Canadian Journal of Anesthesia, Vol 43, 1035-1040, Copyright © 1996 by Canadian Anesthesiologists' Society

ARTICLES

Cricoid pressure impedes positioning and ventilation through the laryngeal mask airway

K Aoyama, I Takenaka, T Sata and A Shigematsu
Department of Anesthesiology, University of Occupational and Environmental Health, Japan, School of Medicine, Kitakyushu, Japan.

PURPOSE: 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). CONCLUSION: Cricoid pressure impedes positioning of and ventilation through the LMA.

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