Nerve Stimulation

Correct: Stimulation of the sacro-lumbar muscles or quadratus lumborum muscle:
This is a usual response which is obtained at the beginning of the needle insertion progression and after the passage of the skin. However, this response is inconstant, especially among old patients in our experiment. It is necessary to continue needle insertion. We suggest that the distance form the cessatin of these contrac-tions to the deepest needle insertion should not exceed 30 mm. When the stimulation of the lumbar plexus is not obtained by this depth, the needle is re-directed 5° more medially. The lumbar plexus stimulation is re-cognized by obtaining stimulation of the femoral nerve (contraction of the quadriceps and sartorius muscles).

Incorrect: Stimulation of the obturating nerve or an obturating root:
Contraction of the interior thigh muscles as detected by the assistant's hand positioned on the internal thigh often suggests a too median position of the needle. It is necessary to reinsert the needle more laterally with an angle of 5° to the initial insertion.
Stimulation causing an adduction of the thigh and a rise of the kneecap: This can signify stimulation of a root which detects a too median position of the needle. In this case, the needle is redirected 5° more laterally.
Stimulation causing an inflection of the thigh: Stimulation of the muscle psoas or a nerve supply to the psoas muscle (stimulation persisting with an intensity < 1.5 mA). In this case assuming that the depth of the needle insertion is appropriate, we suggest to reorient the needle 5° cephalad or caudal.
Stimulation of the sciatic nerve: It alerts to a too caudal puncture or a stimulation of the lumbo-sacral plexus in a too median position. Again, the landmarks should be re-checked.

Test dose:
It is essential to use a test dose with this block. We suggest 3 ml of lidocaine 2% with adrenaline to rule out IV or intraspinal injection. The injections must always be administered slowly and in divided doses.

Onset time

Variable between 5 and 10 minutes.