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

The researchers in this study have tested a spirometry device equipped with mainstream CO2 flow sensors for large animal anaesthesia, particularly horses. They found that the device can adequately measure volume and it performs well within the acceptable limits.

Research Methods

The research was conducted in two stages:

• In the first stage, an in vitro experiment was carried out to measure the resistance of the flow partitioning device (FPD), which has four human CO2 flow sensors. The pressure differences were measured while varying air flows, and one sensor was then connected to a spirometry monitor for volume measurements. The measurements were then compared to a predetermined reference method to assess accuracy.
• In the second stage, this crossover study used five anaesthetised horses to measure tidal volumes (VT) using both the FPD and a horse-lite sensor as reference. The accuracy of the readings from the FPD was analysed using Bland-Altman analysis, ANOVA and linear regression.

Results

The results demonstrated that:

• The pressure differences across each sensor were similar, indicating that the partitioning of flow was even across the device.
• The resistance of the device increased as the flow increased and was found to be higher than that of the horse-lite sensor.
• The limits of agreement for volume measurements ranged within -1 and 2% in vitro, and -12 and 0% in vivo. This shows that the device was fairly accurate in its measurements, both in lab conditions and in live horses.
• Out of 147 tidal volume measurements in horses, nine were outside the acceptable variation of ±10%. However, these erroneous measurements mostly occurred with tidal volumes below 4 litres.
• A correction factor of 3.97 ± 0.03 for volume measurements was determined during the study. This provides a guideline for any necessary adjustments in volume readings in future applications of the device.

Conclusion

The new spirometry device developed for large animals, notably Warmblood horses, meets the acceptable standards for measuring tidal volume within a clinically relevant range of volumes. The researchers therefore recommend this device for use in this context.