Bispectral index response to cricoid pressure during induction of general anesthesia

BACKGROUND: Because the effects of cricoid pressure (CP) on BIS values have not been evaluated, this prospective study was designed to assess the BIS values after application of CP in adult patients during the routine induction of general anesthesia. METHODS: We randomly allocated 70 patients (ASA-I) aged 18-64 years, listed for elective surgery into two groups of cricoid (CP) and non-cricoid (nCP). In the cricoid group, bimanual cricoid pressure was performed after the induction of anesthesia and in the nCP group, simple placement of hands without exerting pressure was performed. Arterial blood pressure, heart rate and BIS were measured and recorded immediately before and after application of cricoid pressure, before laryngoscopy and intubation and then every one minute after intubation until 4 minutes. The data were compared between and within groups using the mixed-design analysis of variance. RESULTS: One minute after application of cricoid pressure and before laryngoscopy, BIS showed significantly higher value compared with the nCP group. Furthermore, one min after intubation, BIS values and arterial blood pressure increased significantly in both groups compared with the baseline values, but the increase in BIS value was more significant in CP group than nCP group. Moreover, BIS values increased significantly 2 minutes after intubation in CP group compared with nCP group. CONCLUSIONS: It was concluded that the application of CP in combination with laryngoscopy and intubation increases the BIS values, which show the inadequacy of anesthesia and hypnosis during the routine induction of anesthesia.