[The effect of halothane, enflurane and isoflurane on resistance and compliance in patients with asthma or chronic obstructive lung diseases]

Abstract

In order to test the hypothesis that halothane is more effective and safer than enflurane and isoflurane in patients with reactive airway disease, a clinical trial was performed to compare these three agents in patients with asthma or chronic obstructive pulmonary disease (COPD). METHODS. After obtaining institutional approval and informed consent, 31 patients with bronchial asthma or COPD were studied (FEV1 less than 65% of FVC); all patients underwent extensive surgery of the paranasal sinuses. Premedication consisted of i.m. atropine and promethazine; anesthesia was induced with diazepam, fentanyl, etomidate, and succinylcholine and maintained with pancuronium and 50% N2O in O2 together with one of the volatile agents, halothane, enflurane, or isoflurane, selected at random. Patients were mechanically ventilated. On the basis of respiratory pressures, volumes, and flows, inspiratory (Rin) and expiratory (Rex) resistance and compliance (C) were calculated after induction (control), 15 min after the addition of the volatile agent (1.25 MAC), every 15 min during the surgical procedure, and at the end of the operation. RESULTS. In 1 case, airway resistance increased markedly a few minutes after administration of isoflurane. The results obtained in this patient were not included in the evaluation of the data. There were no statistically significant differences in the preoperative data or control values of Rin, Rex, and C among the three groups (n = 10 each). With the respective inhalational agents, Rin increased maximally between 3% (halothane) or 8% (enflurane) and 21% (isoflurane), Rex between 16% (halothane, enflurane) and 29% (isoflurane). For the most part, however, these changes were not statistically significant as compared with controls. Intergroup comparisons failed to reveal any statistically significant differences either. In all groups C decreased continuously to about 90% of control. DISCUSSION. The results show that in patients with asthma or COPD, airway resistance remains virtually unchanged during surgery and anesthesia under halothane or enflurane anesthesia. With isoflurane, however, the resistance may rise by a slight but not statistically significant extent. Furthermore, marked bronchospastic reactions occurred in 2 patients in the isoflurane group. Thus, the three volatile anesthetics studied were not found to be unequivocally safe and effective in preventing increases in bronchomotor tone. However, pharmacodynamic effects other than those on respiration (e.g., cardiovascular actions, arrhythmogenic threshold, metabolism, toxicity) must additionally be taken into consideration.