[Minimal effective dose of spinal hyperbaric bupivacaine for adult anorectal surgery: a double-blind, randomized...

The aim of the study was to find minimal effective dose of spinal hyperbaric bupivacaine for adult anorectal surgery.

The study included 93 adult consecutive patients admitted for anorectal operations. Dural puncture was made before surgery in the sitting position at L3-L4 or L4-L5 with 25-26G Tamanho spinal needle (BBraun, Germany) and different volumes of hyperbaric bupivacaine (Marcaine Spinal Heavy 0.5%, AstraZeneca) were injected over 2 minutes: group 1 (n=17) 1.5 ml, group 2 (n=38) 1.0 ml, group 3 (n=38) 0.8 ml. After sitting for 10 minutes patients were asked to lie down and surgery was started. Following variables were assessed: rate of success, level and duration of sensory and motor block, time to voiding and ambulation, complications, consumption of analgesics, quality of anesthesia according to the patient and medical staff.

Groups were comparable in demographics. No case of failure was registered but 4 patients (10.5%) in the group 3 received supplemental i/v fentanyl to treat tension in the abdomen intraoperatively. Level of sensory block in groups 1, 2, 3 was 10.4+/-1.7, 7.013+/-2.2, 6.7+/-1.9 dermatomes, respectively (p<0.0001 ANOVA; p<0.0001 group 1 vs 2, group 1 vs 3, p=1.0 group 2 vs 3, Bonferroni). Extent of motor block was 2-3 scores according to the Bromage scale in 70.5% of group 1 cases, compared to 0-1 score in 97.3% of group 2 and 92.1% of group 3 cases. Median (range) duration of motor block in groups 1, 2, 3 was 90 (0-120), 0 (0-90), and 0 (0-60) min, respectively (p<0.0001 ANOVA; p<0.0001 group 1 vs 2, group 1 vs 3, p=0.13 group 2 vs 3, Bonferroni). Time of ambulation was 181.5+/-41.5, 136.6+/-32.2 and 123.0+/-45.9 min, respectively (p<0.0001 ANOVA; p<0.001 group 1 vs 2, p<0.00001 group 1 vs 3, p=0.43 group 2 vs 3, Bonferroni). There was no significant intergroup difference in time to urinate; retention developed in 20.4% of total cases. No difference was found in morphine consumption, 64.5% of cases did not require rescue analgesics. Quality of anesthesia was stated as excellent by the anesthesiologist and surgeon in all groups. However, quality was rated as excellent by patient in the operating room in groups 1, 2, 3: 58.8, 94.7, and 86.8%, respectively (p=0.003), on day 1 postoperatively: 76.5, 92.1, and 97.4%, respectively (p=0.023); by nursing staff: 82.4, 100, and 97.4%, respectively (p=0.019). Lower rates in group 1 were due to extensive motor block. In conclusion, a minimal recommended dose of spinal hyperbaric bupivacaine for anorectal surgery is 4-5 mg; a dose of 7.5 mg is excessive due to prolonged sensory and motor block.