Circulatory and respiratory responses of spontaneously breathing, laterally recumbent horses to 12 hours of halothane anesthesia

E. P. Steffey From the Departments of Surgery (Steffey, Woliner, Jarvis, Smith, Elliott) and Pharmacology and Toxicology (Giri), School of Veterinary Medicine, and the Statistical Laboratory (Willits), University of California, Davis, CA 95616; Department of Clinical Sciences (Dunlop), College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO 80523; School of Veterinary Studies (Cullen), Murdoch University, Murdoch Western Australia, 6150, Australia; Department of Clinical Sciences (Hodgson), College of Veterinary Medicine, Kansas State University, Manhattan, KS 66506.

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C. I. Dunlop From the Departments of Surgery (Steffey, Woliner, Jarvis, Smith, Elliott) and Pharmacology and Toxicology (Giri), School of Veterinary Medicine, and the Statistical Laboratory (Willits), University of California, Davis, CA 95616; Department of Clinical Sciences (Dunlop), College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO 80523; School of Veterinary Studies (Cullen), Murdoch University, Murdoch Western Australia, 6150, Australia; Department of Clinical Sciences (Hodgson), College of Veterinary Medicine, Kansas State University, Manhattan, KS 66506.

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L. K. Cullen From the Departments of Surgery (Steffey, Woliner, Jarvis, Smith, Elliott) and Pharmacology and Toxicology (Giri), School of Veterinary Medicine, and the Statistical Laboratory (Willits), University of California, Davis, CA 95616; Department of Clinical Sciences (Dunlop), College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO 80523; School of Veterinary Studies (Cullen), Murdoch University, Murdoch Western Australia, 6150, Australia; Department of Clinical Sciences (Hodgson), College of Veterinary Medicine, Kansas State University, Manhattan, KS 66506.

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D. S. Hodgson From the Departments of Surgery (Steffey, Woliner, Jarvis, Smith, Elliott) and Pharmacology and Toxicology (Giri), School of Veterinary Medicine, and the Statistical Laboratory (Willits), University of California, Davis, CA 95616; Department of Clinical Sciences (Dunlop), College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO 80523; School of Veterinary Studies (Cullen), Murdoch University, Murdoch Western Australia, 6150, Australia; Department of Clinical Sciences (Hodgson), College of Veterinary Medicine, Kansas State University, Manhattan, KS 66506.

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S. N. Giri From the Departments of Surgery (Steffey, Woliner, Jarvis, Smith, Elliott) and Pharmacology and Toxicology (Giri), School of Veterinary Medicine, and the Statistical Laboratory (Willits), University of California, Davis, CA 95616; Department of Clinical Sciences (Dunlop), College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO 80523; School of Veterinary Studies (Cullen), Murdoch University, Murdoch Western Australia, 6150, Australia; Department of Clinical Sciences (Hodgson), College of Veterinary Medicine, Kansas State University, Manhattan, KS 66506.

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N. Willits From the Departments of Surgery (Steffey, Woliner, Jarvis, Smith, Elliott) and Pharmacology and Toxicology (Giri), School of Veterinary Medicine, and the Statistical Laboratory (Willits), University of California, Davis, CA 95616; Department of Clinical Sciences (Dunlop), College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO 80523; School of Veterinary Studies (Cullen), Murdoch University, Murdoch Western Australia, 6150, Australia; Department of Clinical Sciences (Hodgson), College of Veterinary Medicine, Kansas State University, Manhattan, KS 66506.

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M. J. Woliner From the Departments of Surgery (Steffey, Woliner, Jarvis, Smith, Elliott) and Pharmacology and Toxicology (Giri), School of Veterinary Medicine, and the Statistical Laboratory (Willits), University of California, Davis, CA 95616; Department of Clinical Sciences (Dunlop), College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO 80523; School of Veterinary Studies (Cullen), Murdoch University, Murdoch Western Australia, 6150, Australia; Department of Clinical Sciences (Hodgson), College of Veterinary Medicine, Kansas State University, Manhattan, KS 66506.

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K. A. Jarvis From the Departments of Surgery (Steffey, Woliner, Jarvis, Smith, Elliott) and Pharmacology and Toxicology (Giri), School of Veterinary Medicine, and the Statistical Laboratory (Willits), University of California, Davis, CA 95616; Department of Clinical Sciences (Dunlop), College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO 80523; School of Veterinary Studies (Cullen), Murdoch University, Murdoch Western Australia, 6150, Australia; Department of Clinical Sciences (Hodgson), College of Veterinary Medicine, Kansas State University, Manhattan, KS 66506.

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C. M. Smith From the Departments of Surgery (Steffey, Woliner, Jarvis, Smith, Elliott) and Pharmacology and Toxicology (Giri), School of Veterinary Medicine, and the Statistical Laboratory (Willits), University of California, Davis, CA 95616; Department of Clinical Sciences (Dunlop), College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO 80523; School of Veterinary Studies (Cullen), Murdoch University, Murdoch Western Australia, 6150, Australia; Department of Clinical Sciences (Hodgson), College of Veterinary Medicine, Kansas State University, Manhattan, KS 66506.

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A. R. Elliott From the Departments of Surgery (Steffey, Woliner, Jarvis, Smith, Elliott) and Pharmacology and Toxicology (Giri), School of Veterinary Medicine, and the Statistical Laboratory (Willits), University of California, Davis, CA 95616; Department of Clinical Sciences (Dunlop), College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO 80523; School of Veterinary Studies (Cullen), Murdoch University, Murdoch Western Australia, 6150, Australia; Department of Clinical Sciences (Hodgson), College of Veterinary Medicine, Kansas State University, Manhattan, KS 66506.

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Summary

Cardiovascular and respiratory changes that accompany markedly long periods (12 hours) of halothane anesthesia were characterized. Eight spontaneously breathing horses were studied while they were positioned in left lateral recumbency and anesthetized only with halothane in oxygen maintained at a constant end-tidal concentration of 1.06% (equivalent to 1.2 times the minimal alveolar concentration for horses). Results of circulatory and respiratory measurements during the first 5 hours of constant conditions were similar to those previously reported from this laboratory (ie, a time-related significant increase in systemic arterial blood pressure, cardiac output, stroke volume, left ventricular work, pcv, plasma total solids concentration, and little change in respiratory system function). Beyond 5 hours of anesthesia, arterial blood pressure did not further increase, but remained above baseline. Cardiac output continued to increase, because heart rate significantly (P < 0.05) increased. Peak inspiratory gas flow increased significantly (P < 0.05) in later stages of anesthesia. There was a significant decrease in inspiratory time beginning at 4 hours. Although PaO2 and PaCO2 did not significantly change during the 12 hours of study, Pv̄O2 increased significantly (P < 0.05) and progressively with time, beginning 6 hours after the beginning of constant conditions. Metabolic acidosis increased with time (significantly [P < 0.05] starting at 9 hours), despite supplemental iv administered NaHCO3, Plasma concentrations of eicosanoids: 6-ketoprostaglandin F (pgf a stable metabolite of pgi1), pgf, pge, and thromboxane (TxB2, a stable metabolite of TxA2) were measured in 5 of the 8 horses before and during anesthesia. Significant changes from preanesthetic values were not detected. Dynamic thoracic wall and lung compliances decreased with time.

Summary

Cardiovascular and respiratory changes that accompany markedly long periods (12 hours) of halothane anesthesia were characterized. Eight spontaneously breathing horses were studied while they were positioned in left lateral recumbency and anesthetized only with halothane in oxygen maintained at a constant end-tidal concentration of 1.06% (equivalent to 1.2 times the minimal alveolar concentration for horses). Results of circulatory and respiratory measurements during the first 5 hours of constant conditions were similar to those previously reported from this laboratory (ie, a time-related significant increase in systemic arterial blood pressure, cardiac output, stroke volume, left ventricular work, pcv, plasma total solids concentration, and little change in respiratory system function). Beyond 5 hours of anesthesia, arterial blood pressure did not further increase, but remained above baseline. Cardiac output continued to increase, because heart rate significantly (P < 0.05) increased. Peak inspiratory gas flow increased significantly (P < 0.05) in later stages of anesthesia. There was a significant decrease in inspiratory time beginning at 4 hours. Although PaO2 and PaCO2 did not significantly change during the 12 hours of study, Pv̄O2 increased significantly (P < 0.05) and progressively with time, beginning 6 hours after the beginning of constant conditions. Metabolic acidosis increased with time (significantly [P < 0.05] starting at 9 hours), despite supplemental iv administered NaHCO3, Plasma concentrations of eicosanoids: 6-ketoprostaglandin F (pgf a stable metabolite of pgi1), pgf, pge, and thromboxane (TxB2, a stable metabolite of TxA2) were measured in 5 of the 8 horses before and during anesthesia. Significant changes from preanesthetic values were not detected. Dynamic thoracic wall and lung compliances decreased with time.

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