Selection of the Proper Size of Laryngeal Mask Airway in Adults

Abstract

To the Editor: We wish to add our experience to the views of Verghese and Brimacombe [1] with regard to the relationship between the size of the laryngeal mask airway (LMA) and the incidence of air leak during positive pressure ventilation. Given that the dimensions of hypopharynx and larynx differ between males (M) and females (F) [2], we designed a prospective study to evaluate the patient's gender as an indicator for the selection of the appropriate size of LMA. Three hundred adult patients ASA physical status I or II were randomly divided into two groups. In the first group (n = 144, M/F = 67/77), the selection of the size of LMA was based on patient's gender, i.e., M: size 5; F: size 4; whenever an LMA could not be inserted, a smaller size (M: 4; F: 3) was used. In the other (control) group (n = 156, M/F = 74/82), the size of the LMA was selected by the body weight [3], i.e., over 90 kg: size 5; 70-90 kg: 4; and less than 70 kg: 3. All patients underwent positive pressure ventilation by using a Kontron Registered Trademark ABT 4300 ventilator (inspiratory/expiratory ratio = 1/3, frequency = 12 breaths/min), and the peak inspiratory pressure at which an air leak occurred was measured. When applying the gender-related method of selection, the use of LMA size 5 was eightfold increased (odds ratio = 7.8) since it was also used in nonobese patients Table 1. The mean peak inspiratory pressure at which leak occurred was greater using the gender-related method (27.9 +/- 3.6 cm H2 O) compared with the conventional weight-related method (22.6 +/- 4.8 cm H2 O) (P < 0.001).Table 1: Demographic Characteristics, DistributionWe conclude that the airtightness of the airway is improved by applying the simple gender-related formula for selection of the size of the LMA. Gregory S. Voyagis, MD Peter G. Batzioulis, MD Pelagia N. Secha-Doussaitou, MD Department of Anesthesiology Laikon General Hospital Athens, Greece