| Abstract |
The clinical complication of bronchospasm can present during general anesthesia, especially during the induction and after endotracheal intubation. It is the clinical feature of airway hyperreactivity and has the potential to be a life-threatening condition.1 The incidence of perioperative bronchospasm is estimated to be 0.2%. However, it can occur in 2-9% of patients with asthma or chronic obstructive disease. 5,6
Stepwise algorithms have been published for the management of patients with bronchospasm during general anesthesia. The use of volatile anesthetics in order to increase the depth of anesthesia and achieve brochodilation is suggested.1 Specifically, the use of sevoflurane and isoflurane is proposed, as bronchodilation action of these drugs are documented in animal and human studies. Data on desflurane action on respiratory resistances are inconsistent.
The purpose of this clinical trial is to clarify the effect of volatile anaesthetics to respiratory resistances, sevoflurane, isoflurane and desflurane, to patients with healthy lungs. The patients were randomized in 6 groups: isoflurane 1 ΜAC, isoflurane 1.5 MAC, sevoflurane 1 ΜΑC, sevoflurane 1.5 ΜΑC, desflurane 1 MAC and desflurane 1.5 MAC. In order to demonstrate the bronchodilation properties of these agents, induction in anaesthesia was performed with pentothal, an anesthetic drug who has been related to increased bronchial tone. Total inspiratory resistance (Rrs), minimal resistance (Rmin) and effective resistance (DRrs) were measured every 5 minutes for a total period of 30 minutes. The method of end-inspiratory occlusion was used.
In total, 53 patients were randomized to the trial. 12 patients received isoflurane 1 MAC, 10 patients received sevoflurane 1 ΜΑC and 10 patients desflurane 1 MAC. 7 patients received isoflurane 1,5 MAC, 7 patients sevoflurane 1,5 MAC and 6 patients received desflurane 1,5 MAC. The randomization of the patients in groups with high concentration of volatile was terminated prematurely because low values of BIS (<30) were monitored.
Initially the increase of bronchial tone due to pentothal was documented (p<0.001). The results showed that all three volatile agents with concentration of 1 MAC exhibit clinically significant bronchodialtion. A significant decrease in total respiratory resistance was documented. Analyzing the components of total resistance, we concluded that the decrease of effective resistance(DRrs) was the main reason for bronchodilation.This finding represents that time constant in homogeneities within the lung and the elastic behavior of the respiratory system was improved. The isoflurane concentration 1,5 MAC was also found to decrease the respiratory resistance. Sevoflurane and desflurane concentration 1,5 MAC did not significantly affected respiratory resistances. Analyzing the parameters of total resistance of the desflurane group, the minimum resistance significantly increased while the elastic resistancewas decreased. The increase of the minimum resistance was attributable to the high density of the used gas mixture.
In conclusion isoflurane, desflurane and sevoflurane in concentration of 1 MAC and isoflurane 1,5 MAC produced bronchodilation. Desflurane and sevoflurane 1,5 MAC neither produced bronchodilation nor bronchospasm. Comparing the parameters of respiratory resistance to the desflurane group 1,5 MAC
significantly increased minimum resistance was documented. The use of desflurane in higher concentration of 1MAC should be carefully administered in patients with hyperreactive airways, and especially in children.
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