A comparison of end-tidal halothane concentrations measured at proximal and distal ends of the endotracheal tube in the horse.

This research observes the consistency of measured halothane gas concentrations on both proximal (closer to mouth) and distal (further from mouth) ends of the endotracheal tube in anesthetized horses during surgery. The findings suggest that the concentrations are highly correlated, despite the tube’s location.

Objective and Study Design

• The primary objective of this study was to compare the concentration of halothane, an anesthetic gas, measured at different points of an endotracheal tube used in anesthetizing horses for surgery.
• The researchers took 126 measurements from 21 horses, obtaining samples from near the oral end of the tube (Y1), the cuffed end of the tube (Y2), and 25 cm beyond the cuffed end (Y3).
• A total of 105 paired measurements allowed for direct comparison between Y1 and Y2, while 21 paired readings compared Y1 to Y3.

Measurement and Data Analysis Methods

• All measurements were taken at 15-minute intervals, beginning 30 minutes after the start of halothane administration.
• To maximize accuracy, readings were collected at the end of expiration and both sites were sampled in close temporal proximity (within a minute of each other).
• The halothane concentraion was measured using rapid infrared analysis and calibrated regularly to ensure accurate readings.
• Differences between readings at various points of the tube were statistically analyzed using general linear models and deemed significant if the p-value was less than 0.05. The study also analyzed the potential effects of time, mode of ventilation, and type of recumbency, finding no significant impact on the results.

Results

• The mean halothane concentrations at Y1 and Y2 were almost identical (2.41 vol% vs 2.39 vol%), indicating a high degree of correlation (Pearson’s correlation coefficient = 0.96).
• The same high correlation was observed between Y1 and Y3 measurements with mean concentrations of 2.31 vol% and 2.32 vol% respectively and a Pearson’s correlation coefficient of 0.98.

Conclusion

• The study concluded that the location of the endotracheal tube has no meaningful impact on the measured halothane concentration in anesthetized horses.