Accuracy of noncontact surface imaging for tidal volume and respiratory rate measurements in the ICU

Abstract

Tidal volume monitoring may help minimize lung injury during respiratory assistance. Surface imaging using time-of-flight camera is a new, non-invasive, non-contact, radiation-free, and easy-to-use technique that enables tidal volume and respiratory rate measurements. The objectives of the study were to determine the accuracy of Time-of-Flight volume (VTTOF) and respiratory rate (RRTOF) measurements at the bedside, and to validate its application for spontaneously breathing patients under high flow nasal canula. Data analysis was performed within the ReaSTOC data-warehousing project (ClinicalTrials.gov identifier NCT02893462). All data were recorded using standard monitoring devices, and the computerized medical file. Time-of-flight technique used a Kinect V2 (Microsoft, Redmond, WA, USA) to acquire the distance information, based on measuring the phase delay between the emitted light-wave and received backscattered signals. 44 patients (32 under mechanical ventilation; 12 under high-flow nasal canula) were recorded. High correlation (r = 0.84; p < 0.001), with low bias (-1.7 mL) and acceptable deviation (75 mL) was observed between VTTOF and VTREF under ventilation. Similar performance was observed for respiratory rate (r = 0.91; p < 0.001; bias < 1b/min; deviation ≤ 5b/min). Measurements were possible for all patients under high-flow nasal canula, detecting overdistension in 4 patients (tidal volume > 8 mL/kg) and low ventilation in 6 patients (tidal volume < 6 mL/kg). Tidal volume monitoring using time-of-flight camera (VTTOF) is correlated to reference values. Time-of-flight camera enables continuous and non-contact respiratory monitoring under high-flow nasal canula, and enables to detect tidal volume and respiratory rate changes, while modifying flow. It enables respiratory monitoring for spontaneously patients, especially while using high-flow nasal oxygenation.

Keywords: P-SILI; Respiratory monitoring; Tidal volume; Time-of-flight; VILI.

Conflict of interest statement

ELH, SN, DV are co-inventors of the technique (Body surface optical imaging for respiratory monitoring; European patent application No. 19306417.7–1115. ELH is a co-founder and shareholder of Oxynov Inc., a Canadian R&D company; he is also consultant for GE Healthcare, Smiths, Sedana Medical. VP, SN, DV have no other conflicts of interest.

© 2021. The Author(s), under exclusive licence to Springer Nature B.V.

Figures

Fig. 1

Position of the TOF Camera and automatic determination of the regions of interest. The TOF camera is positioned perpendicularly at ~ 1.2 m from the patient’s torso – it can be either fixed on the ceiling or on a moving trolley –the patient lying supine with a 30° angulation of the bed’s head. Calibration is automated, as the ROI determination (yellow square). All red numbers corresponds to automated determination of the patient’s points of interest and main joints. In case of discordance, position of the points of interest can be modified by the clinician

Fig. 2

Monitoring of the left and right hemithoraces. Regional ventilation monitoring of the left and right patient’s hemithoraces is depicted. The volume time curve is obtained by analyzing the right and left hemithoraces ROIs separately. The black curve corresponds to the volume time curve of the right thorax and the gray curve corresponds to the volume time curve of the left thorax. Such analysis may enable to depict regional abnormalities such as atelectasis and/or pneumothorax

Fig. 3

Correlation and Bland–Altman plot for reference and estimated respiratory rate and tidal volume. All measurements were performed with the patient lying supine, with a 30° angulation of the bed head. Values are provided as breath per minute (bpm) for the reference respiratory rate (RR) and mL for the tidal volume (Vt). RR values were provided by its chronometric measurement at the bedside during a 60-s period. Reference Vt values were provided by the ventilator expiratory flowmeter for patients under ventilatory assistance. Estimated RR and Vt were performed using the TOF based monitoring system over a 60-s period. On the 31 ICU patients’ recordings, the estimation of the RR and Vt was well correlated with the reference method (Fig. 2-A; R = 0.9; p