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 < 0.0001 / Fig. 2-C; R = 0.8; p < 0.0001). Comparison of the methods using the Bland–Altman method depicted a very low bias for RR (Fig. 2-B; 1 bpm) and Vt (Fig. 2-D; -1 mL) and an acceptable deviation (< ± 3.7 bpm and 80 mL, respectively)