Time-dependent effect of chlorhexidine surgical prep

Despite continued advances in preoperative preventive measures and aseptic technique, surgical site infections remain a problem. The purpose of this study was to evaluate the time-dependent effectiveness of chlorhexidine, a common surgical preparation solution, at various concentrations. Agar plates containing a Mueller-Hinton medium were inoculated with Staphylococcus aureus (lux) bacteria. The bacteria are genetically engineered to emit photons, allowing for quantification with a photon-counting camera system. Standardized amounts of aqueous chlorhexidine at three different concentrations (group 1:4%; group 2:2%; group 3:0.4%) were applied to the agar plates and comparisons in bacterial reduction were made. After 2 min of contact time, groups 1 and 2 had similar reductions in bacterial load with 30% bacterial load remaining in each group (P=0.512), whereas group 3 had a significantly higher bacterial load (33%) when compared to both groups 1 and 2 (1 vs 3, P<0.0001; 2 vs 3, P=0.0002). The bacterial load in all three groups continued to decrease out to the final time point (1h) with group 1 having the least amount of bacterial load remaining, 9% (P<0.0001) and group 3 with the highest bacterial load remaining, 19% (P<0.0001). This study demonstrates two key results: first, dilution of chlorhexidine correlates directly with its bactericidal activity; second, its effectiveness is directly related to its contact time. Based on the results of this study, the authors recommend using 4% chlorhexidine for surgical site preparation and allowing a minimum of 2 min of contact time prior to making the skin incision.