Ovid: Peripheral Nerve Blocks: A Color Atlas

Continuous Sciatic Blocks

A. Parasacral Approach

Elizabeth Gaertner

Patient Position: Sims position.

Indications: Anesthesia and postoperative analgesia for total knee arthroplasty; above and below the knee amputation; popliteal fossa surgery (e.g., tumors, cysts); cancer surgery of the lower limb; and major leg, ankle, and foot surgery with a thigh tourniquet.

Volume and Infusion Rate: A 15 to 20 mL ropivacaine 0.75% bolus followed by an infusion of 7 mL/hour or a patient-controlled analgesia (PCA) ropivacaine 0.2% with a basal rate of 5 mL/hour, bolus 5 mL, lockout time 45 minutes.

Needle Size and Catheter: An 18-gauge, 100-mm plastic introducing cannula with a stimulating short beveled stylet or insulated Tuohy needle and a 20- or 21-gauge catheter.

Anatomic Landmarks: The posterior superior iliac spine (PSIS) and the ischial tuberosity (IT). With this approach, the sciatic nerve is approached at the level of the greater sciatic foramen, where it leaves the pelvis with the pelvic fascia medial, piriformis muscle posterior, and obturator internus muscle lateral.

Approach and Technique: A line is drawn between the PSIS and the lowest point of the IT. The site of needle insertion is three fingerbreadths caudal to the PSIS on the PSIS–IT line. The insulated Tuohy needle with the bevel oriented laterally, connected to a nerve stimulator (2.0 mA, 2 Hz, 0.1 ms) is introduced perpendicularly at a 10° caudal and lateral angle (Fig. 29-1). The position of the needle is adjusted to produce a motor response corresponding to a stimulation of the sciatic nerve, either the common peroneal nerve (inversion of the foot or dorsiflexion of the foot and toes) or the tibial nerve (eversion of the foot or plantar flexion of the foot and toes) with a current less than 0.5 mA. After negative aspiration for blood, local anesthetic is slowly injected with repeated aspiration for

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blood. The catheter is introduced 3 to 5 cm beyond the needle tip. The introducer needle is removed, and the catheter is secured in place with Steri-Strip (3M, St. Paul, MN) and covered with a transparent dressing.

Figure 29-1. The insulated Tuohy needle connected to a nerve stimulator is introduced perpendicularly.

Tips

The site of the introduction of the needle is just below the PSIS.
A motor response at the level of the hip or thigh should not be considered sufficient because it can be produced by direct muscle stimulation or can correspond to a nerve stimulation of the piriformis or the obturator internus muscle (needle too lateral). Conversely, a stimulation of the obturator nerve (adduction of the thigh) indicates that the needle is too anterior and medial. Finally, a gluteal muscle contraction indicates that the position of the needle is too superficial.
In case of bony contact (sacral or iliac bone, near the sacroiliac joint, at the top of the greater sciatic notch), the needle needs to be withdrawn and reintroduced more caudally on the PSIS–IT line. The depth at which the bone was contacted is an important indicator. Since the nerve is approached on the top of the greater sciatic foramen, where the sciatic nerve leaves the pelvis, the needle tip should be introduced no more than an additional 20 mm.
This block is often associated with a block of the obturator nerve (>90%) because of the anatomic proximity of the sacral plexus and the obturator nerve. An extension of the block to the pudendal plexus is also possible, especially to the pudendal nerve (up to 80%). This explains the associated unilateral anesthesia of the perineum. Finally, the proximity of the pelvic splanchnic nerves and the terminal branches of the sympathetic trunks and the inferior hypogastric plexus may explain associated urinary retention.

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Although no specific serious complications have been reported with this technique, caution should be exercised to avoid damaging the pelvic vessels and organs because of the proximity of the sacral plexus and the pelvic vessels and organs.
In the recovery room, a radiograph may be performed after injection of a contrast agent to verify the position of the parasacral catheter.
This is the only approach to the sciatic nerve that allows consistent blocking of the tibial, common peroneal, and posterior cutaneous nerves of the thigh and also the superior and inferior gluteal nerves and the quadratus femoris nerve.
Compared with a single parasacral block, the Tuohy needle is oriented caudally and laterally to facilitate the placement of the catheter.

Suggested Readings

Birnbaum K, Preschera A, Hessler S, et al. The sensory innervation of the hip joint—an anatomical study. Surg Radiol Anat 1997;19:371–375.

Bruell P. Sciatic nerve block: parasacral approach. Reg Anesth Pain Med 1998;23:78.

Cuvillon P, Ripart J, Jeannes P, et al. Comparison of the parasacral approach and the posterior approach, with single- and double-injection techniques, to block the sciatic nerve. Anesthesiology 2003;98(6):1436–1441.

Jochum D, Iohom G, Choquet O, et al. Adding a selective obturator nerve block to the parasacral sciatic block: an evaluation. Anesth Analg 2004;99:1544–1549.

Mansour NY, Bennetts FE. An observational study of combined continuous lumbar plexus and single shot sciatic nerve blocks for post-knee surgery analgesia. Reg Anesth 1996;21:287–291.

Morris GF, Lang SA, Dust WN, et al. The parasacral sciatic nerve block. Reg Anesth 1997;22: 223–228.

Ripart J, Cuvillon P, Nouvellon E, et al. Parasacral approach to block the sciatic nerve: a 400-case survey. Reg Anesth Pain Med 2005;30:193–197.

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B. Gluteal Approaches

Rama Joshi

1. Gluteal Approach

Patient Position: Lateral (Sims position).

Indications: Anesthesia and postoperative analgesia for major surgery at the level of and below the knee, including the foot and ankle.

Needle Size and Catheter: 18-gauge, 100-mm insulated Tuohy needle and a 20-gauge catheter.

Volume and Infusion Rate: 15 to 20 mL of 0.5% ropivacaine followed by either a continuous infusion of 6 to 10 mL/hour or a PCA with a basal infusion rate of 5 mL/hour, bolus of 5 mL, and a 30-minute lockout time 0.2% ropivacaine.

Anatomic Landmarks: The greater trochanter and the ischial tuberosity (IT). At the level of the thigh, the sciatic nerve runs toward the popliteal fossa (sciatic line), lying on the posterior surface of the adductor magnus, within the posterior medial compartment of the thigh. The septum intermusculare femoralis mediale and a reinforcement of the posterior fascia of the adductor magnus muscle limit this compartment.

Approach and Technique: The greater trochanter and the IT are identified and marked, and a line is drawn between these two points. The site of introduction of the needle is the midpoint (Fig. 29-2A). At this level, a skin depression can be palpated, representing the groove between the biceps femoris and semi-tendinous muscles. After proper local skin infiltration, the Tuohy needle with the tip oriented cephalad and connected to a nerve stimulator (1.5 mA, 2 Hz, 0.1 ms) is introduced through the skin at a 90° angle (Fig. 29-2B). The Tuohy needle is advanced until the sciatic nerve is stimulated with either an eversion of the foot or dorsiflexion of the foot and extension of the toes

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(common peroneal nerve) or an inversion or plantar flexion of the foot and toes (tibial nerve). The needle position is adjusted to maintain the same motor response with a current 0.5 mA. After negative aspiration for blood, 15 to 20 mL of local anesthetic solution is slowly injected with repeat aspiration for blood every 5 mL. A 20-gauge catheter is introduced through the Tuohy needle no more than 3 to 4 cm beyond the needle tip. Finally, the needle is removed, and the catheter is secured with Steri-Strip and covered with a transparent dressing.

Figure 29-2. A: Landmark; B: Placement of the needle.

2. subgluteal approach

Approach and Technique: From the midpoint of this latter line, a perpendicular line is extended caudally for 4 cm (Fig. 29-2B). This point represents the site of introduction of the needle.

Tips

The gluteal approaches, as compared with other sciatic approaches (classic posterior approach of Labat, high lateral, mediofemoral), reduces the risk for vascular puncture and reduces the risk for misplacement or dislocation of the catheter after surgery.
This block is usually performed in combination with a single lumbar, femoral, or saphenous block to satisfy the surgical and tourniquet requirements. Less frequently, a combination of a gluteal continuous block and a continuous lumbar plexus or femoral block is indicated (anterior cruciate ligament [ACL] involving the use of hamstring graft) for postoperative analgesia.
This approach is also particularly helpful in obese patients.
Furthermore, compared with the classic posterior approach of Labat, this approach is mostly painless because the needle is introduced into the groove between the biceps femoris and semi-tendinous muscles.
With this approach, the catheter can be easily maintained in place with minimal risk for dislocations.
If the femur is contacted, the needle needs to be withdrawn and redirected medially.

Suggested Readings

di Benedetto P, Casati A, Bertini L. Continuous subgluteus sciatic nerve block after orthopedic foot and ankle surgery: comparison of two infusion techniques. Reg Anesth Pain Med 2002;27:168–172.

di Benedetto P, Casati A, Bertini L, et al. Postoperative analgesia with continuous sciatic nerve block after foot surgery: a prospective, randomized comparison between the popliteal and subgluteal approaches. Anesth Analg 2002;94:996–1000.

McMinn RMH, Hutching RT, eds. Color atlas of human anatomy. Chicago: Year Book Medical Publishers, 1977:296–297.

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C. Lateral Approach

Jacques E. Chelly

Patient Position: Supine, with the knee slightly flexed and a pillow under the leg and ankle.

Indications: Anesthesia and postoperative analgesia for major surgery below the knee, at the ankle, and the foot.

Needle Size and Catheter: 18-gauge, 100-mm insulated Tuohy needle and a 20- or 21-gauge catheter.

Volume and Infusion Rate: 30 to 40 mL 0.5% ropivacaine followed by 8 to 10 mL/hour 0.2% ropivacaine.

Anatomic Landmarks: The top of the patella, the groove between the biceps femoris, and the vastus lateralis muscles (Fig. 29-3A).

Figure 29-3. A: Landmark; B: Placement of the needle and catheter; C: Dressing.

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Approach and Technique: The leg is rotated slightly medially. Next, the groove between the biceps femoris and the vastus lateralis muscles is identified and marked (groove line). A vertical line is drawn from the top of the patella (patella line). The site of needle insertion is located 10 cm cephalad from the intersection of the groove and the patella lines. The insulated Tuohy needle connected to a nerve stimulator (1.5 mA, 2 Hz, 0.1 ms) is introduced 30° posteriorly (Fig. 29-3B). With the bevel oriented cephalad, a local contraction of either the femoris biceps or the vastus lateralis is observed. Within 4 to 8 cm, the local contractions disappear as the needle enters the popliteal fossa. Within an additional 0.5 to 1.0 cm, the sciatic nerve is stimulated and produces either an eversion of the foot or a dorsiflexion of the foot and extension of the toes (common peroneal nerve) or an inversion of the foot or a plantar flexion and flexion of the toes (tibial nerve). The position of the introducer needle is adjusted to maintain the same motor response with a current of 0.5 mA. Then, after negative aspiration for blood, the local anesthetic solution is slowly injected with negative aspiration for blood every 5 mL (Fig. 29-4). The catheter is advanced 2 to 3 cm beyond the needle tip. The introducer needle is removed, and the catheter is secured with Steri-Strip and covered with a transparent dressing (Fig. 29-3C).

Tips

If the procedure fails to identify the sciatic nerve, the needle is withdrawn to the level of the skin and reinserted 45° posteriorly.
If the needle contacts the femur, it is necessary to withdraw the needle to the skin and reorient the needle 30° posteriorly.
This high lateral approach minimizes the risk for vascular puncture, since the popliteal vessels originate from the deep femoral vessels usually below the site of introduction of the needle.

Figure 29-4. Diffusion of local anesthetic solution after a lateral approach to the sciatic move.

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This approach allows the sciatic nerve to be reached before its division into the common peroneal and the tibial nerves, as indicated by the ability to stimulate either branch of the sciatic nerve with minimum displacement of the needle.
In most cases, a block of the saphenous or femoral nerve is also required to complete the anesthesia of the medial aspect of the leg and ankle and to allow the patient to tolerate a tourniquet placed at the thigh (femoral nerve block) or the calf (saphenous nerve).