High Flow Therapy... and a Happy New Year

During the year 2019 the High Flow Therapy (HFT) has reached the age of majority. The publication of papers related to this therapy has grown exponentially in this year and the evidence of its efficacy and usefulness has grown in a parallel way. What we are going to do is a summary of the most important aspects of High Flow Therapy during the year 2019.

- The concept of HFT has evolved from its beginnings to today. First there was considered simply as an oxygen therapy device. It was subsequently recognized that this therapy was more than oxygen therapy (HFT a novel treatment rather a more expensive oxygen device- Eur Respir Rev 2017-; HFT is not an oxygen therapy device-Rev Port Pneumol 2015) . HFT has finally reached the privilege of being considered a ventilatory support system. Thus, it is not surprising to read the recent article by Masip et al, published in Eur Heart J, about "Indications and practical approach to NIV in acute heart failure", and see how HFT is included within the most commonly used modalities of NIV acute settings. Or hear from Dr Ricard that HFT should be the first line of ventilatory support for patients with hypoxemic respiratory failure even the most severe one, always in the abscense of intubation criteria (see figures).

-Throughout the year 2019, new studies have been published looking for a better understanding of the mechanisms of action of HFT. We all know that HFT benefits patients through several mechanisms of action, among others the dead space washout, the CPAP-like effect, the effect upon the ventilatory and hemodynamic pattern, or the ability to enhance mucociliary function. However, I would like to highlight the relevant study from Rittayamai et al (Ann Intensive Care 2019) about the effects of HFT on inspiratory effort in hypercapnic patients with COPD. The conclusions of this study have shown us that applying HFT at 30 L/min for a short duration reduces inspiratory effort in comparison to 10 and 20 L/min, and resulted in similar effect than NIV delivered at modest levels of pressure support in hypercapnic COPD with mild to moderate exacerbation. These results suggest that HFT at 30 L/min might be optimal in many hypercapnic COPD patients with mild to moderate exacerbation and should be tested in future studies.

-Another important pshyiological study has been published by Pérez-Terán et al, entitled "Aeration changes induced by high flow nasal cannula are more homogeneous than those generated by non-invasive ventilation in healthy subjects" (J Crit Care 2019). The authors state that lung aeration and diaphragm changes achieved with NIV and HFT in healthy subjects have not been compared to date. Twenty healthy subjects were recruited. Ten were ventilated with NIV and ten underwent HFNC. Lung impedance and diaphragmatic ultrasound measurements were performed before and after 30 min of respiratory support. The Mar-index was defined as the ratio of the diaphragm excursion-time index to the respiratory rate. The main findings of the study were that NIV and HFT increased the end-expiratory lung impedance (EELI) in healthy subjects, suggesting an increase in the functional residual capacity. The EELI increase may be higher in NIV, but HFT produced a more homogeneous change in lung ventilation. HFNC group has a higher MAR-index that could reflect a different ventilatory system adaptation. Authors describe in this study the Mar-index a new score that combines ultrasound with clinical changes and that could reflect the degree of the ventilatory system adaptation. This study may help to assess certain differences in aeration between these two non- invasive respiratory support techniques and thus develop new ventilatory support strategies for hypoxemic patients.

-It is true that we have more and more evidence of the role of HFT in stable COPD patients. In 2019 has been published a Systematic Review and Meta-Analysis on Nasal High Flow for Stable Patients with Chronic Obstructive Pulmonary Disease (COPD: Journal of Chronic Obstructive Pulmonary Disease, 2019). This systematic review includes the very well-known studies from Nagata (2017) and Storgaard (2018); short-term studies such as the Nilius (2013), Fraser (2016) or McKinstry (2018); and the Study from Cirio (2016) performed during excercise. The conlusion of this Systematic review and Meta-Analysis is that HFT reduced PaCO2, acute exacerbation and improved quality of life in stable COPD patients, although further long-term studies are needed to confirm the present results and provide more data on patient-centered outcome such as quality of life, exacerbation, hospitalization and mortality.

-There is also a lot of new evidences about the role of HFT in acute hypercapnic failure. Studies as "Reduction of PaCO2 by high-flow nasal cannula in acute hypercapnic respiratory failure patients receiving conventional oxygen therapy" (Acute and Critical Care, 2019); "Efficacy and safety of high-flow nasal cannula oxygen therapy in moderate acute hypercapnic respiratory failure" (Rev Bras Ter Intensiva. 2019); "High-flow nasal therapy versus noninvasive ventilation in COPD patients with mild-to- moderate hypercapnic acute respiratory failure: study protocol for a noninferiority randomized clinical trial" (Trials, 2019), have been published through this year. Probably, it would be very interesting to do some comments about the Systematic Review on HFT in exacerbated COPD patients, published by Pisani et al (Pulmonology 2019). It is important to highlight that the work of breathing was reduced with HFT by a similar extent to NIV and HFT was also reported to be more comfortable than NIV. It is true that we need more evidence and there are many unresolved issues before HFT replaces NIV in acute hypercapnic COPD. Randomized consoled trials are needed to clarify the real efficacy of HFT and the best target population during COPD exacerbation. By the moment, Pisani et al have made the following recommendations (see figure).

-Two interesting papers have been published related to the use of HFT in patients with acute exacerbation of pulmonary fibrosis: "Respiratory management of acute exacerbation of interstitial pneumonia using high-flow nasal cannula oxygen therapy: a single center cohort study" (J Thorac Dis 2019) and "High-flow nasal cannula oxygen therapy to treat acute respiratory failure in patients with acute exacerbation of idiopathic pulmonary fibrosis" (Ther Adv Respir Dis, 2019). In both studies, after the implementation of HFT to treat this kind of patients, the reduction on mortality was clearly significant. In the Ito´s study, authors retrospectively reviewed patients with acute exacerbation of interstitial pneumonia who were admitted to their hospital from June 2009 – May 2015 and compared mortality, complications, sedatives and analgesia use, and oral intake between cohorts before (pre-HFT: June 2009 – May 2012) and after (post-HFT: June 2012 – May 2015) the introduction of HFT.

The post-HFT cohort had significantly lower in-hospital mortality than the pre-HFT cohort (27.9% vs. 49.1%, P=0.04). The incidence of complications was not significantly different between the two cohorts. The use of sedoanalgesia during respiratory support and the number of patients who discontinued oral intake for >24 hours were decreased after the introduction of HFT (78.6% vs. 31.6%, P<0.001; 52.8% vs. 23.3%, P=0.003). In conclusion, HFNC could be a feasible option in respiratory management of AE-IP. In the study from Vianello et al, short-term mortality fell to below 50% when a treatment algorithm incorporating HFT was implemented in a group of patients with acute exacerbation of idiopathic pulmonary fibrosis admitted to a RICU for ARF. These results are very promising and provides useful information for physicians staffing intensive care units and entrusted with the care of patients with exacerbated IPF.

-Finally, to finish with this review of the most relevant things of the year 2019, it is mandatory to comment the contribution of Josep Masip to the role of HFT in the Acute Heart Failure (Current Heart Failure Reports, 2019). As we have said before, HFT is considered here as a modality of NIV and it is included in the algorithm for managing these patients, specially in the case of failure or intolerance of CPAP/NIPSV.

I hope you have enjoyed this summary "Year in review 2019" on High Flow Therapy. The 2020 it is going to be a very impressive year for HFT lovers. Thank you all very much for helping to make the HFT World bigger.