Landmark-based approach

As for all regional anesthetic procedures, after checking that emergency equipment is complete and in working order, intravenous access, ECG, pulse oximetry, and blood pressure monitoring are established. Asepsis is observed.

The patient is placed in the supine position with the operator standing on the side to be blocked, at the level of the patient’s thigh. The needle insertion point is infiltrated with local anesthetic using a 25-G needle. A 50-mm 21-G insulated needle is oriented in a 45° cephalad and posterior orientation lateral to the palpated femoral artery at the inguinal crease (Fig. 26.7). The stimulating current is set at 1.0 mA, 2 Hz, and 0.1 ms.

Figure 26.7 Femoral nerve block technique. The needle is inserted adjacent to the femoral artery at the level of the inguinal crease. The needle is oriented in a 45° cephalad orientation.

The needle is advanced slowly until the appropriate muscle response is obtained: quadriceps contraction with resultant rhythmic patellar movement. The needle position is adjusted while decreasing the current to 0.35 mA with maintenance of the muscle response. Initial stimulation currents should be less than 1.0 mA if the patient has a fractured shaft of femur, as muscle twitches can be painful. Frequently a ‘pop’ can be felt as the needle penetrates the fascia (usually at 2–3 cm), although this is often less obvious in elderly patients.

Incremental injections of local anesthetic are made with repeated aspiration. Fifteen milliliters of local anesthetic will adequately block the femoral nerve, but if a three-in-one block is required then use 30 mL in an adult (Figs 26.8 and 26.9). If a quadriceps contraction is not elicited, the needle is aimed 10° laterally. Contraction of the sartorius muscle is not appropriate; the needle should be oriented 10° laterally from this point and inserted slightly deeper. Multi-injection techniques have been described.

Figure 26.8 Axial T1-weighted MR image showing the spread of contrast to the obturator nerve and vessels inferomedial to the psoas muscle. This perhaps would account for the three-in-one block that can occur with this technique. It appears that the contrast spreads in a fascial plane between the psoas and iliacus muscles and ‘spills over’ the psoas on to its inferomedial border where the obturator nerves run. 1; Psoas muscle; 2; contrast; 3; iliacus muscle; 4; obturator nerve.

Figure 26.9 Sagittal T1-weighted MR image of spread after injection of 30 mL of contrast. Note similarity of spread in Figure 26.8. Note that contrast covers the femoral nerve and spreads laterally toward the anterior superior iliac spine, where the lateral cutaneous nerve of the thigh lies. The contrast did not reach the roots of the lumbar plexus. 1: Anterior superior iliac spine; 2: psoas muscle; 3: iliacus muscle; 4: contrast spread; 5: injection site.

Ultrasound-guided approach

The ultrasound machine and block tray should be placed in positions which allow the operator to simultaneously scan the patient and take items from the block tray with minimal movement. This setup may take some forethought but is a worthwhile exercise, and will facilitate successful regional anesthesia.

The operator stands or sits on the side to be blocked, and with the patient in a supine position (Fig. 26.10). The skin is disinfected with antiseptic solution and draped. A sterile sheath (CIVCO Medical Instruments, Kalona, IA, USA) is applied over the ultrasound transducer with sterile ultrasound gel (Aquasonic, Parker Laboratories, Fairfield, NJ, USA). Another layer of sterile gel is placed between the sterile sheath and the skin. The infrainguinal region is scanned with a 6–13 MHz linear transducer. The ultrasound screen should be made to look like the scanning field. That is, the right side of the screen represents the right side of the field. Adjustable ultrasound variables such as scanning mode, depth of field, and gain are optimized.

Figure 26.10 Global view of the block field for the ultrasound-guided femoral nerve block.

A transverse image of the femoral nerve, artery, and vein is obtained (Fig. 26.4). The femoral nerve is kept in the centre of the field of view. The needle entry site is at the lateral-most end of the linear transducer. A 23-gauge needle is advanced under real-time ultrasound guidance and local anesthetic is deposited along the needle entry path. A free hand technique rather than the use of a needle guide is preferred. A 21-GA × 50-mm insulated needle (B. Braun, Bethlehem PA) is inserted parallel to the axis of the beam of the ultrasound transducer, with the bevel facing the transducer (Fig. 26.11). The needle is attached to sterile extension tubing, which is connected to a 20 mL syringe and flushed with local anesthetic solution to remove all air from the system. It is then introduced at the lateral-most end of the transducer and visualized along its entire path to the femoral nerve (Fig. 26.12). It is important not to advance the needle without good visualization. This may require needle or ultrasound transducer adjustment.

Figure 26.11 Ultrasound transducer and needle positioning during ultrasound-guided femoral nerve block. Note the needle orientation in the same plane as the ultrasound beam.

Figure 26.12 Real-time imaging of needle insertion for the ultrasound-guided femoral nerve block. Notice the needle shaft marked with arrows and the needle tip (N) in close proximity to the femoral nerve. N: needle tip; FA: femoral artery; FV: femoral vein; FN: femoral nerve.

Once the needle has approached the femoral nerve, 1–2 mL of local anesthetic may be injected to confirm correct needle placement. Local anesthetic appears as a hypoechoic image. Correct needle placement is confirmed by observing solution surrounding the femoral nerve (Fig. 26.13). Should this not occur, the needle may need to be repositioned, and the procedure repeated. Following confirmation of correct needle placement, 10–20 mL of local anesthetic solution can be injected to achieve blockade.

Figure 26.13 Transverse ultrasound image at the level of the inguinal crease showing local anesthetic spread using an 8–14 MHz linear ultrasound transducer. LA: local anesthetic; FA: femoral artery; FV: femoral vein; FN: femoral nerve.

Continuous technique

Continuous femoral block is similar to the single-shot technique. The insertion point, however, is slightly above the inguinal crease to avoid the catheter kinking at the femoral crease. As with other continuous nerve block techniques, the initial dose of local anesthetic is usually injected and only then is the infusion of a more dilute local anesthetic initiated. Once the local anesthetic is injected, the catheter is carefully inserted some 5 cm beyond the tip of the needle while keeping the needle immobile. When the catheter meets resistance at the tip of the needle, the needle may be repositioned at a different angle, or rotated to facilitate advancement of the catheter. Once the catheter is inserted, the needle is withdrawn while simultaneously advancing the catheter to prevent its dislodgment. The catheter is secured with a transparent dressing. Ultrasound-guided versus neurostimulation-assisted catheter placement is associated with similar postoperative analgesia but decreased procedure-related pain and performance time. Ultrasound can be used postoperatively to assess continued correct positioning of the catheter.

Saphenous nerve block landmark-based approach

The saphenous nerve is a branch of the femoral nerve and provides cutaneous sensation to the medial aspect of the ankle and a variable portion of the medial foot. It is probably most consistently blocked by femoral block; however, it can be blocked separately at the level of the knee.

The saphenous nerve passes within the adductor canal beneath the sartorius muscle, and then curves around the posteriomedial aspect of the knee to divide into branches along the anteriomedial aspect of the proximal tibia (Fig. 26.14).

Figure 26.14 Cadaver structures illustrating anatomy relevant to saphenous nerve block at the knee. 1: Tibial tuberosity; 2: patella; 3: semi-tendinosus and semi-membranosus muscles; 4: saphenous nerve branches; 5: long saphenous vein.

Several techniques for block of the saphenous nerve have been described. The tibial tuberosity can be felt as a bony prominence inferior to the patella. The gastrocnemius muscle can be palpated medially from the tibial tuberosity and is a relevant anatomic landmark for saphenous nerve block. The saphenous nerve is blocked by subcutaneous injection from the tibial tuberosity to the gastrocnemius muscle. An ellipse of local anesthetic is injected with 4–6 mL of solution.

Saphenous nerve block ultrasound-guided approach

The ultrasound machine and block tray should be placed in positions which allow the operator to simultaneously scan the patient and take items from the block tray with minimal movement.

The operator stands on the side to be blocked, with the patient in a supine position, the knee flexed to 45° and the hip externally rotated (Fig. 26.15). The skin is disinfected with antiseptic solution and draped. A sterile sheath (CIVCO Medical Instruments, Kalona, IA, USA) is applied over the ultrasound transducer with sterile ultrasound gel (Aquasonic, Parker Laboratories, Fairfield, NJ, USA). Another layer of sterile gel is placed between the sterile sheath and the skin. The infrainguinal region is scanned with a 6–13 MHz linear transducer. The ultrasound screen should be made to look like the scanning field. That is, the right side of the screen represents the right side of the field. Adjustable ultrasound variables such as scanning mode, depth of field, and gain are optimized.

Figure 26.15 Global view of the block field for the ultrasound-guided saphenous nerve block.

A transverse image of the great saphenous vein is obtained (Fig. 26.16). A thigh tourniquet can facilitate this. The saphenous vein is kept in the centre of the field of view. The saphenous nerve lies in its proximity. The needle entry site is at the lateral-most end of the linear transducer. A 23-gauge needle is advanced under real-time ultrasound guidance and local anesthetic is deposited along the needle entry path. A free hand technique rather than the use of a needle guide is preferred. A 21-GA × 50-mm insulated needle (B. Braun, Bethlehem PA) is inserted parallel to the axis of the beam of the ultrasound transducer (Fig. 26.17). The needle is attached to sterile extension tubing, which is connected to a 10 mL syringe and flushed with local anesthetic solution to remove all air from the system. It is then introduced at the lateral-most end of the transducer and visualized along its entire path to the saphenous nerve. It is important not to advance the needle without good visualization. This may require needle or ultrasound transducer adjustment.

Figure 26.16 Ultrasound identification of saphenous nerve and vein. SN : saphenous nerve; SV : saphenous vein; T: tibia.

Figure 26.17 Ultrasound transducer and needle positioning during ultrasound-guided saphenous nerve block. Note the needle orientation in the same plane as the ultrasound beam.

Once the needle has approached the saphenous nerve, 1–2 mL of local anesthetic may be injected. Local anesthetic appears as a hypoechoic image. Correct needle placement is confirmed by observing solution surrounding the saphenous nerve (Fig. 26.18). Should this not occur, the needle may need to be repositioned, and the procedure repeated. Following confirmation of correct needle placement, 5–10 mL of local anesthetic solution can be injected to achieve blockade. A trans-sartorial peri-femoral technique has also been described.

Figure 26.18 Transverse ultrasound image at medial aspect of the knee showing local anesthetic spread around saphenous nerve using a linear high frequency transducer. LA: local anesthetic; SV: saphenous vein; T: tibia.