Comparison of the effects of thoracic and lumbar epidural anaesthesia on induction and maintenance doses of propofol during total i.v. anaesthesia

Background. In this randomized, double-blind study, the effects of thoracic and lumbar epidural anaesthesia on the induction doses (IDs) and maintenance doses (MDs) of propofol during bispectral index (BIS) guided total i.v. anaesthesia were compared. Methods. Fifty-four patients (three groups, n=18 each) undergoing urological surgery in lumbotomy position were studied in Groups T (Th7-8) and L (L3-4), epidural anaesthesia was performed with initial doses obtaining sensorial block at Th4 (SD 1) followed by 7 ml h(-1) infusion; Group C received no epidural anaesthesia intraoperatively. The ID (BIS < 45) and MD (BIS: 40-50) of propofol and recovery (BIS > 80) and extubation times were recorded. Results. The volume to obtain a block was significantly lower in Group T than in Group L [10.7 (1.5) vs 14.7 (1.0) ml; P < 0.001]. ID was significantly higher in Group C compared with that in Groups T and L [2.16 (0.15) vs 1.33 (0.19) vs 1.46 (0.14) mg kg(-1), respectively; P < 0.001] with no significant difference between Groups T and L. For MD, there were significant differences between all groups [3.82 (0.9) vs 5.8 (1.32) vs 9.21 (0.55) mg kg(-1) h(-1) in Groups T, L, and C, respectively; P < 0.001]. For recovery and extubation times, Group T < Group L < Group C [1.4 (0.5) vs 3.3 (1.2) vs 8.1 (0.99) min, respectively, P < 0.001; and 3.4 (0.52) vs 5.8 (1.32) vs 11.4 (1.96) min, respectively; P < 0.0001]. Conclusions. Similar segments blocked with epidural anaesthesia have resulted in similar ID. During maintenance, identical amounts of bupivacaine applied from different levels have resulted in different MD of propofol. The concentration of the epidural anaesthesia appears to play a more important role than the applied amount of the local anaesthetic.