Week 5 - Sciatic and Popliteal Nerve Blocks Flashcards Preview

Regional 540 - PM > Week 5 - Sciatic and Popliteal Nerve Blocks > Flashcards

Flashcards in Week 5 - Sciatic and Popliteal Nerve Blocks Deck (51):

What is the Sacral nerve formed by?

The Ventral rami of L4, L5, and S1-S3


What is the Tibial nerve formed by?

L4, L5, and S1-S3


What is the Common Peroneal nerve formed by?

L4, L5, S1 and S2


What is larger, peroneal nerve or tibial nerve?

Per PM, Tibial


Sciatic Nerve...

The LARGEST peripheral nerve in the body.


Lumbar plexus...

Know all the nerves and where they come from.. Drawing of lumbar plexus on Youtube -  http://www.youtube.com/watch?v=AnZkTuVjaWs


Indications for sciatic nerve block

Lower limb surgery


True of False: Sciatic block should always be performed alone?

False: Almost always needs to be combined with a supplemental block. (often combined with Femoral or Psoas compartment block)



Pt. refusal, local infection at site of insertion, coagulopathy, preexisting central or peripheral nervous system disorders, allergy to LA.


What two things should you know if someone is coming in for an ORIF of an ankle?

Where incision is going to be, and if there will be a tourniquet used. (want to make sure the right ares are blocked)


Femoral Nerve blocks are always sufficient enough for Total Knee surgeries. True of False?

False... many times they require sciatic blocks as well to innervate the posterior portion of the leg.


What forms the sacral plexus?

Union of lumbosacral trunk with first three sacral nerves.


Strictly speaking what nerve roots form the sacral plexus?



Where is the common peroneal nerve in relation to Tibial nerve?



Common peroneal nerve CDE -

C - common Peroneal nerve D - dorsiflexion E - eversion


Tibial nerve TIP -

Tibial Inversion Plantaflexion


Tibial nerve motions

Knee extension, plantar flexion, toe flexion


Peroneal nerve motions

Knee flexion, foot flexion (away from knee)


Deep superficial nerve motions

Dorsiflexion of foot and ankle (toe's point up to knee)


Common dose (amount) of LA for sciatic nerve blocks?

30 ml (stick with this for now per PM)


You get a local twitch of the gluteus muscle... what do you do?

Continue advancing the needle.


Needle contacts bone but local twitch of the gluteus muscle is not elicited... what do you do?

Slightly laterally and caudally redirect the needle


Needle encounters bone and sciatic twitches elicited... what do you do?

withdraw the needle and redirect slightly medially or laterally (5-10 degrees)


Hamstring twitch... what do you do?

Accept and inject local anesthetic!!


The needle placed deep (10 cm) but no twitches elicited and no bone contact... what do you do?

Withdraw and redirect needle slightly laterally, or cephalad (toward the head).


Paresthesia of the genital organs.. what do you do?

If you like the person, probably want to redirect needle slightly cephalad and laterally! :)


Clinical Pearls ...

1. Twitches of hamstring, calf, foot, or toes at 0.2-0.5 mA is acceptable. 2. Inadequate skin anesthesia despite an apparent timely onset of the blockade can occur 3. It can take up to 30 MINUTES for full sensory-motor anesthesia to develop 4. LA infiltration at the site of injection by the surgeon is often all that is needed to allow the surgery to proceed.


When sciatic block is combined with a femoral or lumbar plexus block....

anesthesia of almost the entire leg can be achieved.


Know all the dermatomes BELOW the knee



Position:  Lateral Decubitus position with slight tilt forward.  Foot on side to be blocked should be visible to observe twitches when present.

Sterilize site, infiltrate with LA, depress skin firmly to decrease needle-nerve distance, insert needle perpendicular to skin, set stimulator to 1.5 mA, first visible twitches will be gluteal muscles, once twitches of hamstring, calf, foot, or toes is observed, DECREASE YOUR CURRENT...

Injection:  Aspirate, Inject 15-25 ml, if resistance withdraw slightly and reattempt


What is neuropraxia?

Damage to a nerve


What is the double crush phenomenon?

If you impede blood flow (via use of LA) to a patient in an already compromised area (IE neuropathy) you risk increasing damage to the area.  


Landmarks of Sciatic nerve block (must know all these for test)

1.  Greater Trochanter

2.  Posterior Superior Iliac spine

3.  Sacral hiatus


Complications of Sciatic nerve block and how to avoid them....

1.  Infection - use asceptic technique

2.  Hematoma - Avoid multple insertions, 

3.  Vascular puncture - (not common) avoid deep needle insertion

4.  LA toxicity - (not common) Avoid using large volumes of LA's in single poses, ensure frequent aspiration checks.

5.  Nerve injury - BIG ONE HERE - Sciatic has a unique predisposition for mechanical and pressure injury - Use slow needle insertion and nerve stimulation.  If stimulation occurs < 0.2 mAs, your too close, withdraw needle slightly.  pain or pressure, STOP. 

6. Perforation of pelvic organs - directing the needle medially should be exercised.

7.  Avoid use of turniquet when possible.  

8.  Anesthesia of the pudendal nerve - a branch of sacral plexus, can occur by diffusion of LA for this block... inform patients of the potential for this problem.  


Block of the Sciatic nerve WITHIN the Popliteal Fossa

1.  Simple technique - good for calf, tibia, fibula, ankle, and foot.

2.  Most commonly used for analgesia of foot, ankle, and lower leg surgery... ensure patient has a BOOT to walk in.

3.  Can performed by either posterior or lateral approaches.

4.  Lateral popliteal block with 0.5& bupivocaine lasted 18 hrs!!!! (versus ankle block at 6.2 hrs)


Indictaions for Sciatic block within popliteal fossa

Corrective foot surgery, foot debridement, saphenous vein stripping (may need saphenous block for this as well) , repair of achilles tendon, 


Difference between this block and the more proximal sciatic nerve block, THIS block anesthetizes the distal leg to the hamstring mucles, allowing patients to RETAIN knee flexion!


Regarding Nerve stimulating needles...  Red and black leads go where?

Red = patient

Black = device


The sciatic nerve is a nerve bundle consisting of what two separate nerve trunks?

1.  Tibial (medial) 

2.  Common Peroneal (lateral)


Which nerve is the larger of the two divisions?

Tibial is larger - gives rise to the medial and lateral plantar nerves as well as sural and posterior tibial nerves.  

-when stimulated causes Plantar FLEXION


Common Peroneal nerve has terminal branches where?  What happens when stimulated?

The Deep and Superficial Peroneal nerves.  When stimulated they cause dorsiflexion and everision 



Where does the Popliteal Sciatic block distribute to? (where does it innervate?)

The entire distal two-thirds of the lower extremity, with the EXCEPTION of the medial aspect of the leg which is supplied by the saphenous nerve ( a superficial terminal branch of the femoral nerve)


Technique for Politeal sciatic block 


1.  Prone position

2.  Allow foot to protrude off the bed - helps detect even the slightest movements

3.  Landmarks:  Popliteal fossa crease, tendon of biceps femoris (laterally) and tendons of semitendinous and semimembranous (medially)

4.  Insert needle 7cm above crease between tendons

5.  After twich observed, inject 35-45 (more volume here to try and hit both nerve branches in one shot)


Technie for 


-Is an advanced technique, best to master the Single-shot block first.

- Similar to single shot except slightly cephalad needle angulation is required to allow the catheter to be threaded.  


Popliteal Block Troubleshooting...  

Responses and Corrective Actions

1.  Local twitch of the biceps (yes.. its biceps) muscle - Withdraw the needle and redirect slightly medially (5-10 degrees)

2.  Local twitch of the semitendinosus/membranosus muscles - withdraw the needle and redirect slightly laterally (5-10 degrees)

3.  Twitch of the calf muslces WITHOUT foot or toe movement - Disregard and continue advancing the needle until the foot/toes twitches are obtained.

4.  Vascular puncture - withdraw and redirect

5.  Bone contact - Withdraw needle slowly and look for the foot twitch; if twitches are not seen, reinsert in another direction.



Popliteal sciatic block 


Main Advantage: Patient does not have to take a prone position.  This block is perfomed while patient is supine.  

Sciatic nerve is poisitioned between the biceps femories and semitendinous muscles

Common peroneal nerve is usually stimulated first (65% of the time) - why?  Is more lateral

100mm needle - 

Landmarks : Popliteal Crease, vastus lateralis, and biceps femories muscles.  


Lateral Popliteal block troubleshooting

Response - Corrective Action


1.  Local twitch of the biceps - Advance the needle deeper

2.  Local twitch of vastus lateralis muscle - withdraw the needle and reinsert posterior

3.  Twitch of the calf muscles without foot or toe movement - disregard and continue advancing the needle until the foot/toes twitches are obtained.

4.  Vasular puncture - Withdraw and redirect laterally

5.  Twitches of the foot or toes - Accept and inject local anesthetic 


Complications of politeal block 

Infection - how do we prevent?

Aseptic technique


Complications of Popliteal block

Hematoma - How do we prevent?

Avoid multipe needle passes with a continues block needle; the larger needle diameter and/or Tuohy design may result in a hematoma of the biceps femoris or vastus lateralis muscles.  When the nerve is not localized on first two or three needle passes, localize the nerve using a smaller guage, single-shot needle first... then reinsert with continuous needle using the exact same angle.


Complications of Popliteal block

Vascular puncture - How do we prevent?

Avoid too deep insertion of needle because the vascular sheeth is positioned medially and deeper to the sciatic nerve.

When the nerve is not localized within 2 cm after the local twitches of the biceps muslce cease, the needle should be withdrawn and reinserted at a different angle, rather than deep


Complications of Popliteal block

Nerve injury - how do we prevent?

Uncommon; use nerve stimulation and slow needle advancement; do not inject when patient complains of pain or pressure, do NOT with stimulation at < 0.2 mA.  Avoid combination of epinephrine in LA and application of a tourniquet over injection site to decrase risk of prolonged ischemia of the nerve.


Complications of Popliteal block

Pressure necrosis of the heal - How do we prevent it?

Instruct patient on the care of the insensate extremity

Use heel padding and frequent repositioning