Calculated vs measured pharyngeal mucosal pressures with the laryngeal mask airway during cuff inflation:: assessment of four locations

We have compared calculated with measured pharyngeal mucosal pressures at four different locations on the surface of the laryngeal mask airway (LMA) during cuff inflation in 10 anaesthetized, paralysed adult patients. Microchip sensors were attached to a size 5 LMA at the following locations: the anterior and lateral side, tip and backplate. Pressures were recorded during inflation of the cuff from 0 to 40 ml in 5-ml increments. Calculated pressures were determined by subtracting in vivo from in vitro intracuff pressures. Calculated pressures were greater than measured pressures at cuff volumes of 5 mi or greater at all locations (P less than or equal to 0.003). The greatest mean calculated and measured pressures were 118 and 14 cm H2O, respectively. We conclude that measured mucosal pressures at the four locations tested were less than calculated pressures and less than capillary perfusion pressure.