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.

The influence of anesthetics on respiratory mechanics is of considerable clinical relevance. During anesthesia an increase in total respiratory resistance can complicate ventilation, particularly in cases with preexisting obstructive bronchial disease. Reduced compliance and a deterioration of resistance can favour or induce postoperative respiratory complications. It is also desirable that anesthetic drugs have as little influence as possible on compliance and resistance. In patients with primarily increase airways resistance, a bronchospasmolytic effect and an inhibition of respiratory secretion are positive.

Der Einfluß von Anästhetika auf die Atemmechanik ist von erheblicher klinischer Bedeutung. So kann — v. a. bei vorbestehenden obstruktiven Bronchialerkrankungen — während der Narkose eine Erhöhung des Atemwegswiderstands die Beatmung erschweren. Eine Abnahme der Compliance und eine Verschlechterung der Resistance können postoperative respiratorische Komplikationen begünstigen oder auslösen. Es ist also wünschenswert, daß zur Narkose verabreichte Pharmaka die Compliance und Resistance so wenig wie möglich beeinträchtigen. Ein bronchospasmolytischer Effekt und eine Hemmung der Atemwegsekretion sind bei Patienten mit primär erhöhten Atemwegswiderständen wünschenswert.

The effects of the inhalational anaesthetic, isoflurane, on two major parameters of respiratory mechanics--resistance and compliance--were studied in a total of 30 patients. With increasing inspiratory concentrations of isoflurane, resistance was measured in 5 spontaneously breathing patients using the oscillation method. In 16 mechanically ventilated patients resistance and compliance were calculated from airway pressure, gas flow, and tidal volume. In 9 patients with asthma or COPD the course of resistance and compliance was recorded intraoperatively. An increase in resistance of up to 117% of the initial volume occurred during spontaneous respiration, and was caused by a decrease in tidal volume. During mechanical ventilation with constant tidal volume, no definite changes in resistance or compliance were seen with increasing isoflurane concentrations. In the patients with elevated airway resistance there were only minor, statistically non-significant changes in resistance and compliance. The results show that the effects of isoflurane on respiratory mechanics do not differ from those of halothane or enflurane. Therefore, isoflurane may be considered appropriate for use in patients with impaired airway resistance.