Effects of using the posterior or anterior approaches to the lumbar plexus on the minimum effective anesthetic concentration (MEAC) of mepivacaine required to block the femoral nerve: a prospective, randomized, up-and-down study.
OBJECTIVE
To evaluate if psoas compartment block requires a larger concentration of mepivacaine to block the femoral nerve than does an anterior 3-in-1 femoral nerve block.


METHODS
Forty eight patients undergoing anterior cruciate ligament repair were randomly allocated to receive an anterior 3-in-1 femoral block (femoral group, n = 24) or a posterior psoas compartment block (psoas group, n = 24) with 30 mL of mepivacaine. The concentration of the injected solution was varied for consecutive patients using an up-and-down staircase method (initial concentration: 1%; up-and-down steps: 0.1%).


RESULTS
The minimum effective anesthetic concentration of mepivacaine blocking the femoral nerve in 50% of cases (ED(50)) was 1.06% +/- 0.31% (95% confidence interval [CI], 0.45%-1.68%) in the femoral group and 1.03% +/- 0.21% (95% CI, 0.6%-1.45%) in the psoas group (P = .83). The lateral femoral cutaneous and obturator nerves were blocked in 4 (16%) and 5 (20%) femoral group patients as compared with 20 (83%) and 19 (80%) psoas group patients (P = .005 and P = .0005, respectively). Intraoperative analgesic supplementation was required by 15 (60%) and 5 (20%) patients in the femoral and psoas groups, respectively (P = .01).


CONCLUSIONS
Using a posterior psoas compartment approach to the lumbar plexus does not increase the minimum effective anesthetic concentration of mepivacaine required to block the femoral nerve as compared with the anterior 3-in-1 approach, and provides better quality of intraoperative anesthesia due to the more reliable block of the lateral femoral cutaneous and obturator nerves.
D000328:Adult; D000779:Anesthetics, Local / Q000008:administration & dosage*; D016118:Anterior Cruciate Ligament / Q000601:surgery; D004305:Dose-Response Relationship, Drug; D004311:Double-Blind Method; D005260:Female; D005267:Femoral Nerve; D006801:Humans; D007267:Injections; D008160:Lumbosacral Plexus; D008297:Male; D008619:Mepivacaine / Q000008:administration & dosage*; D009407:Nerve Block / Q000379:methods*; D011446:Prospective Studies; D016658:Psoas Muscles
D000779:Anesthetics, Local; D008619:Mepivacaine