Continuous Femoral Nerve Block
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Femoral nerve block is a basic nerve block technique that is easy to master, carries a low risk of complications and has a significant clinical applicability for surgical anesthesia and postoperative pain management. This block is well suited for surgery quadriceps muscle biopsy (shown), knee surgery (arthroscopy), quadriceps tendon repair and postoperative pain management after femur and knee surgery. When combined with the block of the sciatic nerve, anesthesia of the almost entire lower extremity from the mid-thigh level can be achieved. The success rate of this block for surgery is very high, nearing 95%, as long as the scope of surgery does not extend the area of coverage of the femoral nerve. |
The femoral nerve is the largest branch of the lumbar plexus. It arises from the second, third, and fourth lumbar nerves. The nerve descends through the fibers of the psoas muscle, emerging from the psoas at the lower part of its border, and passes down between the psoas and the iliacus. Eventually, the femoral nerve passes underneath the inguinal ligament into the thigh, where it assumes a more flattened shape. As the femoral nerve passes underneath the inguinal ligament, it is positioned immediately lateral and slightly deeper than the femoral artery. |
At the femoral crease, the nerve it is covered by the fascia iliaca and separated from the femoral artery and vein by a portion of the psoas muscle and the ligamentum ileopectineum. This physical separation of the femoral nerve from the vascular fascia explains the lack of the spread of a "blind paravascular" injection of local anesthetics toward the femoral nerve. TIP: It is useful to think of the mnemonic "VAN" (vein, artery, nerve) going from medial to lateral, when recalling the relationship of the femoral nerve to the vessels in the femoral triangle. The relationship of the femoral artery, femoral nerve, and sartorius muscle. The motor branches to the sartorius muscle depart from the anteromedial aspect of the femoral nerve toward the sartorius muscle. Because the anesthesiologist can never be sure whether stimulation of the sartorius muscle is obtained in the sheath of the femoral nerve or outside of it, this should always be confirmed by obtaining quadriceps stimulation before injecting local anesthetic. |
Femoral Nerve Branches
- Anterior division:
- Middle cutaneous
- Medial cutaneous
- Muscular (sartorius)
- Posterior division:
- Saphenous nerve (most medial)
- Muscular (individual heads of the quadriceps muscle)
- Articular branches (hip and knee)
| Femoral block results in anesthesia of the entire anterior thigh, most of the femur and knee joint. Femoral block also confers anesthesia of the skin on the medial aspect of the leg bellow the knee joint (saphenous nerve - a superficial terminal extension of the femoral nerve). Femoral nerve block alone is typically sufficient as a sole anesthetic for knee arthroscopy, patella tendon repair, patella fracture repair and biopsy of the anterior thigh (quadriceps muscle). In addition, femoral block is an excellent analgesic technique for pain management after major knee and femur surgery. |
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| The patient is in the supine position with both legs extended. In obese patients, a pillow placed underneath patient's hips may facilitate palpation of the femoral artery and block performance. |
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| Continuous femoral nerve block may be associated with moderate patient discomfort. Thus, small dose of midazolam (1-2 mg IV) and narcotic (250-500 alfentanyl) should suffice for most patients. Deeper sedation is neither recommended or necessary for this block. |
A standard regional anesthesia tray is prepared with the following equipment:
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TIPS:
- Note that this technique differs from common descriptions of the femoral nerve block, where the needle is inserted at the level of the inguinal ligament. Instead, in this technique the needle is inserted at the level of the femoral crease, a naturally occurring, oblique skin fold positioned a few centimeters below the inguinal ligament.
- The femoral crease can be accentuated in obese patients by asking an assistant to retract the lower abdomen laterally. The retraction of the abdomen should be maintained throughout the procedure to facilitate palpation of the femoral artery and block performance.
After a thorough cleaning with an antiseptic solution, local anesthetic is infiltrated subcutaneously at the estimated site of needle insertion. The injection for the skin anesthesia should be shallow and in a line extending laterally to allow for more lateral needle reinsertion when necessary. |
The anesthesiologist is standing on the side of the patient with the pal-pating hand on the femoral artery. The needle is introduced immediately at the lateral border of the artery and advanced in the saggital and slightly cephalad plane. |
Continuous femoral nerve block technique is quite similar to the single-shot injection, however insertion of the needle at a slightly more acute angle is necessary to facilitate threading of the catheter. The most common indications for use of this block are postoperative analgesia after knee arthroplasty, ACL or femoral fracture repair.
With the patient in the supine position, infiltrate the skin with local anesthetic at the injection site using a 25 G needle. The palpating hand is used to keep the middle finger on the pulse of the femoral artery, while the entire hand is slightly pulling the skin caudally to keep it from wrinkling on needle insertion. A 5 cm needle connected to the nerve stimulator (1.0 mA, 2 Hz, 100µsec) is inserted and advanced at a 45-60º cephalad. Care should be taken to avoid medial insertion of the needle and the consequent puncture of the femoral artery.
After the quadriceps muscle twitch is obtained (patella twitch) at 0.5 mA, the initial bolus of local anesthetic is injected (15-20 ml) and the catheter is inserted 5-10 cm beyond the tip of the needle. The catheter is then secured to the skin using a clear dressing applied over the catheter.
Continuous infusion is always initiated after an initial bolus (15-20
ml) of dilute local anesthetic through the catheter. For this purpose we
routinely use ropivacaine 0.2% Diluted bupivacaine or l-bupivacaine
(0.25%) are also suitable, but may result in more motor blockade. The
infusion is maintained at 8 ml/hr or 5 ml/hr when a PCA dose is planned
(5 ml).
The femoral nerve innervates a number of muscle groups. A visible or palpable twitch of the quadriceps muscle (patella twitch) at 0.2-0.5 mA current is the optimal response.
TIPS
- The most common response to nerve stimulation with this technique is twitch of the sartorius muscle. This results in a band-like contraction across the thigh without movement of the patella.
- It should be kept in mind that sartorius muscle twitch is not reliable because the branches to the sartorius muscle may be outside the femoral sheath. When the sartorius muscle twitch occurs, the needle is simply redirected laterally and advanced several mm deeper.
- The femoral nerve supplies muscular branches of the iliacus and pectineus, and the muscles on the anterior thigh, except the tensor fascie femoris. The nerve also provides cutaneous filaments to the front and inner side of the thigh and to the leg and foot (saphenous nerve), as well as the articular branches to the hip and knee joints.
- ASIS - anterior-superior iliac spine
- FN - Femoral nerve
- FA - Femoral artery
- SM - Sartorius muscle
- PT - pubic tubercle
TIPS
When stimulation of the quadriceps muscle is not obtained on the first needle pass, the palpating hand should not be moved from its position. First, visualize the needle plane in which the stimulation was not obtained and follow this algorithm:
- Ensure that the nerve stimulator is properly connected and functional.
- Withdraw the needle to the skin, redirect 10-15o laterally, and repeat the needle advancement.
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| When the above procedure fails to produce a twitch, the needle is withdrawn from the skin, reinserted 1 cm laterally, and the above steps are repeated with progressively more lateral needle insertion. After the initial stimulation of the femoral nerve is obtained, the stimulating current is gradually decreased until twitches are still seen or felt at 0.2 - 0.4 mA current. This typically occurs at a depth of 2-3 cm. After an aspiration that is negative for blood, 20-25 mL of local anesthetic is slowly injected. |
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TIP: Again, it is essential to keep the palpating finger in the same position throughout the procedure. This helps prevent repeatedly reinserting the needle in the same plane.
After the initial stimulation of the femoral nerve is obtained, the stimulating current is gradually decreased until twitches are still seen or felt at 0.2 - 0.4 mA. This typically occurs at a depth of 2-3 cm. |
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Troubleshooting
| Response Obtained | Interpretation | Problem | Action |
| No response | The needle is inserted either too medially or too laterally | Femoral artery not properly localized or the palpating hand moved during the procedure | Follow the systematic lateral angulation and reinsertion of the needle as described in the technique |
| Bone contact | The needle contacts hip or superior ramus of the pubic bone | The needle is inserted too deep | Withdraw to the level of the skin and reinsert in another direction |
| Local twitch | Direct stimulation of the illiopsoas or pectineus muscle | Too deep insertion | Withdraw to the level of the skin and reinsert in another direction |
| Twitch of the sartorius muscle | Sartorius muscle twitch | The needle tip is slightly anterior and medial to the main trunk of the femoral nerve | Redirect the needle laterally and advance deeper 1-3 mm |
| Vascular puncture | Blood in the syringe invariably indicates placement into the femoral artery | Too medial needle placement | Withdraw and reinsert laterally 1 cm |
| Patella twitch | Stimulation of the main trunk of the femoral nerve | None | Accept and inject local anesthetic |
| Infection | - Just like with any other procedure, use a strict aseptic technique - Catheters at his location are difficult to keep sterile and should probably removed after 48 hours |
| Hematoma | - Avoid advancement of the needle when the patient reports pain; this may indicate insertion of the needle through the illiopsoas or pectineus muscles - When the femoral artery or vein are punctured, the procedure should be stopped and a firm and constant pressure applied over the femoral artery for 2-3 minutes before proceeding with the blockade. - In a patient with difficult anatomy or severe peripheral vascular disease, use a single-shot smaller gauge needle to localize the femoral nerve before proceeding with a larger gauge needle for the continuous technique. |
| Vascular Puncture | - Never redirect the needle medially! - The needle is first inserted just lateral to the femoral artery and the consequent insertions and redirections should all be progressively more lateral |
| Nerve Injury | - Use nerve stimulation and slow needle advancement - Distinct paresthesia is almost never elicited with femoral nerve block and should not be sought - Do not inject when the patient complains of pain or when high pressures on injection are met |
| Other | Instruct the patient on the inability to bear weight on the blocked extremity |
