Surgical Infections: Guo Xueli ( )

Surgical Infections Guo Xueli ( 郭学利 ) Dept. General Surgery, First Affiliated Hospital

Nature, Diagnosis, and Treatment of Surgical Infections Surgical infections are distinguished from medical infections by the presence of an anatomic or mechanical problem Surgical infections must be resolved by operations or other invasive procedure to cure ---incising and draining an abscess, opening an infected wound, removing an infected foreign body, repairing or diverting a bowel leak, and draining an intra-abdominal abscess with a percutaneous ---only antibiotic treatment will not resolve ---operative intervention is required

The typical differences Common community-acquired medical infections ---general host defense are usually intact ---some exceptions to intact host defense occur in patients undergoing systemic treatment for malignancy or for transplant rejection and patients with HIV infection

Most surgical infections ---the result of damaged host defense, especially injury to the epithelial barrier Immunologic defects may be acquired, through either trauma or tumor ---nonmechanical host defense defects are global, caused by nutritional deficiency and /or the systemic effects of trauma

Pathogens ---single and aerobic in medical infections ---mixed in surgical infections, involving aerobes and anaerobes, and usually originate from the patient’s own endogenous flora. The pathogens are opportunistic, often depending on an acquired epithelial defect to cause infection.

Soft tissue infections The distinction between surgical and medical infection in superficial tissues---depends on the recognition of dead tissue A surgical infection #a subcutaneous abscess, an infectious process characterized by a necrotic center without a blood supply and composed of debris from local tissues and plasma, and bacteria

#the semiliquid central portion (pus)---surround by a vascularized zone of inflammatory tissue. #a localized swelling with signs of inflammation and tenderness #an abscess will not resolve unless the pus is drained and evacuated

Cellulitis ---another soft tissue infections with intact blood supply and viable tissue, marked by an acute inflammatory response with small vessel engorgement and stasis, endothelial leakage with interstitial edema, and polymorphonuclear leukocyte infiltration ---resolves with appropriate antibiotic therapy alone if treatment is initiated before tissue death occurs

An abscess ---may be mistaken for cellulitis when the central necrotic portion is located deep beneath overlying tissue layers ---also be disguised in anatomic locations where fibrous septa join skin and fascia, dividing subcutaneous tissue into compartments that limit the local expression of fluctuance while leading to high pressures #include perirectal abscess, breast abscess, carbuncles on the posterior neck and upper back, and infections in the distal phalanx of the finger (felon)

Perirectal abscess ---a fistula communicating with the anus at a crypt, should be sought and unroofed at the time a perirectal abscess is drained Breast abscess ---preferably drained by a circumferential incision in natural skin lines Felon---be drained through a lateral incision, all fibrous septa in the infected pulp must be broken to resolve the infection

Superficial abscess On the trunk and head and neck---caused by S. aureus, often combined with streptococci. In the axillae---have a prominent gram-negative component. Below the waist, especially on the perineum---a mixed aerobic and anaerobic gram-negative flora.

Necrotizing soft tissue infections #clostridial and nonclostridial #less common, but much more serious condition #marked by the absence of clear local boundaries or palpable limits #the overlying skin has a relatively normal appearance in the early stages of infection

A clostridial infection ---typically involves underlying muscle, termed clostridial myonecrosis or gas gangrene Most nonclostridial and some nonclostridial necrotizing infections ---spread in the subcutaneous fascia, between the skin and the deep muscular fascia, called necrotizing fasciitis

The earliest signs of a necrotizing soft tissue infection ---a marked hemodynamic response to infection, or the failure to respond to conventional nonoperative therapy An apparent cellulitis with ecchymoses, bullae, any dermal gangrene, extensive edema, or crepitus ---underlying necrotizing infection ---mandates operative exploration to confirm the diagnosis and definitively treat the infection

Diagnosis ---to recognize the nonlocalized, necrotizing nature of the infection and the need for operative treatment Operative treatment Clostridial myonecrosis---excision of involved tissues or amputation (on an extremity) Nonclostridial infection---wide incision and debridement and do not usually require amputation In either case---all areas of necrotic tissue must be unroofed and debrided, which often produces large disfiguring wounds.

Organisms Clostridial infection---Clostridium perfringens, C. novyi, and C. septicum Nonclostridial infection---beta-hemolytic S.pyogens Postoperative and postinjury cases---most often caused by mixed bacterial species, including aerobic and anaerobic pathogens, both gram positive and gram negative

Intra-abdominal and retroperitoneal infection #most serious intra-abdominal infections---require surgical intervention #the specific exceptions---pyelonephritis, salpingitis, amebic liver abscess, enteritis, spontaneous bacterial peritonitis, some cases of diverticulitis, and some case of cholangitis

Fever, tachycardia, and hypotension---common A severe hypermetabolic, catabolic response ---universal #No corrective operation and effective antibiotics ---multiple-organ failure syndrome---death #Early diagnosis and treatment ---improve the outcome #the risk of death and of complication---increases with increased age, pre-existing serious underlying diseases, and malnutrition

Initial treatment Cardiorespiratory support, antibiotic therapy, and operative intervention In most cases The responsible bacteria---are not known No sensitivity information Three to five different aerobic and anaerobic pathogens #Initial antibiotic therapy ---empiric, designed to cover a range of possible organisms

Operative intervention for intra-abdominal or retroperitoneal infection The goal---is to correct the underlying anatomic problem that either caused the infection or perpetuates it #the cause of peritonitis---must be corrected #foreign material (feces, food, bile, mucin, blood) in the peritoneal cavity---should be removed #large deposits of fibrin---should be removed

An intra-abdomial or retroperitoneal abscess ---requires drainage #the abscesses---single and has a straight path to the abdominal wall that does not transgress bowel ---to be drained percutaneously under radiologic or ultrasound guidance # the abscesses---multiple or combined with underlying disease, no safe percutaneous route ---to be drained by an open operation

*A single abscess in the subphrenic or subhepatic position---an extraperitoneal subcostal or posterior twelfthrib approach, which provides open drainage without exposing the entire peritoneal cavity *Most pancreatic abscesses---transabdominal operation and debridement *A pelvic abscess---transrectal or transvaginal *Retroperitoneal phlegmon (necrotizing cellulitis)---extensive debridement

Postoperative fever Approximately 2% of all primary laparotomies are followed by an unscheduled operation for intraabdominal infection Roughly 50% of all serious intra-abdominal infections---postoperative Postoperative fever---occurs frequently and may be a source of concern to physician and patient

#Fever is associated with infection The empiric prescription of antibiotics is common response However, most febrile postoperative patients ---not infected A significant proportion of infected patients ---not febrile #It is important to consider causes of postoperative fever

Diagnosis for detecting infection and determining its location ---taking history, physical examination ---supportive laboratory and x-ray evaluation, including white blood cell count, blood cultures, and CT, can supplement the physical examination

Fever #in the first 3 days after operation--noninfectious cause #starts 5 or more days postoperatively---the incidence of wound infections exceeds the incidence of undiagnosed fevers Only two important infectious cause in the first 36 hours after a laparotomy ---an injury to bowel with intraperitoneal leak ---an invasive soft tissue infection

#an injury to bowel with intraperitoneal leak ---Marked hemodynamic change---first tachycardia and then hypotension and a falling urine output ---Fluid requirements are large ---Physical examination reveals diffuse abdominal tenderness #an invasive soft tissue infection ---Beginning in the wound, caused either by betahemolytic streptococci or by clostridial species ---Inspection of the wound and Gram stain of wound fluid, which shows either gram-positive cocci or gram-positive rods

Nonsurgical infections in surgical patients A variety of nonsurgical postoperative nosocomial infections Urinary tract infections ---most common, any patient who has had an indwelling urinary catheter The best prevention ---to use urinary catheters sparingly and for specific indications ---to employ strict closed drainage techniques for those

Lower respiratory tract infection leading cause of death due to nosocomial infection ---abnormal chest x-ray findings, abnormal blood gas values, and elevated temperatures and white blood cell counts even in the absence of infection Diagnosis ---usually relatively straightforward in a patient who is breathing spontaneously ---extremely difficult in a patient who is intubated and being ventilated because of ARDS Both false-positive and false-negative diagnosis of pneumonia

Prosthetic device-associated infections Some of the most significant complication associated with vascular grafts, cardiac valves, pacemakers, and artificial joints are caused by infections at the site of implantation #the foreign material (the prosthetic device) ---impairs logical host defenses, especially polymorphonuclear leukocyte function #high morbidity and mortality

Treatment #intensive antibiotic therapy #removal of the infected device under antibiotic therapy #replacement with a new uninfected device followed by prolonged antibiotic treatment

Pathogens in Surgical Infections The pathogens are broadly divided into ---aerobic and facultative bacteria in one group and anaerobic bacteria in the other ---gram-positive and gram-negative bacteria ---bacilli( rods )and cocci

Gram-positive cocci Include staphylococci and streptococci Staphylococci ---coagulase-positive and coagulase-negative strains Coagulase-positive staphylococci---S. aureus ---Associated with infections in wound and incisions

---resistant to penicillin and require treatment by a penicillinase-resistant antibiotic ---methicillin-resistant staphylococci must be treated with vancomycin or a similar agent

Coagulase-negative staphylococci ---contaminants and skin flora ---frequently associated with clinically significant infections of intravascular devices ---found in endocarditis, prosthetic joint infections, vascular graft infections, and postsurgical mediastinitis ---methicillin resistant ---vancomycin should be chosen

Streptococcal species Include beta-hemolytic streptococci, S.pneumoniae, and other alpha-hemolytic streptococci ---to be uniformly sensitive to penicillin G and almost all other beta-lactam antibiotics

Enterococci #as part of a mixed flora in intra-abdominal infection #it is rare to recover enterococci alone from a surgical infection #cause significant disease in the urinary and the biliary tract #gentamicin combined with either ampicillin or vancomycin

Aerobic and facultative gram-negative rods Most fall into the family Enterobacteriaceae #the familiar genera Escherichia, Proteus, and Klebsiella ---in mixed surgical infection ---relatively sensitive to a broad variety of antibiotics, especially first- and secondgeneration cephalosporins

#other genera include Enterobacter, Morganella, Providencia, and Serratia ---commonly exhibit greater intrinsic antimicrobial resistance ---requires a third-generation cephalosporin, one of the expanded-spectrum penicillins, a monobactam, carbapenem, quinolone, or aminoglycoside

Anaerobes Most numerous in the normal gastrointestinal tract and mouth The most common---Bacteroides fragilis #B.fragilis and B.thetaiotaomicron---significant resistance to many beta-lactam antibiotics #effective antibiotics---metronidazole, clindamycin, chloramphenicol, imipenem #less resistance patterns---Bacteroides melaninogenicus and most of the anaerobic cocci

The other important genus---Clostridium #all gram-positive, spore-forming rods #C. tetani---responsible for tetanus the prevention of tetanus ---active and passive immunization Anaerobic bacteria grow only in settings with a low oxidation-reduction potential Majority of anaerobic infections require surgical intervention

Fungi (from the Candida genus) ---are infrequently the primary pathogens in deep-seated surgical infections ---may be seen frequently as an opportunistic invader in patients with serious surgical infection who have received broad-spectrum antibiotic treatment suppressing normal endogenous flora

These infections are best avoided ---through judicious use of systemic broadspectrum antibiotics ---through prophylaxis with oral nystatin or ketoconazole when broad-spectrum antibacterial therapy is required

Viruses ---don’t not cause any infections that require operation for resolution Immune suppression to prevent rejection ---transplant patients are at significant risk of viral infection---cytomegalovirus The bloodborne viruses ---may be transmitted through blood transfusion: HBV, HCV, HIV

#the use of accurate tests for screening infected units of blood #to limit blood transfusion to circumstances clearly requiring it