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Single Landmark Technique for Femoral & Sciatic Nerve Blocks


Dr. Prasanna Khare D.A., D.N.B., FCARCSI
Consultant Anaesthesiologist
Department of Anaesthesiology
Deenanath Mangeshkar Hospital & Research center, Pune.



Total kneearthroplasty (TKA) is one of the most common procedures performed to improve early mobility and quality of life in elderly patients.TKA causes severe postoperative pain in 60% of patients and moderate pain in 30% of patients.Femoral & Sciatic nerve blocks are responsible for significant improvement in patient satisfaction, decreased post-operative analgesic requirementand potential for decreased duration of hospital stay.

The femoral nerve provides sensation to the antero-medial aspect of the knee, whereas the sciatic nerve innervates the posterior aspect of the knee.

In our institution we administer Spinal anesthesia for unilateral TKA. Single shot sciatic nerve block andcontinuous femoral nerve block are given for postoperative pain relief.


Technique:8

Patient Positioning:

The patient is in the supine position with both legs extended.The anesthesiologist performing the block should stand on the side of the patient to be able to monitor the patient and his or her responses to nerve stimulation.



Equipment

- Nerve stimulator (Stimuplex HNS 11, B. Braun, Melsungen, Germany)
- 5-cm Contiplex D cannula (B. Braun)
- 15-cm Contiplex cannula (B. Braun)



Local Anesthetic

- Ropivacaine 0.25% 30 ml with Inj. Clonidine 0.5 μg/Kg for each block
- Ropivacaine 0.18% 4-6 ml/hour for continuous infusion.



Surface landmarks

- Femoral crease
- Femoral artery pulsations




The site of injection for both blocks are- 1cm lateral to (outside of) the pulsations of the femoral artery and 5 cms below (distal to) the femoral crease


Sciatic Nerve block

The anterior approach to a sciatic block is an advanced nerve block technique. This is especially useful in post TKA patients who cannot be repositioned into lateral position needed for the posterior approach.
The technique described differs from common descriptions of the anterior approach to sciatic block.


Advantages of this approach:

  • This technique does not rely on identification of the ASIS, pubic tubercle or greater trochanter, which may be difficult to identify in obese patients.
  • This increases the probability of successful block.
  • Need for extra assistant to maintain lateral position is avoided.
  • This causes less inconvenience to patient.

This technique is not suitable for catheter insertion because of the deep location and perpendicular angle of insertion required to reach the sciatic nerve.


Procedure

After cleaning the area with an antiseptic solution, local anesthetic is infiltrated subcutaneously at the determined needle insertion site.




The sciatic nerve is identified using an anterior approach with an 15-cm Contiplex cannula (B. Braun).


Stimulation
The nerve stimulator should be initially set to deliver 1.5 mA current (2 Hz, 100µsec). Stimulation typically occurs at a depth of 10-12 cm. When plantar or dorsal flexion of the ankle is maintained with a current of 0.3 mA,after negative aspiration for blood, 30 ml of Ropivacaine 0.25% is administered.
Femoral nerve stimulation which is encountered while advancing indicates the right plane of needle insertion.


Femoral Nerve block:

This technique differs from common descriptions of the femoral nerve block, where the needle is inserted at the level of the inguinal ligament or femoral crease


Advantage :

  • This avoids need for assistant to retract lower abdomen laterally.
  • At this level, needle and subsequently catheter passes through significant muscle mass wihichhelps in better fixation of catheter.


Postoperatively it allows continuing physiotherapy without fear of catheter dislodgement Stimulation.The nerve stimulator is initially set at 1.0 to 1.2 mA. The needle is directed cephalad at approximately a 30° to 45° angle. A brisk “patellar tap” with the current at 0.3 -0.35 mA is indicative of successful localization of the needle near the femoral nerve.This typically occurs at a depth of 2-3 cms.


After negative aspiration for blood, 25 mls of local anesthetic is slowly injected(It allows for tissue spreading and ease of catheter threading). Thecatheter is threaded 5 cms past the cannula. Then rest of local anesthetic is injected through catheter.




Catheter is secured to the skin with sterile dressing.

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