutic techniques of interventional radiology, improvement of antibiotic efficacy, and evolving critical care medicine have all combined to improve patient outcomes.
IAI are divided into complicated and uncomplicated types. Uncomplicated IAI affect the single organ and do not spread to the peritoneum. In these cases, there is no anatomic disruption of gastrointestinal tract. Complicated IAI describes an extension of the infection into the peritoneal space. It may be localized, as in case of intra-abdominal abscess. For the insult that is not contained, diffuse peritonitis may ensue. The resultant physiologic response may develop into a systemic inflammatory response syndrome (SIRS).
In addition for the type of infection, patient stratification serves as an important guide for the treatment and will assist in with initial resuscitation, treatment options, specifically, antimicrobial therapy. Patients are divided into low risk and high risk categories that take into account the patient’s history, the type of infection, and the resulting physiologic derangements.
Low-risk patients typically have community acquired infections of mild to moderate severity (perforated appendicitis or diverticulitis). The underlying physiologic status in these patients is not compromised. High-risk patients on the other hand are used to define patients who are at risk for multi-drug resistant organisms, failure of source control (SC), and ultimately, increased mortality. Predetermined patient specific and disease-specific factors act together to determine patient morbidity and mortality.
Characteristics of high-risk intra-abdominal infection.
Patient-specific factors Advanced age (>70)
- Poor nutrition status
- Corticosteroid therapy
- Organ transplantation
Presence of malignancy
Pre-existing chronic conditions
- Liver disease
- Renal disease
- High APACHE II score(>15)
- Health care associated infection
- Inability to obtain source control.
Diagnosis of IAI should be suspected in patients with SIRS and gastro intestinal dysfunction. Essential components of the history include any recent surgeries, and the presence of vomiting, diarrhea and constipation. Although physical examination findings are notoriously non-specific, particular findings may give insight. Pain out of proportion to examination is classically associated with acute mesenteric ischemia. Inguinal and umbilical hernia examinations are important to rule out the source of obstruction or incarcerations. Although minimally invasive surgery is increasingly common, abdominal scars are always important to know.
Laboratory workup begins with the assessment of complete blood count and serum electrolytes. Liver function test, amylase and lipase may be added if clinical concern includes hepatobiliary or pancreatic pathologic abnormality. In patient with SIRS and a concern for sepsis, further assessment of end organ perfusion and signs of oxygen debt should be assessed (i.e., serum lactic acid, superior venacaval/ mixed venous oxygenation saturations, arterial blood gas for base deficit).
Initial radiographic imaging should include a CT scan with oral and intravenous (IV) contrast to maximize sensitivity and specificity, oral contrast helps to differentiate bowel loops from adjacent fluid collections and may help guide subsequent drainage procedures. IV contrast helps delineate inflammation, identify hemorrhage, and visualize abscess walls. CT is useful in identifying small areas of free intra abdominal air (pneumoperitoneum) associated with hollow viscous perforation, and in the biliary tree, and air within the intestinal walls (pneumotosis intestinalis). The exception to this is if biliary pathologic abnormality is suspected (right upper quadrant pain, nausea, and vomiting), then right upper quadrant ultrasound is the higher yield.
Microbiologic diagnosis is not important in community acquired IAI because empiric antibiotic therapy is initiated based on clinical impression and risk factors. In the cases of high risk patients, blood and intra abdominal cultures are necessary to guide anti microbial therapy due to the higher risk for multi drug resistant organisms.
One of the most urgent clinical circumstances is the patient present with peritonitis (abdominal rigidity, guarding, and rebound tenderness). These signs are concerning for pending hemodynamic collapse and urgent evaluation and disposition are necessary. Early hemodynamic assessment is a priority; if adequate (systolic blood pressure>90mmHg), there may be a time for further workup. On the other hand, unstable patients (systolic blood pressure <90mmHg) and the need for vasopressor support indicate the need of emergent laparotomy for diagnostic and therapeutic purpose with the understanding that the risk of mortality is higher than in a stable patient.
The principles of treatment require simultaneous resuscitation, SC, and anti-microbial therapy. If not aggressively managed, IAI may progressed to severe sepsis, septic shock, and death.
Intravascular volume depletion should be expected in patients with IAI. A thorough history and physical examination may aid with guiding resuscitation.
It has been learned from the Surviving Sepsis Campaign (SSC) that fluid resuscitation should be initiated after diagnosis of sepsis is suspected. The strategy of early gold directed therapy has been shown to decrease mortality.
SC is a fundamental surgical principle and is defined as the ability to effectively eradicate the infection (i.e. purulent fluid or tissue) and control leakage (i.e., drainage of ongoing enteric contamination) by whatever means necessary.
In general, the least invasive procedure that is safely able to eradicate the infection is preferred. Percutaneous image guided drainage is preferred for isolated IAI that are anatomically amenable to drainage. Surgical debridement, whether laparoscopic or open, remains the mainstay of therapy for failed percutaneous control.
Although secondary to adequate SC, appropriate and timely empiric antibiotic coverage is imperative. In appropriate coverage increases hospital stay, postoperative abscesses and mortality that cannot be reversed if subsequent and appropriate antibiotics are added later in the clinical course. In severe sepsis, appropriate coverage should be started within one hour as recommended by SSC. Patient with IAI are divided into low-risk and high-risk category to stratify the risk for developing complicated infections. In general, beta Lactams/Beta Lactamase (penicillins, cephalosporins, carbepenems, monobactams) antibiotic will provide adequate empiric coverage for low risk patients.
High risk patients on the other hand are at the risk for more resistant microbiologic flora. Specifically,
this include gram negative Pseudomonas Aeruginosa and Acinetobacter species, extended spectrum beta lactamase producing Klebsiella species, Escherichia Coli, enterobacter species, proteus species, methicillin resistant staphylococcal aureus (MRSA), enterococci and candida species. Empiric therapy are institution specific and should be adjusted for individual hospitals/ unit antibiograms. Historically, studies have suggested that antibiotics should be continued until the patient has resolved leukocytosis or fever and is tolerating oral diet, and that may not be necessary.
IAI arise from many sites and range from moderate nuisance to life threatening. Prompt identification, diagnosis and treatment allow optimal patient outcomes. Resuscitation from shock, early appropriate antibiotic administration, and control of the source of infection are necessary components of a 3-pronged approach. Initial antibiotic administration should be broad spectrum and tailored to the most likely pathogen and then narrowed to the best agent for appropriate duration. SC may be obtained using radioghraphically placed percutaneous or traditional operative clinical condition. Patient-specific factors (advanced age and chronic medical conditions as well as disease-specific factors health-care associated infections and inability to obtain SC) combined to affect patient morbidity and mortality.
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