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Basics of Anesthesia > Week 3 - Peripheral Regional Anesthesia > Flashcards

Week 3 - Peripheral Regional Anesthesia Flashcards

1
Q

What are reasons you would use regional anesthesia?

A

Improved postop pain relief

Less nausea

Ability to spare anesthetic complications in comorbid conditions

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2
Q

What are the layers of a peripheral nerve?

A
  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
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3
Q

Define Dermatome, Myotome, and Osteotome

A

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

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4
Q

What is the chemical structure of local anesthetics?

A

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
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5
Q

How are esters and amide LA’s metabolized?

A

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

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6
Q

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

A

Esters

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

**allergy to amides is usually due to a preservative

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7
Q

What LAs can cause Methemoglobinemia?

A

Amides

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

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8
Q

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

A

Max Dose = 12 mg/kg

Duration = 0.5-1 hour

*used for epidural, infiltration, peripheral nerve block

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9
Q

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

A

Max Dose = 3 mg/kg

Duration = 0.5-1 hr

*topical use

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10
Q

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

A

Max Dose = 12 mg/kg

Duration = 0.5-1 hr

*used for spinal, infiltration, peripheral nerve block

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11
Q

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

A

Max Dose = 3 mg/kg

Duration = 1.5-6 hrs

*Use for spinal and topical

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12
Q

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

A

Max Dose = 3 mg/kg

Duration = 1.5-8 hrs

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

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13
Q

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

A

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

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14
Q

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

A

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

Duration = 1-2 hrs

*Used for epidural, infiltration, peripheral nerve block

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15
Q

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

A

Max Dose = 8 mg/kg

Duration = 0.5-1 hr

*used for peripheral nerve block (dental)

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16
Q

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

A

Max Dose = 3 mg/kg

Duration = 1.5-8 hours

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

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17
Q

What is the mechanism of action of local anesthetics?

A

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

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18
Q

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

A

Increased lipid solubility = increased potency and duration

  • also increases toxicity of LA – more lipid soluble = more toxic
  • Nerves have lipid soluble membranes
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19
Q

What is the site of action of local anesthetics?

A

Voltage gated Na+ channels

Binds to receptors INTRAcellularly

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20
Q

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

A

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

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21
Q

How dose the concentration of local anesthetics affect potency?

A

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

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22
Q

What factors affect LA duration of action?

A

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
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23
Q

How factors affect duration and onset of local anesthetics?

A

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
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24
Q

How does nerve fiber prosperities affect duration?

A

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

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25
Q

What proteins do LA bind to?

A

Tightly bound to albumin – high capacity = hard to saturate

AAG = high affinity, low capacity = easily saturated

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26
Q

List the following local anesthetics in degree of protein binding from low to high.

Mepivacaine, Procaine, Lidocaine, Ropivacaine, 2-Chloroprocaine, Bupivacaine, Etidocaine

A 
Low Protein Binding
-2-Chloroprocaine
-Procaine
-Lidocaine
-Mepivacaine
-Ropivacaine
-Etidocaine
-Bupivacaine
High Protein Binding

*higher the protein binding the longer the duration of action

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27
Q

How dose pH affect the amount of free LA?

A

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
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28
Q

What 3 factors affect LA Toxicity?

A

pH

Vascularity of site

Biotransformation of LA

*explains why 150mg at popliteal is safe but not at cervical plexus

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29
Q

What are the symptoms of LAST?

A
  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

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30
Q

How do you treat LAST?

A

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

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31
Q

What is the brachial plexus derived from?

A

Anterior Rami of C5-T1

*innervates pectoral girdle and upper limb

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32
Q

Describe the anatomy of the Brachial Plexus

A
  • 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)
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33
Q

What are the indications of an interscalene nerve block?

A

Surgery of the shoulder or upper arm

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34
Q

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

A

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

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35
Q

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

A

2 in , 22g short bevel insulated stimulating needle (inserted lateral to medial)

15-20 mL 0.5% Ropivacaine

High frequency linear array transducer

36
Q

What are complications of an interscalene nerve block?

A
  • 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
37
Q

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

A

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

38
Q

What arteries and muscles are seen during an interscalene ultrasound?

A

Anterior Scalene
Middle Scalene
Lateral Scalene
Sternocleidomastoid

Carotid (medial to anterior scalene)
Vertebral Artery (deep to anterior scalene)
39
Q

What are the indications for a supraclavicular nerve block?

A

Surgery below the shoulder

40
Q

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

A

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
41
Q

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

A

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

42
Q

What are complications of a supraclavicular nerve block?

A

-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

43
Q

What is the anatomy of the supraclavicular space?

A
  • 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

44
Q

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

A

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
45
Q

What are the indications for a superficial cervical plexus block?

A
  • 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
46
Q

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

A

+/- US with linear probe (8-14 MHz) – can easily be performed w/o US

10-15 mL LA

Short nerve block needle, 25g

47
Q

Describe the anatomy of the cervical plexus

A

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)
48
Q

What are the landmarks for the superficial cervical plexus?

A

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
49
Q

Describe the needle technique of a superficial cervical plexus block

A

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

50
Q

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

A

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

51
Q

Describe the Infraclavicular Anatomy

A
  • 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
52
Q

What are the indications for a infraclavicular block?

A

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
53
Q

What equipment is needed for an infraclavicular block?

A

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

54
Q

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

A

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

55
Q

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

A

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

56
Q

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

A

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

57
Q

Describe the anatomy of the axillary

A

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

58
Q

What are the indications of an axillary block?

A

Elbow, forearm, and hand surgery

*might get a little higher block than with infraclavicular

59
Q

What equipment is needed for an axillary block?

A

US with linear probe (8-14 MHz)

3-4 in 22g block needle (inserted lateral to medial)

20-30 mL of LA

60
Q

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

A

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

61
Q

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

A

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
62
Q

What is the femoral nerve anatomy?

A
  • 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

63
Q

What are the indications of a femoral nerve block?

A

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
64
Q

What are contraindications of a femoral nerve block?

A

Preexisting femoral neuropathy

Local infection

65
Q

What are the palpable landmarks for a femoral nerve block?

A

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
66
Q

What is the US position for a femoral nerve block?

A
  • 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

67
Q

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

A
  • 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
68
Q

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

A

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

69
Q

What are the indications for an adductor canal block?

A

ACL repair

TKA

Ankle/Foot surgery

Complete blockade of lower extremity when combined with sciatic nerve block

Saphenous nerve stripping

*onset 15-20 min

70
Q

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

A

Quadriceps sparing

Fewer falls, better participation in PT

71
Q

What are the landmarks for an adductor canal block?

A

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

72
Q

What muscles border the adductor canal?

A

Sartorius

Vastus Medialis

Adductor Longus

73
Q

What is the anatomy of the adductor canal?

A

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

74
Q

What needle technique is used for an adductor canal block?

A
  • 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

75
Q

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

A

Ankle/Foot surgery

Complete blockade below the knee when combined with sciatic nerve block

  • onset ~10 min
  • Poor success rate (35-70% full success)
76
Q

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

A

Field block

US is not needed

Faster to perform

77
Q

Describe the anatomy of the saphenous nerve

A

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
78
Q

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

A

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
79
Q

Describe the anatomy of the sciatic nerve

A
  • 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
80
Q

What are the indications of a sciatic nerve block?

A

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

81
Q

What are the indications of a popliteal sciatic nerve block?

A

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

82
Q

What equipment is needed for a popliteal sciatic nerve block?

A

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

83
Q

Describe the anatomy of the popliteal fossa

A

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

84
Q

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

A

Supine - knee up/bent

Lateral

Prone

85
Q

What is the anatomy of the lumbar plexus?

A

Arises from ventral rami of L1-L4 (occasionally T12)

Major Nerves from it:

  • Femoral nerve
  • Obturator nerve
  • Lateral femoral cutaneous
  • Ilioinguinal
  • Iliohypogastric
86
Q

What is the anatomy of the lumbosacral plexus?

A

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

87
Q

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

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

Basics of Anesthesia (35 decks)

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