IN-VIVO DIRECT MEASUREMENT OF THE BRONCHODILATING EFFECT OF SEVOFLURANE USING A SUPERFINE FIBEROPTIC BRONCHOSCOPE - COMPARISON WITH ENFLURANE AND HALOTHANE

Objectives: Although volatile anesthetics have been shown to have spas molytic effects on constricted airways, most previous studies were per formed to assess bronchodilation with indirect methods such as measure ment of airway resistance, whose reliability is controversial. As the authors have developed a new direct method using a superfine fiberopti c bronchoscope (SFB) and confirmed the accuracy of this method, this s tudy assessed the spasmolytic effect of sevoflurane (S) as compared wi th enflurane (E) and halothane (H). Design: Open-labeled, randomized s tudy. Setting: The study protocol was approved by the Animal Care Comm ittee in a school of medicine. Participants: Twenty-two mongrel dogs. Interventions: The dogs were anesthetized with pentobarbital, IV, para lyzed with pancuronium, and the lungs were mechanically ventilated. Th e endotracheal tube had an additional lumen to insert the SFB (outer d iameter 2.2 mm). The tip of the SFB was located between a second and t hird bronchial bifurcation to continuously monitor the bronchial cross -sectional area (BCA) of third or fourth generation bronchi. The BCA w as printed out by videoprinter at the end of expiration and was calcul ated on a Macintosh Ilci computer using an NIH (National Institutes of Health) image program. Bronchoconstriction was produced with histamin e (HA: 10 mu g/kg + 500 mu g/kg/hr). In the first protocol, 4 mongrel dogs were used to assess the accuracy of the new method. BCA was measu red 30 and 60 minutes after the placement of the SFB and also 30 and 6 0 minutes after the start of the histamine (HA) infusion. Arterial blo od (4 mL) was collected at 30 and 60 minutes after placement of the SF B to measure the plasma concentration of catecholamines with gas chrom atographic mass spectrometry. In the second protocol, 18 dogs were ran domly allocated to 3 groups of 6 each: group S, group E, and group H. Thirty minutes after the start of the HA infusion. the dogs subsequent ly inhaled the following concentrations of S, E, or H for 15 minutes: 0.2, 0.4, 0.8, and 1.6 minimum alveolar concentrations. The BCA was as sessed before and 30 minutes after the start of HA and at the end of t he inhalation period of each concentration. Measurements and Main Resu lts: In the first study, no significant differences in the BCA were fo und between 30 and 60 minutes after the placement of the SFB and betwe en 30 and 60 minutes after the start of HA. The plasma concentrations of norepinephrine and epinephrine changed from 138 +/- 45 and 162 +/- 18 to 188 +/- 48 and 136 +/- 18 pg/mL, respectively. In the second stu dy, all volatile anesthetics significantly increased the BCA in a dose -dependent manner. There was no significant difference among the three groups. Conclusion: As the BCA did not change in the first study, the tip of the SBF could be well fixed, and the 30-minute interval is lon g enough for the HA infusion to produce stable bronchoconstriction. Th e plasma catecholamine concentrations suggest that the pentobarbital a nesthesia was deep enough to inhibit the direct irritant effect of the endotracheal tube and the SFB on the airway. This new direct method i ndicates that S dilates HA-constricted proximal airway with the same p otency as E and H. (C) 1996 by W.B. Saunders Company