[Parasacral sciatic nerve block: new approach].

INTRODUCTION: The usual technique of parasacral sciatic nerve block seems an approach easily achieved, however, the ischial tuberosity is difficult to palpate. [1] The purpose of the study was to propose new skin landmarks improved by an anatomical and clinical study.

PATIENTS AND METHODS: Three cadaver dissections made previously have shown that our skin landmarks appeared correct. Twenty consenting patients, ASA I to III, proposed for lower limb surgery, were included in this descriptive and prospective study. The patient was positioned in the Sim position. A line was drawn between the anterior superior iliac spine (ASIS) and the sacral hiatus (HS). A second line was drawn from the posterior superior iliac spine (PSIS) and perpendicular to the 1st line. The puncture site (P) was the intersection of these two lines. At point P, the needle was inserted perpendicularly to the skin. Twenty milliliters of a mixture of lidocaine 2% and bupivacaine 0.5% were injected after obtaining an appropriate motor response. Sensory block was assessed 30 minutes after performing block in the territories of the tibial nerve, peroneal and posterior cutaneous of thigh. Parasacral block success was defined by the extension of sensory block in the territories of the tibial and fibular nerves. Complications were noted. An independent observer recorded: the time to perform blocks, the depth of the sciatic nerve, the number of needle redirections, the quality of nerve block of patient, and patient satisfaction.

RESULTS: The success rate was 95% (19 of 20 cases). Seventy-five percent of blocks were performed by residents on training. The point P was determined at the first attempt. The time required to perform the block was 3 + or - 1.7 min and depth of the sciatic nerve was 81 + or - 17 mm. The rate of patient satisfaction was 85%. One vascular puncture was observed. We have not noted other complications.

DISCUSSION: Access to the sciatic foramen appears to be facilitated by these new surface landmarks, which are simple and reliable. Our new skin landmarks seemed valid for all morphotypes.