Effect of head and neck position on respiratory mechanics in horses sedated with xylazine.

This research investigates the effects of head and neck position and certain drugs on the respiratory mechanics of horses sedated with xylazine. The study finds that head and neck position can impact respiratory mechanics and that administering atropine can cause changes in these mechanics as well.

Research Methodology

• The research involved 3 experiments, utilising Thoroughbred geldings aged between 3 to 5 years. In Experiment 1, five horses were used while four horses were used in the subsequent two experiments.
• Respiratory data was collected using a pneumotachograph and differential transducer attached to a mask fitted tightly on the horse’s face. This electronic integration of the flow signal helped in calculating the tidal volume.
• Total pulmonary pressure (PL) was derived as the difference between esophageal pressure, measured with a balloon sealed to the end of a polyethylene catheter, and mask pressure.
• In experiment 3, to estimate the transpulmonary pressure, a blunt cannula was positioned in the dorsal third of the eighth or tenth intercostal space.
• The lateral tracheal pressure was directly measured using a polypropylene catheter inserted percutaneously in the midextrathoracic tracheal lumen.
• Upper and lower airway pressures were defined as the difference between mask pressure or transpulmonary pressure and lateral tracheal pressure.

Findings and Observations

• The researchers found a significant increase in PL from 10 to 40 minutes after the administration of xylazine.
• Though a general correlation between head and neck position and PL was noticed, maximum PL was not always achieved with the horse’s lowest head and neck position.
• Additionally, lower and upper airway resistance were seen to increase with low head carriage, with a greater increase noted in upper airway resistance leading to a decrease in lower-to-total airway resistance ratio.

Importance and Implications of the Study

• This research underscores the importance of considering a horse’s physical positioning and respiratory physiological changes during sedation procedures.
• The findings highlight the necessity of adjusting sedation methods and monitoring strategies according to the horse’s head and neck positioning to ensure optimal respiratory mechanics.