HIGH THORACIC EPIDURAL-ANESTHESIA DOES NOT ALTER AIRWAY-RESISTANCE AND ATTENUATES THE RESPONSE TO AN INHALATIONAL PROVOCATION TEST IN PATIENTS WITH BRONCHIAL HYPERREACTIVITY

Background: The functional relevance of an intact pulmonary sympatheti c innervation for airway resistance is unknown. We therefore evaluated whether or not pulmonary sympathetic denervation by thoracic epidural anesthesia decreases the threshold of an inhalational provocation wit h acetylcholine in 20 patients with documented bronchial hyperreactivi ty scheduled for elective upper abdominal or thoracic surgery. Methods : Baseline inhalational provocation with acetylcholine was performed 2 -4 days before surgery. The acetylcholine threshold concentration for a hyperreactivity response (i.e., for a 20% decrease in forced expirat ory volume in 1 s and a 100% increase in total respiratory resistance by oscillometry) was determined. On the day of surgery a second inhala tive provocation with acetylcholine was performed 45 min after the pat ients had received 6-8 ml epidural bupivacaine 0.75% (n = 10), intrave nous bupivacaine (1.2 mg.min(-1), n = 6), or 6-8 ml epidural saline (n = 4). The acetylcholine threshold concentration for a hyperreactive r esponse was again determined. We also measured vital capacity, forced expiratory volume in 1 s as a percentage of vital capacity, spread of sensory blockade (pin prick), skin temperature on hand and foot (telet hermography). Results: During thoracic epidural anesthesia, C4-T8 skin temperature increased significantly on hand and foot indicating wides pread sympathetic blockade including the lungs. Compared to values obt ained immediately before pulmonary sympathetic blockade, forced expira tory volume in 1 s as a percentage of vital capacity, and total respir atory resistance by oscillometry remained unchanged, while vital capac ity decreased. Compared to baseline the acetylcholine threshold concen tration for the hyperreactive response increased threefold after epidu ral as well as after intravenous bupivacaine. Epidural saline evoked n o directional changes in the acetylcholine threshold concentration. Co nclusions: We conclude that in patients with bronchial hyperreactivity 1. blockade of pulmonary sympathetic innervation seems to be of no re levance for airway resistance and 2. both epidural and intravenous bup ivacaine substantially attenuate the response to an inhalational provo cation with acetylcholine.