Paravascular lumbar plexus block: block extension after femoral nerve stimulation and injection of 20 vs. 40 ml mepivacaine 10 mg/ml

The goal of this prospective randomized study was to assess the extension of the "three-in-one" paravascular lumbar plexus block after femoral nerve stimulation and injection of 20 vs. 40 ml mepivacaine 10 mg/ml. Three-in-one blocks were achieved in 12 of 39 (31%) patients given 20 ml of 1% mepivacine (group 1), and 17 of 41 (41%) patients given 40 ml (Group 2) of the same solution (n.s.). The level of successful blockade at each nerve did not differ between groups. The femoral nerve was blocked in 92% vs. 93% of patients in groups 1 and 2, respectively; the obturator nerve in 62% vs. 78%; and the lateral cutaneous femoral nerve in 41% vs. 44%. We conclude that femoral nerve stimulation is effective in faciliating blockade in the femoral nerve but not the obturator or lateral cutaneous femoral nerve with the tested solution and volumes, and therefore not particularly effective for achieving complete 3-in-1 blockade. Within the clinically relevant range of 20-40 ml, the volume of mepivacaine 10 mg/ml does not appear to influence the extent of blockade.