Beyond Core Measures: Identification of Modifiable Risk Factors for Prevention of Surgical Site Infection after Total Abdominal Hysterectomy

Background: Despite adherence to the Centers for Medicare and Medicaid Services’ (CMS) core measures for preventing surgical site infections (SSI), the rate of SSI after total abdominal hysterectomy (TAH) at our institution is 10%, well beyond the 90^th percentile for SSI rates published in the 2009 NHSN report.

Objective: We aim to identify modifiable risk factors, in addition to CMS core measures, that contribute to SSI after TAH.

Methods: This is a retrospective chart review of patients who underwent elective TAH at a public safety net hospital in Denver CO between Dec 2005 and Mar 2010. Clinical variables were abstracted from medical charts. The primary outcome was development of SSI within 30 days of TAH. A secondary outcome was adherence to CMS core measures designed to prevent SSI. Chi-square and t-tests evaluated for bivariate associations between the variables and outcomes of interest. Multivariate logistic regression models determined if the risk factors detected in bivariate analyses were independently associated with development of SSI. All tests were performed at the 0.05 significance level.

Results: 224 records were reviewed; 26 were excluded due to emergent TAH and 2 were excluded for no follow-up in the 30 days after TAH. Patients who developed SSI were similar to their non-SSI counterparts with respect to the indication for TAH, diabetes, and smoking. With regards to CMS core measures, >95% of patients in both SSI and non-SSI groups received antibiotics in the 60 minutes before surgical incision and >90% received an appropriate antibiotic. Compliance with PACU normothermia was equivalent in SSI and non-SSI groups (81% vs 75.7%, P=0.60). Among non-modifiable risk factors, SSI was more common in obese (BMI ≥ 30) than non-obese patients (70% vs 43.5%, P=0.02) and in patients who had EBL ≥ 500 mL than those with EBL < 500 mL (47.6% vs 26.9%, P=0.05). Obesity remained a significant risk factor in multivariate analyses (OR 3.17, CI 1.14-8.77, P=0.03) while the effect of EBL ≥ 500 mL on SSI was reduced (OR 2.01, CI 0.76-5.26, P=0.16). Among modifiable risk factors, SSI was associated with blood transfusion in bivariate analyses (28.6% vs 12%, P=0.04) and trended toward significance in multivariate analyses (OR 2.87, CI 0.90-9.12, P=0.08). Blood transfusion was not associated with the pre- to post-operative change in hematocrit (Hct); rather it was associated with longer operative times (4.2 hrs vs 2.7 hrs, P<0.001), EBL ≥ 500mL (66.7% vs 22.6%, P<0.001), and both pre- and post-operative Hct (34.6 vs 39.8, P<0.0001; 26.4 vs 32.5, P<0.0001).

Conclusions: Obesity is associated with SSI after TAH in our population. Blood transfusion is a modifiable risk factor that trends toward significance and is not associated with the pre- to post-operative change in Hct; larger studies are needed to confirm this result and determine appropriate thresholds for transfusion in this population.