Selection Criteria of Laryngeal Mask Airway Size in Infants and Children: Comparison between Body Weight and Age

Bahk, Jae Hyon; Park, Chong Doo

Abstract

BACKGROUND: In children, laryngeal mask airways (LMA) almost always show a tendency to come out of the mouth too much before and during inflating the cuff. We hypothesized that the selection criteria based on body weight seemed to be set too low or inappropriate in children.
METHODS
After IRB approval and informed consent from parents, pediatric patients (n = 63; 42 male, 21 female) weighing less than 20 kg, of ASA physical status 1 or 2, and in whom the use of an LMA was not contraindicated, were studied. LMAs were inserted by an experienced investigator and connected to a volume ventilator, and positive pressure ventilation was initiated. Inspiratory and expiratory tidal volume (V(T)) were measured to calculate the fraction of leakage (F(L), %) as ([inspiratory V(T)-expiratory V(T)]/inspiratory V(T)) 100. The larynx was inspected with a fiberoscope (FOB) located just proximal to the aperture bar. For each size of LMA, we divided each group into two subgroups depending on the body weight (4, 7 or 12 kg) and age (2, 9 or 30 months) and compared the FOB finding and F(L) between the two subgroups. In the other 16 patients, LMAs of two different sizes were applied successively to a patient, and its FOB grades were compared.
RESULTS
For size 1 LMAs (n = 22), the FOB finding and F(L) were not different between the subgroups. For size 1.5 LMAs (n = 20), patients weighing 7 to 10 kg or aged < 9 months had a better FOB finding (P = 0.007 and 0.0003) than patients weighing 5 to 7 kg or aged > 9 months. For size 2 LMAs (n = 21), FL was correlated with body weight (P < 0.001, r(2) = 0.448) and age (P < 0.001, r(2) = 0.424). In 8 patients of 5 to 7 kg, use of size 1 LMAs had a better FOB grade than that of size 1.5 LMAs (P = 0.031). In the other 8 patients of 10 to 12 kg, there was no difference of FOB grades between the size 1.5 and 2 LMAs.
CONCLUSIONS
For patients weighing 5 to 7 kg, the use of size 1 LMAs is recommended. Contrary to adults, a smaller LMA may have to be tried if an LMA size turns out to be inappropriate.