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APEX > Unit 12 - Positioning & Nerve Injury > Flashcards

Unit 12 - Positioning & Nerve Injury Flashcards

1
Q

how does the awake patient compensate for moving from sitting to standing position

A

SNS activated (baroreceptor reflex), which combats the effect of gravity (venous pooling) and ensures perfusion of brain and other vital organs

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2
Q

how does GA attenuate the body’s protective mechanisms against position changes

A

impaired baroreceptor responsiveness and decreased SNS tone

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3
Q

now does neuraxial anesthesia attenuate the body’s protective mechanisms against position changes

A

sympathectomy

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4
Q

how does positive pressure ventilation attenuate the body’s protective mechanisms against position changes

A

increased intrathoracic pressure results in decreased venous return

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5
Q

how do muscle relaxants attenuate the body’s protective mechanisms against position changes

A

decreased skeletal muscle tone = decreased venous return

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6
Q

Frank-Starling curve in trendelenburg and lithotomy positions

A

shifts to the right

blood shifts toward central circulation, increasing venous return

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7
Q

MAP in trendelenburg and lithotomy positions

A

stays the same or increases - venous return initially increases but is followed by vasodilation and a slower HR

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8
Q

complications of increased venous pressure in Trendelenburg and lithotomy positions

A

hydrostatic pressure leads to edema of face, eye, and airway

increased ICP

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9
Q

Frank Starling curve in sitting, flexed lateral, and prone positions

A

curve shifts to the left

blood shifts away from central circulation, resulting in venous pooling and decreased venous return

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10
Q

why are sitting, flexed lateral, and prone positions associated with higher incidence of hemodynamic instability?

A

anesthesia impairs baroreceptor responsiveness, so SNS is unable to fully compensate for preload reduction

results in decreased SV, CO, and BP

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11
Q

what 4 positions are assoc. with higher incidence of hemodynamic instability under GA?

A
  1. reverse trendelenburg
  2. sitting
  3. flexed lateral
  4. prone
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12
Q

name 5 common anesthesia techniques that attenuate the body’s compensatory mechanisms for maintaining CV stability in Trendelenburg position

A
  1. general anesthesia
  2. neuraxial anesthesia
  3. positive pressure ventilation
  4. PEEP
  5. muscle relaxants
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13
Q

4 consequences of abdominal shift in Trendelenburg position

A
  1. diaphragm moves cephalad
  2. FRC decreased
  3. pulmonary compliance decreased
  4. risk of endobronchial intubation increased
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14
Q

3 respiratory changes in the awake and spontaneously breathing patient vs. anesthetized and spontaneously breathing patient

A
  • decreased Vt
  • decreased FRC
  • increased closing volume
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15
Q

changes to perfusion in the dependent lung in lateral decubitus position

A
  • increased blood flow
  • increased vascular pressure
  • decreased vascular resistance
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16
Q

ventilation changes in the dependent region of the lung in upright position

A
  • increased alveolar ventilation
  • increased alveolar compliance
  • increased PACO2
  • decreased PAO2
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17
Q

ventilation changes in non-dependent lung region in upright position

A
  • decreased alveolar ventilation
  • decreased alveolar compliance
  • decreased PACO2
  • increased PAO2
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18
Q

perfusion changes in the non-dependent region of the lung in lateral decubitus position

A
  • decreased blood flow
  • decreased vascular pressure
  • increased vascular resistance
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19
Q

how do neck flexion and extension affect ETT placement

A

flexion pushes the ETT tip towards the carina

extension pulls the ETT tip towards vocal cords

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20
Q

how does airway edema form in prone, trendelenburg, and sitting positions

A

prone and trendelenburg: increased hydrostatic pressure results in edema formation

sitting: neck flexion impaires venous drainage from head and results in edema

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21
Q

where may the tip of the endotracheal tube settle when a patient is shifted into Trendelenberg position?

A

mainstem bronchus - abd contents shift cephalad and pushes diaphragm towards ETT, increasing risk of endobronchial intubation

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22
Q

why does every surgical position increase the risk of brachial plexus stretching/injury

when is the risk of stretch injury highest?

A

the brachial plexus is anatomically fixed at the cervical vertebrae and axillary fascia

risk of injury highest when arms ABducted > 90 degrees and head is rotated to other side

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23
Q

what causes compression injury of the brachial plexus

A

brachial plexus is compressed as it passes between the clavicle and first rib or by an external force (ex. shoulder braces, improperly placed axillary roll)

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24
Q

when is there a risk of brachial plexus compression during open heart surgery?

A

excessive sternal retraction during median sternotomy can compress the brachial plexus under the first rib

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25
Q

what is a safer option than shoulder braces in the Trendelenburg position?

if shoulder braces are used, where should they be placed?

A

non-sliding mattress

if used, place at the distal end of each clavicle over the acromion

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26
Q

when might the arms need to be tucked in prone position?

A

assess for thoracic outlet syndrome in preop - ask pt to clasp hands behind their head. if they c/o pain, may be prudent to tuck arms in prone position

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27
Q

where is the axillary roll placed in lateral decubitus position

what is a good monitor for neurovascular compression with an ax roll

A

distal to the axilla

weak SpO2 signal in dependent arm

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28
Q

leg positioning in lateral decubitus position

A

downside thigh and knee are flexed and padded

upside thigh and leg are extended and separated from lower leg with pillows

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29
Q

where should the retaining strap be placed on the patient in lateral decubitus position

A

placed across the hip and fixed to the underbelly of the OR table. strap should be placed between iliac crest and head of femur

second strap can be placed over thorax or shoulders

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30
Q

what type of brachial plexus injury can occur when a bean bag is used for positioning?

A

compression

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31
Q

how high above the head can the arms be safely positioned in prone position?

A

arms should not be extended over the head - keep shoulders and elbows at 90 degrees or less

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32
Q

presentation of ulnar nerve injury

A
  • impaired sensation of 4th and 5th digits
  • inability to ABduct or oppose pinky finger
  • chronic injury presents with claw hand (muscular atrophy)
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33
Q

most commonly injured peripheral nerve

A

ulnar nerve

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34
Q

mechanisms of ulnar nerve injury

A
  1. external compression (tight arm strap on forearm)
  2. elbow flexion = increased distance between medial epicondyle and olecranon = decreased cubital tunnel size = increased pressure on ulnar nerve
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35
Q

5 risk factors for ulnar nerve injury

A
  • male (esp. > 50 yrs old)
  • preexisting ulnar neuropathy
  • body habitus extremes
  • prolonged hospital stay/bedrest
  • cardiac surgery
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36
Q

when does ulnar neuropathy typically present

A

> 24 h postop

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37
Q

what should you do if a pt has ulnar sensory deficits postop?

A
  • neurology consult within first week of injury

- typically resolve in 5 days or less

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38
Q

recovery time for ulnar nerve injuries with motor deficits

A

4-6 weeks if demyelination involved

some are irreversible

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39
Q

what to do for a patient with motor deficits from ulnar nerve injury

A
  • neuro consult with EMG and nerve conduction studies

- physical therapy required for severe injuries

40
Q

which has a better chance of resolving - ulnar nerve injury with motor or sensory deficits?

A

sensory - more common, less serious, tend to resolve in 5 days or less

41
Q

location of median nerve

A

next to basilic and median cubital veins in cubital fossa

42
Q

causes of median nerve injury

A

(rare)

  • IV in AC
  • carpal tunnel syndrome
  • elbow hyperextension
  • forced elbow extension during positioning after a NMB has been admin.
43
Q

only nerve that passes through the carpal tunnel

A

median nerve

44
Q

presentation of median nerve injury

A
  • reduced sensation over palmar surface of thumb, index finger, middle finger, and lateral aspect of ring finger
  • unable to oppose thumb
  • chronic injury can lead to ape hand deformity
45
Q

causes of radial nerve injury

A
  • external compression by IV pole
  • excessive cycling of NIBP cuff
  • sheets that are too tight if arms are tucked
46
Q

nerve that passes along the spiral groove at the lateral aspect of the humerus

A

radial n.

47
Q

presentation of radial nerve injury

A

wrist drop

48
Q

long thoracic nerve arises from:

A

C5-C7

49
Q

what does the long thoracic nerve innervate

A

serratus anterior muscle

SALT (Serratus Anterior Long Thoracic)

50
Q

causes of long thoracic nerve injury

A
  • lateral position
  • trauma
  • preexisting neuropathy
51
Q

nerve injury suspected with dorsal protrusion of scapula (scapular winging)

A

long thoracic nerve

52
Q

what does the suprascapular nerve innervate

A

supraspinatus and infraspinatus muscles

53
Q

etiology of suprascapular nerve injury

how to prevent?

A

patient in lateral decubitus rolling (ventral circumduction) on dependent arm

properly stabilize patient and place an axillary roll distal to axilla to reduce risk of nerve injury

54
Q

where is the suprascapular nerve anchored

A

between cervical spine and suprascapular notch

55
Q

presentation of suprascapular nerve injury

A

dull shoulder pain

56
Q

why is lithotomy position assoc. with common peroneal nerve injury

A

nerve wraps around the fibular head and can be compressed if lateral aspect of leg leans against stirrup bar

57
Q

presentation of common peroneal nerve injury

A
  • foot drop
  • inability to evert foot
  • inability to extend toes dorsally
58
Q

etiology of obturator injury

A
  • excessive flexion of thigh towards groin
  • excessive traction during lower abd surgery
  • forceps delivery
59
Q

what nerve injury should be ruled out with inability to ADDuct leg or reduced sensation over medial aspect of thigh?

A

obturator n.

60
Q

prevention of obturator nerve injury

A

minimize hip flexion

61
Q

cause of femoral nerve injury

A

excessive traction during lower abd surgey

62
Q

presentation of femoral n. injury

A

impaired knee extension and hip flexion

reduced sensation over anterior thigh and anteromedial aspect of leg

63
Q

how to prevent femoral n. injury

A

avoid excessive traction during lower abd. surgery

64
Q

etiology of saphenous n. injury

A

medial aspect of leg leans against supporting cradle in lithotomy position

65
Q

nerve injury to rule out with reduced sensation over anteromedial aspect of leg

A

saphenous n.

66
Q

how to prevent saphenous n. injury

A

place padding between leg and stirrup

67
Q

3 ways to prevent a common peroneal n. injury

A
  1. place padding between leg and stirrup
  2. pad under fibular head
    3, knees should be flexed with minimal rotation
68
Q

etiology of sciatic n. injury

A
  • lithotomy (extreme hip flexion or external rotation of legs)
  • sitting (straight legs)
69
Q

presentation of sciatic n. injury

A

foot drop

70
Q

3 ways to prevent sciatic n. injury

A
  1. ample padding under buttocks
  2. avoid excessive external rotation of hips
  3. flex table at knees
71
Q

etiology of pudendal injury

A

occurs when nerve is compressed against a perineal post on an orthopedic fracture table

72
Q

presentation of pudendal injury

A

loss of perineal sensation

73
Q

prevention of a pudendal n. injury

A

padding between perineal post and patient

74
Q

nerve injuries that can result if patients legs are left crossed

A

top leg = sural n. injury

bottom leg = superfiical peroneal n. injury

75
Q

what is midcervical tetraplegia? what causes it?

A

ischemia results from stretching or compression of mid-cervical spinal cord (usually C5) from neck hyperflexion

most common in sitting position

76
Q

position most associated with compartment syndrome

A

lithotomy

77
Q

risk factors for lower extremity compartment syndrome in lithotomy position

A
  • surgical time > 2-3 hours
  • increased BMI
  • decreased tissue oxygenation (hypotension)
78
Q

consequences of venous air embolism in the right heart

A

can go to pulmonary vasculature and increase dead space and RV workload

79
Q

consequences of a paradoxical air embolism in a pt with PFO

A

embolus travels to left heart, then systemic circulation and can cause a stroke

80
Q

method to prevent lower back pain after anesthesia

A

place a small pad under lumbar spine to preserve lordosis

81
Q

risk factors for paraplegia in supine position

A

extreme hyperextension of lumbar spine

  • maximal retroflexion of OR table
  • raising kidney rest to highest position
  • placing large rolls under lumbar spine
82
Q

how many fingers should you be able to place between the chin and chest of a patient in sitting position

A

2

83
Q

surgery with risk of postoperative midcervical tetraplegia

A

tracheal resection

84
Q

primary objectives when placing pt in prone position and why

A

minimize pressure on abdomen and vena cava - improves pulmonary mechanics and venous return, decreases venous pressure

85
Q

why are positioning devices used to allow pt’s abdomen to hang freely in prone position

A

promotes normal diaphragmatic excursion

a compressed abdomen = increased IAP = decreased pulmonary compliance and increased intrathoracic pressure

86
Q

why can prone positioning increase bleeding in posterior spine surgery

A

increased venous pressure can cause back bleeding via epidural veins

87
Q

best option to preserve normal pulmonary mechanics when prone - Jackson table, Wilson frame, or chest rolls?

A

jackson frame

88
Q

why do we use prone position for pt with ARDS?

A

provides optimal V/Q matching

89
Q

tumors likely to occur in anterior mediastinum

A

4 T’s

  1. thymoma
  2. teratoma
  3. thyroid
  4. “terrible” lymphoma
90
Q

3 vital structures that can be compressed by an anterior mediastinal tumor

A
  1. tracheobronchial tree
  2. pulmonary artery
  3. SVC
91
Q

3 key factors that worsen tracheobronchial compression in patients with medastinal masses

A
  1. supine position
  2. induction of GA
  3. positive pressure ventilation
92
Q

2 procedures that increase risk of midcervical tetraplegia

A
  1. tracheal resection

2. sitting crani

93
Q

foot drop is a sign of injury to which nerves

A

sciatic n.
common peroneal n.

94
Q

which surgical positions shift the Frank Starling curve to the left

A

flexed lateral
prone
sitting

95
Q

which surgical positions shift the frank starling curve to the right

A

trendelenburg
lithotomy

APEX (54 decks)

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