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

Summary: 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.