Transgluteal / Anterior Approach

Indications: surgery on the knee, tibia, ankle, and foot

Landmarks: greater trochanter, superior posterior iliac spine, and the midline between the two

Nerve stimulation: twitch of the hamstring, calf, foot, or toes at 0.2-0.5 mA current

Local anesthetic: 15-20 mL

Indications: surgery on the knee, tibia, fibula, ankle, and foot

Landmarks: femoral crease, femoral artery

Nerve stimulation: twitch of the foot or toes at 0.2-0.5 mA

Local anesthetic: 15-20 mL

Figure 1-2:The course and motor innervation of the sciatic nerve.

Figure 1-3: Anatomy of the sciatic nerve at the subgluteal location. (1) sciatic nerve. (2) nerve branch to the gluteus muscle. (3) ischial bone. (4) greater trochanter. (5) posterior superior iliac spine. (6) gluteus muscle.

Distribution of Blockade

Figure 1-4: Sensory innervation of sciatic nerve and its terminal branches.

Figure 1-5: The patient is positioned in a lateral oblique position with the dependent leg extended and the leg to be blocked flexed in the knee.

A sciatic nerve block results in anesthesia of the skin of the posterior aspect of the thigh, hamstring, and biceps femoris muscles; part of the hip and knee joint; and the entire leg below the knee with the exception of the skin of the medial aspect of the lower leg (Figure 1-4). Depending on the level of surgery, the addition of a saphenous or femoral nerve block may be required to provide coverage for this area.

Single Injection Sciatic Nerve Block

Equipment

A standard regional anesthesia tray is prepared with the following equipment:

Sterile towels and gauze packs

One 20-mL syringe containing local     anesthetic

A 3- to 5-mL syringe plus 25-gauge     needle with local anesthetic for skin     infiltration

A 10-cm, 21-22 gauge short-bevel     insulated stimulating needle

Peripheral nerve stimulator

Sterile gloves; marking pen

Landmarks and Patient Positioning

The patient is in the lateral decubitus position tilted slightly forward (Figure 1-5). The foot on the side to be blocked should be positioned over the dependent leg so that elicited motor response of the foot or toes can be easily observed.

Landmarks for the posterior approach to a sciatic blockade are easily identified in most patients. A proper palpation technique is important to adhere to because the adipose tissue over the gluteal area can obscure these bony prominences. The landmarks are outlined with a marking pen:

1. Greater trochanter (Figure 1-6)

2. Posterior superior iliac spine (PSIS) (Figure 1-7)

3. Needle insertion point 4 cm distal to the midpoint between landmarks 1 and 2 (Figure 1-8)

A line between the greater trochanter and the PSIS is drawn and divided in half. Another line passing through the midpoint of this line and perpendicular to it is extended 4 cm caudal and marked as the needle insertion point.

Technique

After skin disinfection, local anesthetic is infiltrated subcutaneously at the needle insertion site. The operator should assume an ergonomic position to allow precise needle maneuvering and monitoring of the responses to nerve stimulation.

The fingers of the palpating hand should be firmly pressed on the gluteus area to decrease the skin to nerve distance. Also, the skin between the index and middle fingers should be stretched to allow greater precision during block placement (Figure 1-9). The palpating hand should not be moved during the entire procedure. Even small movements of the palpating hand can change the position of the needle insertion site because of the highly movable skin and soft tissues in the gluteal region. The needle is introduced perpendicular to the spherical skin plane. Initially, the nerve stimulator should be set to deliver a current intensity of 1.5 mA to allow for the detection of both twitches of the gluteal muscles as the needle passes through tissue layers and stimulation of the sciatic nerve.

As the needle is advanced, twitches of the gluteal muscles are observed first. These twitches merely indicate the needle position is still too shallow. Once the gluteal twitches disappear, brisk response of the sciatic nerve ensues (hamstring, calf, foot, or toe twitches). After an initial stimulation of the sciatic nerve is obtained, the stimulating current is gradually decreased until twitches are still seen or felt at 0.2 to 0.5 mA. Typically, this occurs at a depth of 5 to 8 cm. At this low current intensity, any observed motor response is from the stimulation of the sciatic nerve, rather than direct muscle stimulation (false twitch). After negative aspiration for blood, 15 to 20 mL of local anesthetic is injected slowly. Any resistance to the injection of local anesthetic should prompt cessation of the injection and withdrawal of the needle by 1 mm before reattempting to inject. Persistent resistance to injection should prompt complete needle withdrawal and flushing to ensure the patency of the needle before reattempting the procedure.

Troubleshooting

Table 1-1 lists some common responses to nerve stimulation and the course of action to take to obtain the proper response.

Block Dynamics and Perioperative Management

This technique may be associated with patient discomfort because the needle passes through the gluteus muscles. Adequate sedation and analgesia are important to ensure the patient is still and tranquil. Typically, we use midazolam 2 to 4 mg after the patient is positioned and alfentanil 500 to 750 µg just before the needle is inserted. A typical onset time for this block is 10 to 25 minutes, depending on the type, concentration, and volume of local anesthetic used. The first signs of onset of the blockade are usually a report by the patient that the foot "feels different" or an inability to wiggle the toes.

 Table 1-1 Some Common Responses to Nerve Stimulation and Course of Action for                    Proper Response

Continuous Lumbar Plexus Block

Adequate experience with the single-injection technique is necessary to ensure efficacy and safety of the continuous block. The procedure is quite similar to the single-injection procedure; however, a slight angulation of the needle caudally is necessary after obtaining the nerve response to facilitate threading of the catheter. This technique can be used for surgery and postoperative pain management in patients undergoing a wide variety of lower leg, foot, and ankle surgeries. In our practice, perhaps the single most important indication for use of this block is for amputation of the lower extremity.

Equipment

A standard regional anesthesia tray is prepared with the fol- lowing equipment:

Sterile towels and gauze packs

Two 20-mL syringes containing local anesthetic

Sterile gloves, marking pen, and surface electrode

A 3- to 5-mL syringe plus 25-gauge needle with local anesthetic for skin infiltration

Peripheral nerve stimulator

Catheter kit (including a 8- to 10-cm large-gauge stimulating needle and catheter)

Kits come in two varieties based on catheter construction: nonstimulating (conventional) and stimulating catheters. During the placement of a nonstimulating catheter, the needle is advanced first until appropriate twitches are obtained. Then 5 to 10 mL of local anesthetic or other injectate (e.g., D5W) is injected to "open up" a space for the catheter to facilitate its insertion. The catheter is threaded through the needle until approximately 3 to 5 cm is protruding beyond the tip of the needle. The needle is withdrawn, the catheter secured, and the remaining local anesthetic is injected via the catheter. Stimulating catheters are insulated and have a filament or core that transmits current to a bare metal tip. After obtaining twitches via the needle, the catheter is advanced with the nerve stimulator guidance while the motor response of the foot, calf, or toes is maintained. With the catheter technique, motor response of ≤1.0 mA is adequate. If the motor response is lost, the catheter can be withdrawn until it reappears, and the catheter is then readvanced while maintaining the response. This method requires that only nonconducting solution be injected through the needle (e.g., dextrose) prior to catheter advancement.

Landmarks and Patient Positioning

Proper patient positioning at the outset and maintenance of this position during performance of a continuous sciatic nerve blockade is crucial for precise catheter placement. The patient is placed in the lateral decubitus position similar to the single-injection block. A slightly forward pelvic tilt prevents "sagging" of the soft tissues in the gluteal area and significantly facilitates block placement. The landmarks for a continuous sciatic block are the same as those in the single-injection technique (Figure 1-8):

1. Greater trochanter

2. Posterior superior iliac spine

3. Needle insertion site 4 cm caudal to the midpoint of the line between landmarks 1 and 2

Technique

Figure 1-10: nsertion of the catheter for continuous sciatic nerve block.

The continuous sciatic block technique is similar to the single-injection technique. With the patient in the lateral decubitus position and tilted slightly forward, the landmarks are identified and marked with the pen. After a thorough cleaning of the area with an antiseptic solution, the skin at the needle insertion site is infiltrated with local anesthetic. The palpating hand is positioned and fixed around the site of needle insertion to shorten the skin to nerve distance. A 10-cm continuous block needle is connected to the nerve stimulator and inserted perpendicularly to the skin (Figure 1-10). The initial intensity of the stimulating current should be 1.0 to 1.5 mA.

As the needle is advanced, twitches of the gluteus muscle are observed first. Deeper needle advancement results in stimulation of the sciatic nerve. The principles of nerve stimulation and needle redirection are identical to those for the single-injection technique. After obtaining the appropriate twitches, the needle is manipulated until the desired response (twitches of the hamstrings muscles or foot) is seen or felt using a current of 0.5-1.0 mA. The catheter should be advanced 3-5 cm beyond the needle tip. The needle is withdrawn back to the skin level, and the catheter advanced simultaneously to prevent inadvertent removal of the catheter. The catheter is checked for inadvertent intravascular placement and secured to the buttock using an adhesive skin preparation such as benzoin or Dermabond, followed by application of a clear occlusive dressing. The infusion port should be clearly marked "continuous nerve block."

Continuous Infusion

Continuous infusion is always initiated after administra- tion of an initial bolus of dilute local anesthetic through the needle or catheter. For this purpose, we routinely use 0.2% ropivacaine 15 to 20 mL. Diluted bupivacaine or levobupivacaine are suitable but can result in more pronounced motor blockade. The infusion is maintained at 5 to 10 mL/h when a patient-controlled regional analgesic dose (5 mL every 60 minutes) is planned.

Complications and How to Avoid Them

Table 1-2 lists some general and specific instructions on possible complications and methods used to avoid them.