135 children ASA I or II undergoing different surgeries scheduled to undergo procedures requiring general anesthesia and endotracheal intubation were enrolled in this protocol.Following applying of ASA standard monitoring and placement of peripheral iv cannula maximal preoxygenation was achieved (end-tidal oxygen > 90%), and anesthesia was induced with propofol 2 mg/kg, fentanyl 1-1.5 µg/kg and sevoflurane in oxygen/air mixture. Cisatracurium or rocuronuim was given to maintain muscle relaxation. Gentle mask ventilation was begun following an oropharyngeal airway placement. CP was applied by the same anesthesiologist in all patients with his back toward the video monitor. 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 to facilitate the manual ventilation. After loss of consciousness, the force was increased to the predertmined force. The applied cricoid force in successive patients was determined by the response of the previous patient within the same group, using Biased coins up-and-down method in each group. The adjustment force interval was 1 N. Successful insertion of the GT with the adjusted force, was considered ineffective CP and the force was increased 1 N for next patient. Conversely, an unsuccessful GT insertion with the adjusted cricoid force was considered effective CP, and the force was decreased 1 N for the next patient. Tracheal intubation was performed with the appropriate size endotracheal tube while using the same cricoid force, initially tested, and the surgical procedure was begun.
Because the cricoid force in children has not been quantified, clinicians wrongly used the 'adult' force. it has been found that the use of the adult force can result in compression and distortion of the child's airway and can lead to airway obstruction and difficult intubation. Based on known measurements of the cricoid surface area in children, the theoretical forces necessary to occlude the esophageal entrance have been calculated . These forces were found to be much less than the recommended adult force and much less than the forces that distort the airway as reported previously. Based on these theoretical calculations, the current study was performed to determine the effective cricoid force for pediatric groups (group 1 and group 2).