Relationship between bispectral index (bis), sedation score and plasma concentration for evaluation of monitoring effect of bispectral index in midazolam sedation

ABSTRACT

PURPOSE: We examined the relationship between BIS, sedation score and plasma midazolam concentration to verify the usefulness of BIS to assess the patient's consciousness during sedation. PATIENTS AND METHODS: Twenty-five young, healthy adult volunteers participated in this clinical study. Midazolam was administered intravenously up to 0.08 mg/kg to induce unconsciousness and we monitored the patient's physiological and conscious status until complete recovery from sedation. BIS and sedation score were measured before sedation, 10, 20, 30 minutes after midazolam administration. Plasma midazolam concentration was measured 10 minutes after midazolam administration. BIS was measured using A-2000 BISTM monitor (Aspect Medical Systems, USA) and the degree of sedation was evaluated with the sedation score. RESULTS: The BIS score correlated with the sedation score (r = 0.676, P < 0.05). With the decreased plasma midazolam concentration, the correlation was better with sedation score(r = -0.656).Although BIS values did not correlate with calculated plasma concentration of midazolam (r = 0.467) at 10 minutes after midazolam administration, values after sedation were well distinguished from those before sedation. CONCLUSIONS: BIS is known for an effective predictor of patient's hypnotic state, and it is correlated with the sedation score. But, it doesn't always coincide with the clinical parameters of depth of sedation. So more attention is needed using BIS only during sedation, and it is advisable that the patient's consciousness is monitored with variable sedation score systems every several minutes.