Lower Peripheral Nerve Blocks Flashcards
What is one of the most important things to continue doing when administering a PNB?
Keep talking to the patient! This ensures rapid identification of any systemic neurological effects from the LA
*can also help reduce anxiety
Why is a benzodiazepine usually administered concurrently or before administration of the PNB?
to reduce anxiety, promote amnesic effects and to reduce the potential risk of LA toxicity (seizures)
What class of drugs should not really be used with COPD patients when giving a PNB?
narcotics. should not use as a sedative because it has a synergistic effect with the benzos and may decrease respiratory drive further
What are the absolute contraindications for PNB?
patient refusal, patient won’t cooperate (AMS, dementia, hyperactivity), skin infection, sepsis
What are some relative contraindications to PNB?
neurologic deficits (just make sure that you document really well what those deficits are if you’re going to proceed)
coagulopathies (just check what specific values are off and the magnitude of the difference)
What are the risks of PNB?
local toxicity, systemic toxicity, permanent or long-lasting neuroblockade, incomplete blocks, uncomfortable positioning
What is the risk of using ester LAs?
Body breaks them down to PABA which has a higher risk of causing an allergic reaction
How are amide LAs cleared by the body?
via hepatic metabolism, less risk of allergy
What is the purpose of using epinephrine with the LA?
causes local vasoconstriction which can decreased systemic absorption of the LA
Under what circumstances should you not use epinephrine?
when you’re doing a distal PNB - like on the ankle, fingers, penis, etc.
It CAN cause severe peripheral vasoconstriction and ultimately results in ischemia to the end organ.
List MAX rate of absorption to MIN rate of absorption
intercostals caudal epidural brachial plexus sciatic lumbar plexus femoral
What should you do if your patient complains of a “weird” or “metallic” taste?
proceed with caution… maybe slow down. It isn’t a sign of systemic toxicity but you need to be aware of it
What are some S&S of CNS toxicity with a PNB?
lightheadedness, double vision, disorientation, tinnitus, seizures, CNS depression
What are the progressive levels of systemic toxicity during PNB?
CNS toxicity –> respiratory depression –> cardiac effects
What is the MAJOR way to avoid intravascular injection of the LA?
ASPIRATE before every 5 mL injection
If you’re giving a high volume of LA you should give a **** concentration of the drug
LOW
If you’re giving a smaller volume of LA, you should give a **** concentration
higher…. but should be used with extreme caution
think about patients body weight before giving a large dose
What has become the gold standard for localization of the nerves during PNB?
Ultrasound guided identification
What specific type of needle should you use if you’re going to locate the nerve using NS?
an insulated needle
What are you cutting off when you block the sciatic nerve?
ventral branches of L4-S3
foot, lower extremity distal to the knee and the posterior leg
What are the major landmarks during a sciatic block?
Greater trochanter and the posterior superior iliac spine… go to the middle of that line and drop down about 5 cm to find the nerve.
If you’re attempting a sciatic nerve block using NS and you see persistent eversion of the foot, what should you do?
move your needle medially
you were too far lateral (sitting in the common peroneal nerve)
If you’re attempting a sciatic nerve block using NS and you see persistent plantar flexion of the toes, what should you do?
move your needle laterally
you were too medial (sitting in the tibial branch)
What is a rare but sometimes serious complication of a sciatic block?
hematoma
How does the femoral nerve flow through the upper leg?
Passes under the inguinal ligament and runs through the iliacus and the psoas muscle
What major areas of the leg does the femoral nerve supply?
hip joint, anterior thigh, knee
Which nerve block will results in inability to abduct and extend the leg?
femoral nerve block
What are the important anatomical landmarks for a femoral block?
femoral artery (go just laterally and you’ll find the nerve) and the inguinal ligament
What is the injection volume for a femoral nerve block?
25-35 mL
What is the injection volume for a sciatic block?
20-30 mL
If you insert the needle and the patient c/o sharp pain, what should you do?
Withdraw the needle immediately and start all over
How should the patient be positioned for a popliteal nerve block?
Prone
can be lateral in some cases
What are the major landmarks for a popliteal block?
locate the popliteal crease when the patient bends their knee in the prone position. Then go about 7 cm up from there and slightly lateral to place your needle
can trace the tendons of the biceps femoris and the semimembranosus/semitendinosus
What should you notice with the NS if you’re attempting a popliteal block?
foot/toe twitching
What is the injection volume for a popliteal block?
20-30 mL
Under what circumstances is an ankle block warranted?
shorter procedures, below the level of the ankle
What is the technique used during an ankle block?
Field techinique or Fanning technique: use the same needle insertion site and just rotate the end around to ensure adequate spread of the LA
What is the injection volume for an ankle block?
5-7 mL per nerve
What are the 5 nerves that you should cut off during an ankle block?
posterior tibial nerve (Largest... do this one first) superficial peroneal nerve saphenous nerve deep peroneal nerve sural nerve
What landmark should you look for when trying to locate the deep peroneal nerve?
have the patient dorsiflex their foot to visualize the hallicus longus tendon and then insert just laterally until you hit bone (then withdraw 2-3 mm and inject)
What landmark should you look for when attempting to locate the posterior tibial nerve?
medial malleolus. Insert needle, hit the bone, withdraw 2-3 mm and then inject
may feel the tibial pulse
How can you locate where to block the saphenous nerve?
after locating the posterior tibial nerve, move just above the medial malleolus and administer a fanning block
How should you administer a superficial peroneal block?
in a circular fashion at the level of the lateral malleolus, moving anterior to posterior
How should you administer a sural nerve block?
locate the lateral malleolus and inject a fan block SQ and below the fascia
What can you add to the LA to make it burn less?
bicarb
In what type of setting should you administer your PNB? Why?
Before you get to the OR (in pre-op holding). This allows for “soak time”
What are the benefits of using the US guided technique for PNB?
reduced chance of toxicity, more successful block, longer duration of action, reduced onset time
What are you looking at during an US?
looking at how the structures resist the acoustics of the machine
What is a hyperechoic structure?
high impedance to the acoustics
appears white on the US, examples would be bone and connective tissue
What are hypoechoic structures?
low impedance to acoustics
appears gray
example would be the LA during injection
What are anechoic structures?
minimal impedance to the acoustics of the US
will appear black, example would be vessels
If you don’t have a reusable sterile sheath to place over your probe, what can you use?
tegaderm
What types of needles are used for PNBs? Why?
B - bevel (short bevel), pencil point and/or Tuohy needles
this helps to reduce damage to the surrounding structures during insertion
What drug can be used to stop or reduce the effects of toxicity during a PNB?
intralipid (20%)
How can you test that you’re in the right place if you’re using the US technique?
inject 5 mL of D5W
How long does it take for complete anesthesia of the ankle if the block was done correctly?
15 minutes
How can US be helpful when attempting to locate the deep sciatic nerve?
You can locate the boney prominences instead and use those as landmarks to find the nerve by default
