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Nerve Stimulation Tips

The correct motor responses are extension or flexion of the foot or toes.
     •A proximal response (hip or thigh) may be a result of muscular contraction of the piriformis
      (too caudal and superficial puncture), or of the obturator internus muscle (too lateral puncture)
      and should not be accepted.
     •Obturator nerve stimulation (adduction of the thigh) is due to an excessively deep and medial
      puncture. This nerve runs in front of the parasacral plexus, in the same fascia plane.
     •Contraction of the gluteal muscles indicates too superficial needle placement.
     •In case of bone contact (sacral or iliac bone, near the sacroiliac joint, at the top of the greater
      sciatic notch), the needle should be re-directed more caudally on the line drawn. The needle
      tip should be no more than 20 mm deeper than the skin-bone contact with proper needle
      placement.

Extension of the Parasacral Block

The advantage of this block is the ability to achieve anesthesia of all three branches of the sciatic nerve (tibial, common peroneal and posterior cutaneous nerve of the thigh) through a single injection of local anesthetic [4]. Additionally, the superior and inferior gluteal branches as well as the branch to the quadratus femoris are also blocked.

Of note, with a "three in one" block, the obturator nerve is often spared. Thus, combining the parasacral block with the "3-in-1" block should result in anesthesia of the entire lower extremity. Finally, extension of the local anesthetic to pudendal plexus (especially to the pudendal nerve) can occur in up to 80% of the patients. One theoretical drawback of the approach is the possibility of urinary retention due to the proximity of the pelvic splachnic nerves (inferior hypogastric plexus).