Of the different nerve fibers, which is the thickest and fastest conducting? These fibers are also most susceptible to damage with tourniquet placement ?
A fibers!! These are the thickest and fastest at transmitting information.
C fibers are the thinnest and not myelinated. These transmit CHRONIC, burning PAIN.
D fibers: are thin but myelinated and transmit short lived pain.
What track transmits pain?
Spinothalamic!
relays sharp pain, temp, crude touch, and noxious stimuli. Originates from periphery and concludes in the dorsal horn on the contralateral side of the thalamus.
- BRAIN STEM LESION: therefore a spinal cord lesion produces contralateral pain deficits,
- ** SPINAL CORD LESION: ipsilateral touch and proprioceptive deficits.
What is the resting state of a nerve cell?
How do local anesthetics act on cells?
-70mv with lots of Na outside the cell.
*** local anesthetics act on the Na/K ATP pump. INHIBIT depolarization of the cell, preventing Na to rush in…therefore propagation of a signal (pain) is not allowed. ( no action potential produced)
Local anesthetics are weak ______?
Weak bases! manufactures in the form of a hydrochloride salt. Contains protonated and unprotonated forms… but only the unprotonated molecules can diffuse across nerve cell membrane. Inside the cell, the molecule becomes protonated and therefore is trapped inside the cell.
Why are local infections weary to have in the use of a local anesthetic?
The infection causes an decreases pH outside the cell, therefore more PROTONATED molecules remain outside the cell membrane.
Therefore infections are acidic and reduce the effectiveness of locals. Inject local proximal to the site.
Tell me about the differences of ESTERS and AMIDES?
ESTERS: (procaine), metabolized in the blood( Hydrolysis by pseudocholinesterases). greater risk for allergies.
AMIDES: (lidocaine), used more frequently. Metabolized in the liver. Less risk for allergy. Excreted by renal system. Concern for toxicity… CHF or hepatic failure warrants extra concern.
Can I use lidocaine with epi in the digits?
according to mcglamry.. YES! research supports use, no need to withhold. But still administer cautiously. using epi means you can do surgery without tourniquet at times.
What is the concentration of Epi used with lido?
Most common side effect?
1:100,000 or 1:200,000
Most common side effect is tachycardia.
Epi reduces need to tourniquet or compression
Epi also increased acidity of the solution! FYI.
What can reduce irritation when administering a local anesthetic?
Quick penetration and slow infiltration.
common side effects: pain, ecchymosis, hematoma, infection, nerve lac, or tissue irritation.
How can anesthetics affect the CNS?
They selectively depress inhibitory centers = excitation -> generalized convulsions.
also could cause coma, resp arrest, and death, most commonly due to toxic dose, IV admin.
What is the order of nerve sensory inhibition with application of anesthetic?
pain > temp > touch > proprioception
Why is sodium bicarb used with local injections?
This can reduce irritation with administeration and also increase the pH to make the solution more basic and more readily diffuse across the cell membrane.
SCIATIC NERVE BLOCK
L4, L5, S1-3
- this nerve goes through the greater sciatic foramen.
- nerve is encountered medial to the ischial tuberosity
-
What is the one nerve that innervates the foot and does not come off the sciatic nerve?
SAPHENOUS NERVE - branch of the femoral nerve.
TIBIAL NERVE
L4-S3
- innervates the posterior leg and sole of foot
- 0.5-1cm lateral to midline of popliteal fossa (follows direction of sciatic before split)
- great for achilles lengthening, grastroc recession, etc
COMMON PERONEAL
- L4-S2
- innervates muscles on lateral and anterior aspects of leg as well as the dorsum of the foot.
- courses laterally across popliteal fossa–> hit it before it divides into deep and superficial peroneal near prox PL fibers. Palpate along fibular neck, it sits shallow here.
- good for post op pain management
SUPERFICIAL PERONEAL BLOCK
- L4-S1
- lower anterior leg and dorsum foot
- intermediate and medial dorsal cutaneous branches
- Hit it along the anterior border of the fibula
- Intermediate branch can be felt along tibiofib syndesmosis and will be visualized when taut ( PF foot)
- medial branch overlies the EDL, parallel to EHL. ( be careful of in ankle arthroscopies): HIT 1 cm prox to medial malleolar level, lateral to EHL
DEEP PERONEAL
- First dorsal interspace
- Travels with anterior Tib artery
- Sits between TA and EHL
HIT it 2.5 cm prox to ankle joint betwen EHL and EDL
POST TIB NERVE
- provides to medial posterior heel and plantar foot, posterior lower leg
- posterior to PT artery
- HIT It: palpate artery at medial malleolus, then most 1cm superior to this and and inject
What is CRPS Type 1 vs 2?
Type 1: regional sympathetic dystrophy. Occurs after illness or injury not directly damaging nerves in the affected limb.
Type 2: follows distinct nerve injury.
SURAL NERVE
Formed by the medial sural nerve ( br of tibial n), and the peroneal communicating branch ( lateral sural n or common peroneal n)
- lateral border to Achilles
- HIT IT: superior or inferior to lateral malleolus,
SAPHENOUS N
L3-4
- only branch to innervate the foot that is not derived from sciatic n.
- HIT IT: LATERAL to the great sapheous vein, before it crosses the ankle joint
ANKLE BLOCK
tibial, superficial peroneal (medial and intermediate dorsal cutaneous),deep peroneal, saphenous, sural
What is a MAYO block
saphenous, deep peroneal, medial plantar, medial dorsal cutaneous.
- performed for 1st MPJ procedure.
1. needle dorso-lateral to plantar
2. then dorso-lateral to dorso-medial
3. then dorsomedial to plantar
4. plantarly, directed medially to laterally
