title: Electromyographic comparison of obturator nerve block to three-in-one block.
abstract: Obturator nerve block during spinal, epidural, or general anesthesia without muscle relaxants has been recommended for transurethral surgery to prevent thigh adductor muscle contractions during operative electrocautery. We investigated the effectiveness of direct obturator and 3-in-1 nerve motor blocks in 44 patients undergoing transurethral surgery during spinal anesthesia with isobaric bupivacaine. Patients were randomly assigned to receive 3-in-1 block with 40 mL (n = 13) or 50 mL (n = 11) of 1.5% lidocaine plus epinephrine, or direct obturator nerve block with 10 mL of 2% lidocaine plus epinephrine (n = 20). After both direct obturator and 3-in-1 blocks, compound muscle action potential (CMAP) testing of the obturator nerve was performed at 1-10-s intervals for 10 min. In patients given direct obturator nerve block (n = 20), CMAP amplitude decreased by 88.8 +/- 21% (mean +/- SD) from baseline. In contrast, 3-in-1 block reduced the evoked CMAP amplitude by 7.4 +/- 19% (P < 0.05). Peak lidocaine plasma levels of 1.6 +/- 0.2 micrograms/mL (range 1.0-2.8 micrograms/mL) were reached 60-90 min after the block in those patients receiving 50 mL of local anesthetic. The 3-in-1 technique fails to predictably result in effective motor block of the obturator nerve and thus may not prevent inadvertent thigh adductor muscle contractions during transurethral surgery. A direct approach to the obturator nerve is significantly more effective in producing motor block, and even when given in larger than recommended dosages it results in subtoxic peak plasma lidocaine concentrations.
authors.affiliation: Department of Anesthesiology, Yale University School of Medicine, New Haven, Connecticut 06510, USA.
authors.forename: P G
authors.initials: PG
authors.lastname: Atanassoff
authors.forename: B M
authors.initials: BM
authors.lastname: Weiss
authors.forename: S J
authors.initials: SJ
authors.lastname: Brull
authors.forename: A
authors.initials: A
authors.lastname: Horst
authors.forename: D
authors.initials: D
authors.lastname: Külling
authors.forename: R
authors.initials: R
authors.lastname: Stein
authors.forename: I
authors.initials: I
authors.lastname: Theiler
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000328:Adult; D000368:Aged; D000775:Anesthesia, Spinal; D001340:Autonomic Nerve Block; D004558:Electric Stimulation; D004576:Electromyography; D006801:Humans; D008012:Lidocaine / Q000097:blood; D008875:Middle Aged; D009043:Motor Activity / Q000187:drug effects; D009046:Motor Neurons / Q000502:physiology; D009119:Muscle Contraction / Q000187:drug effects; D009407:Nerve Block / Q000379:methods*; D009431:Neural Conduction; D009776:Obturator Nerve; D011446:Prospective Studies; D001743:Urinary Bladder / Q000601:surgery
chemical_list: D008012:Lidocaine