Unit 12 - Positioning & Nerve Injury Flashcards
how does the awake patient compensate for moving from sitting to standing position
SNS activated (baroreceptor reflex), which combats the effect of gravity (venous pooling) and ensures perfusion of brain and other vital organs
how does GA attenuate the body’s protective mechanisms against position changes
impaired baroreceptor responsiveness and decreased SNS tone
now does neuraxial anesthesia attenuate the body’s protective mechanisms against position changes
sympathectomy
how does positive pressure ventilation attenuate the body’s protective mechanisms against position changes
increased intrathoracic pressure results in decreased venous return
how do muscle relaxants attenuate the body’s protective mechanisms against position changes
decreased skeletal muscle tone = decreased venous return
Frank-Starling curve in trendelenburg and lithotomy positions
shifts to the right
blood shifts toward central circulation, increasing venous return
MAP in trendelenburg and lithotomy positions
stays the same or increases - venous return initially increases but is followed by vasodilation and a slower HR
complications of increased venous pressure in Trendelenburg and lithotomy positions
hydrostatic pressure leads to edema of face, eye, and airway
increased ICP
Frank Starling curve in sitting, flexed lateral, and prone positions
curve shifts to the left
blood shifts away from central circulation, resulting in venous pooling and decreased venous return
why are sitting, flexed lateral, and prone positions associated with higher incidence of hemodynamic instability?
anesthesia impairs baroreceptor responsiveness, so SNS is unable to fully compensate for preload reduction
results in decreased SV, CO, and BP
what 4 positions are assoc. with higher incidence of hemodynamic instability under GA?
- reverse trendelenburg
- sitting
- flexed lateral
- prone
name 5 common anesthesia techniques that attenuate the body’s compensatory mechanisms for maintaining CV stability in Trendelenburg position
- general anesthesia
- neuraxial anesthesia
- positive pressure ventilation
- PEEP
- muscle relaxants
4 consequences of abdominal shift in Trendelenburg position
- diaphragm moves cephalad
- FRC decreased
- pulmonary compliance decreased
- risk of endobronchial intubation increased
3 respiratory changes in the awake and spontaneously breathing patient vs. anesthetized and spontaneously breathing patient
- decreased Vt
- decreased FRC
- increased closing volume
changes to perfusion in the dependent lung in lateral decubitus position
- increased blood flow
- increased vascular pressure
- decreased vascular resistance
ventilation changes in the dependent region of the lung in upright position
- increased alveolar ventilation
- increased alveolar compliance
- increased PACO2
- decreased PAO2
ventilation changes in non-dependent lung region in upright position
- decreased alveolar ventilation
- decreased alveolar compliance
- decreased PACO2
- increased PAO2
perfusion changes in the non-dependent region of the lung in lateral decubitus position
- decreased blood flow
- decreased vascular pressure
- increased vascular resistance
how do neck flexion and extension affect ETT placement
flexion pushes the ETT tip towards the carina
extension pulls the ETT tip towards vocal cords
how does airway edema form in prone, trendelenburg, and sitting positions
prone and trendelenburg: increased hydrostatic pressure results in edema formation
sitting: neck flexion impaires venous drainage from head and results in edema
where may the tip of the endotracheal tube settle when a patient is shifted into Trendelenberg position?
mainstem bronchus - abd contents shift cephalad and pushes diaphragm towards ETT, increasing risk of endobronchial intubation
why does every surgical position increase the risk of brachial plexus stretching/injury
when is the risk of stretch injury highest?
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
what causes compression injury of the brachial plexus
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)
when is there a risk of brachial plexus compression during open heart surgery?
excessive sternal retraction during median sternotomy can compress the brachial plexus under the first rib
what is a safer option than shoulder braces in the Trendelenburg position?
if shoulder braces are used, where should they be placed?
non-sliding mattress
if used, place at the distal end of each clavicle over the acromion
when might the arms need to be tucked in prone position?
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
where is the axillary roll placed in lateral decubitus position
what is a good monitor for neurovascular compression with an ax roll
distal to the axilla
weak SpO2 signal in dependent arm
leg positioning in lateral decubitus position
downside thigh and knee are flexed and padded
upside thigh and leg are extended and separated from lower leg with pillows
where should the retaining strap be placed on the patient in lateral decubitus position
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
what type of brachial plexus injury can occur when a bean bag is used for positioning?
compression
how high above the head can the arms be safely positioned in prone position?
arms should not be extended over the head - keep shoulders and elbows at 90 degrees or less
presentation of ulnar nerve injury
- impaired sensation of 4th and 5th digits
- inability to ABduct or oppose pinky finger
- chronic injury presents with claw hand (muscular atrophy)
most commonly injured peripheral nerve
ulnar nerve
mechanisms of ulnar nerve injury
- external compression (tight arm strap on forearm)
- elbow flexion = increased distance between medial epicondyle and olecranon = decreased cubital tunnel size = increased pressure on ulnar nerve
5 risk factors for ulnar nerve injury
- male (esp. > 50 yrs old)
- preexisting ulnar neuropathy
- body habitus extremes
- prolonged hospital stay/bedrest
- cardiac surgery
when does ulnar neuropathy typically present
> 24 h postop
what should you do if a pt has ulnar sensory deficits postop?
- neurology consult within first week of injury
- typically resolve in 5 days or less
recovery time for ulnar nerve injuries with motor deficits
4-6 weeks if demyelination involved
some are irreversible
what to do for a patient with motor deficits from ulnar nerve injury
- neuro consult with EMG and nerve conduction studies
- physical therapy required for severe injuries
which has a better chance of resolving - ulnar nerve injury with motor or sensory deficits?
sensory - more common, less serious, tend to resolve in 5 days or less
location of median nerve
next to basilic and median cubital veins in cubital fossa
causes of median nerve injury
(rare)
- IV in AC
- carpal tunnel syndrome
- elbow hyperextension
- forced elbow extension during positioning after a NMB has been admin.
only nerve that passes through the carpal tunnel
median nerve
presentation of median nerve injury
- 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
causes of radial nerve injury
- external compression by IV pole
- excessive cycling of NIBP cuff
- sheets that are too tight if arms are tucked
nerve that passes along the spiral groove at the lateral aspect of the humerus
radial n.
presentation of radial nerve injury
wrist drop
long thoracic nerve arises from:
C5-C7
what does the long thoracic nerve innervate
serratus anterior muscle
SALT (Serratus Anterior Long Thoracic)
causes of long thoracic nerve injury
- lateral position
- trauma
- preexisting neuropathy
nerve injury suspected with dorsal protrusion of scapula (scapular winging)
long thoracic nerve
what does the suprascapular nerve innervate
supraspinatus and infraspinatus muscles
etiology of suprascapular nerve injury
how to prevent?
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
where is the suprascapular nerve anchored
between cervical spine and suprascapular notch
presentation of suprascapular nerve injury
dull shoulder pain
why is lithotomy position assoc. with common peroneal nerve injury
nerve wraps around the fibular head and can be compressed if lateral aspect of leg leans against stirrup bar
presentation of common peroneal nerve injury
- foot drop
- inability to evert foot
- inability to extend toes dorsally
etiology of obturator injury
- excessive flexion of thigh towards groin
- excessive traction during lower abd surgery
- forceps delivery
what nerve injury should be ruled out with inability to ADDuct leg or reduced sensation over medial aspect of thigh?
obturator n.
prevention of obturator nerve injury
minimize hip flexion
cause of femoral nerve injury
excessive traction during lower abd surgey
presentation of femoral n. injury
impaired knee extension and hip flexion
reduced sensation over anterior thigh and anteromedial aspect of leg
how to prevent femoral n. injury
avoid excessive traction during lower abd. surgery
etiology of saphenous n. injury
medial aspect of leg leans against supporting cradle in lithotomy position
nerve injury to rule out with reduced sensation over anteromedial aspect of leg
saphenous n.
how to prevent saphenous n. injury
place padding between leg and stirrup
3 ways to prevent a common peroneal n. injury
- place padding between leg and stirrup
- pad under fibular head
3, knees should be flexed with minimal rotation
etiology of sciatic n. injury
- lithotomy (extreme hip flexion or external rotation of legs)
- sitting (straight legs)
presentation of sciatic n. injury
foot drop
3 ways to prevent sciatic n. injury
- ample padding under buttocks
- avoid excessive external rotation of hips
- flex table at knees
etiology of pudendal injury
occurs when nerve is compressed against a perineal post on an orthopedic fracture table
presentation of pudendal injury
loss of perineal sensation
prevention of a pudendal n. injury
padding between perineal post and patient
nerve injuries that can result if patients legs are left crossed
top leg = sural n. injury
bottom leg = superfiical peroneal n. injury
what is midcervical tetraplegia? what causes it?
ischemia results from stretching or compression of mid-cervical spinal cord (usually C5) from neck hyperflexion
most common in sitting position
position most associated with compartment syndrome
lithotomy
risk factors for lower extremity compartment syndrome in lithotomy position
- surgical time > 2-3 hours
- increased BMI
- decreased tissue oxygenation (hypotension)
consequences of venous air embolism in the right heart
can go to pulmonary vasculature and increase dead space and RV workload
consequences of a paradoxical air embolism in a pt with PFO
embolus travels to left heart, then systemic circulation and can cause a stroke
method to prevent lower back pain after anesthesia
place a small pad under lumbar spine to preserve lordosis
risk factors for paraplegia in supine position
extreme hyperextension of lumbar spine
- maximal retroflexion of OR table
- raising kidney rest to highest position
- placing large rolls under lumbar spine
how many fingers should you be able to place between the chin and chest of a patient in sitting position
2
surgery with risk of postoperative midcervical tetraplegia
tracheal resection
primary objectives when placing pt in prone position and why
minimize pressure on abdomen and vena cava - improves pulmonary mechanics and venous return, decreases venous pressure
why are positioning devices used to allow pt’s abdomen to hang freely in prone position
promotes normal diaphragmatic excursion
a compressed abdomen = increased IAP = decreased pulmonary compliance and increased intrathoracic pressure
why can prone positioning increase bleeding in posterior spine surgery
increased venous pressure can cause back bleeding via epidural veins
best option to preserve normal pulmonary mechanics when prone - Jackson table, Wilson frame, or chest rolls?
jackson frame
why do we use prone position for pt with ARDS?
provides optimal V/Q matching
tumors likely to occur in anterior mediastinum
4 T’s
- thymoma
- teratoma
- thyroid
- “terrible” lymphoma
3 vital structures that can be compressed by an anterior mediastinal tumor
- tracheobronchial tree
- pulmonary artery
- SVC
3 key factors that worsen tracheobronchial compression in patients with medastinal masses
- supine position
- induction of GA
- positive pressure ventilation
2 procedures that increase risk of midcervical tetraplegia
- tracheal resection
2. sitting crani
foot drop is a sign of injury to which nerves
sciatic n.
common peroneal n.
which surgical positions shift the Frank Starling curve to the left
flexed lateral
prone
sitting
which surgical positions shift the frank starling curve to the right
trendelenburg
lithotomy
