Continuous Sciatic Nerve Block: Posterior Approach
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The continuous sciatic nerve block is an advanced regional anesthesia technique and experience with the single-shot technique is recommended to ensure its efficacy and safety. The technique is quite similar to the single-shot injection, however, slight angulation of the needle caudally is necessary to facilitate threading of the catheter. Securing and maintenance of the catheter are easy and convenient. This technique can be used for surgery and postoperative pain management in patients undergoing a wide variety of lower leg, foot, and ankle surgeries. Perhaps the single most important indication for use of this block in our practice is for amputation of the lower extremity.
Proper positioning at the outset and maintenance of the position during the continuous sciatic nerve block is crucially important to allow for precise catheter placement. A slight forward pelvic tilt prevents the "sag" of the soft tissues in the gluteal area and significantly facilitates block placement. |
A standard regional anesthesia tray is prepared with the following equipment:
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The landmarks for a continuous sciatic block are the same as those in the single-shot technique:
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The continuous sciatic block technique is similar to the single-shot technique. With the patient in the lateral decubitus position and a slight forward pelvic tilt, the landmarks are identified and marked with the pen. After a thorough skin cleaning with an antiseptic solution, the skin at the needle insertion site is infiltrated with local anesthetic. The palpating hand is positioned around the site of needle insertion. It is used to fix the skin and shorten the skin-nerve distance. A 10-cm long continuous block needle is connected to the nerve stimulator and inserted at a perpendicular angle to the skin sphere. The opening of the needle should face distally (pointing toward the patient's foot) to facilitate catheter insertion. The initial intensity of the stimulating current should be 1.0-1.5 mA. TIP: It is useful to inject some local anesthetic intramuscularly to prevent pain on advancement of larger gauge and blunt-tipped needles typically used for this block. |
As the needle is advanced, twitches of the gluteus muscle are obtained first. Deeper needle advancement results in stimulation of the sciatic nerve. The principles of nerve stimulation and needle redirection are identical to those in the single-shot technique. After obtaining the appropriate twitches, the needle is manipulated until the desired response is seen or felt using a current of 0.2-0.5 mA. At this point, a bolus of local anesthetic is injected (20 mL) after negative aspiration for blood. This is followed by insertion of the catheter some 5-10 cm beyond the needle tip. The needle is then withdrawn back to the skin, while the catheter is advanced simultaneously to prevent its inadvertent removal. Before administering local anesthetic, the catheter is checked for inadvertent intravascular placement by a negative test for blood. |
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TIP: When insertion of the catheter proves difficult, lowering the angle of the needle can be helpful. 
A number of techniques to secure the catheter to the skin have been proposed. A benzoin skin preparation, followed by application of a clear dressing and a cloth tape is a simple and efficacious method. The infusion port should be clearly marked as "continuous sciatic block". |
Continuous InfusionContinuous infusion is always initiated after an initial bolus of dilute local anesthetic through the catheter. For this purpose, we routinely use 0.2% ropivacaine (15-20 mL). Diluted bupivacaine or l-bupivacaine are also suitable, but can result in more motor blockade. The infusion is maintained at 10 mL/hr or 5 mL/hr when a PCA dose is planned (5 mL). |
TIPS:
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 The course of the catheter (black arrows) and the dispersion of 2 mL of contrast solution (white arrow) injected through the catheter. |
Some general and specific instructions on possible complications and methods to use to avoid them.
| Infection | A strict aseptic technique is used |
| Hematoma | - Avoid multiple needle insertions, particularly in anticoagulated patients |
| Vascular puncture | - Vascular puncture is not common with this technique, however deep needle insertion should be avoided (pelvic vessels) |
| Local anesthetic toxicity | - Systemic toxicity after sciatic blockade is not common; it is important to avoid using large volumes and doses of local anesthetic because of the proximity of the muscle beds and the potential for rapid absorbtion |
| Nerve injury |
- A sciatic block has a unique predisposition for mechanical and pressure injury; nerve stimulation and slow needle advancement should be employed; local anesthetic should never be injected when the patient complains od pain or abnormally high pressure on injection is noted. When stimulation is obtained with current intensity of < 0.2mA, the needle should be pulled back to obtain the same response with current intensity of > 0.2mA before injecting local anesthetic - Advance the needle slowly when twitches of the gluteus muscle cease to avoid impaling the sciatic nerve on the rapidly advancing needle |
| Other | - Instruct the patient and nursing staff on the care of the insensate extremity; explain the need for frequent body repositioning to avoid stretching and prolonged ischemia (sitting) on the anesthetized sciatic nerve |
- Bridenbaugh PO., Wedel DJ: The Lower Extremity. Somatic Blockade . In Cousins, M.J., and Bridenbaugh PO (eds): Neuronal Blockade in Clinical Anesthesia and Management of Pain, 3rd edition. Philadelphia, Lippincott - Raven Publishers, 1998, pp 375-94.
- Chelly JE, Casati A, Fanelli G: Continuous peripheral nerve block techniques. An illustrated guide. London, Mosby International Limited, 2001.
- di Benedetto P, Casati A, Bertini L, Fanelli G, Chelly JE: 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.
- 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; 27:168-72.
- Klein SM, Greengrass RA, Grant SA, Higgins LD, Nielsen KC, Steele SM: Ambulatory surgery for multi-ligament knee reconstruction with continuous dual catheter peripheral nerve blockade. Can J Anaesth 2001; 48:375-8.
- Souron V, Eyrolle L, Rosencher N: The Mansour's sacral plexus block: an effective technique for continuous block. Reg Anesth Pain Med 2000; 25:208-9.
- Sutherland ID: Continuous sciatic nerve infusion: expanded case report describing a new approach. Reg Anesth Pain Med 1998; 23:496-501.
