Association between bispectral index and age and use of sedative drugs in high spinal anaesthesia

Abstract

Objectives A prospective, randomized, double-blind study using bispectral index values to objectively quantify the sedative effect of high spinal anaesthesia in patients stratified according to age, and to determine whether sedative drugs are associated with additional adverse respiratory and haemodynamic effects in older patients. Methods Patients who were electively scheduled for lower limb or abdominal surgery were recruited and allocated into one of three groups according to their age and whether midazolam and fentanyl were used: younger (20–40 years); and older (61–80 years) with or without midazolam and fentanyl intravenous infusion. Results The study recruited a total of 90 patients ( n = 30 per group). Intraoperative bispectral index values were significantly lower than preoperative values in all groups. Patients in the older age group had significantly lower intraoperative bispectral index values than younger patients. Older patients were significantly more likely to experience respiratory depression (arterial oxyhaemoglobin saturation <90%) than younger patients. Conclusions The sedative effect of high spinal anaesthesia is greater in older patients than in younger patients, with an increase in respiratory instability.