Study design and setting
This before-after study was conducted from August 2014 to June 2017 at Tokyo Metropolitan Tama Medical Center, a 790-bed tertiary care center in Tokyo. Approximately 7000 patients annually undergo surgery at the study institution. The patients’ informed consent was obtained before surgery. The institutional review board at Tokyo Metropolitan Tama Medical Center approved this study.
Participants
Patients over age 16 years who underwent any form of laparoscopic surgery including cholecystectomies, colectomies, gastrectomies, appendectomies, and proctectomies at the study institution were included for analysis. Patients who underwent laparoscopic surgery without follow-up information 30 days after the procedure were excluded.
Intervention
During the pre-intervention period (August 2014 – June 2016), the timing of preoperative SAP differed for each operation. In July 2016, the practice of administering SAP immediately after patients enter the operating room was implemented. Once patients were transferred into the operating room, intravenous SAP was immediately administered by anesthesiologists. If vancomycin or fluoroquinolone was used for SAP, administration of the agent was begun in the hospital ward before the patient was transferred to the operating room because both of these agents require a longer period of administration. Besides the intervention noted above, there were no concurrent changes in perioperative management, including the type and dosage of antimicrobials for SAP during the study period. The recommended SAP at the study institution is described in Appendix 1.
Data collection
Clinical data were extracted from the electronic medical records. We also determined the type of laparoscopic surgery done, time of administration and completion of preoperative SAP, the American Society of Anesthesiologists (ASA) score, wound class, demographic characteristics, and underlying illnesses. Because SAP was administered intravenously over 15–30 min, we collected the data on the time of SAP completion and surgical incision. The primary outcome was the incidence of SSI as defined by the CDC criteria [7, 8]. Nurses and physicians in the department of infection control determined whether SSI developed in the study subjects. Patients who were discharged within the follow-up period were observed at follow-up visits as outpatients. The primary interest of this study was to examine if changing the timing of preoperative SAP affected the incidence of SSI.
Statistical analysis
We compared the incidence of SSI between the pre-intervention and intervention periods using the chi-square test. We also compared other, selected factors between the study periods. The changes in SSI incidence due to the intervention were also evaluated by segmented regression analysis of interrupted time series (ITS) data. For the sensitivity analysis, factors associated with SSI in the study period were also investigated. The usual time point of SAP (i.e., 31–60 min prior to surgical incision as a reference, in comparison with 0–30 min and > 60 min) was used as a variable in the final model. Categorical variables were compared using Fisher’s exact test or the chi-square test as appropriate. Continuous variables were compared using the Mann-Whitney U test. All the analyses were performed using Stata version 15 (StataCorp, College Station, TX, USA) and SPSS version 21 (IBM, Armonk, NY, USA).