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Evaluation of the effects of dorsal versus lateral recumbency on the cardiopulmonary system during anesthesia with isoflurane in red-tailed hawks (Buteo jamaicensis)

Michelle G. HawkinsDepartment of Medicine and Epidemiology, School of Veterinary Medicine, University of California-Davis, Davis, CA 95616.

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Shachar MalkaWilliam T. Pritchard Veterinary Medical Teaching Hospital, School of Veterinary Medicine, University of California-Davis, Davis, CA 95616.

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Peter J. PascoeDepartment of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California-Davis, Davis, CA 95616.

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Adrian M. SolanoWilliam T. Pritchard Veterinary Medical Teaching Hospital, School of Veterinary Medicine, University of California-Davis, Davis, CA 95616.

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Philip H. KassDepartment of Population Health and Epidemiology, School of Veterinary Medicine, University of California-Davis, Davis, CA 95616.

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Hajime OhmuraEquine Research Institute, Japan Racing Association, 321-4 Tokami-cho, Utsunomiya, Japan.

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James H. JonesDepartment of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California-Davis, Davis, CA 95616.

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Abstract

Objective—To evaluate the effects of dorsal versus lateral recumbency on the cardiopulmonary system during isoflurane anesthesia in red-tailed hawks (Buteo jamaicensis).

Animals—6 adult 1.1- to 1.6-kg red-tailed hawks.

Procedures—A randomized, crossover study was used to evaluate changes in respiratory rate, tidal volume, minute ventilation, heart rate, mean arterial and indirect blood pressures, and end-tidal Pco2 measured every 5 minutes plus Paco2 and Pao2 and arterial pH measured every 15 minutes throughout a 75-minute study period.

Results—Respiratory rate was higher, tidal volume lower, and minute ventilation not different in lateral versus dorsal recumbency. Position did not affect heart rate, mean arterial blood pressure, or indirect blood pressure, although heart rate decreased during the anesthetic period. Birds hypoventilated in both positions and Paco2 differed with time and position × time interaction. The Petco2 position × time interaction was significant and Petco2 was a mean of 7 Torr higher than Paco2. The Paco2 in dorsal recumbency was a mean of 32 Torr higher than in lateral recumbency. Birds in both positions developed respiratory acidosis.

Conclusions and Clinical Relevance—Differences in tidal volume with similar minute ventilation suggested red-tailed hawks in dorsal recumbency might have lower dead space ventilation. Despite similar minute ventilation in both positions, birds in dorsal recumbency hypoventilated more yet maintained higher Pao2, suggesting parabronchial ventilatory or pulmonary blood flow distribution changes with position. The results refute the hypothesis that dorsal recumbency compromises ventilation and O2 transport more than lateral recumbency in red-tailed hawks.

Abstract

Objective—To evaluate the effects of dorsal versus lateral recumbency on the cardiopulmonary system during isoflurane anesthesia in red-tailed hawks (Buteo jamaicensis).

Animals—6 adult 1.1- to 1.6-kg red-tailed hawks.

Procedures—A randomized, crossover study was used to evaluate changes in respiratory rate, tidal volume, minute ventilation, heart rate, mean arterial and indirect blood pressures, and end-tidal Pco2 measured every 5 minutes plus Paco2 and Pao2 and arterial pH measured every 15 minutes throughout a 75-minute study period.

Results—Respiratory rate was higher, tidal volume lower, and minute ventilation not different in lateral versus dorsal recumbency. Position did not affect heart rate, mean arterial blood pressure, or indirect blood pressure, although heart rate decreased during the anesthetic period. Birds hypoventilated in both positions and Paco2 differed with time and position × time interaction. The Petco2 position × time interaction was significant and Petco2 was a mean of 7 Torr higher than Paco2. The Paco2 in dorsal recumbency was a mean of 32 Torr higher than in lateral recumbency. Birds in both positions developed respiratory acidosis.

Conclusions and Clinical Relevance—Differences in tidal volume with similar minute ventilation suggested red-tailed hawks in dorsal recumbency might have lower dead space ventilation. Despite similar minute ventilation in both positions, birds in dorsal recumbency hypoventilated more yet maintained higher Pao2, suggesting parabronchial ventilatory or pulmonary blood flow distribution changes with position. The results refute the hypothesis that dorsal recumbency compromises ventilation and O2 transport more than lateral recumbency in red-tailed hawks.

Contributor Notes

Dr. Malka's present address is Avian and Exotics Medicine and Surgery, Humane Society of New York, 306 E 59th St, New York, NY 10022.

Dr. Solano's present address is Corral del Sol Animal Hospital, Frente a las Instalaciones del Ministerio de Agricultura y Ganadería, Pérez Zeledón, San José, 11901 San Isidro, Costa Rica.

Presented in abstract form at the 29th Annual Conference of the Association of Avian Veterinarians, Savannah, Ga, August 2008.

Supported by the Center for Companion Animal Health, School of Veterinary Medicine, University of California-Davis.

Address correspondence to Dr. Hawkins (mghawkins@ucdavis.edu).