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. Although a number of individual predictors of perioperative 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 preoperative risk prediction. Methods: The authors conducted a retrospective cohort study of patients who underwent microvascular breast reconstruction at their institution between 2009 and 2017. All intraoperative and postoperative 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 the synergy index (SI). Results: Nine hundred twelve patients were included in the study and 26.1 percent experienced at least one perioperative complication. Obesity (OR, 1.54; p = 0.009), immediate reconstruction (OR, 1.49; p = 0.028), and comorbidities (OR, 1.43; 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; and RERI, 0.54; SI, 1.78; p = 0.001), bilateral reconstruction (RERI, 0.12; SI, 1.15; p = 0.002; and RERI, 0.59; SI, 3.16; p = 0.005), and previous radiotherapy (RERI, 0.62; SI, 4.43; p = 0.01; and 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 percent CI, 1.36 to 118.46; p = 0.026) with a very strong synergistic interaction between variables (RERI, 10.55; SI, 10.33). Conclusion: Patient-and treatment-related variables interact in a synergistic manner to increase the risk of complications following microvascular breast reconstruction.