Effects of a demand valve on pulmonary ventilation in spontaneously breathing, anaesthetised horses.

This study investigates how a demand valve impacts pulmonary ventilation in anaesthetised horses, concluding that the resistance offered by the valve is too high to be recommended for use in spontaneously breathing horses.

Investigation of Demand Valve Pressure Flow Characteristics

• The researchers measured the pressure flow characteristics of a demand valve suggested for use in anaesthetised horses. These measurements were performed at a variety of flow rates that are typically seen in equine anaesthesia.
• The valve’s resistance was found to be significantly higher, both compared to the resistance of normal large animal anaesthetic apparatus and the equine lower respiratory tract.

Effects of the Valve on Pulmonary Ventilation

• Seven anaesthetised, intubated horses were used to investigate the valve’s impact on pulmonary ventilation.
• The respiratory rate and dynamic compliance in the horses remained unchanged upon the valve’s attachment. Dynamic compliance refers to the lungs’ ability to stretch and expand.
• However, mean tidal volumes (the volume of air displaced between normal inhalation and exhalation), minute volumes (the total volume of air breathed in one minute), and peak flow rates were significantly reduced.
• The change in transpulmonary pressure (pressure gradient through the lung) across the respiratory cycle doubled with the use of the valve.
• Similarly, the work of breathing indices increased by a factor of three. This indicates that the energy expenditure for respiration was significantly higher when the valve was used.

Final Conclusions

• Based on these findings, the researchers concluded that the resistance offered by the demand valve is excessively high.
• As a result, the valve is not recommended for use in spontaneously breathing horses. Using the valve could inhibit the horse’s breathing and lead to potential issues with oxygen supply during anaesthesia.