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6903 - Special Populations > PNB - General > Flashcards

PNB - General Flashcards

1
Q

peripheral nerve blood flow is regulated by?

A

sympathetic nervous system

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2
Q

what is the epineurium?

A
  • enveloping external connective sheath

- contains many nerve fascicles

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3
Q

what is contained in a nerve fascicle?

A

-nerve fibers and capillaries in loose connective tissue

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4
Q

what is the perineurium?

A

-multi-layered epithelial sheath that surrounds the individual nerve fascicles

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5
Q

what type of junctions does the nerve capillary endothelium have?

A
  • tight junctions

* similar to BBB

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6
Q

should you perform nerve blocks in patients that are sedated or under general anesthesia?

A

-no: cannot tell you if they are having pain on injection

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7
Q

nerve blocks - mechanism of injury

A
  • mechanical: needle trauma, intraneuronal injection
  • neuronal ischemia
  • neurotoxicity of local anesthetics
  • drug error
  • infection
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8
Q

strategies to avoid mechanical injury

A
  • use short beveled needle
  • avoid high pressure injections
  • avoid fast injections
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9
Q

the ‘perfect storm’ of neuronal ischemia

A
  • endoneural injection
  • epinephrine-containing local anesthetics
  • prolonged tourniquet times
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10
Q

what is the best probe size for PNB?

A

25L

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11
Q

acoustic impedance

A
  • measure of how the ultrasound transverses the tissue

- depends on the density of the medium and velocity of the ultrasound through the medium

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12
Q

acoustic impedance mismatch

A
  • large difference in acoustic impedance

- the larger the mismatch, the more is reflected and less is transmitted

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13
Q

tissue attenuation

A
  • loss of ultrasound as a medium is transversed
  • due to absorption of ultrasound energy
  • increases as distance from probe increases
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14
Q

what is a wavelength? what does a wavelength tell us?

A
  • the distance between two areas of maximal compression (peak of wave)
  • wavelength is proportional to penetration of ultrasound
  • image resolution is no more than 1-2 wavelengths
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15
Q

what is frequency? high versus low frequency?

A
  • the number of wavelengths that pass per unit of time

- higher frequency = clearer image, lower penetration

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16
Q

hypo-echoic

A
  • reflect little amount of sound, absorb wave
  • appear dark
  • blood vessels
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17
Q

hyper-echoic

A
  • reflect large amounts of sound, do not absorb wave
  • appear bright
  • bone, air
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18
Q

in-plane

A
  • longitudinal view of entire length of probe

* best view

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19
Q

out-of-plane

A

-perpendicular to probe

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20
Q

which view is better, in plane or out of plane?

A

-in plane

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21
Q

short axis

A

-cross section of a structure

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22
Q

long axis

A

-longitudinal view of length of structure

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23
Q

where is the interscalene block completed?

A

-at the level of the roots of the brachial plexus

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24
Q

nerve anatomy levels

A
  • roots
  • trunks
  • divisions
  • cords
  • terminal nerves
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25
Q

the brachial plexus is what roots?

A

-C5-T1

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26
Q

what do the brachial plexus roots pass through when coming off the spinal cord?

A
  • posterior fascia of anterior scalene

- anterior fascia of middle scalene

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27
Q

where is the supraclavicular block completed?

A

-at the level of the divisions of the brachial plexus

28
Q

trunks of the brachial plexus

A
  • upper = C5-C6
  • middle = C7
  • lower = C8-T1
29
Q

where do the trunks of the branchial plexus travel through?

A
  • between anterior scalene and middle scalene
  • subclavian artery lies anterior to nerve bundle
  • pass behind the first rib and divide into divisions
30
Q

brachial plexus divisions

A
  • each trunk divides into an anterior and posterior division

- superior and posterior to the subclavian artery

31
Q

where is the infraclavicular block completed?

A

-at the level of the cords of the brachial plexus

32
Q

brachial plexus cords

A
  • three cords branch from divisions at the level of the coracoid process
  • lateral, medial, posterior cords
33
Q

brachial plexus cords: lateral

A
  • combines with a branch from median cord to form median nerve
  • musculocutaneous nerve
  • located in coracobrachialis muscle
34
Q

brachial plexus cords: medial

A
  • combines with a branch from lateral cord to form median nerve
  • ulnar nerve
  • located in subcutaneous tissues
35
Q

brachial plexus cords: posterior

A
  • radial nerve

- axillary nerve branches early

36
Q

brachial plexus terminal nerves

A
  • vary with anatomy

- remain close to axillary artery

37
Q

brachial plexus terminal nerves: radial

A

-posterior to axillary artery

38
Q

brachial plexus terminal nerves: median

A

-superior to axillary artery

39
Q

brachial plexus terminal nerves: ulnar

A

-inferior to axillary artery

40
Q

where is the axillary block completed?

A

-at the level of the terminal nerves of the brachial plexus

41
Q

what nerve is consistently missed in an axillary block? why?

A
  • musculocutaneous nerve

- its branches from the terminal branches early

42
Q

interscalene block - site blocked

A

-most reliable for C5-C7
-not reliable for C8-T1 (ulnar side)
-sensory anesthesia to cervical plexus (C2-C4)
-shoulder and upper arm
surgery
*caution for phrenic nerve paralysis (affects by volume injected)

43
Q

interscalene block - approach

A
  • supine with head turned away
  • landmarks: cricoid cartilage, lateral border of sternocleidomastoid muscle, interscalene groove
  • always aim needle caudal and lateral
44
Q

supraclavicular block - site blocked

A
  • forearm and hand, below mid-humerus level
  • nerves are tightly packed = onset is fast and deep
  • risk of pneumothorax
  • 20 mL to avoid phrenic nerve paralysis (60%)
45
Q

supraclavicular block - approach

A
  • arm at side
  • palpate clavicle and scalene muscles
  • place probe at midpoint of clavicle to locate subclavian artery
  • plexus is located superior and posterior to subclavian artery
46
Q

infraclavicular block - site blocked

A
  • below the mid-humerus
  • musculocutaneous nerve may need separate injection because it can diverge higher
  • longer onset
47
Q

infraclavicular block - approach

A
  • supine with head turned away
  • place probe interior to clavicle and medial to the coracoid
  • visualize axillary artery deep in pectoralis - cords surround it
  • always advance needle posterior and caudal to avoid pneumothorax
48
Q

axillary block - nerves missed

A
  • musculocutaneous
  • medial-brachial cutaneous
  • medial ante-brachial cutaneous
49
Q

axillary block - site blocked

A
  • hand surgeries

- multiple injections because of separation of terminal nerves

50
Q

axillary block - approach

A
  • supine with arm abducted 90 degrees and flexed at elbow

- identify axillary artery

51
Q

axillary block - non-ultrasound approaches

A
  • perivascular: advance needle close to artery while aspirating, withdraw and insert 3-4 mL, repeat twice and then complete on opposite side
  • trans-arterial approach: insert through vessel, inject 10 mL when there is no longer blood return, pull needle back through artery, inject 10 mL where there is no longer blood return
52
Q

mid-humeral approach: median

A
  • place PNS next to brachial artery on superior side in direction of axilla
  • flexion of wrist/fingers, pronation of forearm
53
Q

mid-humeral approach: ulnar

A
  • redirect needle posterior and inferior from brachial artery
  • flexion of wrist/ring finger + pinky, adduction of thumb
54
Q

mid-humeral approach: radial

A
  • close to ulnar

- extension of wrist/fingers

55
Q

mid-humeral approach: musculocutaneous

A
  • redirect needle superior to artery in coracobrachialis muscle
  • flexion of elbow
56
Q

Horner’s syndrome is associated with which block? what are the symptoms

A
  • interscalene

- ptosis, miosis, anhydrosis

57
Q

evaluation of brachial plexus block

A
  • push: radial
  • pull: musculocutaneous
  • pinch: lateral = ulnar
  • pinch: medial = median
58
Q

femoral nerve block -approach

A
  • supine with leg neutral
  • mark inguinal crease
  • lateral to femoral artery, superior to iliopsoas muscle
  • done out of plane
59
Q

intercostal nerve block - anatomy

A
  • VAN: vein, artery, nerve
  • thoracic nerve divided into ventral (intercostal nerves) and dorsal (posterior sensation to skin, muscles, and bones of back)
60
Q

intercostal nerve block - considerations

A
  • need to block above and below site because of crossover of intercostal nerves
  • good for analgesia, not anesthesia
  • local anesthetics are rapidly absorbed from intercostal space
  • blocks above T7 are difficult
61
Q

intercostal nerve block - approach

A
  • angle of the rib=6-8 cm lateral from spinous process
  • angle needle 20 degrees cephalad and advance until you hit the rib
  • readjust needle caudal, and repeat until you do not hit the rib
  • advance a few mm until you feel a pop when entering the neurovascular bundle
  • aspirate and inject 3-4 mL
62
Q

which nerves are blocked more easily?

A

small myelinated nerves

63
Q

potency of LA is determined by?

A

lipid solubility

64
Q

duration of LA is determined by?

A

protein binding

65
Q

onset of LA is determined by?

A

pKa

66
Q

nerve blocked by local anesthetics, in order of being blocked

A

c: pain (dull, pressure), temperature
B: autonomics
A delta: pain (sharp), touch

67
Q

what nerve innervates the posterior thigh?

A

-posterior femoral cutaneous nerve (S1-3)

6903 - Special Populations (16 decks)

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