Risk of Pulmonary Aspiration under General Inhalation Anesthesia with Laryngeal Mask Airway / 대한마취과학회지

BACKGROUND: The laryngeal mask airway(LMA) is a new type of airway that has many advantages compared with the tracheal tube, but its potential problem might be pulmonary aspiration. This study therefore was designed to investigate the risk of pulmonary aspiration during general anesthesia using LMA. METHODS: We studied 101 patients who received general inhalation anesthesia with LMA and mechanical positive pressure ventilation for gynecological operations. Methylene blue was poured into the oropharynx after the LMA was placed, and the presence or absence of the dye staining of the larynx, tracheal and main stem bronchi with fiberoptic bronchoscope through the LMA shaft lumen was observed one and/or two hour(s) after LMA placement. RESULTS: In two out of 101 patients there was staining of the larynx with methylene blue dye. One was one hour after and the other was stained two hours after LMA placement. CONCLUSIONS: Dye staining of the larynx suggests that even mechanical positive pressure ventilation with LMA placement have the risk of pulmonary aspiration. Therefore LMA is contraindicated if the stomach is not emptied.

The Effects of N2O on the Changes in the Cuff Pressure of the Laryngeal Mask Airway during General Inhalation Anesthesia / 대한마취과학회지

The laryngeal mask airway(LMA) is an alternative to tracheal intubation, especially in out-patient surgery or securing emergency airway. Several studies show that N2O diffuses into the cuffs of endotracheal tubes and increases the cuff pressures. Because LMA also has an air-filling cuff, the cuff pressure of LMA may be increased during general anesthesia with N2O. The purpose of this study was to evaluate the effects of LMA on the changes in the cuff pressure of the LMA during general inhalation anesthesia. In this study, we measured the cuff pressure of LMA after administration of 0%(group A), 50%6(group B), 60%(group C) or 66.7%o(group D) N2O with the air-inflated cuffs, and also measured the cuff pressure of LMA after administration of 66.7% N2O(group E) with the 66.7% N2O-inflated cuffs during general inhalation anesthesia. In group A, there was no significant cuff pressure change throughout the study period. In group B, C and D, the cuff pressures gradually increased as time elapsed and the more increased the concentration of N2O, the more increased the cuff pressures. In group E, the cuff pressure abruptly decreased until the first five minute, but recovered gradually and slightly increased than the baseline value for the rest of the measurement period. These findings demonstrate that N2O administration during general inhalation anesthesia significantly increases the cuff pressure of LMA in a concentration- and time-related fashion with the air-inflated cuffs but not with the N2O-inflated cuffs, and suggest that such increases may result in ischemia on cuff-related laryngeal area, and N2O-inflated cuffs may prevent increasing the cuff pressure of LMA.