Abstract ID: A36
Abstract Title: CT-scan guided parasacral sciatic nerve block: modified surface landmarks for safety.
Poster Type: Poster
ABSTRACT BODY
Introduction: The parasacral approach to the sciatic nerve is an effective although deep block. The risk of entering the pelvis and puncturing the bowels constitutes a limitation in the mind of many anesthesiologists. Traditional surface landmarks are not evident as ischial tuberosity is not always easy to palpate. We present here modified surface landmarks based on measurements obtained in block performed under CT-scan guidance.
Methods : Five patients scheduled for sciatic block in order to diagnose a possible involvement of the sciatic nerve in the gluteus maximus pain. The block was performed on alert patients placed in prone position. The prelocation of the parasacral sciatic nerve ipsilateral to the painful side was guided by transverse CT-scanning. After determination of the puncture site (position of a surface lead button that projects on the sciatic nerve in a posterior and anterior plane), an insulated stimulating needle was inserted perpendicular to all cutaneous planes and advanced toward the nerve under CT-scan guidance. When the tip of the needle got very close to the nerve, the nerve stimulator was switched on (2 mA, 2Hz, 0.1ms) searching for motor responses of the foot. After confirming acceptable motor responses at 0.3-0.5mA, 20 mL of lidocaine 2% plus epinephrine were administered. Transverse CT scan imaging was taken after injection of lidocaine. Distance from posterior superior iliac spine (PSIS) level to puncture site, distance from posterior midline to the puncture site, distance from puncture site to nerve were directly acquired during CT-scanning.
Results: Three women and two men were studied. In average, they were 54 y/o, their height 169 cm and weight 69 kg. All blocks were complete blocks. Plantar flexion was elicited in three and foot inversion in two patients at a depth averaging 8.5 cm. The puncture site was situated 7 cm from PSIS in 4 patients 8 cm in one patient but constantly situated 5.5 cm lateral to the midline prolonging the natal cleft. Bowels were noted right medial to the nerve (Figure).
Discussion: These results suggest that the puncture site for parasacral sciatic nerve block is situated 7 cm below PSIS and 5.5 cm lateral to posterior midline. From this point, the redirection caudad or cephalad of the needle has to be kept in paramedian plane to prevent bowels puncture. Never redirect medially the needle.
Reg Anesth 1997; 22: 223-8.
ATTACHED FILES
A36_Sur meas fig.doc
Reg Anesth Pain Med 2004; 29(2):A36