MICRO: Microsurgical Index for Complication Risk and Outcomes

Free tissue transfer (FTT) is determined by a multitude of patient and surgeon factors. However, no tool exists to quantify patient risk for complications following FTT. This study developed the microsurgical index for complication risk and outcomes (MICRO) to address this.Patients were queried from the 2007 to 2015 MarketScan Databases with CPT codes for FTT requiring microsurgical anastomosis. ICD-9 codes were used to query comorbidity and 90-day postoperative complication data for each patient. The Charlson and Elixhauser Comorbidity Indexes were constructed for each patient. The MICRO was then constructed with a forward stepwise selection from Elixhauser comorbidities and domain expert input. Indexes were used as covariates in multivariate logistic regression models with patient age, sex, and flap tissue type to predict complications following FTT. The area under the receiver operating characteristic curve and fivefold cross-validation classification accuracy was determined.A total of 5,595 patients were included. The final MICRO consists of seven variables (Charlson: 19; Elixhauser: 30). It had the highest area under the receiver operating characteristic curve (0.60) and accuracy (60.4%) of all indexes when predicting complications.The MICRO outperforms available patient comorbidity indexes at predicting complications following FTT with far fewer variables. Future studies could augment the MICRO with more granular or institutional data consisting of surgeon, donor-site, and recipient-site data to create a sharper risk-stratification tool for the plastic surgeon.