Does the Position of the Esophageal Entrance Determine the Cricoid Force Necessary to Occlude the Esophageal Lumen?

80 adult patients (40 women, 40 men) scheduled to undergo elective surgical procedures requiring general anesthesia and necessitating endotracheal intubation, were included in this study. Patients eligible for participation were aged 18-60 yrs., ASA physical status I or II and BMI < 30 kg/m2. Before anesthesia induction, CP was verified as follow: the cricoid cartilage was first identified and then held between the thumb and middle finger and the pressure was applied by the index finger with a force that could be tolerated by the patient. After loss of consciousness, four predetermined forces: 0 , 10 , 20 and 30 N were chosen in a randomized method. Therefore, after applying the predetermined force, a GT 20 F insertion trial was performed and two outcomes were considered: 1) Failure of GT insertion: effective CP. The next trials were not attempted. 2) Success of GT insertion: ineffective CP. The patient received a second attempt with increasing force to the next scale of force. If the attempt was effective (failure of GT insertion) , the relevant force is considered as the effective CP force. Same trial was repeated using 0, 10, 20 and 30 N respectively in in a randomized fashion for each patient. The cricoid force was standardized by reproducing 10, 20 and 30 N on a weighing scale prior to each application.

Four anesthesia providers (operators) participated in the study: The first operator performed CP in all patients with his back towards the video monitor; the second operator performed laryngoscopy using GVL and GT insertion trials and he was not aware about the nature of study ; the third operator assessed the effectiveness of the applied CP and determined the position of the esophageal entrance in relation to the glottis. The fourth operator, who was standing behind the second operator, signaled to the second operator to start attempt for each trial with the predetermined CP forces and to the first operator who applying CP to stop or continue accordingly.

In order to "blind" the second operator, a screen separated the laryngoscopist and the first operator applying CP, while the hand position for the CP was maintained, even when CP was not applied. Data collected before staring surgery.