Week 3 - Peripheral Regional Anesthesia

Question 1

What are reasons you would use regional anesthesia?

Answer 1

Improved postop pain relief

Less nausea

Ability to spare anesthetic complications in comorbid conditions

Question 2

What are the layers of a peripheral nerve?

Answer 2

1. Fascicle - injections within are “intrafascicular”
2. Perineurium - membrane surrounding each fascicle
3. Endonerium - injections within are “intraneural”
4. Epineurium - membrane surrounding nerve, loose membrane of connective tissue that easily expands (where you inject the LA)
5. Perineural - injection, feel a pop when you enter and there is a lot of pressure behind the syringe – could cause nerve ischemia if injection occurs here

Question 3

Define Dermatome, Myotome, and Osteotome

Answer 3

Dermatome = area of skin supplied by dorsal root of spinal nerve

Myotome = innervation of skeletal muscle by ventral root

Osteotome = innervation of bones, does not coincide with peripheral structures

**these are a GUIDE.. don’t be fooled by being strict

Question 4

What is the chemical structure of local anesthetics?

Answer 4

Weak bases with alkaline pKa values that are greater than physiologic pH

Lipophilic aromatic benzene rings joined to a hydrophilic amine or ester link

• Esters: procaine, chloroprocaine, cocaine, tetracaine, benzocaine
• Amides: lidocaine, prilocaine, mepivacaine, bupivacaine, ropivacaine

Question 5

How are esters and amide LA’s metabolized?

Answer 5

Esters - metabolized by plasma cholinesterases (pseudocholinesterase - if abnormal, risk for LA toxicity)
**there are no cholinesterases in CSF

Amides - metabolized by the liver (slower metabolism than esters)
**hepatic disease may slow clearance and lead to toxicity

Question 6

What type of LA are people most likely to be allergic to?

Answer 6

Esters

*allergen is PABA, a byproduct of the metabolites of esters

**allergy to amides is usually due to a preservative

Question 7

What LAs can cause Methemoglobinemia?

Answer 7

Amides

*Prilocaine is most common followed by lidocaine – treat with methylene blue

Question 8

What is the max dose of chloroprocaine? Typical duration of neural blockade?

Answer 8

Max Dose = 12 mg/kg

Duration = 0.5-1 hour

*used for epidural, infiltration, peripheral nerve block

Question 9

What is the max dose of cocaine? Typical duration of neural blockade?

Answer 9

Max Dose = 3 mg/kg

Duration = 0.5-1 hr

*topical use

Question 10

What is the max dose of procaine? Typical duration of neural blockade?

Answer 10

Max Dose = 12 mg/kg

Duration = 0.5-1 hr

*used for spinal, infiltration, peripheral nerve block

Question 11

What is the max dose of tetracaine? Typical duration of neural blockade?

Answer 11

Max Dose = 3 mg/kg

Duration = 1.5-6 hrs

*Use for spinal and topical

Question 12

What is the max dose of bupivacaine? Typical duration of neural blockade?

Answer 12

Max Dose = 3 mg/kg

Duration = 1.5-8 hrs

*Used for epidural, spinal, infiltration, peripheral nerve block

Question 13

What is the max dose of lidocaine? Typical duration of neural blockade?

Answer 13

Max Dose = 4.5 mg/kg (7 mg/kg with epi)

Duration = 0.75-2 hours

*Used for epidural, spinal, infiltration, peripheral nerve block, IV regional, topical

Question 14

What is the max dose of mepivacaine? Typical duration of neural blockade?

Answer 14

Max Dose = Max Dose = 4.5 mg/kg (7 mg/kg with epi)

Duration = 1-2 hrs

*Used for epidural, infiltration, peripheral nerve block

Question 15

What is the max dose of prilocaine? Typical duration of neural blockade?

Answer 15

Max Dose = 8 mg/kg

Duration = 0.5-1 hr

*used for peripheral nerve block (dental)

Question 16

What is the max dose of ropivacaine? Typical duration of neural blockade?

Answer 16

Max Dose = 3 mg/kg

Duration = 1.5-8 hours

*used for epidural, spinal, infiltration, peripheral nerve block

Question 17

What is the mechanism of action of local anesthetics?

Answer 17

Interrupt conduction of nerve pathway by binding of the drug in ionized form to Na+ channels in the nerve membrane decreasing the action potential

Must be in a nonionized state to cross the membrane – it will become ionized intracellularly and must be in the ionized state to bind to the receptor

Causes differential blockade: sympathetic first affected, then temp, followed by touch, pin-prick and proprioception and finally motor function

Question 18

How does lipid solubility of the local anesthetic affect potency and duration?

Answer 18

Increased lipid solubility = increased potency and duration

• also increases toxicity of LA – more lipid soluble = more toxic
• Nerves have lipid soluble membranes

Question 19

What is the site of action of local anesthetics?

Answer 19

Voltage gated Na+ channels

Binds to receptors INTRAcellularly

Question 20

What are the potency, onset of action, and duration of action of local anesthetics correlated with?

Answer 20

Potency: correlates directly with lipid solubility and molecular weight — more potent agents have a greater affinity for Na Channels

Onset: depends on lipid solubility and relative concentration of nonionized form — closer the pKa to physiologic pH, the greater the nonionized fraction (high pKa = slow onset – exception is chloroprocaine which has high pKa but still a fast onset due to its higher concentration of 3%)

Duration: correlated with lipid solubility and vascularity of area — more lipid soluble, longer DOA (less likely to be cleared by blood flow) – more protein bound, longer DOA (to AAG) and slower elimination

Question 21

How dose the concentration of local anesthetics affect potency?

Answer 21

Concentration of LA can overcome potency IF concentration is high enough for degree of clinical blockade, but does not affect duration of action (risk toxicity)

*exception is Chloroprocaine – it has high pKa so would normally have slow onset, but we can give such a large percentage that it overcomes its lack of potency

Question 22

What factors affect LA duration of action?

Answer 22

It is the extent to which the LA stays in the nerve ending vicinity that affects duration of LA

• Lipid solubility
• Vascularity of tissue
• Presence of vasoconstrictors

Question 23

How factors affect duration and onset of local anesthetics?

Answer 23

pH: onset is faster when LA is closest to the body’s pH
-adding bicarb can improve onset by 1-2 min (minimally clinically practical)

Diffusion: local anesthetics diffuse along gradient from periphery of nerve to interoir

• outer nerves = more proximal structures
• core nerves = motor fibers
• block moves from proximal structures to distal
• smaller amount and concentration of LA block only outer fibers, and the smaller more sensitive fibers

Question 24

How does nerve fiber prosperities affect duration?

Answer 24

Smaller fiber = shorter length = faster blockade

Myelin = faster block than unmyelin (LA pool by lipid) – why C fibers (smaller diameter) resist block (no myelin on C fibers)

In mixed nerve: motor is usually in large nerve trunk and outer portion of nerve: blocked first – lose motor before sensory

Question 25

What proteins do LA bind to?

Answer 25

Tightly bound to albumin -- high capacity = hard to saturate AAG = high affinity, low capacity = easily saturated

Question 26

List the following local anesthetics in degree of protein binding from low to high. Mepivacaine, Procaine, Lidocaine, Ropivacaine, 2-Chloroprocaine, Bupivacaine, Etidocaine

Answer 26

``` Low Protein Binding -2-Chloroprocaine -Procaine -Lidocaine -Mepivacaine -Ropivacaine -Etidocaine -Bupivacaine High Protein Binding ``` *higher the protein binding the longer the duration of action

Question 27

How dose pH affect the amount of free LA?

Answer 27

Low pH (acidic) = increased free LA High pH (basic) = decreased free LA * *LA toxicity = acidosis = more unbound LA = increased toxicity * Bupivacaine toxicity more pronounced than lidocaine

Question 28

What 3 factors affect LA Toxicity?

Answer 28

pH Vascularity of site Biotransformation of LA *explains why 150mg at popliteal is safe but not at cervical plexus

Question 29

What are the symptoms of LAST?

Answer 29

1. Drowsiness 2. Paresthesias in mouth and tongue 3. Tinnitus, auditory hallucinations 4. Muscular spasm 5. seizures 6. Coma 7. Respiratory arrest 8. Cardiac arrest *CNS is more sensitive to LA

Question 30

How do you treat LAST?

Answer 30

20% Intralipid -- 1.5-2 mL/kg bolus May repeat every 5 min if no ROSC Start infusion at 0.25 up to 1 mL/kg/min until ROSC MAX recommended dose is 10 mL/kg

Question 31

What is the brachial plexus derived from?

Answer 31

Anterior Rami of C5-T1 *innervates pectoral girdle and upper limb

Question 32

Describe the anatomy of the Brachial Plexus

Answer 32

- Roots: C5, C6, C7, C8, T1 - Trunks: Superior (C5/C6), Middle (C7), Inferior (C8/T1) - Cords: Lateral (Superior/Middle), Medial (Inferior), Posterior (Superior/Middle/Inferior) Peripheral Nerves: - Musculocutaneous (branch of lateral cord) - Median Nerve (lateral/medial cord merge) - Ulnar Nerve (branch of medial cord) - Axillary (branch of posterior cord) - Radial Nerve (continuation of posterior cord)

Question 33

What are the indications of an interscalene nerve block?

Answer 33

Surgery of the shoulder or upper arm

Question 34

What part of the brachial plexus does an interscalene nerve block occur? What do the nerves look like on ultrasound?

Answer 34

Block occurs at level of the ROOTS of the brachial plexus as they exit between the anterior and middle scalene muscles at the level of C6 (cricothyroid membrane) *Roots should appear as stacked round hypoechoic (black) densities -- stoplight appearance

Question 35

What needle type and local anesthetic should be used for an interscalene nerve block? (technique)

Answer 35

2 in , 22g short bevel insulated stimulating needle (inserted lateral to medial) 15-20 mL 0.5% Ropivacaine High frequency linear array transducer

Question 36

What are complications of an interscalene nerve block?

Answer 36

- Pneumothorax - Intravascular injection (vertebral artery enters at C6) - Horner's syndrome - Phrenic nerve block (diaphragm paralysis) - Hoarseness (block of recurrent laryngeal nerve) - Stellate ganglion block - LA toxicity

Question 37

What is Horner's Syndrome a result of? What are the symptoms?

Answer 37

Results from unintended blockage of superior cervical ganglion of sympathetic chain Triad of Symptoms: - Ipsilateral ptosis - Miosis - Nasal Congestion *Symptoms should disappear as brachial plexus block dissipates

Question 38

What arteries and muscles are seen during an interscalene ultrasound?

Answer 38

Anterior Scalene Middle Scalene Lateral Scalene Sternocleidomastoid ``` Carotid (medial to anterior scalene) Vertebral Artery (deep to anterior scalene) ```

Question 39

What are the indications for a supraclavicular nerve block?

Answer 39

Surgery below the shoulder

Question 40

What part of the brachial plexus does a supraclavicular nerve block occur? What does it look like on ultrasound?

Answer 40

Block occurs at the level of the TRUNKS/DIVISIONS of the brachial plexus as they cross over the first rib before traversing under the clavicle (get between the 1st rib and clavicle) * Plexus will be found lateral and superficial to the subclavian artery * called "supraclavicular block" because needle entry and US probe placement occur superior to the clavicle

Question 41

What needle type and local anesthetic should be used for a supraclavicular nerve block?

Answer 41

2 in 22g short bevel insulated stimulating needle (inserted lateral to medial) 15-20 mL 0.5% Ropivacaine High frequency linear array transducer place in supraclavicular fossa behind the clavicle

Question 42

What are complications of a supraclavicular nerve block?

Answer 42

-Pneumothorax (always keep needle tip in view) -Nerve Injury -Intravascular injection -Bleeding/Hematoma -LA toxicity -Obese pts may have supraclavicular fat pads - difficult to identify anatomy Individuals with short neck may increase difficulty of anatomic identification *higher risk than with interscalene block

Question 43

What is the anatomy of the supraclavicular space?

Answer 43

- Brachial plexus in a sheath with subclavian artery - Passes below the clavicle and above the 1st rib - Close proximity to the cupola of the lung - Plexus is positioned cephaloposterior in relation to the subclavian artery *brachial plexus looks hyperechoic on the US lateral to the subclavian artery

Question 44

What position should the patient be in for a supraclavicular nerve block?

Answer 44

Supine with head turned slightly to contralateral side Length of US prove resting superior to clavicle -- firmly over the supraclavicular fossa * probe should be in a coronal oblique position * want to obtain as cylindrical a view of the subclavian artery as possible

Question 45

What are the indications for a superficial cervical plexus block?

Answer 45

- Carotid Endarterectomy (may need additional local intraoperativley as it does not provide innervation to carotid intima and profound bradycardia may be seen w/o additional LA by surgeon) - Neck Surgery (lympth node dissection) - Supplementation to shoulder surgery** --- ISB may not fully cover cutaneous innervation for things such as trochar placement during shoulder arthroscopy

Question 46

What equipment do you need for a superficial cervical plexus block?

Answer 46

+/- US with linear probe (8-14 MHz) -- can easily be performed w/o US 10-15 mL LA Short nerve block needle, 25g

Question 47

Describe the anatomy of the cervical plexus

Answer 47

Arises from C2-C4 ventral rami and lies in the plane just behind the SCM giving off both superficial and deep branches - Lesser Occipital - Greater Auricular - Transverse Cervical - Supraclavicular nerves (composed of 3 branches)

Question 48

What are the landmarks for the superficial cervical plexus?

Answer 48

Nerves exit into subQ tissue posterior to SCM - with pt head turned slightly away, identify posterior border of SCM belly -- have pt lift head slightly off bed to better visualize - identify mastoid process and transverse process of C6 at level of cricoid - mark midway point between the two * Alternative = create imaginary line along posterior border of SCM from mastoid to clavicle insertion -- insert needle 2/3 the way up from clavicle * C5-C7 roots look hypoechoic on US

Question 49

Describe the needle technique of a superficial cervical plexus block

Answer 49

performed in the SubQ tissue so needle is NOT inserted deeply A "Fan" technique is used, depositing 3-5 mL in 3 directions *needle should never be inserted more than 1-2 cm

Question 50

What part of the brachial plexus does a infraclavicular nerve block occur?

Answer 50

Block occurs at the level of the 3 CORDS of the brachial plexus

Question 51

Describe the Infraclavicular Anatomy

Answer 51

- Cords are arranged around the axillary artery - Lateral cord will be lateral and superior to AA - Posterior cord will be posterior to AA - Medial cord will be posterior and medial to AA - Pectoralis minor and major are anterior to brachial plexus while scapula is posterior

Question 52

What are the indications for a infraclavicular block?

Answer 52

Surgery for elbow, forearm, hand For patients who may not be amenable to other brachial plexus blocks * doesn't block shoulder or really any upper arm * alternative to supraclavicular block in pts with COPD or respiratory insufficiency

Question 53

What equipment is needed for an infraclavicular block?

Answer 53

US with linear probe (8-14 MHz) 3/4 in 22g block needle (very shallow block) -- inserted cephalad to caudal 20-30 mL of LA

Question 54

What position should the patient be in for an infraclavicular block?

Answer 54

Supine with head turned away from extremity Abduct arm 90 degress (will cause brachial plexus to be taut, bringing the cords closer together US probe is positioned in a sagittal plane below clavicle medially to the coracoid process and inferior to the clavicle -- nerves look hyperechoic on the US surrounding the axillary artery

Question 55

Due to anatomic variation what is a key for an infraclavicular block?

Answer 55

Don't block each cord specifically, but rather surround the artery sufficiently with LA to cover probable locations of the cords

Question 56

What part of the brachial plexus does an axillary nerve block occur?

Answer 56

The most distal brachial plexus block, targeting the individual main terminal branches except for the axillary nerve which doesn't enter the upper extremity *doesn't actually block axillary nerve

Question 57

Describe the anatomy of the axillary

Answer 57

At the level of the axilla, the musculocutaneous nerve has departed from the rest of the BP and is coursing through the coracobrachialis muscle The remaining three (median, ulnar, & radial) nerves are situated in a neurovascular bundle containing the brachial artery and brachial vein. - median = superficial and lateral to brachial artery - ulnar = superficial and medial - radial = posterior *wide anatomic variation from individual to individual

Question 58

What are the indications of an axillary block?

Answer 58

Elbow, forearm, and hand surgery *might get a little higher block than with infraclavicular

Question 59

What equipment is needed for an axillary block?

Answer 59

US with linear probe (8-14 MHz) 3-4 in 22g block needle (inserted lateral to medial) 20-30 mL of LA

Question 60

What position should the patient be in for an axillary block?

Answer 60

Supine, head turned away from extremity to be blocked Arm abducted 90 degrees with arm flexed at the elbow US probe in axilla transverse to brachial artery -- probe placed immediately distal to where pec major inserts into humerus

Question 61

Describe what you see on the US when doing an axillary block

Answer 61

Musculocutaneous - often found in fascial place between biceps and coracobrachialis, often oval shaped and very hyperechoic Three terminal branches around the artery are also usually hyperechoic * even slightly firm pressure can easily occlude the axillary vein -- vein should be identified prior to needle placement to reduce risk of puncture * needle insertion is a shallow angle * 10-15 mL of LA around each terminal nerve branch

Question 62

What is the femoral nerve anatomy?

Answer 62

- dorsal divisions of anterior rami L2-L4 - descends through lateral border of the psoas - enters thigh under inguinal ligament - then divides in the anterior and posterior branches Anterior branch - motor innervation to sartorious and pectineus and sensory to skin of anterior and medial thigh Posterior branch - motor to quads and sensory to medial aspect of lower leg via saphenous nerve

Question 63

What are the indications of a femoral nerve block?

Answer 63

Surgery of the anterior thigh Knee Arthroscopy TKA Femoral shaft fractures Complete blockade of lower extremity when combined with sciatic nerve block * onset 15-20 min * anterior thigh, knee and medial aspect of lower leg

Question 64

What are contraindications of a femoral nerve block?

Answer 64

Preexisting femoral neuropathy Local infection

Question 65

What are the palpable landmarks for a femoral nerve block?

Answer 65

Position = Supine - ASIS - Pubic Symphysis - Line between ASIS and PS is inguinal ligament (usually femoral crease) - Femoral artery -- Femoral nerve lies 1-2 cm lateral

Question 66

What is the US position for a femoral nerve block?

Answer 66

- Linear probe for most pts - Begin by placing probe parallel with inguinal crease - Crease will appear lower than inguinal ligament in the obese - Find femoral artery and look for structures - If both superficial and deep branches of femoral artery are visible scan more cephalad just above their convergence - Counter traction of large pannus or abdomen by an assistant or tape is helpful *lymph nodes in groin appear as nerves -- scanning proximal/distal will help distinguish as they are not continuous

Question 67

How should you insert the needle for a femoral nerve block?

Answer 67

- In plane, lateral to medial approach - Needle entry 1-2 cm lateral of transducer - Keep fem artery in the medial edge of image, and nerve in the center - Tilting the transducer may help identify the nerve from surrounding structures - Advance the needle tip until it is adjacent to the nerve - Needle passage through fascia iliaca is often felt as a pop - Circumferential spread of 20-40mL of LA - May require needle reposition, but is often not needed

Question 68

If doing a femoral nerve block in conjunction with nerve stimulator, what should you look for?

Answer 68

Quad stimulation or patellar snap *if needle and LA are placed below the fascia iliaca and lateral the artery, successful blocks occur despite the lack of twitches

Question 69

What are the indications for an adductor canal block?

Answer 69

ACL repair TKA Ankle/Foot surgery Complete blockade of lower extremity when combined with sciatic nerve block Saphenous nerve stripping *onset 15-20 min

Question 70

What are the benefits of an adductor canal block over a femoral nerve block?

Answer 70

Quadriceps sparing Fewer falls, better participation in PT

Question 71

What are the landmarks for an adductor canal block?

Answer 71

Position: supine with leg externally rotated (frog-leg) Typically linear probe -- transverse probe placement Mid-thigh halfway between inguinal ligament and patellar tendon Superficial FA and FV If femur is visible you're too lateral

Question 72

What muscles border the adductor canal?

Answer 72

Sartorius Vastus Medialis Adductor Longus

Question 73

What is the anatomy of the adductor canal?

Answer 73

Saphenous in the AC is pure sensory branch of the posterior division of the femoral nerve Bound by three muscles (sartorius, vastusmedialis, adductor longus) Courses beneath sartorius and passes through AC in its entirety Exits in the distal canal between sartorius and gracilis alongside the descending geniculate artery and continues along greater saphenous vein

Question 74

What needle technique is used for an adductor canal block?

Answer 74

- In plane, lateral to medial approach - Needle entry 1-2 cm lateral of transducer - Keep superficial femoral artery in the center of the screen - Tilting the transducer may help identify nerve from surrounding structures - Advance needle tip until it is adjacent to the nerve - Circumferential spread of 10-20mL of LA (should displace artery and obscure AC contents) - If nerve is not obviously identifiable inject LA on both sides of the superficial femoral artery *high frequency linear array transducer -- short axis image, in plane needle insertion

Question 75

What are the indications of a saphenous below the knee block?

Answer 75

Ankle/Foot surgery Complete blockade below the knee when combined with sciatic nerve block * onset ~10 min * Poor success rate (35-70% full success)

Question 76

What are the benefits of a saphenous below the knee block over an adductor canal block?

Answer 76

Field block US is not needed Faster to perform

Question 77

Describe the anatomy of the saphenous nerve

Answer 77

Largest sensory branch of femoral nerve Only nerve below the knee not derived from sciatic nerve Cutaneous innervation of medial, anteromedial, and posteromedial lower leg * Can also be anesthetized with femoral or AC block * Often blocked in conjunction with sciatic for complete block below the knee

Question 78

What are the landmarks for a saphenous below the knee block?

Answer 78

Position = Supine 1) Tibial tuberosity 2) Medial head of gastrocnemius - infiltrate the deep subQ tissue in a line from tibial tuberosity to head of gastroc -- 5-10mL of LA - Beware of saphenous vein that runs near anterior aspect of gastroc

Question 79

Describe the anatomy of the sciatic nerve

Answer 79

- Largest nerve in the body - formed from anterior rami of L4-S3 - contains most of the sciatic plexus (L4-S4) - exits the pelvis at the greater sciatic foramen - travels under the gluteus maximus - contains the tibial and common peroneal nerves - sciatic nerve bundle separates at mid thigh Mixed motor and sensory: - motor to posterior thigh, leg, and foot muscles - sensory to skin of posterior thigh, anterior/lateral leg and foot

Question 80

What are the indications of a sciatic nerve block?

Answer 80

Provides anesthesia to the leg below the knee (knee, tibia, ankle, foot) Block results in anesthesia of posterior aspect of the knee, hamstring muscles, and entire lower limb below the knee -- both motor and sensory with the exception of skin on medial leg and foot *complete LE blockade requires additional blockade of femoral nerve

Question 81

What are the indications of a popliteal sciatic nerve block?

Answer 81

Foot and ankle surgery - offers improved tourniquet tolerance over ankle block for foot surgery - must combine with saphenous or femoral block for complete anesthesia below the knee *spares the hamstring muscles

Question 82

What equipment is needed for a popliteal sciatic nerve block?

Answer 82

US with high frequency linear transducer (8-12 MHz) -- curved probe for obese Syringes of your choice of LA Standard nerve block tray 50-100mm 4in stim needle Peripheral nerve stimulator Sterile gloves

Question 83

Describe the anatomy of the popliteal fossa

Answer 83

Bordered by biceps femoris (laterally) and semimembranosus and semitendinosus muscles (medially) Sciatic nerve splits 5-10 cm from popliteal crease -- tibial nerve and common peroneal nerve *located superficial to popliteal artery & vein and is slightly lateral

Question 84

What are the possible patient positions for a popliteal sciatic nerve block?

Answer 84

Supine - knee up/bent Lateral Prone

Question 85

What is the anatomy of the lumbar plexus?

Answer 85

Arises from ventral rami of L1-L4 (occasionally T12) Major Nerves from it: - Femoral nerve - Obturator nerve - Lateral femoral cutaneous - Ilioinguinal - Iliohypogastric

Question 86

What is the anatomy of the lumbosacral plexus?

Answer 86

Arises from L4-5 - S1-5 Sciatic nerve is major nerve that arises from the plexus *supplies sensory and motor innervation to the posterior thigh, knee, and lower extremity below the knee with exception to sensory innervation provided by saphenous nerve

Question 87

What are the five nerves that supply innervation to the foot?

Answer 87

- Tibial n. (medial aspect) - Deep peroneal n. - Superficial peroneal n. (top of foot) - Saphenous n. (medial ankle) - Sural n. (lateral aspect)