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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.