Size of the laryngeal mask airway for normal adults

Voyagis 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. 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 oesophagus 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.