Optimizing high-flow nasal cannula flow settings in adult hypoxemic patients based on peak inspiratory flow during tidal breathing

Abstract

Background: Optimal flow settings during high-flow nasal cannula (HFNC) therapy are unknown. We investigated the optimal flow settings during HFNC therapy based on breathing pattern and tidal inspiratory flows in patients with acute hypoxemic respiratory failure (AHRF).

Methods: We conducted a prospective clinical study in adult hypoxemic patients treated by HFNC with a fraction of inspired oxygen (FIO2) ≥ 0.4. Patient's peak tidal inspiratory flow (PTIF) was measured and HFNC flows were set to match individual PTIF and then increased by 10 L/min every 5-10 min up to 60 L/min. FIO2 was titrated to maintain pulse oximetry (SpO2) of 90-97%. SpO2/FIO2, respiratory rate (RR), ROX index [(SpO2/FIO2)/RR], and patient comfort were recorded after 5-10 min on each setting. We also conducted an in vitro study to explore the relationship between the HFNC flows and the tracheal FIO2, peak inspiratory and expiratory pressures.

Results: Forty-nine patients aged 58.0 (SD 14.1) years were enrolled. At enrollment, HFNC flow was set at 45 (38, 50) L/min, with an FIO2 at 0.62 (0.16) to obtain an SpO2/FIO2 of 160 (40). Mean PTIF was 34 (9) L/min. An increase in HFNC flows up to two times of the individual patient's PTIF, incrementally improved oxygenation but the ROX index plateaued with HFNC flows of 1.34-1.67 times the individual PTIF. In the in vitro study, when the HFNC flow was set higher than PTIF, tracheal peak inspiratory and expiratory pressures increased as HFNC flow increased but the FIO2 did not change.

Conclusion: Mean PTIF values in most patients with AHRF were between 30 and 40 L/min. We observed improvement in oxygenation with HFNC flows set above patient PTIF. Thus, a pragmatic approach to set optimal flows in patients with AHRF would be to initiate HFNC flow at 40 L/min and titrate the flow based on improvement in ROX index and patient tolerance.

Trial registration: ClinicalTrials.gov (NCT03738345). Registered on November 13th, 2018. https://ichgcp.net/clinical-trials-registry/NCT03738345?term=NCT03738345&draw=2&rank=1.

Keywords: Flow setting; High-flow nasal cannula; Hypoxemia; Peak inspiratory flow.

Conflict of interest statement

Dr. Li declares to receive research funding from Fisher & Paykel Healthcare Ltd, Aerogen Ltd, and Rice Foundation and lecture honorarium from American Association for Respiratory Care, Aerogen Ltd, Heyer Ltd, and Fisher & Paykel Healthcare Ltd outside the submitted work. Dr. Li is the section editor for respiratory care journal. Dr. Scott declares to receive research funding from Teleflex. Dr. Fink is Chief Science Officer for Aerogen Pharma Corp. Dr. Dhand reports remuneration from GSK Pharmaceuticals, Boehringer-Ingelheim, Bayer, Mylan, Teva, and Astra-Zeneca Pharmaceuticals outside the submitted work. Dr. Roca discloses a research grant from Hamilton Medical and speaker fees from Hamilton Medical, Ambu, Aerogen Ltd, and Fisher & Paykel, and non-financial research support from Timpel and Masimo Corporation. None of the companies/institutions had a role in the study design, data collection, analysis, preparation of the manuscript, or the decision to publish the findings. Ms. Reed has no conflicts to disclose.

© 2021. The Author(s).

Figures

Fig. 1

The correlation between SpO2/FIO2 ratio and flow ratio. The flow ratio of setting HFNC flow to the patient’s peak tidal inspiratory flow is shown on the X-axis. The ratio of patients’ SpO2/FIO2 at one flow setting to SpO2/FIO2 achieved when HFNC flow was set to match patient’s peak inspiratory flow during tidal breathing (matching flow) is shown on the Y-axis. The scatterplot shows significant correlation between the two ratios. SpO2, pulse oximetry; FIO2, fraction of inspired oxygen; HFNC, high-flow nasal cannula.

Fig. 2

Patient response to different flow ratios. On the top 2 figures, X-axis is the flow ratio of setting HFNC flow to patients’ peak inspiratory flow during tidal breathing and the flow ratios are divided into four groups (≤ 1, 1.01–1.33, 1.34–1.67, and ≥ 1.68). On the Y-axis, the ratio of patients’ SpO2/FIO2 (left top) or ROX (right top) at the flow setting to SpO2/FIO2 or ROX at their matching flow are shown. As the flow ratio increased, the SpO2/FIO2 ratio increased. Similarly, compared to ROX ratio with flow ratios ≤ 1.33, ROX ratio was higher with flow ratios ≥ 1.34–1.67 and 1.68, but ROX ratio did not increase beyond flow ratios of 1.34–1.67. RR ratio was lower with flow ratios of 1.34–1.67 than with flow ratios ≤ 1 (left bottom). No significant differences of comfort score ratios were found at different flow ratios (right bottom). *p < 0.05 compared to flow ratios ≤ 1. #p < 0.05 compared to flow ratios of 1.01–1.33. &p < 0.05 compared to flow ratios of 1.34–1.67. SpO2, pulse oximetry; FIO2, fraction of inspired oxygen; RR, respiratory rate; ROX = (SpO2/FIO2)/RR

Fig. 3

The correlation between flow ratio and FIO2, peak inspiratory and expiratory pressure at trachea in the in vitro study. X-axis is the flow ratio of setting HFNC flow to peak tidal inspiratory flow, Y-axis is the trachea FIO2 (left), peak inspiratory (middle) and peak expiratory pressure (right). As the flow ratio increased, both peak inspiratory and expiratory pressure increased, while FIO2 stabilized when flow ratio was ≥ 1. FIO2, fraction of inspired oxygen