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 microg kg[-1] i.v.) or histamine (His, 3 microg 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.
Yuan
H B
HB
Department of Anesthesiology, Veterans General Hospital-Taipei and National Yang-Ming University, Taiwan, ROC.
Tang
G J
GJ
Kou
Y R
YR
Lee
T Y
TY
D000109:Acetylcholine; D000403:Airway Resistance / Q000187:drug effects / Q000502:physiology*; D000704:Analysis of Variance; D000767:Anesthesia, Epidural / Q000379:methods*; D000779:Anesthetics, Local / Q000008:administration & dosage* / Q000494:pharmacology; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology; D016535:Bronchial Hyperreactivity / Q000503:physiopathology*; D001985:Bronchial Provocation Tests; D016084:Bronchoconstriction / Q000187:drug effects / Q000502:physiology; D002045:Bupivacaine / Q000008:administration & dosage* / Q000494:pharmacology; D002245:Carbon Dioxide / Q000494:pharmacology; D002302:Cardiac Output / Q000187:drug effects / Q000502:physiology; D004195:Disease Models, Animal; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology; D006439:Hemodynamics / Q000187:drug effects / Q000502:physiology; D006632:Histamine; D008297:Male; D011312:Pressure; D011669:Pulmonary Wedge Pressure / Q000187:drug effects / Q000502:physiology; D013562:Sympathectomy; D013564:Sympathetic Nervous System / Q000187:drug effects; D013565:Sympatholytics / Q000494:pharmacology; D013904:Thoracic Vertebrae; D013997:Time Factors
D000779:Anesthetics, Local; D013565:Sympatholytics; D002245:Carbon Dioxide; D006632:Histamine; D000109:Acetylcholine; D002045:Bupivacaine