Surgical Infections

SURGICAL INFECTIONS Cerard V. Yu, D.P.M. Patrick A. Landers, D.P.M. Definition and Classification Bacteria release proteinases which aid the process of tissue liquefaction. Collagenase is an example of such an enzyme and aids in the spread of the infection. Surgical infection is the product of entrance, growth, metabolic activities, and resultant physiologic effects of Bacteria and their metabolic products may be carried microorganisms in the tissues of a patient. There are four from the area of primary infection into the lymph fluid characteristics to all surgical infections. and distributed to large areas through the lymphatics and 1. They involve postoperative wounds. larger lymph nodes. ln doing so they may cause lym- 2. The infection is unlikely to resolve phangitis (red streaking) and lymphadenitis (palpable spontaneously or with simple antibiotic lymph nodes). treatmen! suppuration, necrosis, Sangrene/ osteomyelitis, prolonged morbidity and lnvolvement of local blood vessels may result in throm- mortality may occur if untreated. bophlebitis and further spread of the infection. Necrotiz- 3. Excision or incision and drainage are very ing fasciitis is usually of regional extent but can 80 on often necessary. to involve the foot and/or lower leg. 4. Surgical infections are usually monomicrobic but may be polymicrobic. They are often Systemic infections occur through the dissemination invasive with rapid growth and regional or of microorganisms from a distributing focus into the systemic spread. blood stream resulting in either bacteremia or septicemia. Bacteremia is present when the primary focus Classification o{ surgical infections by location and distributes bacteria once or intermittently, resulting in pathophysiologic changes is as follows: their transient appearance in the blood. Septicemia 1. A wound infection: presents with increased results when the bacterial distribution is more or less inflammation and cellulitis, suppuration or constant, causing their continued presence within the liquefication of tissues, abscess formation, bloodstream. Therefore, the difference is in the rate of septic necrosis. Further involvement dissemination and density of release from the involves number 2. distributing focus with the rate constant in septicemia 2. Regional extension: this occurs by direct and intermittent in bacteremia. extension into adjacent tissues by lym phangitis and lymphadenitis, by septic Bacteremia and/or septicemia can cause distant organ thrombophlebitis and by spreading fasciitis involvement. Examples include those infections which or necrotizing fasciitis. Further involvement develop in the liver, pancreas, biliary tract, Iung, or involves number 3. kid neys. 3. Bacteremia and septicemia. The presence and complete identification of Characteristics of infection are as follows. lnfection microorganisms in a surgical infection is important. starts as an exaggerated inflammatory response without Although staphylococcus aureus is most frequently suppuration. The marked erythema and warmth of the found in the postoperative patient it must be skin is termed cellulitis. Pain, swellinE, and edema also remembered that surgical infections may be mixed occur. Suppuration and liquefaction of tissues follows bacterial infections produced by a variety of bacteria in72to 96 hours and the presence of a pus-filled abscess both gram-positive and gram-negative, aerobic and is soon noted. The abscess is walled off by a membrane anaerobic. The incidence of gram-negative, fungal, and which produces induration about the abscess, giving a viral surgical infections has steadily increased with the rather solid feel to the tumor. Regional involvement oc- expanding clinical use of steroids, immunosuppressive curs from direct extension of microorganisms along agents, and multiple antibiotic agents. This is especially areolar, fascial, muscular, and other anatomical planes' prevalent in the burn Patient. The enteric gram-negative bacteria are found in almost bacterially induced inflammation and pus encountered 50% of postoperative wounds which become infected. during the operation. Also staphylococcus is found in over 60% of cases where postoperative wounds become infected. Because of this prevalence patients are usually given prophylactic first Laboratory Support in Surgical lnfections generation cephalosporin in increased risk and con_ taminated cases. It is effective on not only staphylococ_ The microbiology lab is of particular importance in the cus, but also on many of the enteric gram-negative prevention and control of surgical infections. Clinicians organisms. using the lab should become familiar with its work since specimens are selected and taken more intelligently when it is known what the lab can do, how Certain criteria are established in order to provide it is done, ob_ and how the results are interpreted. jective definitions and understanding of surgical infections that will permit consistent evaluation. Microbial reports alone are unreliable because of limitation of Effective management of patients with surgical infec- some bacteriology labs, inadequate sampling and testing, tions necessitates constant surveillance of hospital prac- or positive results secondary to outside contaminants. tices and regular assessment of sensitivity of causative Therefore, universal or uniform clinical criteria are used organisms in order to employ proper therapy. The to promote understanding and agreement among physi_ laboratory support begins with the culture techniques cians. These are as follows: employed. lt is the responsibility of the physician to recognize the need for culture and to use proper method 1. Wounds are definitely not infected when and timing for collection of culture material. The follow- there is a healing ridge by five to eight days ing rules should be followed to ensure proper and/or primary intention healing is noted. m icrobiological diagnosis. 2. Wounds are definitely infected when there is 1. Obtain an appropriate specimen for the type purulent drainage noted even if no of disease and organism anticipated. Exam- organisms are found under the microscope. ple is to culture the walls of an abscess rather than the center only. Also bone 3. Wounds are possibly infected when there is tissue is needed for culture material in marked inflammation without discharge or suspected osteomyelitis. Culturing sinus when there isculture positive serous tracks in osteomyelitis and other infections drainage from the wound. Other helpers in is worthless. identifying infected wounds include the vital signs, the CBC with differential. 2. Collect specimens prior to the initiation of antimicrobial therapy by means of aseptic Wound classification is based on clinical estimation of technique. Transport the specimen in a bacterial density, contamination, and risk of subsequent sterile container using transport media infection. Clean wounds are elective wounds which are appropriate for the specimen concerned. primarily closed and do not drain. They are non- 3. Swab cultures of open, draining wounds or traumatic, uninfected wounds. There is very minimal in- tracks should first be cleaned with betadine, flammation encountered, and there is no break in the milked, and then cultured. aseptic technique. lean wounds have an infection rate of 1% to 2%. 4. Provide the microbiologist with a presumptive diagnosis based on clinical presentation. Also describe antibiotic Clean contaminated wounds constitute a minor break therapy if it is being used. in aseptic technique. There is some mechanical drainage noted and the infection rate in these is approximately g%. 5. Ensure appropriate transport and timely delivery to the laboratory of each Contaminated wounds are open wounds which are specimen. This is especially important in flushed and are usually traumatic in nature. There are cases of suspected anaerobic infections. major breaks in aseptic technique and infection is 5. At the time of the culture, submitting prevalent in 15% to 23% of these cases. additional specimen material for direct gram strain smears may permit presumptive Finally, dirty or infected wounds include traumatic diagnosis, thus enabling the initiation of wounds with devitalized tissue and there is acute appropriate antibiotic therapy. Mycology plate, and the effectiveness of the antibiotic is measured as the zone of inhibition or the zone of bacterial death nonbacterial infections The increased occurrence of around that disc. in surgical patients has accentuated the need for accurate removed from surgical diagnosis of yeasts and fungii The terms "susceptible" or "resistant" are based on a stain of a peripheral patients. Examination of Wright the zones of inhibition produced by the concentrations reveal a systemic fungal infection or blood smear may of antimicrobial agents usually obtainable in blood levels in ln general, swabs the presence of fungii the blood. with usual doses of that drug. and surface culture techniques are ineffective in the yeast, and tissue biopsies are isolation of fungii and Many labs now report microbe sensitivity to antibiotics necessary. as MIC (minimal inhibitory concentration) levels. This measures the amount of antibiotic needed to inhibit the clinical impor- Fungal organisms causing infections of growth of the microbe cultured, or the inhibitory con- aspergillus, tance in surgery include Candida albicans, centration. The MIC level differs for every organism fusarium, histoplasma coccidioides, and blastomyces. cultured and the different antibiotics

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