LAUSR

Abstract Background High-flow nasal cannula (HFNC) therapy is used in the treatment of acute respiratory failure (ARF), and is both safe and effective in reversing hypoxemia. In order to minimize mortality and clinical complications associated to this practice, a series of tools must be developed to allow early detection of failure. The present study was carried out to: (a) examine the impact of respiratory rate (RR), peripheral oxygen saturation (SpO2), ROX index (ROXI = [SpO2/FiO2]/RR) and oxygen inspired fraction (FiO2) on the success of HFNC in patients with hypoxemic ARF; and (b) analyze the length of stay and mortality in the ICU, and the need for mechanical ventilation (MV). Methods A retrospective study was carried out in the medical-surgical ICU of Hospital de Montilla (Cordoba, Spain). Patients diagnosed with hypoxemic ARF and treated with HFNC from January 2016 to January 2018 were included. Results Out of 27 patients diagnosed with ARF, 19 (70.37%) had hypoxemic ARF. Fifteen of them (78.95%) responded satisfactorily to HFNC, while four (21.05%) failed. After two hours of treatment, RR proved to be the best predictor of success (area under the ROC curve [AUROC] 0.858; 95%CI 0.63–1.05; p = 0.035). For this parameter, the optimal cutoff point was 29 rpm (sensitivity 75%, specificity 87%). After 8 h of treatment, FiO2 and ROXI were reliable predictors of success (FiO2: AUROC 0.95; 95%CI 0.85–1.04; p = 0.007 and ROXI: AUROC 0.967; 95%CI 0.886–1.047; p = 0.005). In the case of FiO2 the optimal cutoff point was 0.59 (sensitivity 75%, specificity 93%), while the best cutoff point for ROXI was 5.98 (sensitivity 100%, specificity 75%). Using a Cox regression model, we found RR   5.98 after 8 h of treatment, to be associated with a lesser risk of MV (RR: HR 0.103; 95%CI 0.11−0.99; p = 0.05; FiO2: HR 0.053; 95%CI 0.005−0.52; p = 0.012; and ROXI: HR 0.077; 95%CI 0.008−0.755; p = 0.028, respectively). Conclusions RR after two hours of treatment, and FiO2 and ROXI after 8 h of treatment, were the best predictors of success of HFNC. RR   5.98 were associated with a lesser risk of MV.