EFFECTS OF HIGH THORACIC EPIDURAL-ANESTHESIA ON THE PERIPHERAL AIRWAYREACTIVITY IN DOGS

Background: It has been speculated that epidural anaesthesia may induc e bronchoconstriction via the mechanism of a sympathetic blockade. How ever, this hypothesis has not been confirmed by any experimental evide nce. Therefore, we investigated the effects of high thoracic epidural anaesthesia with neural sympathetic blockade on basal airway resistanc e and airway reactivity in response to bronchoconstrictive stimuli in a canine periphery lung model. Methods: Acetylcholine (Ach, 8 mu g kg( -1) i.v.) or histamine (His, 3 mu g kg(-1) i.v.) was administered to 7 anaesthetized mongrel dogs before and after thoracic epidural anaesth esia. Successful neuronal sympathectomy was confirmed by nitroglycerin test. The changes of peripheral airway resistance (Rp), haemodynamics , cardiac output (CO), and the recovery time for Rp from peak returnin g to baseline in each challenge were studied. Results: Thoracic epidur al anaesthesia altered neither the baseline Rp nor the peak Rp evoked by Ach or His. However the recovery time of the Rp was prolonged signi ficantly after epidural anaesthesia (P<0.01) and correlated inversely with the CO in response to Ach or His challenge (Ach, r=0.542; His, r= 0.651). Conclusions: Our results suggest that epidural anaesthesia wit h neural sympathetic blockade has no influence on the basal peripheral airway resistance; however, it prolongs the airway reactivity to Ach or His challenge, probably by the mechanism of reducing CO. (C) Acta A naesthesiologica Scandinavica 42 (1998).