Surgical Infections

chapter 6 Schwartz's Principles of Surgery short review

By Anas Mk Hindawi PGY1 surgery straight intern MGH 23/08/2012

PATHOGENESIS OF INFECTION

• Endogenous defense mechanisms are either at tissue level or systemic /circulate in bld or lymph / .

• Natural skin barrier + resident skin microflora and sebacous secretions

• Upper and lower resp. tract defense mechs.

• The urogenital, biliary, pancreatic ductal, and distal respiratory tracts do not possess resident microflora in healthy individuals

• significant numbers of microbes are encountered in many portions of the gastrointestinal tract

• The relatively low-oxygen, static environment of the colon is accompanied by anaerobic microbes that outnumber aerobic species approximately 100:1 in the distal colorectum,

• Microbes encounter host defense mechanisms by mean of resident macrophages and complement (C) proteins and Ig antibodies .

• Macrophages secretes (TNF-α), interleukins (IL)-1, 6, and 8; and interferon-γ (INF-γ )

• A counterregulatory response is initiated consisting of binding proteins TNF-BP ,cytokine receptor antagonists IL-1ra and antiinflammatory cytokines IL-4 and IL-10 .

• As an outcome opsonization, phagocytosis and extracellular and intracellular destruction of the microbe … followed by further influx of inflammatory fluid and PMNs into the area of incipient infection

Outcomes of microbial and resident host defenses interaction

1. Eradication

2. Containment often leading to the presence of purulence

3. Locoregional infection (cellulitis, lymphangitis) with or without distant spread of infection (metastatic abscess)

4. Systemic infection (bacteremia or fungemia).

• Sepsis : infection plus systemic manifestations of infection

• Severe sepsis : sepsis plus sepsis-induced organ dysfunction or tissue hypoperfusion. The threshold for this dysfunction has varied somewhat from one severe sepsis research study to another.

• Sepsis-induced hypotension : SBP < 90 mm Hg or MAP < 70 mm Hg or a SBP decrease 40 mm Hg or 2 SD below normal for age in the absence of other causes of hypotension.

• Septic shock : sepsis-induced hypotension persisting despite adequate fluid resuscitation.

• Sepsis-induced tissue hypoperfusion : either septic shock, an elevated lactate, or oliguria.

MICROBIOLOGY OF INFECTIOUS AGENTS

• Gram-positive bacteria frequently cause infections in surgical patients include aerobic skin and enteric organisms.

• Gram-negative bacilli of note include Pseudomonas species, including Pseudomonas aeruginosa and P. fluorescens and Xanthomonas species

• Aerobic skin commensals are the most frequent cause of surgical site infections (SSIs)

• Enterococci can cause nosocomial infections in immunocompromised or chronically ill patients

• Anaerobic : GI bacteroides fragilis

• culture. Fungi of relevance to surgeons include those that cause nosocomial infections in surgical patients as part of polymicrobial infections or fungemia

• (e.g., Candida albicans and related species)• • rare causes of aggressive soft tissue infections (e.g., Mucor,

Rhizopus, and Absidia species

• opportunistic pathogens that cause infection in the immunocompromised host (e.g., Aspergillus species, Blastomyces dermatitidis, Coccidioides immitis, and Cryptococcus neoformans)

Viruses• viruses are difficult to culture

• Recent advances in technology have allowed for the identification of viral DNA or ribonucleic acid (RNA) like pcr .

• Most viral infections in surgical patients occur in the immunocompromised host, particularly those receiving immunosuppression to prevent GVH .

• Relevant viruses include adenoviruses, CMV , EBV , HSV , and VZV .

• Surgeons must be aware of the manifestations of hepatitis B and C virus, and HIV infections, including their capacity to be transmitted to health care workers

PREVENTION AND TREATMENT OF SURGICAL INFECTIONS

• General Principles

• Source Control

• Appropriate Use of Antimicrobial Agents

General Principles

• preoperative scrub by operating room personnel

• preoperative skin preparation (with clipping, not shaving)

• intraoperative aseptic technique

• Preparation of areas of the body

Source Control

Source Control

Appropriate Use of Antimicrobial Agents

• Timing of prophylaxis for surgery is critical

• Agents are selected according to their activity against microbes likely to be present at the surgical site :

• Infections not involving the GI tract or biliary/pancreatic tract a dose of first generation cephalosporin is appropriate

• Infections involving GI/biliary/pancreatic tracts, any one of a number of agents may be utilized (e.g., cefotetan, ampicillin-sulbactam, ertapenem, many others).

• Additional doses can be given acc. To duration of procedure and half life time of Abx.

• Empiric therapy is restricted to

• underlying disease process (e.g., ruptured appendicitis)

• when significant contamination during surgery has occurred (e.g., inadequate bowel preparation or considerable spillage of colon contents).

• Critically ill patients in whom a potential site of infection has been identified and severe sepsis or septic shock occurs.

• Empiric therapy should be limited to a short course of drug (3–5 days)

• Narrowing the spectrum of coverage and reducing the duration of therapy : reduce the likelihood that the patient will develop superinfection with resistant organism

• However, the desire to minimize superinfections should not take precedence over the need to give the patient an adequate course of therapy to cure the infection that caused the severe sepsis or septic shock.

• Among surgical patients therapy is employed, particularly in relation to the use of microbiologic data (culture and antibiotic sensitivity patterns)

• Monomicrobial infections frequently are nosocomial infections occurring in postoperative patients, such as UTIs, pneumonia, or catheter-related infection.

• Polymicrobial infections, culture results are less helpful because it is difficult to identify all microbes that comprise the initial polymicrobial inoculum.

• For this reason, the antibiotic regimen should not be modified solely on the basis of culture information, as it is less important than the clinical course of the patient.

• In clinical trials of antimicrobial therapy for appendicitis including antimicrobials with activity against appropriate gram-negative and anaerobic organisms

• most failures could not be attributed to antibiotic selection, but rather were because of the inability to achieve effective source control.

• prophylaxis is limited to a single dose immediately prior to incision.

• Empiric therapy limited to 3–5 days or less, and should be curtailed if the presence of a local site or systemic infection is not revealed.

• Absence of laboratory and physical signs of infection provide assurance that infection has been eradicated.

• The incidence of cross-reactivity appears highest for carbapenems, much lower for cephalosporins (approximately 5–7 percent)

• Anaphylaxis is a contraindicated cause of usage of any class of the drug

INFECTIONS OF SIGNIFICANCE IN SURGICAL PATIENTS

• Surgical Site Infections

• Intraabdominal Infections

• Infections of the Skin and Soft Tissue

• Postoperative Nosocomial Infections

• Sepsis

• Blood-Borne Pathogens

In healthy individuals :

• Class I and II wounds may be closed primarily

• Skin closure of class III and IV wounds is associated with high rates of incisional SSIs (approximately 25–50 percent).

• The superficial aspects of these latter types (class III and IV ) should be packed open and allowed to heal by secondary intention, although selective use of delayed primary closure has been associated with a reduction in incisional SSI rates.

• Effective therapy for incisional SSIs consists solely of I&D without the addition of antibiotics.

• Unless there is evidence of severe cellulitis or signs of concurrent sepsis.

Intraabdominal Infections

Primary microbial peritonitis • Monomicrobial • Either haematogenous or direct inoculation • Rarely require surgical intervention. • Treatment rarely surgical

Secondary microbial peritonitis• Due to perforation or severe inflammation and infection of an intraabd. Organ• Effective therapy requires source control and administration of antimicrobial agents

directed against aerobes and anaerobes• If successful mortality rate 5-6 % , if not mortality rate … 40 %

tertiary (persistent) peritonitis• In immunosuppressed peritoneal defenses that do not effectively recover from the initial

secondary microbial peritonitis• Typically in combination• Even with effective antimicrobial agent therapy mortality rates in excess of 50 percent .

Surgery role in Intraabdominal Infections

Intraabdominal abscess diagnosed by CT Abd and drained percutaneously

Surgical intervention is reserved for those who :

• Harbor multiple abscesses• Abscesses in proximity to vital structures such that percutaneous

drainage would be hazardous• An ongoing source of contamination (e.g., enteric leak) is identified

Surgical management combined with a short course (3–7 days) of antibiotics that posses aerobic and anaerobic

Infections of the Skin and Soft Tissue

• Superficial skin and skin structure infections such as cellulitis, erysipelas, and lymphangitis invariably are effectively treated with antibiotics of grampositive skin microflora alone

• Search for a local source of infection should be undertaken. • Furuncles or boils may drain spontaneously or surgicaly

• Aggressive soft tissue infections are rare, require immediate surgical intervention plus administration of antimicrobial agents.

• Extremely high mortality rate (approximately 80–100 percent), and even with rapid recognition and intervention 30–50 percent.

• These infections are classified based on the soft tissue layer(s) involved (skin and superficial soft tissue, deep soft tissue, muscle) and the pathogen(s) that cause them.

Infections of the Skin and Soft Tissue• Patients at risk are older adult, immunosuppressed, or diabetic ,pvd or those with a

combination of these factors

• Aggressive necrotizing soft tissue infections is most commonly clinical. • sepsis syndrome or septic shock without an obvious cause is likely to occur . • Affected areas include the extremities, perineum, trunk, and torso.

• Examination for an entry site from which grayish, turbid semipurulent material (“dishwater pus”) can be expressed, and for the presence of skin changes (bronze hue or brawny induration), blebs, or crepitus. The patient often pain at the site of infection that appears to be out of proportion

• Radiologic studies should be undertaken only in patients in doubt of diagnosis

• Acc. To findings above immediate surgical intervention, is mandatory for exposure and direct visualization

• Antimicrobial agents against gram-positive and gram-negative aerobes and anaerobes (e.g., vancomycin plus a carbapenem), and high-dose aqueous penicillin G

• 60–70 percent of such infections are polymicrobial

Postoperative Nosocomial Infections

• SSIs, UTIs, pneumonia, and bacteremic episodes are most common ones

• UTI considered acc. To U/A with +LE and WBC ,and confirmed by culture with greater than 104 CFU/mL of microbes in symptomatic patients, or greater than 105 CFU/mL in asymptomatic patients

• Tx with adequate Abx and removing indwelling catheter as quickly as possible (1-2 days )

Postoperative Nosocomial Infections

• VAP is highly resistant• Dx by clinical criteria of of purulent sputum, fever, elevated

WBC, pulmonary consolidation ,BAL • Weaning of surgical patients as feasible to avoid this kind of

infections

• Indwelling IV catheters are used for physiologic monitoring, vascular access, drug delivery, and parenteral nutrition

• 25 percent will become colonized, and 5 percent will be associated with bacteremia

• Mainly asymptomatic elevated wbc or manifest as fever of unknown origin

Sepsis

Sepsis

• Drotrecogin alpha (activated), also known as Xigris, is a recombinant form of human activated protein C

• Its usage in sepsis syndrome has been associated with a 6 percent overall reduction in mortality for patients with at least two organ failures

• Its infusion should be interrupted for procedures or surgery, or for significant life-threatening bleeding

• A number of randomized, controlled trials have demonstrated the benefit of replacement doses of corticosteroids in patients with severe shock states.

• In patients who develop septic shock, these authors currently initiate low-dose hydrocortisone (100 mg/8 h) after performing a corticotropin stimulation test

Blood-Borne Pathogens

• Risk of HIV transmission to physicians is as 1 in 200.000 surgeons if no postexposure prophylaxis taken

• Hep B and C infections

Sources

• chapter 6 Schwartz's Principles of Surgery short review

• Surviving Sepsis Campaign: International guidelines for management of severe sepsis and septic shock: 2008