There is no question that antibiotic prophylaxis for cardiac surgery reduces surgical site infections.1 The successful implementation of prophylactic regimens, however, is often inconsistent or inadequate. The use of prophylaxis protocols or decision-support systems as either a single measure2 or as part of a patient care pathway3 has been demonstrated to improve adherence to prophylaxis, with a reduction in surgical site infections. In this issue of the Journal (page 141), a study by Haydon and colleagues4 shows that antibiotic prophylaxis protocol use in 45 Australian cardiac surgery units increased significantly between 2004 and 2008 (from 58% to 80%), but concordance with version 13 of the Australian Therapeutic guidelines: antibiotic5 was poor when both choice of agent and duration of administration were considered. In particular, there was an increased use of multidrug regimens, an increased use of vancomycin for routine prophylaxis, and a prolonged duration. The study did not examine surgical site infection rates.

As prophylaxis protocols improve patient outcomes, and adherence to protocols in Australian cardiac surgery units seems to be high, it is timely to consider the optimum elements of such protocols in terms of timing of prophylaxis, duration of prophylaxis, and choice of agent.

There have been a number of studies that show the relationship between timing of antibiotic administration and surgical site infections. An observational cohort study in a consecutive series of 3836 surgical procedures (vascular, trauma and abdominal) showed the optimal time for administration of β lactams was 30–60 minutes before incision.6 The risk-adjusted odds ratio of surgical site infections was 3.16 (95% CI, 1.4–7.0) if given 75–120 minutes before, 2.82 (95% CI, 1.5–5.3) for administration 15–29 minutes before, and 1.75 (95% CI, 0.9–3.4) if given in the last 14 minutes before incision. In a prospective study of 2048 patients given vancomycin prophylaxis for cardiac surgery (coronary artery bypass graft [CABG] or valve replacement), the optimum time for the start of a vancomycin infusion was shown to be 16–60 minutes before incision.7 The relative risk of infection was 7.8 (95% CI, 2.5–24.7) if started 0–15 minutes before incision and 2.2 (95% CI, 0.99–5.09) if started 61–120 minutes before.

Duration of prophylaxis has been a controversial issue. The Society of Thoracic Surgeons practice guidelines8 recommend that prophylactic antibiotics be given for 48 hours or less, citing some evidence for effectiveness of single-dose or 24-hour regimens, but comment that additional studies are required to confirm the effectiveness of shorter courses. This has been addressed in a study on 838 patients undergoing CABG or valve replacement.9 Patients received cephazolin as either a single dose before incision or a prolonged regimen, with a dose before incision, then 8-hourly for 24 hours. There was a statistically significant difference in surgical site infections between the two groups (8.3% v 3.6%; P = 0.004).

The choice of agent is mainly between a β lactam and vancomycin, although alternative choices are possible (eg, flucloxacillin plus gentamicin). The Society of Thoracic Surgeons practice guidelines10 recommend cephazolin for standard practice in populations that do not have a high incidence of methicillin-resistant Staphylococcus aureus (MRSA). Haydon et al’s study showed that routine vancomycin use for CABG surgical prophylaxis increased from 13% in 2004 to 44% in 2008, with similar increases seen for valve surgery — from 31% to 62% over the same period.4 Vancomycin prophylaxis for cardiac surgery is recommended in the current Therapeutic guidelines: antibiotic for institutions with a high prevalence of MRSA, for β lactam-allergic patients, or for procedures where there is a higher risk of infection with a coagulase-negative staphylococcus (eg, valve surgery, reoperations).5 Excessive vancomycin use is to be discouraged, as its activity is inferior to β lactam antibiotics for susceptible organisms and it will add selective pressure for hVISA (heteroresistant vancomycin-intermediate S. aureus), particularly if the duration of administration is prolonged. With the advent of rapid MRSA molecular detection tests, it is now possible to screen patients before surgery and use vancomycin selectively in those found to carry MRSA. An alternative is to use intranasal mupirocin routinely in the absence of a documented negative test for MRSA (and methicillin-sensitive S. aureus [MSSA]), as this agent has been shown to reduce both MSSA and MRSA surgical site infections.11

How do these recommendations relate to the Therapeutic guidelines: antibiotic? The current guidelines, version 13 (published in 2006),5 are concordant, except for the duration of therapy. It is very likely that this is the major issue that has resulted in the lack of adoption of the guidelines’ cardiac surgery prophylaxis regimens found by Haydon and colleagues. Version 14 of Therapeutic guidelines: antibiotic is currently in preparation and due to be published in 2010, and the recent studies described here have been noted by the writing committee. It is very likely that version 14 will recommend a 24-hour prophylaxis regimen and that the recommended antibiotic agents will remain unchanged.

The purpose of any surgical prophylaxis protocol is to ensure adherence to the optimum choice of agent, timing of administration and duration of prophylaxis. With such adherence, surgical site infections will be minimised, thereby reducing morbidity and mortality for patients undergoing cardiac surgery.