The nerve stimulation technique versus the loss of resistance technique for the posterior approach to lumbar plexus block: a randomized, prospective, observer-blinded, pilot study.

BACKGROUND: This prospective, randomized, observer-blinded, pilot study compares the effects of the nerve stimulation guidance technique (NS) with the loss of resistance technique (LOR) on readiness for surgery during the posterior approach to lumbar plexus block.

METHODS: Thirty ASA status I-III patients who were 18-85 years old and who were undergoing hip fracture repair were enrolled. After parasacral sciatic nerve block, patients were randomly allocated to receive a continuous posterior lumbar plexus block using nerve stimulation (n=15) or a continuous psoas compartment block using the loss of resistance technique (n=15) with 20 ml of 1.5% mepivacaine. A blinded observer monitored for sensory and motor block onsets every 5 minutes. We defined readiness for surgery as complete numbness to the pinprick test and complete motor block on the surgical side. If incomplete, the lumbar plexus block was supplemented with 10 mL of 1.5% mepivacaine through the catheter before surgery. Intraoperative fentanyl or general anesthesia requirements, pain scores, local anesthetic consumption, morphine requirements for breakthrough pain and side effects were monitored.

RESULTS: The mean time to readiness for surgery was 12±6 min Group NS and 22±6 min in Group LOR (P=0.03). Three patients in Group NS and 9 patients in Group LOR required additional boluses of local anesthetic through the lumbar plexus catheter before surgery (P=0.113).

CONCLUSION: Nerve stimulation allowed faster readiness for surgery than loss of resistance. Nevertheless, the two techniques seem to be comparable in terms of local anesthetic consumption, morphine requirements and pain scores.