ABSTRACT & COMMENTARY
Effects of High-Flow Nasal Cannula vs Conventional Oxygen Therapy in Recently Extubated Patients
By David J. Pierson, MD, Editor
This short-term crossover study showed that in the first hour after extubation, patients were less dyspneic and had lower respiratory and heart rates while breathing oxygen via high-flow nasal cannula than with a conventional non-rebreathing mask.
Rittayamai N, et al. High-flow nasal cannula versus conventional oxygen therapy after endotracheal extubation: A randomized crossover physiologic study. Respir Care 2014;59:485-490.
This study from Siriraj Hospital in Bangkok sought to determine whether the use of a high-flow nasal cannula (HFNC) system to deliver oxygen to patients following extubation had physiological advantages over a traditional non-rebreathing mask. The authors selected 17 patients recovering from acute respiratory failure (mean age 67 years, 41% female) whose acute illness requiring invasive mechanical ventilation was precipitated evenly among chronic obstructive pulmonary disease exacerbations, pneumonia, and other etiologies. After improving from the acute episode, the patients had to meet usual criteria for weaning and pass a 120-minute spontaneous breathing trial on either a T-piece or low-level pressure support. Once informed consent for the study was obtained, patients were extubated and then placed randomly either on HFNC or a non-rebreathing mask for 30 minutes. After measurement of respiratory and heart rates and quantitation of dyspnea using a 10-point analog scale, the patients were then switched to the other mode of oxygen delivery and the assessments were repeated after another 30 minutes. HFNC was delivered at 35 L/min, with FIO2 sufficient to maintain SpO2 94% or more. Oxygen was delivered to the non-rebreathing mask at 6-10 L/min to maintain the same saturation. Patients randomized to the two oxygen delivery sequences did not differ statistically with respect to the demographic or clinical variables assessed, and all of them remained extubated without the need for reintubation. Noninvasive ventilation was not used.
Nine patients received HFNC first and switched after 30 minutes to a non-rebreathing mask; eight patients had this sequence reversed. By the scores in the visual analog scale, the patients had less dyspnea with HFNC (P = 0.04) and subjectively 88% of them preferred the HFNC to the non-rebreathing mask. Their respiratory and heart rates during the 30-minute sessions were significantly lower with the HFNC: 19.8 ± 3.2 vs 23.1 ± 4.4 breaths/min (P = 0.009) and 89.5 ± 9.5 vs 95.4 ± 10.4 (P = 0.006) beats/min, respectively. Two patients reported subjective discomfort ("gas flow too high" and "temperature too warm") with HFNC in comparison with the non-rebreathing mask, but no serious adverse events occurred.
COMMENTARY
The development of HFNC, its rationale, and its reported effects (documented mainly in neonates and young children) have recently been reviewed by Ward.1 More directly pertinent to readers of this newsletter is a special feature published last year by Walter2 that summarized what we know about the potential value of HFNC in adult critical care. Walter pointed out that HFNC is relatively easy to use, appears to fill a niche between low-flow nasal cannula/face mask systems and noninvasive ventilation, and has the advantage of allowing patients to talk, eat, drink, and more easily clear secretions compared to noninvasive ventilation.2 However, he also cautioned that, like so much of the technology of critical care, HFNC has been widely adopted by clinicians on the basis of plausible rationale and effective marketing in advance of definitive research to show whether its claimed clinical benefits are real.
The findings from this and other studies to date support the postulated mechanisms for improved gas exchange and ventilatory mechanics with HFNC as compared with low-flow nasal or non-rebreathing mask oxygen. These are the substantially increased flow (which can better match patients’ peak inspiratory flows during spontaneous breathing), the creation of a better reservoir of oxygen in the upper airway during expiration (which would increase lower-airway oxygen concentration and perhaps serve to reduce dead space), and the promotion of continuous positive airway pressure (CPAP) because of the high flow (something of a misnomer since the pressure may not actually remain positive throughout inspiration). A CPAP effect would theoretically increase functional residual capacity and thus might reduce patient work of breathing, although as Rittayamai et al point out in their discussion the available data suggest that HFNC produces only 1.5-7.0 cm H2O of positive airway pressure.
A sound rationale is important but does not by itself establish the clinical value of a device or intervention, and the current study takes us a little bit closer to the patient-relevant evidence we need. It suggests using noninvasive bedside assessments during the first hour after removal of the endotracheal tube — among patients who have already met current best-practice criteria for extubation — that spontaneous breathing was more effective and comfortable with HFNC than with a non-rebreathing mask. However, this was a short-term physiologic study with only 17 low-risk patients, none of whom required reintubation or had other adverse extubation outcomes.
Hopefully, the clinical study we really need on HFNC after extubation (that is, compared to other support, will it reduce the need for reintubation) will be performed soon. In the meantime, clinicians should keep two things in mind: Although patients tolerate it well, the effects of HFNC on ventilation remain unknown (and the current study’s short-term findings could actually be compatible with decreased spontaneous ventilation); and, recently extubated patients still need close monitoring in the ICU. At this point, HFNC should not be used as a means for getting patients recovering from acute respiratory failure out of the ICU faster, particularly within the first 24 hours after extubation.
REFERENCES
- Ward JJ. High-flow oxygen administration by nasal cannula for adult and perinatal patients. Respir Care 2013;58:98-122.
- Walter EC. High-flow nasal cannula — what is it, how does it work, and do we know if it works? Critical Care Alert 2013;21:1-4.
