X3.2.1 Humidified nasal high flow therapy (hNHF)

Humidified nasal high flow therapy (hNHF) delivering flows of up to 60 L/minute has been used successfully for the management of acute hypoxaemic respiratory failure, while in acute exacerbations of COPD associated with hypercapnia and acidemia, NIV is accepted as standard of care (see below).

In a multi-centre Italian study of hNHF, (Optiflow and MR850 or Airvo) patients (n=80) with mild-moderate AECOPD and hypercapnia (PaCO2> 55mmHg, pH 7.25-7.35) before support were randomised to receive NIV or hNHF, with oxygen titrated to oxygen saturations of 88-92%. hNHF was statistically non-inferior to NIV as initial ventilatory support in reducing PaCO2 at 2 hrs (-6.8mmHg HFNT + 8.7, v -9.5 mmHg +8.5), p=0.4, considering a non- inferiority margin of 10 mmHg. However, by 6 hours 32% of patients in hNHF group had switched to NIV due to worsening or no improvement of respiratory failure; n=1 due to intolerance, while from the NIV group only one patient switched to hNHF due to intolerance and one to invasive ventilation. The authors of this study concluded that further trials with a superiority design examining patient related outcome measures are needed. NIV remains standard of care at present as it has been consistently shown to reduce mortality (Cortegiani 2020) [evidence level I].

In a multi-centre RCT of patients from 16 hospitals in China admitted with AECOPD and mild hypercapnia (pH ³7.35 and PCO2>45mmHg) there was no difference in the primary outcome of proportion of patients needing intubation in the HFNC group (AirVo2 started at 25L/min and increased to maximal tolerance with maximal humidification and maintaining SPO2 90-95%) versus the controlled oxygen group (low flow oxygen at 1-5L/min to maintain SPO2 90-95%). There was no difference between the groups in rate of treatment failure (15.8% versus 14.5%) and the most common reason for treatment failure in the HFNC group was intolerance, whereas in the controlled oxygen group it was need for NIV. The numbers of patients upgraded to NIV in both groups were comparable. However, the median duration from randomisation to commencement of NIV was longer in the HFNC group. Patients in the HFNC group had longer lengths of stay (9 v 8 days) and increased treatment costs (by 14.6%) compared to those on controlled oxygen therapy (Xia 2022) [evidence level II].

Overall, taking together the results of these two studies, there was no clear benefit to the use of HFNC in these patients hospitalised with mild-moderate exacerbations of COPD, and potential for harm.