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Anesthesia Principles II > Regional Lecture I part II > Flashcards

Regional Lecture I part II Flashcards

1
Q

mechanisms of nerve injury?

A

mechanical
stretch
pressure/compression
chemical
vascular (prolonged disruption of BF to nerve)

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2
Q

are LA drugs neurotoxic?

A

yes they all are to some degree. Cause histological changes, but usually not clinically significant

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3
Q

how does lidocaine affect blood flow?

A

inhibits neural blood flow

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4
Q

have neural injury rates changed with introduction of ultrasound?

A

no

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5
Q

are nerve injuries primarily from intraneural injections?

A

no, we used to think so though.

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6
Q

does intrafascular injection equal nerve injury?

A

yes

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7
Q

is it okay to inject into a nerve?

A

No, it might not cause injury (unless intrafasicular) but we still want to avoid this.

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8
Q

where do axons run?

A

in the fassicules

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9
Q

what is epinerium?

A

protective connective tissue forming the outer covering of nerves, as well as inner supportive tissue

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10
Q

how would an intrafasicular injection feel to the anesthesia provider?

A

there is higher injection pressure

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11
Q

why do risks of nerve injury decrease distally?

A

there are only a few large fascicles bound by a sheath proximally. these are easy to needle

distally there are many small fascicles without a sheath so needles have a hard time entering the fasicle.

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12
Q

two kinds of vascular nerve injuries?

A

intrinsic within epineurium and extrinsic around nerve

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13
Q

key factors in post op neuropathy mgmt?

A

communication (ensure pt you are on it and don’t blow it off)

surgeon - possible procedural component

neurology - involve them earlier than later (can do electrophysiological testing)

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14
Q

when should you immediately involve neurology for post op neuropathy?

A

motor involvement in nerve injury

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15
Q

how long should you follow patient after post op nerve injuyr?

A

until symptoms resolve or stabilize

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16
Q

how quickly do sensory symptoms resolve in post-op neuropathy?

A

95% in 4-6 weeks
99% in 1 year

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17
Q

Techniques for finding nerves?

A

landmarks
paresthesia
nerve stimulator
ultrasound
fluoroscopy
CT guided

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18
Q

what kind of images to fluroscopy and CT provide?

A

still and live images

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19
Q

when is fluroscopy for PNB used?

A

mostly in pain blocks and is expensive

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20
Q

when is CT used to guide PNBs?

A

rarely in pain blocks, is extremely expensive

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21
Q

What is the paresthesia technique and how is it done?

A

old technique that creates a feeling of tingling, tickling, burning, prickly or buzzing.

goal is to place needle in direct contact with the nerve to produce a paresthesia, then slightly withdraw the needle and inject.

this has a risk of neural injury and higher block failure rates

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22
Q

should you inject LA if the pat has sharp pain or paresthesia?

A

NO!!!

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23
Q

how does nerve stimulator technique affect motor or sensory nerves?

A

motor nerve - muscle twitch

sensory nerve - paresthesia over target nerve distribution

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24
Q

what kind of impulse does nerve stimulator use?

A

negative polarity impulse

this neutralizes the positive current outside the nerve dropping the membrane potential

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25
Q

what does black lead attach to?

A

the needle

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26
Q

what does red lead attach to?

A

the skin

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27
Q

are highly myelinated nerves motor or sensory?

A

motor

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28
Q

are unmyelinated nerves motor or sensory?

A

sensory

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29
Q

which nerves have the lowest threshold of external stimulation to generate an AP?

A

(highly myelinated) motor nerves

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30
Q

which nerves have the highest threshold for external stimulation to generate an AP?

A

(unmyelinated) sensory nerves

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31
Q

what is amplitude?

A

strength of an electrical stimulus

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32
Q

what impulses are best for discrimination of distance?

A

short duration

33
Q

current duration for motor?

A

0.1ms

34
Q

current duration for sensory?

A

0.3ms (longer duration needed to reach threshold level)

35
Q

frequency used with nerve stimulator?

A

1-2 Hz

36
Q

amplitude for nerve stimulator?

A

start at 1.5 mA

37
Q

what is the goal with nerve stimulator technique?

A

loss of motor response at 0.3-0.5mA

this indicates needle is in correct position

38
Q

is it okay to inject at 0.29mA?

A

No! never inject at less than 0.3mA (0.2mA by some sources)

39
Q

is the nerve stimulator technique reliable?

A

No, only 74.5% sensitivity for needle to nerve contact

40
Q

how often do you get no muscle twitch even wheen needle is actually touching the nerve with the nerve stimulator technique?

A

25% of the time

41
Q

what does it mean if you have a twitch present at 0.2-0.3mA?

A

you are ALWAYS intranural

42
Q

if > 0.3mA can you be in a nerve?

A

No

43
Q

What is SENSe Mode?

A

sequential electrical nerve stimulation

44
Q

how does SENSe mode work?

A

2 short at 0.1ms

0.2ms @ 0.3 mA
0.42ms @ 1 mA
0.84ms @ 2 mA

longer pulse reaches further in tissue

45
Q

what is the goal with SENSe mode?

A

current at 0.3-0.5 mA with 3 twitches

46
Q

is insulated/coated or non insulated needle ideal for nerve stimulation technique?

A

insulated is best

47
Q

what kind of bevel do stimulating needles use?

A

blunt bevel

48
Q

how does piezoelectric material in US probe work?

A

converts electricty to sound waves adn then sound waves back to elecricity. Sends out cyclical pulses of US energy

49
Q

how many crystals in ultrasound probe?

A

100-300

sum of all crystals creates the US beam

50
Q

how much does US probe talk vs listen?

A

talk 2%

Listen 98%

51
Q

where does the majority of US energy go?

A

gets converted to heat

52
Q

4 things that can happen to US waves?

A

reflection
scatter
absorption
attenuation (degredation)

53
Q

what frequency is commonly used for ultrasound?

A

2-15 MHz

54
Q

what is the primary determinant of lateral and axial resolution?

A

wavelength

55
Q

what is primary determinant of temporal resolution?

A

frame rate (typically 30 frames/sec)

56
Q

is curvelinear probe low or high frequency?

A

low frequency

best for deep structures

57
Q

linear ( high frequency) probe can be used for up to what depth?

A

6cm

58
Q

curvelinear ( low frequency) probe can be used for up to what depth?

A

up to 14cm

59
Q

another name for curvilinear probe?

A

phase aray

60
Q

What is B-mode?

A

brightness

2D image that is typically used

61
Q

what is M-mode used for?

A

useful in assessment of specific tissues

heart valves, lung

62
Q

is high pitch moving towards or away from the probe? What color?

A

toward the probe (red color)

63
Q

is low pitch moving towards or away from the probe? What color?

A

away (blue color)

64
Q

what is gain?

A

brightness of image on the screen

65
Q

when is doppler mode used?

A

aide in detecting vascular structures

66
Q

what shape are nerves on US?

A

round, oval, or triangular

67
Q

how do nerves appear on US?

A

hyper or hypo echoic, or honeycomb

68
Q

what can US waves not penetrate?

A

air or bone

69
Q

what kinds of artifact can you get with US?

A

shadowing
enhancement
reverberation
mirror image
velocity error

70
Q

what is enhancement?

A

overly intense echogenicity behind an object.

blood vessel or cyst

71
Q

what is reverberation?

A

equally spaced bright linear echoes below an object, like your US needle

72
Q

when is out of plane mode used?

A

mostly for vascular access

73
Q

what plane would you need for direct visualization of LA injection?

A

needle in plane mode

74
Q

Pros and cons of single shot PNB?

A

easier to do
fewer risks
effects generally limited to < 24 hours

75
Q

how long can perineural catheter stay in?

A

up to 72 hours

76
Q

do continuous catheters work well in femoral location?

A

Eh, just associated with quad weakness and falls

77
Q

what area are continuous perineural catheters being used more often?

A

adductor canal

78
Q

why are ergonomics so important, especially when you are learning PNBs?

A

so you don’t fatigue and can actually finish the block

79
Q

what is the triad of safety for PNBs?

A

nerve stimulator
injection monitoring
ultra sound guidance

Anesthesia Principles II (14 decks)

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