Although the Safer Healthcare Now! initiative in Canada supports surveillance of systemic antibiotics used for prophylaxis in conjunction with surgical procedures, the use of ABC is not included in the initiative’s systematic approach. Fifty-nine percent of the patients (65/109) whose charts were reviewed in the present audit received a premixed antibiotic in bone cement as prophylactic therapy. The variant practice for different patients cannot be ascribed to buying contracts, since all patients were treated in one health care region. As such, differences in the use of ABCs constitute yet another variable, in addition to differences in the design or ventilation of operating theatres, workflow, organizational culture, and human resources, that may affect rates of surgical site infection. Overall, the rates of infection in the Calgary Health Region are in keeping with current practice and are closely monitored by the region’s infection control practitioners. The quarterly rates of deep infection and organ space infection for primary total hip surgery ranged from 0.40% to 2.15% for the first 3 quarters of 2004/2005, whereas for primary total knee arthroplasty they ranged from 0.48% to 2.01% (W. Runge, Infection Control Practitioner, Calgary Health Region; personal communication by telephone, December 14, 2005).
About 2000 patients undergo primary total hip or total knee replacement each year in the Calgary Health Region. Extrapolating from this audit, we estimate that about 1000 of these patients may receive ABC each year. The association between prophylactic use of ABC and the prevalence of antibiotic-resistant organisms has not been well studied, but the possibility of such an association exists. For example, emergence of antibiotic resistance after primary arthroplasty in which gentamicin was included in bone cement has been reported. Bone cement is an optimal surface for bacterial colonization, and prolonged exposure to an antibiotic at subinhibitory levels allows mutational resistance to occur. If the use of ABC in the operating room were to be captured electronically and entered into a provincial surveillance registry database, the effect of ABC on resistance could be better analyzed through prospective population-based studies.
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Three commercial types of ABC were used in the Calgary Health Region during the audit period (Table 2). Tobramycin was more commonly used (54/65 [83%]) than gentamicin (11/65 [17%]), and tobramycin was always used at one of the hospitals. It was unclear from this audit if surgeons selected particular ABCs on the basis of perceptions of local microbial epidemiology, susceptibility patterns, or other subjective factors such as the texture or workability of the cement. The preference for tobramycin is consistent with practice in the United States, but is inconsistent with practice in Europe. For infectious diseases in general, tobramycin is typically reserved for Pseudomonas and for situations in which gentamicin resistance is too strong a possibility to risk failure by administering the latter. Local community patterns for the Calgary Health Region indicate that the organisms of concern are adequately susceptible to gentamicin (92% susceptibility for coagulase-negative staphylococci and 98% susceptibility for Staphylococcus aureus, for the period July 2004 to June 2005); therefore, it remains unclear why tobramycin-containing bone cement was most frequently chosen for elective procedures. A qualitative survey of the orthopedic surgeons would be helpful to elicit their opinions and beliefs. An initial survey of orthopedic surgeons to determine their practice preferences regarding ABCs was aborted because of anticipated low participation rates. It seems doubtful that 3 different aminoglycoside- containing products are needed for prophylaxis in this setting, and efforts are therefore under way to limit the number of products, although consensus and simplification of ABC selection may be difficult to achieve. levitra plus
In the 1995 survey of US orthopedic surgeons, 11% of respondents reported incorporating liquid antibiotics as an admixture into the bone cement. Surgeons must be mindful that the addition of large amounts of antibiotic can significantly damage the mechanical properties of the bone cement and can lead to systemic toxic effects. To provide perspective, use of up to 8 g of antibiotic per 40 g of bone cement has been reported for cases of active infection. From the charts reviewed, it was reassuring to find that the surgeons did not add extra antibiotics (e.g., vancomycin) to the commercial products. Instead, premixed commercial products were used. The actual amount of bone cement (and therefore the “dose” of antibiotic) deposited in the patient’s joint was not known with precision because, although the batches of cement prepared for the procedure were counted, excess cement was discarded without measurement. The audit showed that surgeons used a relatively low dose of ABC, which never exceeded 1 g of antibiotic per 40 g of cement. Although there have been no cases of toxicity reported with the low-dose ABC used for primary prophylaxis, the safety of higher- dose ABC for arthroplasty revisions warrants more caution and greater study.