G Zaneti, R Giardina, R Platt Emerging Infectious Diseases Vol 7 (September/October 2001) 828-831
Antibiotic prophylaxis refers to the administration of a brief course of an antimicrobial agent just before making a surgical incision. It is used to reduce the risk of surgical site infections (SSIs) in certain surgical procedures. Guidelines from the Centers for Disease Control and Prevention (CDC) on SSI prevention list antibiotic prophylaxis as a category IA recommendation (ie, strongly recommended for implementation and supported by well-designed experimental, clinical, or epidemiological studies).
The goal of antibiotic prophylaxis is to retard the growth and proliferation of microorganisms from intraoperative contamination and reduce the bioburden to a level that would not overcome the natural defenses of the patient. Observational studies have inferred that intraoperative redosing of an antibiotic may have a positive effect on prevention of SSI. The assumption is that maintaining therapeutic levels of an antimicrobial agent throughout the surgical procedure prevents the protective effect of antibiotic prophylaxis from waning over time. This assumption has not been confirmed in clinical trials. The authors, therefore, investigated the effect of intraoperative antibiotic redosing on the risk for SSI.
Methods. This was a retrospective cohort study consisting of 2,751 patients who underwent cardiac surgery. It was restricted to patients who received antibiotic prophylaxis consisting of I g of cefazolin beginning less than 90 minutes before the incision and whose procedure lasted more than 240 minutes after that dose. Patients were excluded if they received therapeutic antibiotics at the time of surgery. Intraoperative redosing was defined as the administration of a second dose of cefazolin at any time before the surgical incision was closed.
An infection control practitioner prospectively identified SSI using criteria and definitions from the CDC. The practitioner did not know whether patients had received intraoperative redosing. A two-sided Wilcoxon rank sum test for continuous variables and chi-square test for proportions were used to compare patients who received intraoperative redosing with those who had not. Significance level was set at P = .05 in all tests. Significant univariate predictors for SSI were included subsequently in a logistic regression model that was built through a forward selection process in which the absence or presence of antibiotic intraoperative redosing was forced into the model. The Wald test was used to report the significance level of the predictors in the model.
The likelihood of contracting an SSI also was compared for intraoperative redosing. This was categorized as either absent, given after 240 minutes, or given within 240 minutes with odds ratio (OR) used to determine deviance from linearity. An interaction term was created to determine whether intraoperative redosing had different effects on the risk for SSI across different procedure durations. The likelihood ratio test was used to assess significance of this interaction term.
Results. After excluding patients that did not meet the study criteria, data were available for 1,548 patients. Intraoperative redosing of the antibiotic was administered to 459 (30%) patients, including 276 (18%) who were redosed within 240 minutes. The mean duration of surgery was significantly higher for patients who were redosed compared to those who were not redosed (P = .0001). Surgical site infection occurred in 144 (9.3%) patients. There was no significant difference in the risk for SSI in patients who received intraoperative redosing versus those who did not (43 [9.4%] versus 101 [9.3%], OR 1.01, 95% confidence interval 0.07-1.47).
Multivariate analysis revealed that the risk for SSI increased with the duration of the procedure and that there was a significant association between surgery duration and intraoperative redosing (P = .015), with intraoperative redosing associated with lower infection rates in the procedures of longer duration. Intraoperative redosing had a significant protective effect only in those procedures lasting more than 400 minutes (OR 0.44, 95% confidence interval 0.23-0.86), reducing the risk for SSI 56%. Researchers estimated that if all patients whose procedure lasted more than 400 minutes were redosed, there would be a 16% reduction in the expected SSI rate (7.9% versus 9.4%).
Discussion. This study demonstrates that intraoperative redosing of cefazolin for patients undergoing cardiac procedures lasting longer than approximately six and one-half hours provides additional protection against SSI. Current guidelines for intraoperative redosing with cefazolin generally recommend redosing at intervals ranging from 180 minutes to 240 minutes. The benefit of redosing for cardiac procedures has been demonstrated; however, this study did not identify a precise threshold beyond which intraoperative redosing is beneficial.
These results cannot be generalized to other surgical procedures. Additional studies examining other surgical procedures in which antibiotic prophylaxis is indicated should be conducted.
Perioperative implications. With increasing emphasis being placed on patient safety and positive outcomes, strategies to reduce SSI must be sought and implemented. This study has profound implications for perioperative nurses. It highlights nurses' role as advocates. Perioperative nurses are positioned to remind surgeons to order an intraoperative antibiotic redose at 240 minutes for those patients who received antibiotic prophylaxis. They are qualified to work with administrators and surgeons in developing and implementing cogent procedures to ensure that this patient safety issue is addressed effectively. The result, as evidenced by this study, is a positive impact on patient safety and a reduction in the risk for development of SSI.
COPYRIGHT 2002 Association of Operating Room Nurses, Inc.
COPYRIGHT 2002 Gale Group