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Summary

To investigate the cardiopulmonary effects of positive end-expiratory pressure (peep), values of 10, 20, and 30 cm of H2O, were applied to anesthetized, dorsally recumbent, ventilated ponies. After iv induction of general anesthesia, peep was superimposed on controlled ventilation with 100% oxygen, and changes in gas exchange and cardiac function were measured. Increasing values of peep in these ponies caused a linear increase in the mean (± SEM) functional residual capacity, from a control value (zero end-expiratory pressure) of 1.7 ± 0.24 L to 2.2 ± 0.31, 2.9 ± 0.32 and 3.4 ± 0.3 L at peep of 10, 20, and 30 cm of H2O, respectively (P < 0.05). Paralleling these changes, intrapulmonary shunt fraction decreased significantly (P < 0.05) from a control value of 12.9 ± 0.5%, to 7.5 ± 1.1 and 2.1 ± 0.6%, at peep of 20 and 30 cm of H2O, respectively. Cardiac output was decreased by increasing values of peep, from control value of 11.7 ± 1.56 L/min to 9.9 ± 1.51, 8.8 ± 1.33 and 5.62 ± 0.56 L/min at peep of 10, 20, and 30 cm of H20, respectively. Related to decreasing cardiac output, tissue oxygen delivery also decreased as peep was increased, from control value of 2.0 ± 0.09 L/min to 1.8 ± 0.07, 1.6 ± 0.06, and 1.03 ± 0.04 L/min at peep of 10, 20, and 30 cm of H2O, respectively.

Thus, the effects of increasing values of peep in these ponies included increased functional residual capacity and arterial oxygenation, but marked reduction in cardiac output, resulting in no improvement or decrease in total oxygen delivery. Although peep is useful for improving arterial oxygenation, the deleterious cardiovascular effects should be anticipated or ameliorated by use of volume loading and/or inotrope administration.

Free access
in American Journal of Veterinary Research

Abstract

Objective

To examine, in horses, the disposition and excretion of the active metabolite 6-methoxy-2-naphthylacetic acid (6MNA) of the nonsteroidal anti-inflammatory prodrug nabumetone.

Design

Pharmacokinetic analysis of 6MNA after oral administration of nabumetone and IV administration of 6MNA.

Procedure

Using a crossover design, 5 horses were orally administered 3.7 mg of nabumetone/kg of body weight. After a 3-week washout period, 4 horses were administered 2.5 mg of 6MNA/kg, IV.

Results

Absorption of nabumetone from the gastrointestinal tract and its metabolism to 6MNA had a median appearance half-life of 0.88 hour. The elimination half-life was 11 hours. Area under the plasma concentration time curve for 6MNA after oral administration of nabumetone was 120.6 mg/h/L. A dose of 2.5 mg/kg of 6MNA administered IV resulted in plasma concentration nearly equivalent to that induced by the orally administered dose. Disposition of 6MNA was modeled as a one-compartment, first-order elimination. The area under the plasma concentration time curve for IV administration of 6MNA was 117.0 mg/h/L, and the specific volume of distribution was 0.247 L/kg. The distribution half-life and the elimination half-life were 0.56 and 7.90 hours, respectively. Percentage of total dose recovered in urine for the 36-hour collection period after the oral and IV administrations was 7.4 and 5.3%, respectively.

Conclusions

Metabolism of nabumetone to 6MNA, as reported in other species, also occurs in horses. There were a number of additional metabolites of nabumetone in urine that could not be fully identified and characterized. (Am J Vet Res 1996;57:517–521)

Free access
in American Journal of Veterinary Research

SUMMARY

Effects of furosemide, exercise, and atropine on tracheal mucus transport rate (tmtr) in horses were investigated. Atropine (0.02 mg/kg of body weight) administered iv or by aerosolization significantly (P < 0.05) decreased tmtr at 60, but not at 30 minutes after its administration in standing horses. Furosemide (1.0 mg/kg, iv) did not have any significant effect on tmtr when measured at 2 or 4 hours after its administration in standing horses. Exercise alone or furosemide (1.0 mg/kg, iv) administration followed 4 hours later by exercise did not alter tmtr, compared with values for standing control or exercised horses administered saline solution. Atropine (0.02 mg/kg, iv) administered after exercise significantly (P < 0.05) decreased tmtr, compared with values for no exercise standing controls, for exercise after administration of saline solution, and for furosemide and exercise.

Free access
in American Journal of Veterinary Research