In vitro and in vivo evaluation of a new large animal spirometry device using mainstream CO2 flow sensors

Reasons for performing study A spirometry device equipped with mainstream CO2 flow sensor is not available for large animal anaesthesia. Objectives To measure the resistance of a new large animal spirometry device and assess its agreement with reference methods for volume measurements. Study design In vitro experiment and crossover study using anaesthetised horses. Methods A flow partitioning device (FPD) equipped with 4 human CO2 flow sensors was tested. Pressure differences were measured across the whole FPD and across each sensor separately using air flows (range: 90-720l/min). One sensor was connected to a spirometry monitor for in vitro volume (3, 5 and 7l) measurements. These measurements were compared with a reference method. Five anaesthetised horses were used for tidal volume (VT) measurements using the FPD and a horse-lite sensor (reference method). Bland-Altman analysis, ANOVA and linear regression analysis were used for data analysis. Results Pressure differences across each sensor were similar suggesting equal flow partitioning. The resistance of the device increased with flow (range: 0.3-1.5 cmH2O s/l) and was higher than that of the horse-lite. The limits of agreement for volume measurements were within -1 and 2% in vitro and -12 and 0% in vivo. Nine of 147 VT measurements in horses were outside of the +/- 10% limits of acceptance but most of these erroneous measurements occurred with VTs lower than 4l. The determined correction factor for volume measurements was 3.97 +/- 0.03. Conclusions The limits of agreement for volume measurements by the new device were within +/- 10% using clinically relevant range of volumes. The new spirometry device can be recommended for measurement of VT in adult Warmblood horses.