Predicting the optimal minimal cuff volume of the laryngeal mask airway from physical examination parameters

ABSTRACT

BACKGROUND: Head and neck anatomy affects the laryngeal mask airway (LMA) cuff volume. The purpose of this study was to identify physical parameters that can be standardized to predict LMA cuff volume and measure the optimal and minimal LMA cuff volume in adults. METHODS: The predictors of volume or pressure of the LMA cuff were investigated in 167 patients. Manufacturers recommend a maximal cuff pressure (MCP) (i.e., 40 ml for size 5, 30 ml for size 4), an optimal cuff volume (OCV) at a cuff pressure of 60 cmH2O, and a minimal cuff volume (MCV) just before audible air leakage. The physical parameters measured included height, weight, body mass index, modified Mallampati classification (MMP), neck circumference, neck length, and thyro-mental distance. Data were analyzed by stepwise multilinear analysis. RESULTS: The regression equations (REs) were as follows: OCV (1.2 + [0.1 × height] + [0.5 × neck length]); MCV for men (−35.7 + [0.25 × height] + [0.7 × neck length] − [4.1 × MMP]); and MCV for women (−42.5 + [0.27 × height] + [0.75 × neck length] − [2.5 × MMP]). The mean values were as follows: MCP > 200 cmH2O, minimal cuff pressure < 20 cmH2O, OCV of 24.7 ml for men and 15.9 ml for women, and MCV of 12.1 ml for men and 7.1 ml for women. CONCLUSIONS: LMA cuff volume is estimated from the patient's height, neck length, and MMP. The RE for calculating the MCV shows a high correlation with height, neck length, and MMP.