Hernandez and co. recently reported the results of the first large, adequately powered, randomised, controlled trial comparing the effect of postextubation nasal high-flow oxygen (NHF) and standard low-flow oxygen (non-rebreathing face mask and low-flow nasal cannula, (LFO)) on weaning outcome in critically ill patients not at high risk of extubation failure. Nasal high-flow oxygen was shown to reduce reintubation rate within 72 hours (4.9% vs. 12.2%) and postextubation respiratory failure (8.3% vs 14.4%). In order to better interpret authors’ findings, some methodological aspects may need to be clarified.
In this recent study, NHF was given at a mean gas flow of about 30 L/min (maximum 38.5 L/min in most severe patients) for a duration of 24h; nevertheless, previous studies showed that the beneficial effect of NHF seems to arise after 24 hours of treatment  and is proportional to the gas flow delivered . Surprisingly, reintubation rate already differed after 24 hours of treatment extubation (7.2% vs. 3.0%, p=0.03). However, more patients undergoing LFO showed immediate postextubation stridor (4.1% vs. 0.9%) and required reintubation due to laryngeal oedema (3.1% vs. 0%). It is remarkable that such relevant effects may have occurred though the low used flows and in a such short time. In addition, more patients in the LFO (3 vs. 14) group experienced postextubation respiratory failure due to inability to clear secretions, as a claimed consequence of the better conditioning of inspired air during NHF: nonetheless, we cannot know to what extent the higher rate of neurological comorbidities in the LFO group (12.9% vs. 7.6%) may have affected the different rate of reintubation due to this particular cause.
In both groups, oxygen therapy was administered irrespectively of patients’ condition, while previous investigations involved patients that were accurately selected according to their oxygen need and relevant amount of eligible subjects were excluded due to the absence of this criterion [2, 4, 5]. Interestingly, in a recent study involving patients with de novo acute respiratory failure NHF reduced the intubation rate (over LFO and noninvasive ventilation) in patients with Pa/FiO2<200 mmHg, but not in those with PaO2/FiO2<300 mmHg , thus suggesting that NHF efficacy may significantly vary according to the degree of oxygenation impairment. We may argue that the great benefit from NHF observed in Hernandez’s cohort might have been limited to the subgroup patients with most severe oxygenation impairment, that, despite expected to be at low-risk of weaning failure, happened to be reintubated. Unfortunately, the lack of data concerning PaO2/FiO2, respiratory rate and degree of dyspnoea after extubation hampers any speculation on this point, does not allow to clarify the categories of patients in which the treatment is more likely to be effective, finally limiting the generalisability of the results. Such issue may represent a major point of discussion, given the unavoidable costs related to NHF treatment and the fact that its application requires specific instrumentation and competences that may not be available in every ICU for all extubated patients.
Finally, the use of noninvasive ventilation was rigorously discouraged in both groups, despite previous data showing that an amount of weaned patients failing LFO and undergoing a NIV trial may avoid reintubation  and a recent large study supporting the use of NIV as compared to LFO in patients experiencing acute respiratory failure after abdominal surgery  (to note, 50% of the cohort in the present study show a surgical admission). Moreover, we wonder how the 5 patients with respiratory acidosis (4 in LFO group) did not receive NIV before intubation. We might speculate that if only a NIV trial were allowed, the intubation rate in LFO group would have been lower.
In conclusion, we believe that the results of the present paper lack of the necessary generalisability. Despite recognising that raising body of evidence suggests NHF as the best way to provide oxygen to critically ill patients, further rigorous studies are warranted to better identify patients that benefit most from NHF after extubation.
Article review was submitted by ESICM Journal Review Club member Domenico Luca Grieco.
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