We performed a retrospective observational monocenter study over a 2-year period (from January, 1st 2016 to December, 31th 2017). The study was approved by the local ethics committee, and given its non-interventional nature, informed consent was waived (CHU86-R2018-10-07).
Weaning from HFOT encompasses the reduction of FiO2 and flow to achieve a minimal support, and the separation attempt from HFOT per se. Given the design of the study, the reduction of HFOT support could not be assessed. Therefore, our primary outcome was to identify clinical variables associated with successful separation from HFOT.
All patients treated with HFOT for acute respiratory failure were included. Patients who died or were intubated without prior HFOT separation attempt, those who were treated with non-invasive ventilation at the time of HFOT separation, or who received HFOT as a preventive treatment during the post-extubation period (defined as the use of HFOT immediately after extubation for less than 48 h in the absence of clinical sign of respiratory failure) were excluded.
All patients were monitored until intubation, death, or successful separation from HFOT defined as discontinuation of HFOT for more than 48 h or until ICU discharge. In our unit, HFOT weaning was supervised by the attending physician and its separation usually considered when SpO2 was ≥ 92% with FiO2 ≤ 60%, independently from gas flow. HFOT separation failure was defined by respiratory failure requiring HFOT resumption, NIV initiation, intubation, or death within the first 48 h after switch from HFOT to standard oxygen.
Demographic data, ventilatory settings, and vital parameters under HFOT were collected before each separation attempt, and then under standard oxygen therapy after the separation from HFOT. For patients who failed at the first separation attempt from HFOT, these data were collected after HFOT resumption. Comorbidities, such as chronic cardiac failure (including coronary artery disease, severe valvulopathy, chronic atrial fibrillation, and heart failure of any cause) [8], chronic respiratory failure (defined as pulmonary function test alterations), and immunosuppression [9] were collected. The pulse oximetry to fraction of inspired oxygen ratio (SpO2/FiO2) and the respiratory rate-oxygenation (ROX) index (SpO2/FiO2 to respiratory rate) were calculated under HFOT before each separation attempt [10]. When available, last arterial blood gases under HFOT before each separation attempt were collected.
Continuous variables were expressed in mean ± standard deviation or median (interquartile range) according to their distribution and compared using the Mann–Whitney or the t test as appropriate. Categorical variables were expressed in number (percentage) and compared using the Fisher’s or Chi-square test as appropriate. Univariate analysis was performed to identify variables associated with successful separation from HFOT. For continuous variables, receiver-operating curves were plotted and the best threshold associated with successful separation from HFOT was assessed using the Youden’s index. A p value < 0.05 was considered significant.