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

Background. In this prospective, clinical study we tested thehypothesis whether two different doses of spinal administeredbupivacaine and accordingly, two different levels of spinalanaesthesia can affect the dose requirement of propofol duringBIS guided sedation. Methods. Fifty women undergoing vaginal hysterectomy (high spinalgroup, HS) or transvaginal tape (TVT) procedure for urinaryincontinence (low spinal group, LS) under spinal anaesthesiawere enrolled to the study. In group HS, 17.5 mg and in groupLS, 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 µg kg^–1min^–1 to reach a BIS level of less than 75 (onset time),and titrated to maintain the BIS value between 65 and 75. Propofolinfusion was stopped 45 min after placing the spinal to measurethe time to reach a BIS level of 90 (recovery time). Results. Median anaesthetic level was T3 (T1–4) in theHS group and T10 (T9-11) in the LS group. In both the HS andthe 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 doseof 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 bupivacaine17.5 mg was associated with a faster onset, delayed recoveryand lower doses of propofol sedation compared with a low spinalblock with 7.5 mg of the same drug.