The ROX index (ratio of pulse oximetry/FIO2 to respiratory rate) has been validated to predict high\nflow nasal cannula therapy (HFNC) outcomes in patients with pneumonia. We evaluated a modified ROX index\nincorporating heart rate (HR) in patients initiated on HFNC for acute hypoxemic respiratory failure and as a\npreventative treatment following planned extubation.\nMethods: We performed a prospective observational cohort study of 145 patients treated with HFNC. ROX-HR\nindex was defined as the ratio of ROX index over HR (beats/min), multiplied by a factor of 100. Evaluation was\nperformed using area under the receiving operating characteristic curve (AUROC) and cutoffs assessed for prediction of\nHFNC failure: defined as the need for mechanical ventilation.\nResults: Ninety-nine (68.3%) and 46 (31.7%) patients were initiated on HFNC for acute hypoxemic respiratory failure\nand following a planned extubation, respectively. The majority (86.9%) of patients had pneumonia as a primary\ndiagnosis, and 85 (56.6%) patients were immunocompromised. Sixty-one (42.1%) patients required intubation (HFNC\nfailure). Amongst patients on HFNC for acute respiratory failure, HFNC failure was associated with a lower ROX and\nROX-HR index recorded at time points between 1 and 48 h. Within the first 12 h, both indices performed with the\nhighest AUROC at 10 h as follows:................
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