Dose response study of lidocaine 1% for spinal anaesthesia for lower limb and perineal surgery

Abstract

Purpose: To compare the sensory and motor block produced by three different volumes of intrathecal lidocaine I% and thereby determine the appropriate volume to administer for surgery of the lower limbs and perineum. Methods: Forty-eight patients scheduled for perineal or lower limb surgery were randomly assigned to receive 4, 6 or 8 ml lidocaine 1% intrathecally. The onset, spread, duration and regression of analgesia and motor block and side effects were evaluated (by a blinded observer whenever possible). Results: The maximum cephalad spread in the 6 ml (T8 ± 3) and 8 ml (T4 ± 1.7) groups were higher than the 4 ml group (T12 ± 2.2, P < 0.01). In the 4 ml group, six patients (33%) did not achieve analgesia to T12 and four (22%) did not have complete motor blockade. Patients given 8 ml had longer duration of block (duration at T12: 104 ± 23 vs 60 ± 24, 67 ± 14 min, P < 0.01; 8 ml vs 4, 6 ml) and slower recovery times (sensory recovery: 188 ± 27 vs 142 ± 27, 157 ± 28 min, P < 0.01; 8 ml vs 4, 6 ml). Two patients (18%) from the 8 ml group and one (5%) from the 6 ml group had transient hypotension. Conclusion: Four millilitres intrathecal lidocaine 1% is adequate for perineal surgery but for lower limb procedures, 6 ml is more appropriate as it consistently provides sensory analgesia above L1 dermatome and complete motor block. Eight ml gives an Unnecessarily high block with higher incidence of hypotension.