Noninvasive Tidal Volume Measurements, Using a Time-of-Flight Camera, Under High-Flow Nasal Cannula—A Physiological Evaluation, in Healthy Volunteers*

Abstract

OBJECTIVES: The mechanisms of high-flow nasal cannula are still debated but may be mediated by the generation of low positive end-expiratory pressure and a washout of the airway dead space. The aims of this study were to assess the effects of high-flow nasal cannula on tidal volume using a noninvasive method using a time-of-flight camera, under various conditions. DESIGN: A physiologic evaluation in healthy volunteers. SETTING: An university hospital ICU. SUBJECTS: Ten healthy volunteers were included in a physiologic study (CamOpt study, ClinicalTrials.gov identifier: NCT04096183). INTERVENTIONS: All volunteers were submitted to 12 different conditions (i.e., gas flow [baseline = 0; 30–60 L/min]; mouth [open/closed]; respiratory rate [baseline; baseline + 10 breaths/min]). Tidal volume measurements were performed every minute, during a 6-minute recording period. In all combinations, reference respiratory rate was measured by using chronometric evaluation, over a 30-second period (RRREF), and by using the time-of-flight camera (RRTOF). MEASUREMENTS AND MAIN RESULTS: Tidal volume increased while increasing gas flow whatever the respiratory rate and mouth condition (p < 0.001). Similar results were observed whatever the experimental conditions (p < 0.01), except one (baseline respiratory rate + 10 breaths/min and mouth closed). Tidal volume increased while decreasing respiratory rate (p < 0.001) and mouth closing (p < 0.05). Proportion of tidal volume greater than 10, 15, and 20 mL/kg changed while increasing the flow. RRTOF was in agreement with RRREF (intraclass correlation coefficient, 0.96), with a low mean bias (0.55 breaths/min) and acceptable deviation. CONCLUSIONS: Time-of-flight enables to detect tidal volume changes under various conditions of high-flow nasal cannula application. Tidal volume increased significantly while increasing gas flow and mouth closing. Such technique might be useful to monitor the risk of patient self-inflicted lung injury or under assistance.

The effects of flow settings during high-flow nasal cannula support for adult subjects: a systematic review

“…One hundred and forty-eight full-text articles were assessed for eligibility, and 44 studies were finally included, of which 11 were in vitro studies [ 26 , 28 – 37 ], 2 combined in vitro and in vivo studies to investigate patients with AHRF [ 6 , 14 ], 13 studies investigated healthy individuals [ 13 , 15 – 20 , 38 – 43 ], 9 investigated patients with AHRF [ 7 – 10 , 27 , 44 – 46 , 50 ], 5 studies examined patients with COPD [ 11 , 12 , 21 – 23 ], 1 study investigated both AHRF and COPD patients [ 24 ], and 3 investigated patients during procedural sedation [ 47 – 49 ]. Among the in vivo studies, only four were randomized controlled trials [ 27 , 47 – 49 ], while 18 were randomized crossover studies [ 7 , 8 , 10 , 12 , 13 , 16 , 17 , 22 – 24 , 38 , 40 – 43 , 45 , 46 , 50 ]. None of the included randomized trials had incomplete outcome data reporting but 10 did not have registration [ 7 , 8 , 10 , 13 , 41 , 43 , 46 , 48 – 50 ].…”

Reply to Li et al.

“…To the best of our knowledge, there does exist only a few monitoring techniques that enable VT measurement under HFNC, such as a time-of-flight camera ( 2 ). However, it has not been widely used at the bedside.…”

The authors reply

“…We read the letter by Garcia et al (1), concerning our recent article (2) about noninvasive tidal volume (Vt) monitoring using a time-of-flight (TOF) camera under high-flow nasal cannula (HFNC). The authors do insist that there are several controversial points within our methodology that should be considered, first one certainly being the fact that V t and respiratory patterns of a patient are on either compliance or resistance, whereas our study was performed on healthy volunteers.…”