Postpregnancy Genital Tract and Wound Infections

Nell Tharpe, CNM, CRNFA, MS


J Midwifery Womens Health. 2008;53(3):236-246. 

In This Article

Surgical Site Infections

The CDC's National Nosocomial Infection Surveillance system (NNIS) defines surgical site infection as an infection that occurs at an incision site, or any part of the anatomy that was opened or manipulated during the procedure, within 30 days after surgery, or within 1 year in the presence of an implant. Surgical site infections are further classified by such criteria as the presence of purulent drainage, isolation of organisms from the wound, fever, pain, spontaneous wound dehiscence, and/or the presence of an abscess.[2] The NNIS system defines surgical site infections by location -- i.e., infection occurring in the superficial tissues (skin and subcutaneous), deep tissues (fascia and muscle), or in an organ/space (such as the uterus or the abdominal cavity). These definitions are based on specific objective criteria, and exclude infected episiotomies, which have separate diagnostic criteria.[2,28] The British modification of the NNIS system requires the presence of pus cells as evidence of microorganisms in the wound and excludes the need for physician diagnosis of wound infection.[31]

Another system for evaluating wound infection is based on the need for additional treatment; the presence of serous discharge, erythema, purulent exudate, and separation of the deep tissues; the isolation of bacteria, and the duration of inpatient stay (ASEPSIS). Known as the ASEPSIS system, this method utilizes a quantitative scoring method to assign a numerical score to objective criteria, with a score of more than 20 defined as infected, and a score of more than 30 as moderately to severely infected.[31]

Wilson et al.[32] performed a prospective observational study to assess agreement between common definitions of wound infections and found that the mean percentage of wounds classified as infected varied widely based on the criteria used: 19.2% using the CDC definition (95% CI, 18.1-20.4%), 14.6% (95% CI, 13.6-15.6%) using the British modification of the NNIS system, 12.3% (95% CI, 11.4-13.2%) using the presence of pus alone, and 6.8% (95% CI, 6.1-7.5%) using an ASEPSIS score of more than 20. These differences led to the observation that while a single definition that is used consistently is an effective means of assessing change in wound rates within a facility, it may be inadequate when comparing rates between facilities. There is a need for an evidence-based definition of wound infections that is reproducible, acceptable, and reliably captures infections that are clinically significant.[32]

The risk of surgical site infections is more common in women with an elevated body mass index.[33] Robinson et al.[33] compared maternal outcomes in women based on prepregnancy weight. The incidence of cesarean wound infections and episiotomy infections in women who were non-obese (prepregnant weight, 55-75 kg) was 0.8% (n = 633), whereas 1.4% (n = 129) of the women who were moderately obese (prepregnant weight, 90-100 kg) and 3.9% (n = 30) of those who were severely obese (prepregnant weight, >120 kg) were diagnosed with cesarean wound infection. After adjusting for factors that are known to affect the incidence of cesarean birth and infection, women who were moderately obese were 1.6 times (95% CI, 1.31-1.95) more likely to have a wound infection when compared to non-obese women, and women who were severely obese were 4.45 times (95% CI, 3.00-6.61) more likely to have a wound infection when compared to non-obese women.[32] In a retrospective analysis of women admitted for a diagnosis of necrotizing fasciitis (n = 23), Gallup et al.[30] noted that obesity was present in over 85% of the women who were treated for necrotizing faciitis.

Most wound infections are attributed to the introduction of endogenous flora into the wound during the surgical procedure. Procedures involving the female reproductive tract are considered clean-contaminated; that is, the normal flora of the vagina are presumed to contaminate the wound.[34,35] Additional potential sources of bacterial contamination include the members of the surgical team, the surgical environment, and the instruments and supplies used during the procedure.[2] Obstetric and gynecologic wound infections are most likely to result from Gram-negative bacilli, enterococci, group B streptococci, and anaerobes.[2] Current perioperative care includes simple, easily performed measures intended to create an environment that discourages growth of these organisms.

In order to perform the Pfannenstiel incision commonly used during low transverse cesarean, hair removal may be necessary. While clipping and depilatory use result in lower rates of surgical site infections than shaving, leaving hair intact is associated with the lowest surgical site infection rates.[2] In a 2006 review of 11 randomized, controlled trials comparing no hair removal and hair removal by shaving, clipping, or depilatory creams, Tanner et al.[36] found that there were more surgical site infections when shaving was compared to clipping (3 trials, n = 3193; RR, 2.02; 95% CI, 1.21-3.36), and when shaving was compared to depilatory (7 trials, n = 1213; RR, 1.54; 95% CI, 1.05-2.24). Three trials demonstrated no difference in surgical site infections when hair was removed by depilatory or clipper or left intact. They concluded that when hair removal is necessary, the use of clippers or depilatory creams results in fewer surgical site infections than shaving.[36]

Additional measures, such as use of preprocedure antiseptic showers using 2% chlorhexidine gluconate,[2] the use of preoperative betadine vaginal preparation before nonemergent cesarean,[5] the provision of supplemental oxygen during and after surgical procedures,[37] the maintenance of normothermia through the use of warming blankets during surgery,[38] and thorough patient education regarding postoperative wound care may effectively reduce the incidence of postoperative endometritis and surgical site infection.[2,7,14,16]

Tissues that become ischemic or hypoxic are more easily colonized by pathogenic bacteria. Wound tissue oxygenation relies on ample tissue perfusion and adequate circulating oxygen. Peripheral vasoconstriction, which occurs in the cool environment of the operating room or as a consequence of anesthesia, results in decreased superficial tissue perfusion, which leads to limited oxygenation. An elevated partial pressure of oxygen (PaO2) is necessary to force oxygen into tissues where the microcirculation is disrupted by surgery or is naturally limited, such as in subcutaneous tissues and fascia. Tissue oxygenation is supported through supplemental oxygen administration, the use of warming devices, good pain control, and moderation of stress.[14]

In a trial evaluating the effects of supplemental oxygen on wound infection rates in patients undergoing nonemergent colon resection, the administration of 80% oxygen in the perioperative period (including 2 hours postsurgery) resulted in a decreased rate of surgical wound infections (n = 250; 5.2%; 95% CI, 2.4-8%) compared to administration of 30% oxygen (n = 250; 11.2%; 95% CI, 1.2-10.8).[37] Meticulous attention to adequate fluid volume and normothermia was maintained to prevent vasoconstriction and ensure adequate perfusion of the wound.

The use of warming devices to maintain normothermia and optimize tissue oxygenation in the perioperative period is thought to decrease rates of wound infection, although conflicting data exist. In one retrospective study of women undergoing cesarean delivery, higher maternal temperatures noted in the recovery room (36.4 ± 0.8°C vs. 35.9 ± 0.7°C; P < .001) were associated with an increased incidence of postoperative infection. The investigators postulated the higher temperatures represented subclinical infection present at the time of delivery.[39] A randomized, controlled trial by Melling et al.[38] (n = 416) evaluated the effects of preoperative warming before clean surgical procedures (breast, varicose vein, or hernia surgery) and found fewer wound infections in the patients who were warmed 30 minutes before surgery (5% vs. 14%; P = .001) .[8] Additional studies are needed to determine the extent of the benefit derived from preoperative and intraoperative warming for obstetric and gynecologic procedures. A comprehensive list of surgical site infection prevention measures can be found in the CDC Guidelines for Prevention of Surgical Site Infection.

The presence and severity of a surgical site infection is determined by temperature elevation, pain, induration, the presence or absence of serous and/or purulent exudate, erythema, and sometimes tissue separation. A suspected wound infection should prompt consultation or referral to a physician colleague. When a postoperative patient experiences pain, redness, or drainage (or if these are noted during routine dressing changes), the surgical incision should be examined for signs of infection or seroma. A seroma is a sterile accumulation of serum that forms in a closed dead space or cavity just beneath the skin incision. Ideally, seromas are prevented through meticulous approximation of tissues during wound closure. Seromas are not associated with fever, induration, or erythema and are treated conservatively with warm packs, and the fluid is able to absorb.

Direct observation and palpation of the wound is performed using aseptic technique.[29] The amount of wound edge separation and surrounding edema, erythema, or induration is noted.[5] Infected wounds are characteristically red, hot, and tender. The presence, amount, and characteristics of wound exudates are noted. Serous fluid is a common early surgical finding and is not indicative of infection, although it does provide an ideal medium for bacterial growth.[29] The wound is then gently probed using a sterile swab to determine the depth of the separation. Purulent material should be sent for culture if present. Evaluation of fascial integrity is necessary to determine the presence or absence of wound dehiscence.[16,29] A culture of discharge or infected tissue is performed to identify the causative organisms and plan antibiotic therapy. Common causative organisms include Gram-negative rods, group B streptococcus, and Staphylococcus aureus.[2,29] Additionally, community- or hospital-acquired antibiotic resistant bacteria such as methicillin-resistant S aureus may cause local or systemic infection.[40]

Additional physical examination components include palpation of the abdomen for masses, auscultation of lung fields, assessment for deep vein thrombosis, and assessment of pain. In women with persistent fever or symptoms after 48 to 72 hours of parenteral antibiotic therapy, imaging studies (ultrasound, computerized tomography, or radiographs) should be considered to evaluate for the presence of hematoma, abscess formation, or the "gas" associated with necrotizing fasciitis.[30]

The severity of a surgical site infection is defined by the need for additional antibiotic therapy (beyond routine prophylaxis); the presence of pathogens in the wound; and the need for drainage or debridement of the wound, a prolonged hospital stay, or readmission.[31,32,33,41]

The majority of surgical site infections occur after hospital discharge and within the first 3 weeks postoperatively.[2] Many patients are successfully treated on an outpatient basis and do not require readmission. Midwives who provide postoperative care to women may find it helpful to have practice guidelines that clearly specify wound assessment criteria, and parameters for consultation and referral in the presence of suspected wound infection.[42]

The primary treatment of a surgical site infection without fascial disruption is irrigation with normal saline, drainage, and debridement. Wet to dry gauze dressings are used for 2 to 3 debridements per day until the necrotic tissue is replaced with granulation tissue. Once granulation tissue is present, dressings that prevent moisture loss from the wound help healing. Hydrogels, transparent films, and absorptive wound fillers are commonly used during this phase of healing.

Appropriate wound cultures and antibiotic sensitivities are used to guide antibiotic selection. Medical care consists of initiating prompt oral or parenteral antibiotic therapy, modified as indicated by culture results and clinical response, and antipyretics for fever.[16,29] The route of antibiotic treatment is based on the patient's clinical presentation, the severity of the infection, the organisms suspected, and the antibiotic selected. Initial treatment is provided with broad-spectrum antibiotics. A multidrug regimen using cephalosporins, extended-spectrum penicillins, and fluoroquinolones is often used empirically while awaiting culture results.[23]

Women who have persistent fever, continued signs of infection in spite of oral antimicrobial therapy, multiple comorbidities, or suspected necrotizing fasciitis are candidates for inpatient therapy. Evaluation for surgical debridement of the wound and/or evacuation of abscess or hematoma requires prompt referral to a surgeon. Severe infections or necrotizing fasciitis may necessitate patient transfer to a tertiary care center and admission to the intensive care unit for fluid management, cardiac monitoring, and anticoagulation.[16,29,30]