Relationship between Bispectral Index and Observer’s Assessment of Awareness/Sedation Score during Onset of Sedation: Study with Midazolam, Propofol and Dexmedetomidine

Abstract

Introduction: Supplementation of sedation along with regional anaesthesia is a good practice to reduce anxiety and amnesia related to surgery. Monitoring the level of sedation is important to prevent excessive sedation. Propofol, midazolam and dexmedetomidine have been studied individually using either BIS index or OAA/S scale. Aim: To compare the time of onset of sedation for propofol, midazolam and dexmedetomidine using both Bispectral index monitor and simultaneous clinical assessment. Materials and Methods: Ninety patients of ASA Grade I and II, of either sex and aged 20-60 years scheduled for lower limb surgeries under spinal anaesthesia were randomly allocated into three groups (n=30). After subarachnoid block, when sensory block reached T-10 level, sedation was started using either propofol (Group P), midazolam (Group M) or dexmedetomidine (Group D) and level of sedation was assessed using BIS monitor and OAA/S scale. The dose of sedation was titrated to maintain BIS value between 60-75. Time to reach BIS value 70 and OAA/S score 3, intraoperative haemodynamic parameters, BIS value, OAA/s score and complications were recorded. Results: The Spearman’s correlation between time to reach BIS score 70 and OAA/S score 3 in Group P, Group M, Group D were 0.925, 0.211 and 0.512, respectively with p-values of 0.022, 0.133 and 0.163, respectively. The time to reach BIS score 70 was significantly less in Group P as compared to Group D and Group M (6.00±1.87 minutes v/s 7.97±1.62 minutes and 12.23±1.92 minutes). The time to reach OAA/S score 3 was significantly less in Group P as compared to Group M and Group D (6.27±1.92 minutes v/s 12.77±3.19 minutes and 15.20±2.69 minutes). Conclusion: A poor correlation was found between clinical observation and EEG based monitor while assessing sedation using dexmedetomidine and midazolam. On the other hand, a better correlation was observed when propofol was used. Onset of sedation was earlier with propofol compared to dexmedetomidine and midazolam.

Keywords

• correlation
• consciousness monitors
• spinal anaesthesia