Do Laryngeal Mask Airway Devices Attenuate Liquid Flow Between the Esophagus and Pharynx? A Randomized, Controlled Cadaver Study

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Abstract
In this randomized, controlled cadaver study, we tested the hypothesis that the standard laryngeal mask airway (LMA) and flexible laryngeal mask airway (FLMA) attenuate liquid flow between the esophagus and pharynx.Fifty fresh cadavers were studied in four LMA groups. Ten female cadavers had a size 4 LMA and 10 had a size 4 FLMA; 10 male cadavers had a size 5 LMA and 10 had a size 5 FLMA; 5 male and 5 female cadavers functioned as controls. The chest was opened, and the infusion set of a pressure-controlled, continuous flow pump was inserted into the esophagus and ligated into place. Esophageal pressure was increased in 2-cm H2 O increments. Regurgitation pressure was the esophageal pressure at which fluid was first seen with a fiberoptic scope in the hypopharynx (control group) and above the cuff or within the bowl (LMA groups). This was performed in the LMA groups at 0-40 mL cuff volume in 10-mL increments. Mean (95% confidence interval) regurgitation pressure for the control group was 7 (6-8) cm H2 O and for the LMA groups combined was 19 (17-20) cm H2 O at 0 mL cuff volume, 47 (41-52) cm H2 O at 10 mL, 51 (44-55) cm H2 O at 20 mL, 52 (45-56) cm H2 O at 30 mL, and 52 (45-55) cm H2 O at 40 mL. The increase in regurgitation pressure with increasing cuff volume from 0 to 10 mL was statistically significant (P < 0.0001). Regurgitation pressure was higher for the LMA groups at all cuff volumes compared with the control group (P < 0.0001). There were no differences in regurgitation pressure among the LMA groups. We conclude that the correctly placed LMA and FLMA attenuate liquid flow between the esophagus and pharynx. Implications: We have shown, in cadavers, that the correctly placed standard and flexible laryngeal mask airways attenuate liquid flow between the pharynx and esophagus. (Anesth Analg 1999;88:904-7)