BIS guided sedation with propofol during spinal anaesthesia: influence of anaesthetic level on sedation requirement

Background. In this prospective, clinical study we tested the hypothesis whether two different doses of spinal administered bupivacaine and accordingly, two different levels of spinal anaesthesia can affect the dose requirement of propofol during BIS guided sedation. Methods. Fifty women undergoing vaginal hysterectomy (high spinal group, HS) or transvaginal tape (TVT) procedure for urinary incontinence (low spinal group, LS) under spinal anaesthesia were enrolled to the study. In group HS, 17.5 mg and in group LS, 7.5 mg of hyperbaric bupivacaine were given intrathecally. After 15 min to obtain the appropriate level of spinal anaesthesia, propofol infusion was started at a rate of 100 mu g kg(-1) min(-1) to reach a BIS level of less than 75 (onset time), and titrated to maintain the BIS value between 65 and 75. Propofol infusion was stopped 45 min after placing the spinal to measure the time to reach a BIS level of 90 (recovery time). Results. Median anaesthetic level was T3 (T1-4) in the HS group and T10 (T9-11) in the LS group. In both the HS and the LS groups, onset time was 226 (47) vs 273 (48) s (P=0.001), recovery time was 234 (47) vs 202 (56) s (P=0.03), total dose of propofol was 2.17 (0.43) vs 3.14 (0.56) mg kg(-1) (P < 0.001), respectively. Conclusion. A high spinal block obtained with hyperbaric bupivacaine 17.5 mg was associated with a faster onset, delayed recovery and lower doses of propofol sedation compared with a low spinal block with 7.5 mg of the same drug.