RESPIRATORY MECHANICS, GASTRIC INSUFFLATION PRESSURE, AND AIR LEAKAGEOF THE LARYNGEAL MASK AIRWAY

A potential risk of the laryngeal mask airway (LMA) is incomplete mask seal, which causes air leakage or insufflation of air into the stomac h. The objective of the present study was to assess respiratory mechan ics, quantify air leakage, and measure gastric air insufflation in pat ients ventilated via the LMA. Thirty patients were studied after induc tion of anesthesia but prior to any surgical manipulations. After the insertion of the LMA, patients were ventilated with increasing tidal v olumes until one of the three following end points were reached: 1) ga stric air insufflation, 2) airway pressure >40 cm H2O, or 3) limitatio n of further increase in tidal volume by air leakage. The following va riables were determined: inspired volume (V-I), expired volume (V-E), maximum inspiratory pressure (P-max), airway pressure at gastric infla tion (P-infl), respiratory time constant (RC), compliance (C), resista nce (R), and leakage fraction (F-I). Respiratory mechanics were in the physiological range. Gastric insufflation occurred in 27% of the pati ents at inspiratory pressures between 19 and 33 cm H2O. Air leakage of more than 10% was evident at inspiratory pressures between 25 and 34 cm H2O. The end point of 40 cm H2O airway pressure was reached in only three patients. We conclude that the LMA is not better in preventing airway pressure transmission to the esophagus than a conventional face mask. However, a high F-L is associated with reduced gastric air insu fflation.