Surgical Site Infections
Thursday, April 9, 2009
Definitions
Overall, surgical site infections (SSIs) are the leading cause of nosocomial infections, accounting for 38% of these complications. By definition, to be an SSI, an infection must occur within 30 days of the operation. SSIs can be broken down into three general categories. Superficial incisional SSIs involve only the skin or subcutaneous tissue of the incision. Signs and symptoms of this type of infection may include pain, swelling, redness, warmth and tenderness. Deep incisional SSIs demonstrate either purulent drainage from deeper tissue, a deep incisional dehiscence, or an abscess in the depth of the incision. Lastly, organ or deep space SSIs involve infections in manipulated regions other than the skin and subcutaneous tissue that was opened during the procedure. By definition, these infections must contain purulent drainage, positive cultures with fluid aspiration or documentation of the presence of an abscess. If a foreign body such as mesh or titanium was left in the wound an SSI can occur up to one year postoperatively.
Overall, surgical site infections (SSIs) are the leading cause of nosocomial infections, accounting for 38% of these complications. By definition, to be an SSI, an infection must occur within 30 days of the operation. SSIs can be broken down into three general categories. Superficial incisional SSIs involve only the skin or subcutaneous tissue of the incision. Signs and symptoms of this type of infection may include pain, swelling, redness, warmth and tenderness. Deep incisional SSIs demonstrate either purulent drainage from deeper tissue, a deep incisional dehiscence, or an abscess in the depth of the incision. Lastly, organ or deep space SSIs involve infections in manipulated regions other than the skin and subcutaneous tissue that was opened during the procedure. By definition, these infections must contain purulent drainage, positive cultures with fluid aspiration or documentation of the presence of an abscess. If a foreign body such as mesh or titanium was left in the wound an SSI can occur up to one year postoperatively.
Risk Factors
Generally speaking, the overall well being and the severity of any comorbid conditions determine how susceptible a patient is to wound infections. The American Society of Anesthesiology rates patients’ operative risk according to their level of illness and comorbidities, termed the ASA class. There is a close correlation between the severity of the preoperative risk and the risk of wound infection. Furthermore, greater operative time is also associated with an increased risk of developing an SSI. When planning an operation, the surgeon must consider the level of expected contamination. Clean surgical procedures are those that involve only skin and the musculoskeletal soft tissue and carry approximately a 2% chance of developing an SSI (although it must be noted that wound infection rates are probably underreported). Clean-contaminated procedures are those that involve the planned opening of a hollow viscus (e.g., the respiratory, biliary or gastrointestinal tracts) and have a 7-15% risk of becoming infected. Contaminated procedures are those that introduce nonsterile, bacteria-rich contents into the wound for a short period of time (e.g., penetrating abdominal trauma, unplanned enterotomies) and lead to SSIs in 20% of cases. Dirty procedures take place in an infected setting (e.g., bowel resection for an abscess related to Crohn’s disease, removal of infected prosthesis). Approximately 20-40% of these wounds will become infected if closed primarily.
Generally speaking, the overall well being and the severity of any comorbid conditions determine how susceptible a patient is to wound infections. The American Society of Anesthesiology rates patients’ operative risk according to their level of illness and comorbidities, termed the ASA class. There is a close correlation between the severity of the preoperative risk and the risk of wound infection. Furthermore, greater operative time is also associated with an increased risk of developing an SSI. When planning an operation, the surgeon must consider the level of expected contamination. Clean surgical procedures are those that involve only skin and the musculoskeletal soft tissue and carry approximately a 2% chance of developing an SSI (although it must be noted that wound infection rates are probably underreported). Clean-contaminated procedures are those that involve the planned opening of a hollow viscus (e.g., the respiratory, biliary or gastrointestinal tracts) and have a 7-15% risk of becoming infected. Contaminated procedures are those that introduce nonsterile, bacteria-rich contents into the wound for a short period of time (e.g., penetrating abdominal trauma, unplanned enterotomies) and lead to SSIs in 20% of cases. Dirty procedures take place in an infected setting (e.g., bowel resection for an abscess related to Crohn’s disease, removal of infected prosthesis). Approximately 20-40% of these wounds will become infected if closed primarily.
Bacteria and Prophylaxis
Whereas most SSI are caused by skin derived Gram-positive cocci, including Staphylococcus aureus, coagulase-negative staphylococci such as Staphylococcus epidermidis and Enterococcus species, site-specific pathogens, may infect wounds. Consideration for Gram-negative bacilli should be given to any wound that is located near the site of bowel injury or repair, and when either bowel or tracheopharyngeal structures are violated, both enteric aerobic bacteria such as Escherichia coli and anaerobic bacteria such as Bacteroides fragilis may be of concern. Prophylaxis for clean surgery is controversial. It is generally accepted that when bone is violated (e.g., during cranial vault reconstruction) or when a prosthesis is inserted, preoperative antibiotics are indicated. Less convincing data exists for straightforward soft tissue surgery (e.g., scar revisions).
Whereas most SSI are caused by skin derived Gram-positive cocci, including Staphylococcus aureus, coagulase-negative staphylococci such as Staphylococcus epidermidis and Enterococcus species, site-specific pathogens, may infect wounds. Consideration for Gram-negative bacilli should be given to any wound that is located near the site of bowel injury or repair, and when either bowel or tracheopharyngeal structures are violated, both enteric aerobic bacteria such as Escherichia coli and anaerobic bacteria such as Bacteroides fragilis may be of concern. Prophylaxis for clean surgery is controversial. It is generally accepted that when bone is violated (e.g., during cranial vault reconstruction) or when a prosthesis is inserted, preoperative antibiotics are indicated. Less convincing data exists for straightforward soft tissue surgery (e.g., scar revisions).
Anemia (postoperative)
Ascites
Chronic inflammation
Corticosteroid therapy (controversial)
Obesity
Diabetes
Extremes of age
History of irradiation
Hypocholesterolemia
Hypoxemia
Malnutrition
Peripheral vascular disease
Recent operation
Remote infection
Skin carriage of staphylococci
Skin disease in the area of infection (e.g., psoriasis)
Environmental factors
Contaminated medications
Inadequate disinfection/sterilization
Inadequate skin antisepsis
Inadequate tissue oxygenation
Treatment factor
Drains
Emergency procedure
Hypothermia
Inadequate antibiotic prophylaxis
Prolonged preoperative hospitalization
Prolonged operative time When choosing an antibiotic agent, the following factors should be considered:
Contaminated medications
Inadequate disinfection/sterilization
Inadequate skin antisepsis
Inadequate tissue oxygenation
Treatment factor
Drains
Emergency procedure
Hypothermia
Inadequate antibiotic prophylaxis
Prolonged preoperative hospitalization
Prolonged operative time When choosing an antibiotic agent, the following factors should be considered:
- It should have minimal side-effects and be safe for the patient.
- It should have a narrow spectrum of coverage for the expected organisms.
- It should not be overused (making it less likely that bacteria have developed resistance).
- It should cover typical infections that are specific for the institution.
- It can be used for a brief period of time (less than 24 hours).
Long prophylactic courses have been associated with an increased risk of nosocomial infections and multi-drug resistance. For clean and most clean-contaminated cases, a first-generation cephalosporin should be used. If a patient has a documented penicillin allergy, clindamycin is an alternative. Only in the setting of a hospitalized patient in an institution that carries a high rate of methicillin-resistant S. aureus (MRSA), should vancomycin be considered for prophylaxis. It is important to recall that the timing of the antibiotic dose determines its effectiveness. Preoperative prophylaxis should be closed within two hours of incision time. Given too early, the antibiotic can be cleared before the case is started. Some benefit can be gained from intraoperative dosing if antibiotics are not given before the case begins, but no benefit has been shown when the first dose is given after the case ends. This loss of benefit after skin closure is related to the fact that sutured wounds exist in a low blood flow state owing to vasoconstriction, the use of electrocauterization for hemostasis, and the constrictive effects of the suture closure. Therefore, antibiotics will not reach the surgical site. In extremely lengthy cases, redosing intraoperatively is recommended.
Prevention and Treatment
In the weeks to months before a planned operation, much can be done to maximize the immune state and wound healing capabilities of the patient. Smokers should be encouraged to stop at least one month prior to their surgery. Smoking is a known vasoconstrictor that can reduce oxygen delivery to wounded tissue, and its effects have been found to last weeks beyond the point of smoking cessation. The nutritional status of the patient should be taken into consideration as well. Obese patients should be encouraged to lose as much weight as possible while maintaining a healthy, protein-rich diet, and in the malnourished hospitalized patient, even a short 5-7 day course of parenteral or enteral nutrition has been shown to significantly reduce the risk of SSIs. Studies show that having a patient take a preoperative shower with an antiseptic soap (e.g., hexachlorophene) can reduce skin bacterial load. However, shaving the planned surgical site with a razor either the night before surgery or immediately preoperatively should be discouraged due to the transient bacterial infestation that it promotes. Studies report greater than a 3-fold increase in infection rates with shaving versus hair clipping (5.6 vs. 1.7%). Finally, known S. aureus carriers should have their nasal orifices treated with topical 2% mupirocin. Intraoperatively, care should be taken to keep the patient warm and well hydrated. This will improve blood flow to the wound and maximize oxygen delivery. Even 30 minutes of preoperative warming can reduce patient risk for SSI by two-thirds in some cases. Adequate oxygenation is important for cellular function and bacterial destruction via superoxide and peroxide formation. Case length should be kept to a minimum, given the fact that infection rates almost double for each hour an operation lasts. Tissues should be handled gently and electrocautery for hemostasis should be kept to a minimum. During the case, wounds should be kept moist and retractors should be released periodically to restore blood flow. The smallest possible suture diameter should be used to minimize foreign material in the wound (studies show that on average, surgeons use sutures one size larger than needed), and the prudent use of drains should be encouraged. By acting as a conduit for bacterial invasion and preventing epithelial closure of wounds, drains probably cause more SSIs than they prevent and they should be removed as soon as possible. Antibiotic prophylaxis of an indwelling drain is never indicated. High pressure pulse irrigation and topical antiseptic washes have been proven to be of some benefit in the contaminated or dirty wound. Both during the case and postoperatively, blood glucose concentration should be kept under tight control (80-110 mg/dl). And finally, postoperative nutrition should be optimized. Controversy exists on whether it is appropriate to close contaminated wounds primarily. Studies in adults show that this practice can lead to a higher rate of wound failure and a greater cost of care. It is recommended that a delayed primary closure of the incision be used. This involves either placing untied sutures during the case that can later be cinched down, or using adhesive strips for closure when the wound is ready. Until the time when the wound appears to have minimal debris and no apparent progressing erythema, wet-to-dry, twice daily packing should be used (usually for 4-5 days).
In the weeks to months before a planned operation, much can be done to maximize the immune state and wound healing capabilities of the patient. Smokers should be encouraged to stop at least one month prior to their surgery. Smoking is a known vasoconstrictor that can reduce oxygen delivery to wounded tissue, and its effects have been found to last weeks beyond the point of smoking cessation. The nutritional status of the patient should be taken into consideration as well. Obese patients should be encouraged to lose as much weight as possible while maintaining a healthy, protein-rich diet, and in the malnourished hospitalized patient, even a short 5-7 day course of parenteral or enteral nutrition has been shown to significantly reduce the risk of SSIs. Studies show that having a patient take a preoperative shower with an antiseptic soap (e.g., hexachlorophene) can reduce skin bacterial load. However, shaving the planned surgical site with a razor either the night before surgery or immediately preoperatively should be discouraged due to the transient bacterial infestation that it promotes. Studies report greater than a 3-fold increase in infection rates with shaving versus hair clipping (5.6 vs. 1.7%). Finally, known S. aureus carriers should have their nasal orifices treated with topical 2% mupirocin. Intraoperatively, care should be taken to keep the patient warm and well hydrated. This will improve blood flow to the wound and maximize oxygen delivery. Even 30 minutes of preoperative warming can reduce patient risk for SSI by two-thirds in some cases. Adequate oxygenation is important for cellular function and bacterial destruction via superoxide and peroxide formation. Case length should be kept to a minimum, given the fact that infection rates almost double for each hour an operation lasts. Tissues should be handled gently and electrocautery for hemostasis should be kept to a minimum. During the case, wounds should be kept moist and retractors should be released periodically to restore blood flow. The smallest possible suture diameter should be used to minimize foreign material in the wound (studies show that on average, surgeons use sutures one size larger than needed), and the prudent use of drains should be encouraged. By acting as a conduit for bacterial invasion and preventing epithelial closure of wounds, drains probably cause more SSIs than they prevent and they should be removed as soon as possible. Antibiotic prophylaxis of an indwelling drain is never indicated. High pressure pulse irrigation and topical antiseptic washes have been proven to be of some benefit in the contaminated or dirty wound. Both during the case and postoperatively, blood glucose concentration should be kept under tight control (80-110 mg/dl). And finally, postoperative nutrition should be optimized. Controversy exists on whether it is appropriate to close contaminated wounds primarily. Studies in adults show that this practice can lead to a higher rate of wound failure and a greater cost of care. It is recommended that a delayed primary closure of the incision be used. This involves either placing untied sutures during the case that can later be cinched down, or using adhesive strips for closure when the wound is ready. Until the time when the wound appears to have minimal debris and no apparent progressing erythema, wet-to-dry, twice daily packing should be used (usually for 4-5 days).
Pearls and Pitfalls
Antibiotic prophylaxis of clean surgical procedures (e.g., elective operations on skin and soft tissue) is controversial based on a single randomized trial that showed benefit in breast and groin hernia surgery. The controversy persists because the incidence of superficial surgical site infection was so high (4%, versus an expected incidence of about 1%) in the placebo group. Evidence that antibiotic prophylaxis is indicated for soft tissue procedures of other types is lacking entirely, and prophylaxis cannot be recommended. If administered, antibiotic prophylaxis should be given before the skin incision is made, and only as a single dose. Additional doses are not beneficial because surgical hemostasis renders wound edges ischemic by definition until neovascularization occurs, and antibiotics cannot reach the edges of the incision for at least the first 24 hours. Not only is there lack of benefit, prolonged antibiotic prophylaxis actually increases the risk of postoperative infection. Increasingly in the practice of plastic surgery, there is a tendency to leave closed-suction drains in place for prolonged periods in the erroneous belief that the incidence of wound complications is reduced by prolonged drainage. Nothing could be further from the truth. Data indicate that the presence of a drain for more than 24 hours increases the risk of postoperative surgical site infection with MRSA. Closed suction drains must be removed as soon as possible, ideally within 24 hours. Prolonged antibiotic prophylaxis is often administered to “cover” a drain left in place for a prolonged period. This is a prime example of error compounding error, and is a practice that must be abandoned.
Antibiotic prophylaxis of clean surgical procedures (e.g., elective operations on skin and soft tissue) is controversial based on a single randomized trial that showed benefit in breast and groin hernia surgery. The controversy persists because the incidence of superficial surgical site infection was so high (4%, versus an expected incidence of about 1%) in the placebo group. Evidence that antibiotic prophylaxis is indicated for soft tissue procedures of other types is lacking entirely, and prophylaxis cannot be recommended. If administered, antibiotic prophylaxis should be given before the skin incision is made, and only as a single dose. Additional doses are not beneficial because surgical hemostasis renders wound edges ischemic by definition until neovascularization occurs, and antibiotics cannot reach the edges of the incision for at least the first 24 hours. Not only is there lack of benefit, prolonged antibiotic prophylaxis actually increases the risk of postoperative infection. Increasingly in the practice of plastic surgery, there is a tendency to leave closed-suction drains in place for prolonged periods in the erroneous belief that the incidence of wound complications is reduced by prolonged drainage. Nothing could be further from the truth. Data indicate that the presence of a drain for more than 24 hours increases the risk of postoperative surgical site infection with MRSA. Closed suction drains must be removed as soon as possible, ideally within 24 hours. Prolonged antibiotic prophylaxis is often administered to “cover” a drain left in place for a prolonged period. This is a prime example of error compounding error, and is a practice that must be abandoned.
