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Canadian Journal of Anesthesia, Vol 32, 112-118, Copyright © 1985 by Canadian Anesthesiologists' Society
1 Department of Anaesthesiology, State University Hospital, Downstate Medical Center, Brooklyn, New York
Address correspondence to: Dr. Pierre A. Casthely, Department of Anesthesiology, State University Hospital, Downstate Medical Center, 450 Clarkson Avenue, Brooklyn, New York 11203.
We evaluated cardiovascular effects and effectiveness of isoetharine, metaproterenol and salbutamol, when administered intratracheally to relieve methacholine-induced bronchospasm in dogs anaesthetized with 50 per cent nitrous oxide, oxygen, halothane and mechanically ventilated. Methacholine 2 µg·kg-1·hour-1 was administrated first followed by halothane (1 MAC) for 30 minutes (control), then metaproterenol, isoetharine or sulbutamol. Metaproterenol (15 mg) significantly decreased transpulmonary pressure to 20.1 ±0.5 (SE) from 22.5 ± 1.15 cmH2O (p < 0.025) after three min and to 15 ± 0.5 cmH2O (p < 0.005) after 90 min. Isoetharine (2.5 mg) decreased transpulmonary pressure after five min to 22.1 ± 1 from 24.5 ± 1.5 cmH2O (p < 0.05), and to 21.75 ± 0.55 mmH2O after 90 min. Salbutamol 25 µg·kg-1 decreased transpulmonary pressure to 20.7 ± 0.75 from 24.25 ± 1.28 after three min and to 16 ± .5 after 90 min.
The peak effects on airway pressure occurred at 15 min for metaproterenol, 25 min for salbutamol and 20 min for isoetharine. Pulmonary vascular resistance was not significantly changed during halothane anaesthesia alone but decreased significantly after metaproterenol and isoetharine infusion. Heart rate increased ten per cent after metaproterenol, three per cent after isoetharine, and five per cent after salbutamol. No arrhythmias occurred in any group. Cardiac output increased significantly to 3.25 ± 0.2 from 1.5 ± 0.17 L·min-1 (p <0.025) after metaproterenol to 3.2 ± .025 from 1.45 ± .009 after salbutamol and was unchanged after isoetharine.
Metaproterenol and salbutamol in the presence of 1 MAC halothane anaesthesia relieved methacholine-induced bronchospasm more rapidly than did isoetharine. The onset of effect was 3 ± 0.05 min for metaproterenol and salbutamol and 5 ± 0.01 min for isoetharine. The effect lasted 210 ± 10.5 min for metaproterenol, 170 ± 12.5 min for salbutamol and 90 ± 4.75 min for isoetharine.
Key Words: LUNG: bronchospasm BRONCHODILATORS: metaproterenol, isoetharine, methacholine
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