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  • SURGICAL INFECTIONS William G. Cheadle, MDPURPOSE: Familiarize the student with the diagnosis and treatment of infections that involve carerendered by surgeons. These infections can be defined as those that require surgicalinterventions to resolve completely or infections that develop as a complication of surgery – orboth.OVERVIEW: This chapter will cover both infections that present to surgeons and those that occurafter operations.I. LECTURE OBJECTIVES A. To become familiar with infections treated by surgeons. B. To understand kinds of infections that develop following operations.II. GENERAL A. Surgical infection characteristics 1. Often involve a penetrating injury (e.g., from trauma), a perforating injury (e.g., a perforated ulcer), or an operative site (e.g., the surgical wound). 2. Usually multiple organisms – complicates treatment. 3. Treatment may require surgical drainage of the infection or debridement of necrotic or grossly contaminated tissue; antibiotics alone often will not resolve the infection. B. Surgical wound infections 1. The incidence of wound infections is related directly to the nature of the surgical procedure performed. 2. Clinical presentation. Wound infection often presents as a spiking fever at approximately the fifth to eighth postoperative day. Know the W’s of fever: • Wind—atelectasis, pneumonia, pulmonary embolism • Water—UTI • Wound—incision site • Wings—peripheral thrombophlebitis (IV site) • Walking—deep venous thrombosis, pulmonary embolus • Wonder drugs—drug induced fever (rare!) There may be localized wound tenderness, cellulitis, or drainage from the wound. 3. Treatment. Simple incision and drainage will resolve most postoperative wound infections. Deeper wound infections or extensive necrosis may require operative debridement and antibiotics. C. Prosthetic infections. Prostheses are synthetic implantable devices, including vascular grafts, heart valves, artificial joints, fascial mesh replacements, and metallic bone supports. 1. Clinical presentation. An infected prosthesis usually causes symptoms of either local infection or generalized sepsis. The most common organisms infecting prostheses are staphylococci; these infections are life threatening. 154
  • 2. Treatment. Prophylactic antibiotics are always used when implanting a prosthesis; however, an infected prosthesis usually cannot be sterilized with antibiotics and, therefore, removal of the prosthesis is usually necessary. D. Prophylactic antibiotics are given during the perioperative period to combat bacterial contamination of tissues that occurs during the operative procedure. The general rules for the use of prophylactic antibiotics are: 1. The operation must carry a significant risk of a postoperative infection. A clean procedure would not require prophylactic antibiotics, but the following situations would: a. A procedure in which a prosthesis is to be implanted. b. Clean-contaminated procedures, where a non-sterile area is entered; for example, the respiratory or upper GI tract. c. Contaminated procedures, such as colon or rectal surgery 2. The antibiotics used should be effective against the pathogens likely to be present in the operative site. 3. The antibiotics must reach an effective tissue level at the time of the incision. Therefore, they should be given 1-2 hours before surgery. 4. The antibiotics should be given for only 6-24 hours after surgery. Longer- lasting regimens offer no additional protection and carry risks of superinfection. 5. The benefits of the prophylactic antibiotic should outweigh its potential dangers, such as allergic reactions or the risk of bacterial or fungal superinfections from overgrowth of pathogens.III. ABSCESSES A. Cutaneous abscesses 1. Types a. Furuncles (boils) are cutaneous staphylococcal abscesses. They are frequently seen with acne and other skin disorders. Bacterial colonization begins in hair follicles and can cause both local cellulitis and abscess formation. b. Carbuncles are cutaneous abscesses that spread through the dermis into the subcutaneous region. They are common in individuals with diabetes. c. Hidradenitis suppurativa is an infection involving the apocrine sweat glands in the axillary, inguinal, and perineal regions. The infection results in chronic abscess formation and often requires complete excision of the apocrine gland- bearing skin to prevent recurrence. 2. Causative organisms a. Staphylococcal organisms (Staphylococcus epidermidis, Staphylococcus aureus) frequently infect cutaneous lesions. Staphylococci usually produce pus, which must be drained to allow healing. b. Other organisms, including anaerobic and gram-negative organisms, can also cause cutaneous abscesses. Coliform organisms are often present in axillary, inguinal, and perineal cutaneous abscesses. 3. Diagnosis. The microbiologic diagnosis is made by incising the abscess, then culturing and Gram staining the pus. Most staphylococcal organisms are resistant to penicillin; therefore, one of the semisynthetic penicillins, erythromycin, a cephalosporin, or a fluoroquinolone should be used. 155
  • 4. Treatment a. Drainage b. Appropriate antibiotic therapy c. Wound care with irrigation and debridement when necessary d. Excision of the involved area when it contains multiple small abscesses, sinus tracts, or necrotic tissue. B. Intra-abdominal abscesses 1. Causes a. Extrinsic causes include penetrating trauma and surgical procedures. b. Intrinsic causes include perforation of a hollow viscus, such as the appendix or duodenum; seeding of bacteria from a source outside the abdomen, e.g., tubo-ovarian abscess; or ischemia and infarction of tissue within the abdomen. 2. The most common sites are the a. Subphrenic space b. Subhepatic space c. Lateral gutters posteriorly d. Pelvis e. Periappendiceal or pericolonic areas f. Multiple abscesses are present in up to 15% of cases. 3. Signs and symptoms of abdominal abscess are fever, pain, and leukocytosis. a. These abscesses may be large and usually produce spiking fevers. b. Postoperative abscesses usually product fever during the second postoperative week. c. When there is a delay in seeking medical attention or a delay in diagnosis, patients may present with generalized sepsis. 4. Diagnosis. The key to an expeditious diagnosis is a high index of suspicion. a. The patient may have tenderness or an abdominal mass, but often no physical finding is present (particularly with a pelvic abscess). b. Ultrasonography and CT scan are essential for diagnosis. 5. Treatment a. The mainstay of intra-abdominal abscess treatment is drainage. b. Diagnosis and localization with imaging studies allows proper choice of modality. c. Unilocular and accessible abscesses can be drained percutaneously with Radiologic guidance. d. Abscesses that are complex, multilocular, include significant amounts of necrotic debris, or are inaccessible require surgical drainage.IV. CELLULITIS is inflammation of the dermal and subcutaneous tissues secondary to nonsuppurative bacterial invasion. It may result from a puncture wound or any other type of skin break. A. Signs and symptoms 1. Cellulitis produces redness, edema, and localized tenderness. Fever and leukocytosis are usually present. 2. The bacteria may also infect the lymphatics, resulting in red, tender streaks on an extremity (lymphangitis). 156
  • 3. A deep abscess can result in overlying cellulitis and should be suspected when a patient does not rapidly respond to antibiotics. B. Treatment. The usual organism is a Streptococcus, which is almost always sensitive to penicillin.V. NECROTIZING FASCIITIS is a rapidly progressive bacterial infection in which multiple organisms invade fascial planes. The infection travels rapidly and causes vascular thrombosis as it progresses, resulting in necrosis of the tissue involved. The overlying skin may appear normal, leading the clinician to underestimate the severity of the infection. Necrotizing fasciitis may result from a puncture wound, a surgical wound, or open trauma. A. Signs and symptoms 1. Hemorrhagic bullae may develop on the skin, accompanied by edema and redness, and crepitus may be present; however, the skin also may appear normal. 2. The patient shows signs of progressive toxicity (fever, tachycardia) and may have localized wound pain. 3. The necrotic wound or tissue involved has a foul-smelling serous discharge. 4. A plain radiograph of the wound area may reveal air in the soft tissues. B. Diagnosis. Gram stain reveals multiple organisms, which act synergistically, giving the fasciitis its rapidly progressive and destructive character, including: 1. Microaerophilic streptococci 2. Staphylococci 3. Gram-negative aerobes and anaerobes. C. Treatment is surgical, and early diagnosis is extremely important. 1. The surgeon attempts to remove all infected or devitalized tissue at the first debridement because remaining necrotic tissue will allow the process to continue. 2. The removal of large amounts of skin and surrounding tissue and, occasionally, amputation of an extremity may be required. 3. Daily debridement may be needed. 4. Appropriate antibiotics in high doses are required. 5. This infection is life threatening and prompt treatment is essential.VI. INFECTIONS AFTER SURGERY A. Gastrointestinal surgery B. Upper GI tract surgery 1. The rate of serious infections after operations on the upper GI tract is 5%-15%. 2. The oral cavity is colonized by large numbers of aerobic and anaerobic bacteria. These bacteria are generally killed in the low pH environment of the stomach. 3. Gastric cultures become positive when obstruction or blood is present; therefore, prophylactic antibiotics should be used in these settings. 4. Patients without the protective low gastric pH, e.g., those taking anti-ulcer medications (H2-blockers, proton pump inhibitors, etc.), achlorhydira, or gastric malignancy also should be given prophylactic antibiotics. 5. The usual antibiotics are a cephalosporin or a fluoroquinolone to cover both aerobes and anaerobes. C. Biliary tract surgery 1. The biliary tree is not colonized with bacteria in the normal individual. The colonization rate rises to 15%-30% for patients with chronic calculous 157
  • cholecystitis and to over 80% in patients with common duct obstruction. Of those patients with positive cultures: a. Escherichia coli is present in over one half of the cases; other gram-negative organisms account for most of the remainder. b. Streptococcus faecalis, the aerobic gram-positive enterococcus, may also be present, and Salmonella strains are occasionally present. Anaerobic organisms, especially C. perfringens, are present in up to 20% of cases. 2. For elective cholecystectomy, simple prophylaxis with cephalosporin is adequate. 3. Therapeutic antibiotics are needed in patients with common duct stones, cholangitis, and empyema or gangrene of the gallbladder. A cephalosporin or penicillin-combination should be given.D. Colonic and rectal surgery 1. Wound and intraperitoneal infections often (6%-60%) follow colorectal surgery. 2. Normal human colonic flora is composed of both aerobes and anaerobes. a. Aerobes are present at levels of 108-109 bacteria per gram of stool. E. coli, the most common aerobe, is the organism most often found in wound infections after colonic surgery. b. Anaerobes are present at levels of 1011 bacteria per gram of stool (1000-fold greater numbers than those aerobes). Many types are present, but Bacteriodes fragilis is the most common and usual cause of anaerobic wound infections. c. Mixed aerobic and anaerobic infections are typical. 3. An effective preoperative regimen combines the removal of gross feces (mechanical preparation of the bowel) with the use of oral nonabsorbable antibiotics). a. Mechanical removal of the feces is the most important factor in lowering the bacterial counts and the incidence of wound infections. Regimens include aggressive purgation - with potent oral laxatives such as mannitol or polyethylene glycol – plus enemas. b. Antibiotic prophylaxis will lower the incidence of wound infection only after adequate mechanical preparation. To be effective, the antibiotics must be active against both aerobic and anaerobic organisms. i. Oral antibiotics, such as neomycin and erythromycin base started 10-22 hours before surgery. Longer treatment period allows resistant bacterial overgrowth. ii. IV antibiotics may further lower the incidence of wound infection. c. Preparation of the colon and rectum should be carried out before all elective operations unless a high grade (complete) obstruction is present. An obstruction will compromise the mechanical bowel preparation and may require the creation of a proximal stoma to relieve the obstruction. d. In emergency procedures (e.g., after trauma) when no bowel preparation is possible, IV antibiotics should be given, and the wound should not be closed primarily. Colonic anastomoses are riskier in these situations than in elective situations.E. Gynecologic surgeries are usually clean-contaminated procedures and prophylactic antibiotics are appropriate.F. Urologic surgery 158
  • 1. Although the normal urinary tract is sterile, the most common pathogen encountered is E. coli, followed by other gram-negative rods and enterococci. 2. The general principle is that elective surgery should be postponed until any infection has been successfully treated; this principle is especially true for urologic surgery. 3. Chronic indwelling tubes (e.g., suprapubic bladder catheters nephrostomies) are generally colonized with bacteria but do not require antibiotic therapy, unless the patient has a symptomatic local infection, generalized sepsis, or catheter obstruction; or unless a urea-splitting organism, such as Proteus, is present. 4. In the presence of urinary tract pathology, it may be impossible to sterilize the urine. Therefore, antibiotics are used periopertively as both treatment and prophylaxis. G. Vascular surgery 1. The risk of vascular prosthetic graft infection is 1%-6%. Infection may develop early (within months) or years later. 2. The most common infecting organism is S. Aureus, followed by coagulase- negative S. epidermidis. Coliform infections are becoming more common. 3. Perioperative prophylactic antibiotics will lower the incidence of graft infections from a high of 6% down to 1%. The recommended antibiotic is a cephalosporin. 4. Prophylactic antibiotics (amoxicillin) should also be used when a patient with prosthetic graft undergoes a procedure associated with a transient bacteremia (such as dental extraction). H. Cardiac surgery. The sources of infection for cardiac surgery are the same as those for vascular surgery. Severe infections include sternal osteomyelitis and dehiscence and prosthetic valve endocarditis. I. Noncardiac thoracic surgery. Lung surgery has a high risk of infection when the lung is already infected or when a significant volume of lung is removed (as in pneumonectomy) and a large dead space remains. For elective pulmonary resections, many surgeons use prophylactic antibiotics for the gram-positive cocci that colonize the upper respiratory tree. J. Orthopedic surgery. Postoperative infections of bone or implanted prostheses are major life-threatening complications (similar to vascular and cardiac surgery). The most common organisms are slime-forming staphylococci. Prophylactic antibiotics against these organisms are used routinely.VII. INFECTIONS AFTER TRAUMA A. Deep burns (second and third degree). Tetanus prophylaxis must be assured. 1. Burns are prone to develop group A streptococcal infection during the first 5 days. If present, penicillin G or a penicillinase-resistant synthetic penicillin is used. Prophylactic antibiotics are not usually given, however. 2. To reduce the colonization of injured tissues, topical antibiotics are applied. These antibiotics should be effective against both gram-negative rods and gram- positive cocci. 3. Purulent infection of IV catheter and cutdown sites is called suppurative thrombophlebitis and must be treated by excision of the vein. B. Penetrating abdominal trauma should be treated with an antibiotic regimen that covers both anaerobic and aerobic organisms. 159
  • C. Penetrating chest wounds should be treated with antibiotics effective against organisms commonly found in the respiratory tract. D. Bites. Human bites should be treated with penicillin, as they are likely to contain mixed anaerobic and aerobic organisms. Animal bites warrant prophylactic antibiotics if injury is extensive.VIII. WHEN TO REFER A. Acute abdominal pain lasting longer than 6 to 8 hours. B. Soft tissue infections not clearly responsive to 48 hours of antibiotics. C. Abscesses that are fluctuant.IX. PITFALLS A. The skin changes seen with underlying fasciitis are often deceptively subtle, usually erythema and blistering. Check for fever, elevated WBC, and tenderness on range of motion. Consult surgeon if in doubt.X. SUGGESTED READING Wrightson WR. Surgical complications. In: Wrightson WR, ed. Pocket Surgery. Malden, MA: Blackwell Science, 2002:69-85. Polk HC Jr, Christmas AB. Prophylactic antibiotics in surgery and surgical wound infections. Am Surg 2000;66:105-111. Wickel DJ, Cheadle WG, Mercer-Jones MA, Garrison RN. Poor outcome from peritonitis is caused by disease acuity and organ failure, not recurrent peritoneal infection. Ann Surg 1997;225:744-753. 160