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Re-Intubation Scale Calculation (RISC): Predicting Extubation Failure in Critically Ill patients Vikas Bansal. MBBS,1 MPH; Zhuo Li, M.S.;2 Alberto Marquez, RRT, CCRP, EDD;3 Rahul Kashyap MBBS,MS;3 Christopher P. Smelick, M.D.;4 Jose L. Diaz-Gomez, M.D.;1 Carla P. Venegas-Borsellino, M.D.;1Daniel A. Diedrich, M.D.;5 Nathan J. Smischney, M.D.;5 Ayan Sen, M.D.;6 William D. Freeman, M.D.7 Department of Critical Care Medicine, Mayo Clinic Jacksonville; Departments of Biomedical Statistics and Informatics, Mayo Clinic Jacksonville; 3 4 Department of Anesthesia Clinical Research Unit, Mayo Clinic Rochester; Department of Neurology, Mayo Clinic Jacksonville; 5 6 7 Department of Anesthesia/Critical Care Medicine, Mayo Clinic Rochester; Department of Critical Care Medicine, Mayo Clinic Arizona; Department of Neurocritical Care Medicine, Mayo Clinic Jacksonville 1

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Abstract Background: Extubation involves removal of an endotracheal tube (ETT) and is a common intensive care unit (ICU) procedure. Extubation failure occurs in 8-20% of ICU patients and can be difficult to predict accurately. We hypothesized that a multivariate Re-Intubation Scale Calculation (RISC) model could predict extubation failure better than a single variable like Rapid Shallow Breathing Index (RSBI). Methods: After IRB approval, we conducted a retrospective review of data on mechanically ventilated ICU patients above 18 years of age who were not receiving mechanical ventilation through a tracheostomy tube from January 1, 2006, through December 31, 2015 at Mayo Clinic Rochester. Various data points were gathered on these patients via electronic medical records search, and reintubations within 72 hours of extubation were identified. Univariate and multivariate logistic regression models were used to predict reintubation after extubation and construct a RISC estimate. Results: We included a total of 6161 patients which were randomly divided into a derivation set (N=3080) and validation set (N=3081). In the derivation set, patients had a mean age of 62±17 years, and 59% were men. Three hundred and ninety three extubation failures occurred within 72 hours. Predictors of extubation failure included underweight status, GCS score>=10, mean airway pressure at 1 minute=1500mL and total mechanical ventilation days>=5 in the final multivariable model. RISC score was calculated using the validation set and ranged from 0 to 8. Logistic model result shows that, as RISC increased by 1, the odds of having extubation failure was 1.6 fold higher (C-index=0.72). ROC analysis shows that the best cut off for RISC was >=4 vs. =4 vs. =4 vs.