NAMDRC

The National Association for Medical Direction of Respiratory Care

Nasal High Flow Oxygen Therapy

Nasal High Flow (NHF) oxygen therapy is a technique devised to deliver high flow oxygen in a maximally humidified, comfortable, and easily administered fashion. Conventional bubble humidifiers are most commonly used for humidifying medical gas delivered to spontaneously breathing patients, but the absolute humidity of the emergent gas remains low. Any time compressed gas is released the expansion results in significantly cooling and drying of the gas and when delivered directly especially in higher flows causes discomfort and increased airway resistance. NHF is administered via an air/oxygen blender that is more aggressively heated and humidified being delivered by a single limb heated circuit capable of up to 60 LPM and an FiO2 of 100%.

When originally designed, the focus was to enhance mucociliary clearance and found efficacy in bronchiectasis. While applying this therapy, it was noted that along with the marked improvement in oxygenation and ventilation, there was high patient tolerance and it was easily transitioned to the hospitalized patient when introduced to the market in 2006. Aside from the increased comfort and dyspnea relief as well as secretion clearance benefit, other mechanisms contributing to therapeutic efficacious are believed to be related to high gas flow and FiO2. This leads to less air entrainment, low level PAP, reduced dead space, and perhaps stretch receptor and other central and reflex neurally-mediated alterations in breathing pattern.

Several recent RCT studies lend further support and credence to aggressive clinical use in the hospital. An Italian study entitled “Nasal High-Flow versus Venturi Mask Oxygen Therapy after Extubation- Effects on Oxygenation, Comfort, and Clinical Outcome” by Maggiore et al was published in AJRCCM 2014. Vol. 190(3): 282-88. They compared the effects of the Venturi mask O2 and nasal high-flow (NHF) therapy on PaO2/FIO2 SET ratio after extubation over 48 hours with secondary endpoints of effects on patient discomfort, adverse events, and clinical outcomes. They used an RCT open-label trial on 105 pts with a PaO2/FIO2 ratio < 300 immediately before extubation. They showed from the 24th hour on, PaO2/FIO2SET was higher with the NHF (287 vs. 247 at 24 h; P = 0.03) and there were fewer pts that had interface displacements (32% vs. 56%; P = 0.01), oxygen desaturations (40% vs. 75%; P , 0.001), required reintubation (4% vs. 21%; P = 0.01), or any form of ventilator support (7% vs. 35%; P , 0.001) in the NHF group. They concluded that compared with the Venturi mask, NHF results in better oxygenation for the same set FIO2 after extubation was associated with better comfort, fewer desaturations and interface displacements, and a lower re-intubation rate. The study can be criticized because it was unblended, did not measure the true FIO2 delivered to patients, the comfort assessment purely subjective, and the ABG was done only and end of treatment period.

A large Spanish trial lends further support and credence to aggressive clinical use in the hospital and examined this issue and was published as the “Effect of Post-extubation High-Flow Nasal Cannula vs Conventional Oxygen Therapy on Re-intubation in Low-Risk Patients- A Randomized Clinical Trial” by Hernandez et al. JAMA. 2016; 315(13): 1354-1361. These investigators primary outcome was assessment of re-intubation within 72 hours in 527 adult critical patients at low risk for re-intubation and were randomized to undergo either high-flow (HFT) or conventional oxygen therapy (COT) for 24 hours after extubation. They found that the re-intubation rate within 72 hours was less in HFT group (13 pts [4.9%] vs 32 [12.2%] using COT (P = .004). the post-extubation respiratory failure rate was also less common with HFT (22/264 patients [8.3%] vs 38/263 [14.4%] with COT (P = .03) but there was no differences in ICU LOS or mortality. There was concern about this study because there was an unusually higher risk of re-intubation in control groups which may be due to more medical than surgical patients in this group. This was also a heterogeneous patient population that was unblinded, and many re-intubated for secretion issues which had no a priori identified criteria. Lastly the number needed to treat for benefit is very high and therefore costly.

This same group of researchers followed with the “Effect of Post-extubation High-Flow Nasal Cannula vs Non-invasive Ventilation on Re-intubation and Post-extubation Respiratory Failure in High-Risk Patients- A Randomized Clinical Trial” in JAMA. 2016; 316(15):1565-1574. There were 604 patients randomized to either nasal high-flow O2 or NIV for 24 hours after extubation with the primary outcome being proof of non-inferiority of HFT vs NIV for re-intubation and post-extubation respiratory failure within 72 hours. There was no significant difference for the 66 pts (22.8%) in the HFT group vs 60 (19.1%) in the NIV group who were re-intubated and the 78 pts (26.9%) in HFT group vs 125 (39.8%) in the NIV group who experienced post-extubation respiratory failure. Median time to re-intubation and other secondary outcomes were similar in the 2 groups. However, t median post-randomization ICU LOS was lower in the high-flow group, 3 days vs 4 days (P=.048). Adverse effects requiring withdrawal of the therapy were observed in none of patients in the HFT group vs 42.9%patients in the NIV group (P < .001). Aside from the similar unblinded heterogeneous population concerns above, there is the obvious point that most of the patients were hypoxic and did not fall into categories typically defined for NIV intervention.

For those with further interest, a nice summation of recent findings can be obtained in “Can high-flow nasal cannula reduce the rate of endotracheal intubation in adult patients with acute respiratory failure compared with conventional oxygen therapy and noninvasive positive pressure ventilation? A systematic review and meta-analysis. Yue-Nan Ni et al. In Press, available online- 10.1016/ j.chest.2017.01.004.

Peter C. Gay MD, Mayo Clinic Rochester, MN

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