Synergistic Interaction Increases Complication Rates Following Microvascular Breast Reconstruction.

BACKGROUND: Microvascular breast reconstruction is a complex procedure that can be associated with high complication rates. While a number of individual predictors of peri-operative complications have been identified, few studies have explored interaction between risk factors. Understanding the synergistic effects of multiple risk factors is central to accurate and personalized pre-operative risk prediction.

METHODS: We conducted a retrospective cohort study of patients who underwent microvascular breast reconstruction at our institution between 2009 and 2017. All intra- and post-operative complications were recorded. A multivariable logistic regression exploratory model identified independent predictors of complications. Interactions between individual variables were then assessed using the Relative Excess Risk Index (RERI) and Synergy Index (SI).

RESULTS: Nine hundred and twelve patients were included in the study and 26.1% experienced at least one peri-operative complication. Obesity (OR1.54, p=0.009), immediate reconstruction (OR1.49, p=0.028), and comorbidities (OR1.43, p=0.033) were identified as independent predictors of complications. Obesity and comorbidities had significant synergistic interactions with immediate reconstruction (RERI 0.86, SI 2.35, p=0.0002; RERI 0.54, SI 1.78, p=0.001), bilateral reconstruction (RERI 0.12, SI 1.15, p=0.002; RERI 0.59, SI 3.16, p=0.005) and previous radiotherapy (RERI 0.62, SI 4.43, p=0.01; RERI 0.11, SI 1.23, p=0.040). Patients undergoing immediate breast reconstruction who were both obese and smokers had a 12-fold increase in complication rates (OR 12.68, 95% CI 1.36-118.46, p=0.026) with a very strong synergistic interaction between variables (RERI 10.55, SI 10.33).

CONCLUSIONS: Patient and treatment related variables interact in a synergistic manner to increase the risk of complications following microvascular breast reconstruction.