Selection of the Proper Size of Laryngeal Mask Airway in Adults

Abstract

In Response: Voyagis et al. have proposed an alternative method of size selection for the laryngeal mask airway (LMA) based on a common misconception that the No. 3 is for females and the No. 4 for males. In fact, their new proposal strongly reflects current European practice, which is to use a No. 4 for normal adults and a No. 5 for large adults, and to use the No. 3 rarely. We consider, however, that further conclusive trials are required before the manufacturer's weight-based recommendations are altered. Judging the correct size of LMA can be difficult since the relationship between gender, weight, height, and upper airway geometry appears inconsistent [1]. No factors have yet been identified that give an easy measurement of potential pharyngeal volume directly correlating with appropriate LMA size, and certainly there is no known anatomical difference between the male and the female adult or child pharynx at a given weight. Some practitioners consider that the smaller sizes are satisfactory for spontaneous ventilation, since a less effective seal is required. However, too small a mask may still result in local soft tissue damage due to poor fit around the laryngeal inlet or misplacement into the upper esophagus or the glottic inlet. The problems associated with insertion of too large a mask (airway obstruction, airway reflex activation) are probably fewer than those associated with insertion of too small a mask. It is important not to attempt to compensate for leak around too small a mask by exceeding the recommended maximum inflation volumes. Overinflation of the cuff paradoxically produces loss of seal as the stiffening mask changes shape and is displaced away from the laryngeal inlet [2]. The correct/optimal cuff inflation for a given patient should always be checked by anterior neck auscultation and ballotment of the pilot balloon. While there is a low probability that the mask will be exactly the right size for a given patient, there is a high probability that appropriate size selection combined with optimal cuff inflation will produce a near-perfect fit [3]. Joseph R. Brimacombe, MB, ChB, FRCA Department of Anaesthesia and Intensive Care Cairns Base Hospital Cairns 4870, Australia Alison M. Berry, MB, ChB, FRCA Department of Anaesthesia Nambour Hospital Australia Robert C. Campbell, MB, ChB, FRCA, FHKAM Prince Philip Dental Hospital Hong Kong Chandi Verghese, MbCB, FRCA Royal Berkshire Hospital Reading, UK