Dissertationen 1996-2013
Cardiopulmonary effects of hypoxia and application of the medetomidine isomers levomedetomidine and dexmedetomidine in sheep during sevoflurane anaesthesia
Jolanda Boller, 2005
Vetsuisse-Fakultät Universität Zürich, Pferdeklinik
Contact: gschmid@vetclinics.unizh.ch
The aim of this study was to evaluate the cardiopulmonary effects of a low intravenous bolus of dexmedetomidine (DEX), an intravenous infusion of DEX, as well as an intravenous bolus of levomedetomidine (LEVO), in 6 domestic sheep. Anaesthesia was induced and maintained with sevoflurane. The mechanism of hypoxemia was tested by reducing the oxygen concentration. At specific time points, 8 different cardiopulmonary parameters, respiratory and circulatory gas levels and several indices were assessed.
During phase 1, hypoxemia was induced by ventilation with a hypoxic gas mixture (FiO2 = 0.1) for 10 minutes. The bolus of LEVO (2 Mikrogramm/kg) was given in the second phase of the study. In the third phase, the low DEX dose (0.01 Mikrogramm/kg) was administered. Finally, the study was completed by the DEX infusion (2 Mikrogramm/kg/h for 1 hour).
In all animals, the hypoxic gas mixture induced a sympathetic stimulation with varying increases of blood pressure and heart rate. LEVO elicited no measurable effects on the cardiovascular or respiratory performance. However, diastolic arterial blood pressure, mean central venous pressure and systolic vascular resistance decreased significantly following the low-dose DEX application. Pronounced hypoxemia was observed only after the DEX infusion in one sheep: 10 minutes after the beginning of phase 4, the oxygen partial pressure fell from 409.4 to 34.5 mmHg. This animal showed no marked effects during the prior hypoxic challenge, indicating that the individually different sensitivity to alpha-2-agonists is attributable to variable densities of alpha-2-receptors in the lung. Deutsche Version