8 Timing of surgical antibiotic prophylaxis and surgical site infection rates: timing within the hour before incision may not matter

Aim The impact of surgical prophylaxis timing within the hour before incision on surgical site infection (SSI) rates is undefined. We analysed the SSI rates for timing within the hour before incision to see if there was evidence for an optimal timing to reduce SSIs. Method We analysed the SSI rates for hip and knee arthroplasty and cardiac surgery procedures from the prospective Health Quality and Safety Commission’s (HQSC) national Surgical Site Infection Improvement Programme (SSIIP)1,2. Procedures from 2014–2023 were included. Patients were followed for 90-days after surgery and USA CDC NHSN SSI definitions were applied. The SSI rates for 10-min time periods within the hour before incision were compared. Late prophylaxis was defined as given at, or after incision and early as more than 60 min before incision. Uni- and multivariable analysis were performed. Results There were 102 211 procedures; 66 292 (65%) had the timing of antibiotic prophylaxis recorded in minutes versus incision time (48 912 arthroplasties and 17 380 cardiac). 99.8% were clean procedures and cefazolin was the prophylactic antibiotic for 95% of operations. After multivariable analysis the independent risk factors for SSI in orthopaedic surgery were male sex (odds ratio 1.5), BMI (OR up to 2.4 for BMI > 40), surgical risk score (OR 2.9 for score ≥2), and revision procedures (OR 1.9) and for cardiac surgery they were female sex (OR 1.5), BMI (OR up to 3.2 for BMI > 40), type of procedure (bypass procedures OR 2.7), and diabetes (OR 1.6). For cardiac surgery the SSI rates were not associated with prophylaxis timing, for arthroplasties the lowest SSI rate was for prophylaxis given 1–10 min before incision (1.0%) and after multivariable analysis prophylaxis given 51–60 min and >60 min before incision had higher risk for SSI, ORs 2.4 (95% c.i. 1.5–3.9) and 2.1 (95% c.i. 1.1–3.8) respectively. When all procedures were combined the lowest SSI rate was for prophylaxis given 21–30 min before incision, Table:TableTiming of cefazolin prophylaxis and surgical site infection rates in clean orthopaedic and cardiac surgeryTime (mins)No SSISSITotalSSI %OR95% c.i.P valueLate17113717482.121.441.02–2.030.051–10780713979461.751.180.96–1.450.1211–2018 90334219 2451.781.21.03–1.410.02521–3018 54027918 8191.48REF31–4010 11720610 3232.01.351.13–1.620.00141–50450612446302.681.831.48–2.27<0.00151–6024398625253.412.341.83–2.99<0.001Early10203610563.412.351.65–3.34<0.001Total65 043124966 2921.88The SSI rate for prophylaxis given 1–30 min before incision was 1.7%, for prophylaxis >30 min before incision the SSI rate was 2.4% (OR 1.5, 95% c.i. 1.3–1.7, P < 0.001). REF- Reference group (the group that the other times were compared to). Conclusion The SSI rates for prophylaxis given >30 min before surgery appear higher than prophylaxis given within 30 min of incision. However, combination of all data was needed to show this. More outcome data are required before firm recommendations can be made for fine tuning of prophylaxis within the hour before incision. The finding may not be applicable to non-clean procedures and for non-cefazolin prophylaxis.