Effects of high thoracic epidural anaesthesia on the peripheral airway reactivity in dogs

Background: It has been speculated that epidural anaesthesia may induce bronchoconstriction via the mechanism of a sympathetic blockade. However, this hypothesis has not been confirmed by any experimental evidence. Therefore, we investigated the effects of high thoracic epidural anaesthesia with neural sympathetic blockade on basal airway resistance and airway reactivity in response to bronchoconstrictive stimuli in a canine periphery lung model. Methods: Acetylcholine (Ach, 8 μg kg^-1 i.v.) or histamine (His, 3 μg kg^-1 i.v.) was administered to 7 anaesthetized mongrel dogs before and after thoracic epidural anaesthesia. 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 returning to baseline in each challenge were studied. Results: Thoracic epidural anaesthesia altered neither the baseline Rp nor the peak Rp evoked by Ach or His. However, the recovery time of the Rp was prolonged significantly 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 with 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.