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Effects of duration of isoflurane anesthesia and mode of ventilation on intracranial and cerebral perfusion pressures in horses

Robert J. BrosnanDepartment of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California, Davis, CA 95616.

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 DVM, PhD
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Eugene P. SteffeyDepartment of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California, Davis, CA 95616.

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 VMD, PhD
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Richard A. LeCouteurDepartment of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California, Davis, CA 95616.

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Thomas B. FarverDepartment of Population Health and Reproduction, School of Veterinary Medicine, University of California, Davis, CA 95616.

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Ayako ImaiDepartment of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California, Davis, CA 95616.

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 DVM, MS

Abstract

Objective—To test the hypothesis that isofluraneanesthetized horses during controlled ventilation and spontaneous ventilation exhibit temporal changes in cerebral hemodynamics, as measured by intracranial pressure and cerebral perfusion pressure, that reflect temporal changes in systemic arterial pressure.

Animals—6 healthy adult horses.

Procedure—Horses were anesthetized in left lateral recumbency with 1.57% isoflurane in O2 for 5 hours in 2 experiments by use of either controlled ventilation (with normocapnia) or spontaneous ventilation (with hypercapnia) in a randomized crossover design. Intracranial pressure was measured with a subarachnoid strain-gauge transducer. Carotid artery pressure, central venous pressure, airway pressures, blood gases, and minute ventilation also were measured.

Results—Intracranial pressure during controlled ventilation significantly increased during constant dose isoflurane anesthesia and thus contributed to decreasing cerebral perfusion pressure. Intracranial pressure was initially higher during spontaneous ventilation than during controlled ventilation, but this difference disappeared over time; no significant differences in cerebral perfusion pressures were observed between horses that had spontaneous or controlled ventilation.

Conclusions and Clinical Relevance—Cerebral hemodynamics and their association with ventilation mode are altered over time in isoflurane-anesthetized horses and could contribute to decreased cerebral perfusion during prolonged anesthesia. (Am J Vet Res 2003;64:1444–1448)

Abstract

Objective—To test the hypothesis that isofluraneanesthetized horses during controlled ventilation and spontaneous ventilation exhibit temporal changes in cerebral hemodynamics, as measured by intracranial pressure and cerebral perfusion pressure, that reflect temporal changes in systemic arterial pressure.

Animals—6 healthy adult horses.

Procedure—Horses were anesthetized in left lateral recumbency with 1.57% isoflurane in O2 for 5 hours in 2 experiments by use of either controlled ventilation (with normocapnia) or spontaneous ventilation (with hypercapnia) in a randomized crossover design. Intracranial pressure was measured with a subarachnoid strain-gauge transducer. Carotid artery pressure, central venous pressure, airway pressures, blood gases, and minute ventilation also were measured.

Results—Intracranial pressure during controlled ventilation significantly increased during constant dose isoflurane anesthesia and thus contributed to decreasing cerebral perfusion pressure. Intracranial pressure was initially higher during spontaneous ventilation than during controlled ventilation, but this difference disappeared over time; no significant differences in cerebral perfusion pressures were observed between horses that had spontaneous or controlled ventilation.

Conclusions and Clinical Relevance—Cerebral hemodynamics and their association with ventilation mode are altered over time in isoflurane-anesthetized horses and could contribute to decreased cerebral perfusion during prolonged anesthesia. (Am J Vet Res 2003;64:1444–1448)