Continuous Sciatic Nerve Infusion

Patients with CRPS I and II, vascular insufficiency, and unilateral leg edema from many causes are frequently managed with lumbar epidural catheters. There are, however, inherent risks with long-term placement of an epidural catheter. The sciatic catheter can be an alternative in such patients. It can eliminate the risk of epidural abscesses, hematoma formation, or catheter erosion of the dura. The unilateral affected limb can be specifically treated without numbing or weakening the opposite limb. Thus, ambulation can be maintained. Contraindications include (1) anticoagulant therapy, (2) septicemia, (3) local infection, (4) recent injury at the site of injection to the nerve, and (5) inability of the patient to lie in the prone position.

Anatomy

The sciatic nerve is formed from the nerve roots of L4 to L5 and S1 to S3. After formation at the sciatic notch, the nerve passes through the gluteal region between the greater trochanter and the ischial tuberosity. In the buttocks, it runs posterior to the gemelli and the obturator internus. It lies anterior to the piriformis muscle as it descends to the thigh, as first described by Labat in 1923.™ My approach is based on the identification of the piriformis muscle and the placement of the catheter on the sciatic nerve in the gluteal region.

Technique

The patient is placed in the prone position. The gluteal regional ipsilateral to the affected side is sterilized and draped. The following landmarks are located by fluoroscopy: (1) posterior superior iliac spine, (2) greater trochanter, and (3) ischial tuberosity ( Fig. 16-5 ). A line is drawn connecting the posterior iliac spine and the greater trochanter. The midpoint is identified and a perpendicular line is drawn in a caudal direction. A second line is drawn from the greater trochanter to the ischial tuberosity. This line is divided into thirds. A line is drawn vertically from the medial third mark upward to intersect the other line. The point of entry is where the two lines meet ( Fig. 16-6 ). A skin wheal is raised at the site with a 25-G needle. A larger needle (16-G or 18-G) can pierce the skin. A blunt, 16-G, 7-inch needle is introduced perpendicularly, approximately 1 cm through the skin to reach the piriformis muscle ( Fig. 16-7 ). A 22-G needle is inserted subcutaneously and attached to a positive lead from the Medtronic test stimulator (or equivalent peripheral nerve stimulator). The Medtronic test stimulator should be set to deliver 6 to 8 V at 1 impulse per second. (If a peripheral nerve

Medtronic Quattro Lead Fluoro Image

Figure 16-5 Drawing depicting the landmarks to be identified by fluoroscopy. A, Posterior superior iliac spine. B, Greater trochanter. C, Ischial tuberosity. (From Racz G, Raj P, Lou L, et al: Posterior sacral approach to the sciatic nerve for continuous lidocaine infusion: A new technique. Presented at 1997ASA Annual Meeting, San Diego, CA.)

Figure 16-5 Drawing depicting the landmarks to be identified by fluoroscopy. A, Posterior superior iliac spine. B, Greater trochanter. C, Ischial tuberosity. (From Racz G, Raj P, Lou L, et al: Posterior sacral approach to the sciatic nerve for continuous lidocaine infusion: A new technique. Presented at 1997ASA Annual Meeting, San Diego, CA.)

Posterior Approach Sacrum

Figure 16-6 Surface landmarks and entry point of needle. A, Posterior superior iliac spine. B, Greater trochanter. C, Ischial tuberosity. D, Insertion site. (From Racz G, Raj P, Lou L, et al: Posterior sacral approach to the sciatic nerve for continuous lidocaine infusion: A new technique. Presented at 1997ASA Annual Meeting, San Diego, CA.)

Figure 16-6 Surface landmarks and entry point of needle. A, Posterior superior iliac spine. B, Greater trochanter. C, Ischial tuberosity. D, Insertion site. (From Racz G, Raj P, Lou L, et al: Posterior sacral approach to the sciatic nerve for continuous lidocaine infusion: A new technique. Presented at 1997ASA Annual Meeting, San Diego, CA.)

stimulator is used, the current should be adjusted from 3 to 0.5 mA at 1 impulse per second.) The needle is slowly advanced anteriorly until the piriformis muscle, which is identified by contrast solution, is twitching ( Fig. 16-8 ). The needle is further advanced until the piriformis muscle stimulation stops and foot twitching (dorsiflexion) is observed in the affected limb. A stimulating catheter is then inserted through the needle. The

Sciatic Nerve Catheter
Figure 16-7 Surface view of the catheter after placement. (From Racz G, Raj P, Lou L, et al: Posterior sacral approach to the sciatic nerve for continuous lidocaine infusion: A new technique. Presented at 1997ASA Annual Meeting, San Diego, CA.)
Sciatic Nerve Block Injection Notes

Figure 16-8 Fluoroscopic image of catheter with the piriformis muscle superficially and with contrast solution over the sciatic nerve.(From Racz G, Raj P, Lou L, et al: Posterior sacral approach to the sciatic nerve for continuous lidocaine infusion: A new technique. Presented at 1997ASA Annual Meeting, San Diego, CA.)

Figure 16-8 Fluoroscopic image of catheter with the piriformis muscle superficially and with contrast solution over the sciatic nerve.(From Racz G, Raj P, Lou L, et al: Posterior sacral approach to the sciatic nerve for continuous lidocaine infusion: A new technique. Presented at 1997ASA Annual Meeting, San Diego, CA.)

negative lead of the stimulator is attached to the distal connecting wire of the catheter. The catheter is passed to the level of the lesser trochanter for foot movement. The needle is then removed, and the catheter is attached to the hub connector. Confirmation of placement can be made with 3 mL of contrast dye via the catheter ( Fig. 16-9 ). An additional 3 mL of local anesthetic (ropivacaine 0.2%) may be injected, and stimulation of the sciatic nerve should cease.™ Ropivacaine 2%, 15 to 30 mL, is injected through an attached bacteriostatic filter in divided doses for immediate pain relief and nerve blockade. The constant infusion of ropivacaine 0.1% with fentanyl 5 ^g/mL may range from 4 to 10 mL/hour. Occasional bolus doses may be required and may be delivered by the patient through the pump with a bolus of 5 mL and a 30-minute lockout.™ The catheter may be connected to a drug infusion balloon (DIB) for outpatient care through home health services. This DIB delivers 4 mL/hour of the drug to the patient for 24 hours. (The volume of the DIB reservoir is 100 mL.)

Complications

Potential complications with the CI sciatic catheter include bleeding, infection, hematoma, intravascular injection, and residual dyschesia.

Figure 16-9 Fluoroscopic image of the catheter with contrast solution following the sciatic nerve sheath. (From Racz G, Raj P, Lou L, et al:

Posterior sacral approach to the sciatic nerve for continuous lidocaine infusion: A new technique. Presented at 1997ASA Annual Meeting, San Diego, CA.)

Figure 16-9 Fluoroscopic image of the catheter with contrast solution following the sciatic nerve sheath. (From Racz G, Raj P, Lou L, et al:

Posterior sacral approach to the sciatic nerve for continuous lidocaine infusion: A new technique. Presented at 1997ASA Annual Meeting, San Diego, CA.)

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