Cricoid pressure impedes positioning and ventilation through the laryngeal mask airway.
OBJECTIVE
To assess the effect of cricoid pressure on the positioning of and ventilation through the laryngeal mask airway (LMA).


METHODS
In a double-blind, randomized design, the LMA was inserted with (CP[+] group, n = 20) or without double-handed cricoid pressure (CP[-] group, n = 20). Ventilation through the LMA was assessed by measuring expiratory tidal volume and judged as adequate when a mean expiratory tidal volume of > or = 10 ml.kg-1 could be obtained. The LMA position was examined by fibreoscopy. The position of the mask relative to the cricoid cartilage and the cervical spine was radiologically examined (n = 10 in each group).


RESULTS
Ventilation was adequate in all patients in the CP[-] group but in only five patients (25%) of the CP[+] group (P < 0.001). The glottis was visible fibreoptically below the mask aperture in all patients in the CP[-] group, but in only three patients in the CP[+] group (P < 0.001). Fibreoscopy showed that the mask was not inserted far enough in the remaining 17 patients of the CP[+] group. The reason for unsuccessful ventilation in the CP[+] group was excessive gas leakage (n = 2) and/or partial or complete airway obstruction (n = 13), which was noted fibreoptically. The radiographs showed that the tip of the mask in the CP[-] group was located below the level of the cricoid cartilage (C6 or C7 vertebra). The mask tip in the CP[+] group was above this level (C4 or C5 vertebra) (P < 0.01).


CONCLUSIONS
Cricoid pressure impedes positioning of and ventilation through the LMA.
Department of Anesthesiology, University of Occupational and Environmental Health, Japan, School of Medicine, Kitakyushu, Japan.
K
K
Aoyama
I
I
Takenaka
T
T
Sata
A
A
Shigematsu
D000328:Adult; D000368:Aged; D003413:Cricoid Cartilage / Q000502:physiology*; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D017214:Laryngeal Masks; D008297:Male; D008875:Middle Aged; D011312:Pressure; D012121:Respiration, Artificial