[Peripheral nerve stimulator for femoral nerve block. Is it really necessary?]

There are several methods to locate the femoral nerve in the perivascular inguinal space, being the most common the use of a peripheral nerve stimulator. This study aimed at evaluating femoral nerve block performed with peripheral nerve stimulator as compared to the loss of resistance to air technique, both by single injection or with catheter insertion.

Sixty patients undergoing femoral nerve blocks were divided in four homogeneous groups (GA, GB, GC, GD). Thirty blocks were performed with single injection technique: 15 with disposable 21G needle (GA) and 15 with insulated needle adapted to the peripheral nerve stimulator (GC). The remaining 30 blocks were divided in 15 blocks performed with intravenous catheter (GB) and 15 with long Contiplex catheter (GD). All femoral nerve blocks were performed in the perivascular inguinal space. Perifemoral space was identified after the second loss of resistance to air (iliac fascia, GA and GC), and with 0.3 to 0.4 mA stimuli from peripheral nerve stimulator (GB and GD). The following parameters were evaluated: time to blockade performance, presence or absence of paresthesias or disesthesias, puncture difficulties and failures.

There were no paresthesias or disesthesias. There have been two failures (p < 0.26) in the same GA patient, and two puncture difficulties due to recent and multiple blocks on the same site. There have been no significant efficacy differences between loss of resistance and peripheral nerve stimulator methods. Time for peripheral nerve stimulator block was longer (p < 0.001).

Whereas the peripheral nerve stimulator is more widely used in the inguinal region, our study has shown that the loss of resistance to air technique is an effective and feasible alternative.