Chung O T in Lower Limb Reconstruction and Amputation 978197

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Chapter 1 Femoral and Adductor Canal Blocks

■ Crutch training, if appropriate, should take place prior to surgery. ■ Inpatients should be labeled as a “fall risk” and should not get out of bed without assistance. ■ Femoral nerve blocks for outpatients should be carefully considered and only performed with close follow-up and an otherwise low risk of falls. ■ The use of crutches and a knee immobilizer may attenu- ate fall risk with ambulation after a femoral nerve block. Positioning ■ The patient should be positioned supine with the opera- tive leg slightly externally rotated. ■ The bed should be flat with hips extended. ■ The patient’s ipsilateral hand may be kept out of the ster- ile field by lightly taping it to the chest. ■ The operator should stand on the side to be blocked, with the ultrasound machine on the other side of the patient. Approach ■■ With the use of ultrasound, the nerve may be approached either in-plane (needle parallel to transducer surface) or out- of-plane (needle perpendicular to transducer surface) with the ultrasound probe placed in a transverse orientation. ■ When a nerve stimulator technique is used, the needle approach is generally with the long axis of the nerve, at a 45-degree angle to the skin.

SM

A

N

V

FIG 2  • Ultrasound image of adductor canal block. SN, saphenous nerve; SM, sartorius muscle; A, femoral artery; V, femoral vein.

■■ A nerve block in the adductor canal is less likely to cause quadriceps weakness than a femoral nerve block; how- ever, local anesthetic may spread proximally and affect motor nerves. ■■ The nerve to the vastus medialis is reliably anesthe- tized with an adductor canal block, but the overall effect on quadriceps function is minimal. 3 Preoperative Planning ■■ Surgical site, extent of incision, anticipated degree of pain, and any pre-existing conditions that increase risk of complications should be considered before offering the patient a nerve block. ■■ Postoperative ambulatory status should be determined to optimize dosing. ■ Femoral Block: Ultrasound-Guided Technique ■■ Position the patient as described above, with ASA (American Society of Anesthesiologists) standard moni- tors and supplemental oxygen applied. ■■ IV sedation, usually with fentanyl and midazolam, may be titrated to patient comfort. ■■ Using a high-frequency linear transducer, scan at the level of the inguinal crease in a transverse orientation to visualize the femoral artery and nerve in cross-section. ■■ The best image may be obtained in a location proxi- mal to the bifurcation of the femoral artery where the neurovascular bundle is closest to the skin. ■■ Identify the fascia lata, fascia iliaca, femoral nerve, and iliacus muscle. ■■ Slowly tilt the ultrasound transducer to optimize nerve imaging. ■■ Estimate the depth of the nerve in the ultrasound image. ■■ After sterile skin preparation, place a skin wheal just lat- eral to the ultrasound probe. ■ The depth of the nerve should guide the insertion site; start closer to the probe for more superficial tar- gets, and farther away if the target is deeper. ■■ Insert the block needle in the plane of the ultrasound image, visualizing the tip of the needle in real-time as the target is approached ( TECH FIG 1 ). ■■ The needle should pass through the fascia iliaca just lateral to the nerve. ■■ Tactile feedback through the needle may include a “pop” as the needle traverses fascial layers.

T E C H N I Q U E S

TECH FIG 1  • Positioning and approach for ultrasound-guided in- plane femoral nerve block.

■ Take care to avoid the lateral edge of the nerve. The patient may experience a paresthesia if the nerve is contacted directly. ■ The lateral circumflex femoral artery or one of its branches may be in the needle path or pass through the nerve, and should be avoided. ■ After careful aspiration, inject a small amount of local anesthetic. ■ Local anesthetic spread should appear as hypoechoic fluid filling the space deep to fascia iliaca and sur- rounding the nerve. ■ The needle may be advanced closer to the nerve as a local anesthetic pocket is formed (hydrodissection); this reduces the risk of needle-nerve contact. ■ When the needle is positioned in close proximity to the nerve, and local anesthetic spread is confirmed around the nerve, an additional 10 to 15 mL of local anes- thetic can be injected.

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