The effect of the alpha 2-agonist dexmedetomidine on the cerebral blood flow (CBF) and the metabolic rate for oxygen was studied by a sagittal sinus outflow technique in dogs during halothane anesthesia. Dexmedetomidine was given in a dose (10 micrograms/kg) reported to reduce the anesthetic requirement of halothane by 90%. During 0.9% halothane anesthesia dexmedetomidine caused a significant reduction in CBF without influencing the metabolic rate for oxygen. Reducing the halothane concentration to 0.1% caused no further change in CBF, but increased the metabolic rate for oxygen 19%. The cerebral vasoconstrictive effect, combined with the 90% reduction in MAC for halothane, indicates that dexmedetomidine might be a useful adjunct to inhalation anesthetics during neurosurgery in situations where an increase in CBF should be avoided.
The selective 5-hydroxytryptamine2-(5-HT2)-receptorblocking agent ketanserin was given in a dose of 10 mg intravenously to nine patients with Raynaud's phenomenon. The effect on blood flow was assessed by photoplethysmography and measurements of skin temperature. Digital blood flow and skin temperature increased significantly after ketanserin injection, whereas the placebo (saline 9 g/l) had no such effect.This study suggests that ketanserin may be useful in the treatment of Raynaud's phenomenon.
The cerebral effects of adding theophylline to 1.4% isoflurane anaesthesia were studied in five dogs by a sagittal sinus outflow technique with direct measurement of the cerebral blood flow (CBF) and calculation of the cerebral metabolic rate for oxygen (CMRo2). Three 3 mg.kg-1 doses of theophylline were given with intervals of 10 min. Five min after the second and third dose, when the mean theophylline plasma concentration was 41 and 65 mumols.1(-1), respectively, CMRo2 had increased significantly with a mean value varying between 15% and 13%, and the EEG had changed from a sleep pattern to a more awake pattern in the four dogs with evaluable recordings. There were no significant changes in CBF or mean arterial blood pressure (MABP). It is concluded that the adenosine receptor antagonist theophylline in this study partially reversed the cerebral effects of isoflurane.
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