Intraoperative Redosing of Cefazolin and Risk for Surgical Site Infection in Cardiac Surgery

Discussion

This retrospective study demonstrates that intraoperative redosing of cefazolin provided additional protection against surgical site infection among patients undergoing cardiac surgery lasting longer than approximately 6.5 to 7 h. Although this group includes only a minority of procedures, we estimate from our data that a strategy of redosing in all procedures >240 min long results in a 16% reduction in the overall infection rate in cardiac surgery. This rate in our study population was comparable with that reported by others^{[10,11,14,15]}. The benefit from redosing had been assumed but had not been proven, and the minimum duration at which redosing is beneficial had been derived from theoretical considerations. Redosing provided similar protection from both deep and superficial infections (data not shown).

The positive association between duration of surgery and risk for surgical site infection has been reported^[7,8,9]. Our data show that this association persists even when antibiotic is redosed. This observation suggests that the risk related to duration not only reflects a diminution of antibiotic concentration over time but also may be a proxy for risk factors independent of antibiotic use, such as the technical difficulty of the procedure.

Guidelines usually recommend redosing intervals of 3 to 4 h for cefazolin^[1,3,4,5,6]. In a study on hysterectomy, for instance, a protective effect of prophylaxis was no longer observed when the operation lasted >3.3 h^[8]. The benefit extended beyond this threshold in our study, a finding that may reflect the markedly prolonged serum half-life of cefazolin during cardiopulmonary bypass. Although the half-life of cefazolin is 1.8 h in healthy persons^[3], several studies have shown a slower elimination during cardiopulmonary bypass^[14,16,17]. Therefore, any benefit of redosing in noncardiac surgery may be observed for shorter procedures than in cardiac surgery.

This study has several limitations. Because of its retrospective design, the results were adjusted for a limited number of risk factors for surgical site infection, including surgery duration, age of the patient, and need for reoperation. Certain coexisting conditions, such as diabetes mellitus or obesity, smoking status, length of previous hospital stay, and a violation of asepsis during surgery, are among the predictors of surgical site infection that might confound our results, should they be related to the probability of an intraoperative antibiotic redose. Since the most plausible effect of a high-risk profile is to increase the likelihood of intraoperative redosing, adjustment for this profile would increase the apparent benefit. If patients undergoing more complicated (and therefore more infection-prone) procedures were less likely to be redosed for any reason, the effect of redosing would be overestimated. However, in that case, we would expect to see an effect for all procedures, not only longer ones. Our study also provides no information about the utility of additional doses of prophylaxis after surgery. Finally, our sample size limits the precision of our estimates, especially the ability to identify a precise threshold beyond which redosing is beneficial. Thus, we do not know whether similar protection could be obtained by redosing cefazolin only beyond the 400-min threshold. In an exploratory analysis of timing of the redose, there was a significant trend toward higher benefit when a redose was given within 240 min. Therefore, our results should not be used to support an extension of the 3- to 4-h redosing interval recommended by most guidelines^[1,3,4,5,6].

We conclude that redosing of cefazolin prophylaxis for most cardiac procedures can prevent a substantial fraction of surgical site infections. It will be worthwhile to examine the effects of intraoperative redosing in other procedures.

Emerging Infectious Diseases. 2001;7(5) © 2001 Centers for Disease Control and Prevention (CDC)

Cite this: Intraoperative Redosing of Cefazolin and Risk for Surgical Site Infection in Cardiac Surgery - Medscape - Sep 01, 2001.