SURGICAL

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 . 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 . 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, , 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 sep- ticemia. 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 infection: presents with increased results when the bacterial distribution is more or less 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 , , 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 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 infec- tions 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 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 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 include Candida albicans, centration. The MIC level differs for every organism fusarium, histoplasma coccidioides, and blastomyces. cultured and the different antibiotics used on them. Therapeutic dose is equal to four times the MIC. This test is preferred. It gives the physician a dose as well as Antibiotic Therapy sensitivity or resistance of the organism. Certain criteria must be met if antimicrobial agents are only help the usual defense to be effective in the treatment of established infection Antimicrobial agents infection. Some drugs or prevention of potential infection. They are: mechanisms of the host against are bactericidal (that is, they destroy bacteria) while (they inhibit the multiplication 1. The pathogen must be sensitive to the others are bacteriostatic When antimicrobial agent of the bacteria without destroying it)' bacteriostatic agents are used the f inal resolution of the 2. The agent must make contact with the infection depends on the natural defenses of the body. pathogen. Therefore, these agents should be reserved for use in whose usual host mechanisms are intact. 3. There should be nothing at the site of those patients in patients in whom the microbial activity that interferes with the When dealing with infections mechanisms are impaired, action of the antimicrobial agent. natural microbial defense bacteriocidal agents are preferred. 4. Untoward consequences of drug therapy should be anticipated, recognized and Antibiotic Pathogen Contact Of critical importance to treated. eff ective antibiotic therapy is contact between drug' To 5. Unsatisfactory response during treatment microorganism and an adequate amount of the must be evaluated. start with, the route of administration is important. In surgical patients, particularly in the perioperative period, oral administration is an inadequate method of delivery' Pathogen SensitivitY lntravenous administration provides more rapid tissue perfusion and usually higher tissue concentrations A pathogen is considered sensitive to an antibiotic without adverse reaction' ln many infections, intermit- agent if its growth in vitro is inhibited with a concen- tent administration of intravenous bolus antibiotics tration usually obtained in tissue fluid or blood follow- resulting in intermittent yet very high tissue levels of the ing the customary dose. Selection of an antimicrobial drug is preferred to continuous infusion. agent should involve identification of the microbe and determination of the agents to which it is susceptible. Another important consideration is that when an- This is done by the collection and culturing of tibiotics are used systemically, blood f low to the area of pathological material and in vitro testing for sensitivity infection must be adequate to permit delivery of an ef- to commonly used drugs. Specimens should be obtained fective concentration to that site of the pathogens. In before starting the administration of an antimicrobial acute and localized infection such as cellulitis or lym- agent. Susceptibility testing of these specimens is done phangitis, blood flow is usually abundant and tissue per- with disc diffusion tests or the so called Kirby Bauer fusion by the drug most adequate' On the other hand, sensitivity test. areas of fluid accumulation or tissue death, such as abscesses or necrotizing fasciitis may be penetrated very ln disc diffusion tests, once the pathogen is grown on poorly and inadequate tissue levels of antibiotic will a culture plate, antibiotic discs are placed on that culture resu lt. Another consideration is interference with the an- considering their narrow toxic-therapeutic ratio and the timicrobial action. This should be avoided for adequate wide variation in elimination and dose requirements antibiotic therapy to be effective. The penicillins are most among different patients. Patients with a moderate to susceptible to interference by the enzyme peniciilinase. marked infection requiring aminoglycosides are often in This enzyme is produced by certain staphylococci and a hyperdynamic state with increased intravascular coliform bacilli (E. Coli). The cephalosporins are inhibited volume, increased cardiac output, and increased by cephalosporinase (believed to be very similar to glomerular filtration rate. ln these patients, penicillinase), and the sulfanomides are inhibited by aminoglycosides are rapidly excreted by the kidney, and paraaminobenzoic acid. the patient may need to be dosed every four to six hours to maintain proper antibiotic levels. Conversely, elderly lnfections caused by penicillinase producing staph individuals with decreased glomerular filtration rate and aureus are very common in the postoperative patient. decreased kidney function may not excrete the drug as ln these patients, resistant penicillinase antibiotics are rapidly and effectively as normal and may require a used. lf the result of culture and sensitivity show staph longer interval between doses. Therefore, for agents that to be resistant to methocillin (the proiotype of all pose a serious medical threat to patients because of their penicillinase resistant penicillins), Vancomycin is the low therapeutic-toxic dose ratio, serum drug levels are drug of choice. determined throughout therapy. Still another consideration is that one should always Agents where this routinely done include anticipate, recognize, and promptly treat untoward con- is aminoglycosides and Vancomycin. The level of the an- sequences of drug therapy. No antibiotic is free of poten- tibiotic is measured from a sample of the patient's blood tially adverse effects, therefore, one must always be alert after 72 hours of therapy. The peak level of the drug is when prescribing antibiotics, especially in higher doses measured 30 minutes after the infusion of the drug, and where the margin between therapeutic and toxic doses the trough is measured 30 minutes before the infusion is narrowed. Adverse reactions include hypersensitivity of the drug. If the peak level fails to reach true minimal of the patient, changes in microbial flora resulting in inhibitory concentrations, the dose of the drug should superinfection, and patient idiosyncracy. A final con- be increased to allow therapeutic levels of the drug in sideration is that if a patient does not improve during the tissues. If the trough level of the drug does not fall drug therapy, diagnostic reevaluation is essential. The below a certain safe level, the dose of the drug is lowered evaluation should include a physical examination, to prevent toxic reactions to the drug from occurring. laboratory tests, including blood culture and diagnostic x-rays/ isotopic studies, and search for new sites of infection. Surgical lntervention and lts Relationship to Antibiotic Therapy Causes of failure include the wrong initial diagnosis, resistance of the pathogen, new pathogen introduction. The relationship between surgical intervention and For most acute surgical infections, it is not necessary to antimicrobial therapy in the management of infection prescribe antibiotic therapy for more than ten days. depends upon the characteristic of the clinical lesion. However, chronic infections such as osteomyelitis and In many cases of postoperative infection a surgical opera- tuberculosis usually require prolonged antimicrobial tion is the primary therapeutic modality, and antibiotics therapy. are of secondary importance. These include all cases of pyogenic abscess formation, infected , and in- fected tissue necrosis.

Antibiotic Dosing In unlocalized infection the use of an antibiotic without operative intervention is often recommended provided For an antibiotic to be effective its concentration at the the tissues at the site of bacterial activity are intact, well site of infection must exceed the minimal concentration vascularized, and not threatened by pressure (edema). of antibiotic required to kill or inhibit bacteria involved. Lymphangitis and cellulitis meet these requirements. Factors determining the concentration of antibiotic within the body include absorption, protein binding, When the inflammatory process localizes and presents distribution, and excretion. as a pyogenic abscess, tissue necrosis or confinement within a closed space, surgical intervention is of primary Rapid and accurate measurement of antibiotic concen- importance. Antimicrobial therapy alone is minimally or trations in blood have made it possible to apply phar- not at all effective. The antibiotics are used to deal with macokinetics to antibiotic dosing. This is especially the residual elements o{ the infection and prevent ex- important in managing the dosage of aminoglycosides tension to uninvolved tissues. l Surgical intervention in the management of localized These patients usually present with a history of sud- infection includes the following: den onset of chills, high fever, nausea/ anorexia, tachycardia, and general malaise. Progressive bone pain 1. lncision and drainage of purulent material. will also be noted that is aggravated with movement. 2. Excision of devitalized tissue including sinus tracks. Fluctuant swelling of subperiosteal abscesses may be 3. Decompression of tension in closed space. palpable. 4. Removal of foreign bodies. Subacute osteomyelitis may result f rom the presence The prophylactic use of antibiotics employs the drugs of infection by an organism with reduced virulence in during the period of primary lodgement prior to col- an individual with a high level of resistance or in a pa- onization and before the contamination is localized. tient treated for osteomyelitis with less than optimal levels of antibiotics. The majority of these cases involve Osteomyelitis staph aureus, salmonella, and tuberculosis. Four types of bone lesions are identified: 1) Brodie's abscess, 2) Osteomyelitis is an inflammation of bone secondary Carre's sclerosing osteomyelitis, 3) osteolytic lesions, 4) to pyogenic infection of the bone. Although numerous diaphyseal lesions. microbes have been implicated in the disease process Brodie's abscess is the most common form of subacute only a handful are seen with regularity, especially in the osteomyelitis. It is a lytic area of bone in which the in- postoperative patient. Effective treatment of fection is walled off and effectively contained by reac- on early and accurate diagnosis, osteomyelitis depends tive formation of a surrounding layer of granulation appropriate antibiotic selection, and oftentimes surgical tissues. This lesion presents primarily in metaphyseal resection of infected necrotic bone. bone.

Osteomyelitis presents as an acute, subacute, or Chronic osteomyelitis is a sequel to untreated or in- chronic infection of bone. lt is also classified according adequately treated acute osteomyelitis. The patient has to endogenous or exogenous sources of bacterial origin. a history of recurrent attacks of fever, swelling, and pain Endogenous infection represents blood-borne infection in the involved area over a period of months or years. which seeps into the osseous architecture and is com- There may be a persistent draining sinus over the area monly referred to as hematogenous osteomyelitis. Bran- with drainage from the sinuses increased during acute ches of the nutrient arteries to the long bones and episodes of osteomyelitis. metaphyseal arterioles which take very acute turns back on themselves in the metaphyseal epiphyseal junction of the bone appear especially vulnerable. These arterioles Patients are generally over 20 years of age. The present- end in larger sinusoidal veins, making circulation in this ing symptom is commonly that of pain which is worse area very sluggish. It is in these areas of sluggish circula- at night, aggravated by activity, and relieved by rest. The tion that bacteria are able to proliferate and cause infec- presence of persistent or intermittent drainage of tion. purulent material from the sinus is the usual presentation. Exogenous osteomyelitis results from direct extension or contiguous foci and direct implantation such as punc- Laboratory studies which are used in cases of ture wounds or intraoperative contamination. osteomyel itis i ncl ude:

Clinical Presentation Acute osteomyelitis is most often 1) CBC with differential, looking for leukocytosis, and a found in the pediatric patient with a male predominance. shift to the left in acute stages, It is most commonly noted in the femur, tibia, and humerus, although the foot is involved in 10% to 13% 2) ery.throcyte sedimentation rate and C-reactive protein, of the cases. Endogenous or hematogenous seeding of both are accelerated by the body in response to infec- bacteria from a distant site accounts for the etiology in tion and other inflammatory stimuli. These are both the majority of cases. A previous history of trauma to the nonspecific but give the clinician an idea of response to involved area is reported in 30% to 50% of the cases. therapy. Primary foci include abscesses, furuncles, impetigo, eczema, upper respiratory tract infections, acute otitis 3)Teichoic acid antibodies. Teichoic acid is a component media, tonsillitis, urinary tract infections, and paronychia. of the cell structure in staphylococcus bacteria. The body Bacteria from these foci allow microbes to enter the bone produces antibodies against this protein which are and start the septic process. measured. Large levels indicate a staph infection. 4)ASO anti-DNAse D, and anti-hyaluoronidase. These are reliable cultures are mandatory. Soft tissue cultures are three antibodies produced in response to Group A strep- inadequate, especially cultures of open ulcers and sinus tococci. Antistreptolysin O is usually available and easi- tracts. Bone cultures are necessary to make proper ly reproducible. diagnosis of the causative organism. Bone cultures must be made through uncontaminated skin which often Radiographic Studies. Localization of bacteria within necessitates a separate incision. AII antibiotics should be bone causes an inflammatory reaction and lowering pH discontinued 48 hours before the culturing is done. due to increased metabolism locally. With this, there is a removal of bone matrix (collagen) and calcium. Antibiotic therapy alone is usually insufficient for Therefore, the earliest x-ray change seen in osteomyelitis resolution of osteomyelitis. This is due to the build up is a loss of bone density in the involved areas. As the of fluid within the bone and subsequent increased infective process continues there is a spread of it to ad- pressure on the vessels to the bone. Once the circula- jacent bone through the Haversian and Volkmann's tion is impeded, antibiotics are not able to reach the in- canals. This destroys the normal vascular network and fection to be effective. Also necrotic bone harbors causes further bone death. As the bone dies, it appears bacteria which are able to produce a protective film sclerotic and radiodense on x-ray. Large islands of around themselves and wall themselves off from white devitalized bone form and are referred to as sequestra blood cells and antibiotics. Therefore, when (isolation of dead bone from iiving bone). osteomyelitis is diagnosed it should be surgically resected and antibiotic therapy utilized. Simultaneously, spreading edema and fluid causes compression of soft tissue structures such as vessels, ldentification of the pathogen is done in the lymphatics, and nerves which lie between the bone microbiology laboratory. However, the majority of lamellae. The produced by the compressive ac- postoperative osteomyelitis cases are caused by tion of edema, together with the tendency toward em- staphylococcus aureus. The other common pathogens bolic infarction, increases the extent of bone necrosis. include gram-negative bacilli such as e. coli, proteus, Fluid passes the outer Iimits of the cortex and the elastici- pseudomonas, and salmonella in those patients with ty of the periosteum replaces the rigid structures of the sickle cell disease. Hematogenous osteomyelitis caused bone. Edema collects here and is soon replaced by pus. by gram-negative bacilli is associated with When infection reaches the outer cortex, it may cause gastrointestinal and genitourinary infections while acute the invasion of the slow periosteal blood flow and thus respiratory infections cause pneumococcal and gain access to the subperiosteal space resulting in bacteroides osteomyel itis. Mycobacteri u m tu bercu losis subperiosteal abscess. These abscesses are evidenced by and fungal osteomyelitis are usually traced to chronic reactive subperiosteal calcification. This induces ex- pulmonary processes. uberant growth of periosteal bone termed involucrum Appropriate antibiotic therapy is initiated once the formation. culture and sensitivity results are known. Intravenous an- tibiotic therapy is mandatory for a four to six week Osseous changes on x-ray is not evident for 10 to 14 period. Recurrence of the infection can be expected with days postinfection. However, early soft tissue changes treatment for a shorter period of time, or with oral are recognized and aid in the early accurate diagnosis. antibiotics. The first radiographic finding consistent with osteomyelitis is an increase in density and swelling in the anatomical configuration of involved muscles. Other Surgery is performed as soon as possible after the ex- early changes include subperiosteal calcif ication which tent of involvement is defined. Only in cases of acute corresponds with subperiosteal abscess formation. After osteomyelitis prior to bone necrosis, in cases of chronic 14 days the radiolucency described above appears and hematogenous osteomyelitis, and in patients with the involved bone takes on a mottled look due to bone vascular disease, is antibiotic therapy alone attempted. lysis. The formation of cloaca or a lytic tract through the Surgically, all soft tissue and bone which appears cortex may be noted this early. By the end of the second necrotic is resected, including a small portion of ap- week opaque areas of new bone formation are noted. parently good bone. lf the infection continues to a joint, The formation of so called sequestra are noted by the disarticulation is felt to be the best surgical approach, third week of infection. This characterizes the beginning in that it maintains the cartilage at the head of the adja- of the chronic osteomyelitis. cent bone/ and the cartilage provides a protective bar- rier to pathogens entering the osseous structure. lf Treatment of Osteomyelitis transcortical bone is cut and removed, the pathogens have easy access to the Haversian and Volkmann's canals When osteomyelitis is highly suspected accurate and and continued spread of infection occurs.