Effects of sedation, anesthesia, and endotracheal intubation on respiratory mechanics in adult horses.

This research investigates how endotracheal intubation, a medical procedure wherein a tube is inserted into the windpipe through the mouth or nose, affects respiratory mechanics in horses under different forms of sedation or anesthesia.

Research Methods

In this study, the researchers used:

• Five healthy adult horses as the subjects of the research.
• Measurements derived from recordings of respiratory gas flow, and transpulmonary and transtracheal pressures – these are pressures in different parts of the horse’s respiratory system.
• Calculations of total pulmonary resistance (RT), which was partitioned into upper airway resistance (RUA) in areas like the trachea, larynx, pharynx, and nasal cavity, and lower airway resistance in areas like the bronchi and bronchioles – these are measures of how hard it is for air to flow through these parts of the horse’s respiratory system.
• Baseline measurements were taken in unsedated horses, again after administration of xylazine (a sedative), and following intubation. Further measurements were obtained after induction of xylazine-diazepam-ketamine anesthesia (a stronger form of sedation) and subsequent to more endotracheal intubations with tubes of varying diameters.
• Nasotracheal intubation was performed during the recovery of the horses, and measurements were taken upon standing and after extubation (removal of the tube).

Research Results

The research found:

• The mean work of breathing (W), RT, and RUA increased significantly with xylazine sedation. These increases were variably attenuated (decreased) by the introduction of nasotracheal intubation.
• When the horses were given xylazine-diazepam-ketamine anesthesia, the highest values for W, RT, RUA, and pulmonary pressures developed when the horses were not intubated. The magnitudes of resistance and pressure values were inversely proportional to the diameter of the intubation tube, meaning that smaller tubes resulted in more resistance and higher pressures.
• During recovery, the resistance and pressure measurements were significantly increased compared with presedation values.
• Extubation further increased these measurements, suggesting that removal of the tube can have significant effects on a horse’s respiratory mechanics.

Research Conclusions

This research concluded that:

• The work of breathing in horses is increased when the RUA is raised during xylazine sedation and xylazine-diazepam-ketamine anesthesia.
• Endotracheal intubation reduces the work of breathing by reducing the upper airway resistance. This indicates that intubation may be beneficial for managing respiratory function in horses during sedation or anesthesia.