Unit 12 - Positioning & Nerve Injury

Question 1

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

Answer 1

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

Question 2

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

Answer 2

impaired baroreceptor responsiveness and decreased SNS tone

Question 3

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

Answer 3

sympathectomy

Question 4

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

Answer 4

increased intrathoracic pressure results in decreased venous return

Question 5

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

Answer 5

decreased skeletal muscle tone = decreased venous return

Question 6

Frank-Starling curve in trendelenburg and lithotomy positions

Answer 6

shifts to the right

blood shifts toward central circulation, increasing venous return

Question 7

MAP in trendelenburg and lithotomy positions

Answer 7

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

Question 8

complications of increased venous pressure in Trendelenburg and lithotomy positions

Answer 8

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

increased ICP

Question 9

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

Answer 9

curve shifts to the left

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

Question 10

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

Answer 10

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

results in decreased SV, CO, and BP

Question 11

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

Answer 11

1. reverse trendelenburg
2. sitting
3. flexed lateral
4. prone

Question 12

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

Answer 12

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

Question 13

4 consequences of abdominal shift in Trendelenburg position

Answer 13

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

Question 14

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

Answer 14

• decreased Vt
• decreased FRC
• increased closing volume

Question 15

changes to perfusion in the dependent lung in lateral decubitus position

Answer 15

• increased blood flow
• increased vascular pressure
• decreased vascular resistance

Question 16

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

Answer 16

• increased alveolar ventilation
• increased alveolar compliance
• increased PACO2
• decreased PAO2

Question 17

ventilation changes in non-dependent lung region in upright position

Answer 17

• decreased alveolar ventilation
• decreased alveolar compliance
• decreased PACO2
• increased PAO2

Question 18

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

Answer 18

• decreased blood flow
• decreased vascular pressure
• increased vascular resistance

Question 19

how do neck flexion and extension affect ETT placement

Answer 19

flexion pushes the ETT tip towards the carina

extension pulls the ETT tip towards vocal cords

Question 20

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

Answer 20

prone and trendelenburg: increased hydrostatic pressure results in edema formation

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

Question 21

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

Answer 21

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

Question 22

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

when is the risk of stretch injury highest?

Answer 22

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

Question 23

what causes compression injury of the brachial plexus

Answer 23

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)

Question 24

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

Answer 24

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

Question 25

what is a safer option than shoulder braces in the Trendelenburg position? if shoulder braces are used, where should they be placed?

Answer 25

non-sliding mattress if used, place at the distal end of each clavicle over the acromion

Question 26

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

Answer 26

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

Question 27

where is the axillary roll placed in lateral decubitus position what is a good monitor for neurovascular compression with an ax roll

Answer 27

distal to the axilla weak SpO2 signal in dependent arm

Question 28

leg positioning in lateral decubitus position

Answer 28

downside thigh and knee are flexed and padded upside thigh and leg are extended and separated from lower leg with pillows

Question 29

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

Answer 29

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

Question 30

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

Answer 30

compression

Question 31

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

Answer 31

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

Question 32

presentation of ulnar nerve injury

Answer 32

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

Question 33

most commonly injured peripheral nerve

Answer 33

ulnar nerve

Question 34

mechanisms of ulnar nerve injury

Answer 34

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

Question 35

5 risk factors for ulnar nerve injury

Answer 35

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

Question 36

when does ulnar neuropathy typically present

Answer 36

> 24 h postop

Question 37

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

Answer 37

- neurology consult within first week of injury | - typically resolve in 5 days or less

Question 38

recovery time for ulnar nerve injuries with motor deficits

Answer 38

4-6 weeks if demyelination involved some are irreversible

Question 39

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

Answer 39

- neuro consult with EMG and nerve conduction studies | - physical therapy required for severe injuries

Question 40

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

Answer 40

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

Question 41

location of median nerve

Answer 41

next to basilic and median cubital veins in cubital fossa

Question 42

causes of median nerve injury

Answer 42

(rare) - IV in AC - carpal tunnel syndrome - elbow hyperextension - forced elbow extension during positioning after a NMB has been admin.

Question 43

only nerve that passes through the carpal tunnel

Answer 43

median nerve

Question 44

presentation of median nerve injury

Answer 44

- 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

Question 45

causes of radial nerve injury

Answer 45

- external compression by IV pole - excessive cycling of NIBP cuff - sheets that are too tight if arms are tucked

Question 46

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

Answer 46

radial n.

Question 47

presentation of radial nerve injury

Answer 47

wrist drop

Question 48

long thoracic nerve arises from:

Answer 48

C5-C7

Question 49

what does the long thoracic nerve innervate

Answer 49

serratus anterior muscle SALT (Serratus Anterior Long Thoracic)

Question 50

causes of long thoracic nerve injury

Answer 50

- lateral position - trauma - preexisting neuropathy

Question 51

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

Answer 51

long thoracic nerve

Question 52

what does the suprascapular nerve innervate

Answer 52

supraspinatus and infraspinatus muscles

Question 53

etiology of suprascapular nerve injury how to prevent?

Answer 53

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

Question 54

where is the suprascapular nerve anchored

Answer 54

between cervical spine and suprascapular notch

Question 55

presentation of suprascapular nerve injury

Answer 55

dull shoulder pain

Question 56

why is lithotomy position assoc. with common peroneal nerve injury

Answer 56

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

Question 57

presentation of common peroneal nerve injury

Answer 57

- foot drop - inability to evert foot - inability to extend toes dorsally

Question 58

etiology of obturator injury

Answer 58

- excessive flexion of thigh towards groin - excessive traction during lower abd surgery - forceps delivery

Question 59

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

Answer 59

obturator n.

Question 60

prevention of obturator nerve injury

Answer 60

minimize hip flexion

Question 61

cause of femoral nerve injury

Answer 61

excessive traction during lower abd surgey

Question 62

presentation of femoral n. injury

Answer 62

impaired knee extension and hip flexion reduced sensation over anterior thigh and anteromedial aspect of leg

Question 63

how to prevent femoral n. injury

Answer 63

avoid excessive traction during lower abd. surgery

Question 64

etiology of saphenous n. injury

Answer 64

medial aspect of leg leans against supporting cradle in lithotomy position

Question 65

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

Answer 65

saphenous n.

Question 66

how to prevent saphenous n. injury

Answer 66

place padding between leg and stirrup

Question 67

3 ways to prevent a common peroneal n. injury

Answer 67

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

Question 68

etiology of sciatic n. injury

Answer 68

- lithotomy (extreme hip flexion or external rotation of legs) - sitting (straight legs)

Question 69

presentation of sciatic n. injury

Answer 69

foot drop

Question 70

3 ways to prevent sciatic n. injury

Answer 70

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

Question 71

etiology of pudendal injury

Answer 71

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

Question 72

presentation of pudendal injury

Answer 72

loss of perineal sensation

Question 73

prevention of a pudendal n. injury

Answer 73

padding between perineal post and patient

Question 74

nerve injuries that can result if patients legs are left crossed

Answer 74

top leg = sural n. injury | bottom leg = superfiical peroneal n. injury

Question 75

what is midcervical tetraplegia? what causes it?

Answer 75

ischemia results from stretching or compression of mid-cervical spinal cord (usually C5) from neck hyperflexion most common in sitting position

Question 76

position most associated with compartment syndrome

Answer 76

lithotomy

Question 77

risk factors for lower extremity compartment syndrome in lithotomy position

Answer 77

- surgical time > 2-3 hours - increased BMI - decreased tissue oxygenation (hypotension)

Question 78

consequences of venous air embolism in the right heart

Answer 78

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

Question 79

consequences of a paradoxical air embolism in a pt with PFO

Answer 79

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

Question 80

method to prevent lower back pain after anesthesia

Answer 80

place a small pad under lumbar spine to preserve lordosis

Question 81

risk factors for paraplegia in supine position

Answer 81

extreme hyperextension of lumbar spine - maximal retroflexion of OR table - raising kidney rest to highest position - placing large rolls under lumbar spine

Question 82

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

Answer 82

2

Question 83

surgery with risk of postoperative midcervical tetraplegia

Answer 83

tracheal resection

Question 84

primary objectives when placing pt in prone position and why

Answer 84

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

Question 85

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

Answer 85

promotes normal diaphragmatic excursion a compressed abdomen = increased IAP = decreased pulmonary compliance and increased intrathoracic pressure

Question 86

why can prone positioning increase bleeding in posterior spine surgery

Answer 86

increased venous pressure can cause back bleeding via epidural veins

Question 87

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

Answer 87

jackson frame

Question 88

why do we use prone position for pt with ARDS?

Answer 88

provides optimal V/Q matching

Question 89

tumors likely to occur in anterior mediastinum

Answer 89

4 T's 1. thymoma 2. teratoma 3. thyroid 4. "terrible" lymphoma

Question 90

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

Answer 90

1. tracheobronchial tree 2. pulmonary artery 3. SVC

Question 91

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

Answer 91

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

Question 92

2 procedures that increase risk of midcervical tetraplegia

Answer 92

1. tracheal resection | 2. sitting crani

Question 93

foot drop is a sign of injury to which nerves

Answer 93

sciatic n. common peroneal n.

Question 94

which surgical positions shift the Frank Starling curve to the left

Answer 94

flexed lateral prone sitting

Question 95

which surgical positions shift the frank starling curve to the right

Answer 95

trendelenburg lithotomy