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  • Author or Editor: C. Kurpershoek x
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SUMMARY

We studied the temporal changes in respiratory mechanics associated with xylazine administration (1.1 mg/kg of body weight, iv) in standing horses (experiment 1), and determined the effects of head and neck position (experiment 2) and atropine administration (experiment 3) on the observed changes.

Thoroughbred geldings, 3 to 5 years old (5 in experiment 1, 4 in experiments 2 and 3) were used. Flow rates were obtained from a pneumotachograph and a differential transducer attached to a tight-fitting mask. Electronic integration of the flow signal gave tidal volume. Total pulmonary pressure (PL) was defined as the difference between esophageal pressure, measured with a balloon sealed to the end of a polyethylene catheter, and mask pressure. In experiment 3, a blunt cannula positioned in the dorsal third of the eighth or tenth intercostal space was used to estimate transpulmonary pressure. Lateral tracheal pressure was measured, using a polypropylene catheter inserted percutaneously in the mid-extrathoracic tracheal lumen. Upper and lower airway pressures were defined as the difference between mask pressure or transpulmonary pressure and lateral tracheal pressure, respectively.

Five observations were made: (1) There was a significant (P < 0.05) increase in PL from 10 to 40 minutes after administration of xylazine. (2) Although an overall agreement between head and neck position and PL was detected, the maximal PL value was not always obtained with lowest head and neck position. (3) Lower and upper airway resistance increased with low head carriage, with a greater increase in upper airway resistance resulting in a decrease in lower to total airway resistance ratio. (4) Increased airway resistance was reversed by elevating the head and neck. (5) Atropine did not prevent the increase in airway resistance during sedation with xylazine and had no effect on resistance with changes in head position.

Free access
in American Journal of Veterinary Research

Summary

The effects of 3 commonly used dosages (0.3, 0.5, and 1.1 mg/kg of body weight, iv) of xylazine on ventilatory function were evaluated in 6 Thoroughbred geldings. Altered respiratory patterns developed with all doses of xylazine, and horses had apneic periods lasting 7 to 70 seconds at the 1.1 mg/kg dosage. Respiratory rate, minute volume, and partial pressure of oxygen in arterial blood ( Pa o 2 ) decreased significantly (P < 0.001) with time after administration of xylazine, but significant differences were not detected among dosages. After an initial insignificant decrease at 1 minute after injection, tidal volume progressively increased and at 5 minutes after injection, tidal volume was significantly (P < 0.01) greater than values obtained before injection. Partial pressure of carbon dioxide in arterial blood ( Pa co 2 ) was insignificantly increased. After administration of xylazine at a dosage of 1.1 mg/ kg, the mean maximal decrease in Pa o 2 was 28.2 ± 8.7 mm of Hg and 22.2 ± 4.9 mm of Hg, measured with and without a respiratory mask, respectively. Similarly, the mean maximal increase in PaCO2 was 4.5 ± 2.3 mm of Hg and 4.2 ± 2.4 mm of Hg, measured with and without the respiratory mask, respectively. Significant interaction between use of mask and time was not detected, although the changes in PaO2 were slightly attenuated when horses were not masked. The temporal effects of xylazine on ventilatory function in horses should be considered in selecting a sedative when ventilation is inadequate or when pulmonary function testing is to be performed.

Free access
in American Journal of Veterinary Research
in Journal of the American Veterinary Medical Association

Summary

A rebreathing method for measurement of pulmonary diffusing capacity for carbon monoxide (Dl CO) and functional residual capacity (frc) was evaluated in conscious horses. Horses were manually ventilated through an endotracheal tube, using a custom-made syringe filled with a gas mixture containing 18-carbon monoxide (18CO) and helium (He). The 18CO and He concentrations were continuously monitored by use of a mass spectrometer connected to the rebreathing circuit. Values for Dl CO and frc were calculated from changes in the concentration of these 2 gases. In 11 Thoroughbreds, mean (± sd) Dl CO was 330.3 ± 56.9 ml•min−1•mm of Hg−1, and frc was 20.21 ± 3 35 L. Body weight normalization yielded mean (± sd) values of 0.652 ± 0.114 ml•min−1•mm of Hg−1•kg−1 for Dl CO, and 39.9 ± 6.4 ml•kg−1 for frc.

Free access
in American Journal of Veterinary Research