Contact-free assessments of respiratory rate and volume with load cells under the bed legs in ventilated patients: A prospective exploratory observational study.

Abstract

Development of reliable non-contact unrestrained respiratory monitoring is capable of augmenting the safety of hospitalized patients in the recovery phase. We previously discovered respiratory-related centroid shifts along the long axis of the bed with load cells under the bed legs (bed sensor system: BSS). This prospective exploratory observational study examined whether non-contact measurements of respiratory-related tidal centroid shift amplitude (TA-BSS: primary variable) and respiratory rate (RR-BSS: secondary variable) were correlated with tidal volume (TV-PN) and respiratory rate (RR-PN), respectively measured by pneumotachograph in 14 ICU patients under mechanical ventilation. Among the 10-minute average data automatically obtained for a 48-hour period, 14 data were randomly selected from each patient. Successfully and evenly selected 196 data points for each variable were used for the purpose of this study. A good agreement between TA-BSS and TV-PN (Pearson's r = 0.669) and an excellent agreement between RR-BSS and RR-PN (r = 0.982) were observed. Estimated minute ventilatory volume as 3.86*TA-BSS*RR-BSS (MV-BSS) was found to be in very good agreement with true minute volume (MV-PN) (r = 0.836). Although Bland-Altman analysis evidenced accuracy of MV-BSS by a small insignificant fixed bias (-0.02 liter/min), a significant proportional bias of MV-BSS (r = -0.664) appeared to produce larger precision (1.9 liter/min) of MV-BSS. We conclude that contact-free unconstraint respiratory monitoring with load cells under the bed legs may serve as a new clinical monitoring system, when improved.