Positioning - Exam 3 Flashcards
CVP (preload) and SV will _ in response to blood pooling dependently
decrease
BP effects from NMBD:
decreases venous return due to abolished muscle tone
Under normal circumstances in healthy pt, low BP is compensated for by increased _ and _
HR and SV
GA blocks which compensatory mech for low BP
increased HR
Hemodynamic changes are LEAST likely to be seen as a result from which position/s?
lateral and supine
Which positions are likely to decrease CO and BP
sitting
prone
FLEXED lateral when LE are DEPENDENT
In the prone position what happens to CVP and LV volume?
CVP increases
LV volume decreases
-decreased venous return and increased intrathoracic pressure
Opioids can decreased CO and BP because they can decrease _
HR
GA blunts HR when hypoTN happens, making it more reliant on _ for venous return
gravity
What impact does the prone position have on CI?
can possibly reduce
What can cause BP to APPEAR normal of higher in the lithotomy position?
autotransfusion from gravity redistributing blood in dependent structures more centrally (raising CVP)
Acute issues/ comorbidities contributing to risk for positioning injury:
-body habitus extremes
-preexisting neurological issues
-Arthritis/ joint mobility issues
-DM - neuropathy
-ETOH / liver disease(malnourished)
-PVD
-HTN/HoTN
-anemia
-smoking
-temperature extremes
-old, male
-Anticoags (hematoma risk)
Intraop (equipment) factors influencing positioning injury risk
-table straps
-leg holders/stirrups
-axillary rolls
-bolsters
-shoulder braces
-fracture table post
-positioning frames
-headrests
-ether screen
-case length > 4-5hr
-GA
-HoTN technique
-NMBD
-tourniquette >3hrs
Peripheral nerves consist of a cell body and an _
axon
Axons of peripheral nerves are wrapped in _ _ which form the myelin sheath and this is all surrounded by _ protecting the individual nerve cell
SchwannCells
endoneurium
Collections of nerve fibers (endoneurium) are surrounded by a layer called _
perineurium
The perineurium is encapsulated with other perineuria and blood vessels by a layer called the _, forming the peripheral nerve
epineurium
Injury to the myelin sheath or axon of a nerve can lead to:
-focal conduction block
-degeneration
-demyelination
Arteries inside nerves are called _ _ and they supply the internal nerve and its outside layer
vasa nervorum
Most common cause of nerve injury is ISCHEMIA from _ or _ of the neural vasa nervorum
stretching or compression
MAP increases or decreases by approximately __ mmHg per inch each change in height between the heart and a body region
2
Gravity favors perfusion of ______ portion and ventilation in ________ region
Dependent; Nondependent
In relation to the respiratory system, what is the preferred position and why?
Sitting Position
Forced vital capacity and FRC are within normal parameters. Sitting causes less change in distribution, ventilation and perfusion
What is the most detrimental positions for the respiratory system and why?
Prone Positioning:
-GOOD for ARDS: posterior lung segments better
ventilated and alleviation of pressure of anterior mass
-BAD for Healthy: diaphragmatic excursion limited by
abdominal viscera (free-hanging belly increases FRC)
Lateral Position:
-abdomen displaces diaphragm up, decreasing
ventilation in dependent lung (reducing its compliance) but
increasing ventilation in nondependent lung (increasing comp)
Lithotomy or Trendelenburg Positioning:
-shift in abdomen limits diaphragmatic movement
Worse in obese individuals
May shift ETT right mainstem
What is the common component of all peripheral nerve injuries?
Ischemia (occlusion, emboli, edema)
What may augment development of ischemia?
Low MAP
What are the primary mechanisms for nerve injuries?
Transection, compression, and stretch
What are the patient related factors of PPNI?
Gender, Advanced age, extremes in body habitus
Lung capacities are typically _ in most positions
reduced
What preexisting conditions contribute to development of PPNI?
DM, hypertension, and tobacco use
What intraoperative occurrences contribute to PPNI risk?
Hypothermia, hypoxia, and electrolyte imbalances
Arm abduction should be limited to __ degrees while in a supine position
90
Arm abduction may tolerate more than 90 degrees while in what position
Prone
Stretching of hamstring muscle group beyond range may stretch what nerve resulting in limited hep flexion?
Sciatic Nerve
While in Trendelenburg, what increases the risk of periop neuropathies?
Shoulder braces
What should be assessed after surgery relating to this positioning lecture?
Extremity Nerve Function
In supine, trendelenburg, and lithotomy positions, what are some potential causes of brachial plexus injury?
Supine:
Arm abuducted >90 degrees on board
Arm falls off table edge
Arm abduction and lateral flexion of the head to the opposite side
Trendelenburg:
Shoulder braces placed too medial or lateral
Lateral: thorax pressure exertion on dependent shoulder and axilla
What are the positioning recommendations to protect the brachial plexus while in supine, trendelenburg, and lithotomy?
Do not abduct arm >90 degrees
Ensure arms are adequately secured
Support head in neutral alignment
To protect the brachial plexus, how should the shoulder brace be placed while in Trendelenburg?
Over the acromioclavicular joint, but avoid if possible.
To protect the brachial plexus, how should a roll be placed while in lateral position?
Place roll caudad to axilla supporting the upper part of the thorax
What is a frequent cause of ulnar nerve injury?
Arm pronated on arm board
What are the positioning recommendations to protect the ulnar nerve?
Supinate/neutral forearm on padded arm board
do not flex elbows more than 90 degrees
Pad elbows
Draw sheet should extended avoid elbow and be tucked between patient and mattress
Tucked arms in neutral position with palms facing inward
To protect the sciatic nerve, what are the positioning recommendations?
Minimal external rotation of legs
knees should be flexed
Recommendation to protect obturator nerve?
minimal hip flexion
What is the most frequently reported injury after surgery and anesthesia that is more frequently associated with males?
Ulnar neuropathy
What is ulnar neuropathy characterized by?
Inability to oppose/A the fifth finger and diminished sensation to fourth and fifth finger
Claw like contracture with atrophy
What is typically the site of injury for ulnar n injury? Why?
Cubital tunnel retinaculum(CTR)
-results from nerve compression/direct pressure on CTR from unpadded surface
T/F: Ulnar Neuropathy is from increased pressure with arm extension
False - flexion
When elbow is flexed, the distance between the olecranon and medial epicondyle increases, stretching the CTR, decreasing the size of the tunnel and can result in increased pressure on the nerve
In a supine position, why does abduction of the arms beyond 90 degrees put the brachial plexus at risk?
It stretches the plexus around the humeral head. Turning head to the side with arms abducted can cause stretching and compression of the contralateral brachial plexus beneath the clavicle
In a lateral position, the weight of the chest and compress the lower shoulder and axilla. Why is this an issue?
This puts pressure on the axillary neurovascular bundle aka brachial plexus
In a lateral decubitus position, what are the 4 reasons for brachial plexus injury?
arm abduction >90
external rotation
extension of lateral flexion of the head
posterior shoulder displacement
Shoulder braces placed too close to the base of the neck results in this injury (in reverse trendelenburg)
Compress structures resulting in brachial plexus neuropathy. Shoulder braces should be placed at distal end of clavicle over AC joint, but ARE BEST AVOIDED*
during cardiac surgery, what causes the first rib to rotate up pinching the plexus?
Sternal retractors
To prevent injury, caudal placement of the sternal retractor and avoidance of excessive prolonged asymmetric chest wall retraction are recommended
Mammary dissection requires this and may predispose to brachial plexus neuropathy
Wider asymmetric chest retraction
How can hyperflexion of the head on the neck be avoided in any position
Allow a minimum of 2 fingerbreadths between the sternum and mandible
Increased vertebral venous pressure can cause what type of injury?
spinal cord injury :((
Transcranial electric motor evoked potential is recommended for the detection of what 3 injuries?
Spinal cord, brachial plexus, and ulnar nerve injury due to positioning
What are the 5 main causes of Postoperative visual loss (POVL)
Ischemic optic neuropathy
central retinal artery occlusion
Central retinal vein occlusion
Cortical blindness
Glycine toxicity
What makes up 89% of prone injuries?
Ischemic optic nerve
What is the difference between anterior ION and posterior ION?
Anterior to lamina cribrosa
Posterior to lamina cribrosa
What is an anatomical cause of increased hypoperfusion of the optic nerves?
Supplied by central retinal and posterior ciliary arteries that are end arteries. This means that blood supply is from a “watershed region” indicating the region receives blood supply from the most distal branches of two arteries
Name the two factors that disrupt autoregulatory mechanisms and may contribute to ischemia of the optic nerve during hypotension
DM and hypertension
T/F: treatment for POVL can result in full recovery of vision and generally has a positive prognosis.
False! usually results in perminent visual loss and has a poor prognosis
What therapy has the highest chance of improvement in visual acuity when treatment is started within 6 hours of symptom onset?
Hyperbaric oxygen therapy
Name the 7 significant factors for POVL
Obesity
Sex
Wilson frame
Long operative times
Greater blood loss
Lower colloid:crystalloid ratio in the nonblood fluid loss
Colloid: albumin
Crystalloid: .9NS, LR, D5 ect
T/F: ION does not seem to be associated with pressure injury on the globe while CRAO does
True!
Define ocular perfusion pressure OPP
OPP = MAP - IOP
avoid increased IOP
avoid decreased OPP
T/F: venous pressure, IOP, and OPP all have a direct relationship
False, venous pressure and IOP have a direct relationship, but have an inverse relationship in OPP
Intraoperative events that decrease MAP and reduce OPP are (4)
GA
Hypotension
Hemorrhage
Hypovolemia
What is characterized by severe unilateral vision loss immediately following surgery?
CARO
What is the most common cause of CARO?
External pressure on the eyes due to improper head position
Because of this, CRAO is characterized by unilateral blindness
Emboli (hypercoagulation) migrating to CRA
What are the 3 perioperative risk factors for CRAO?
Prone spinal surgery
cardiopulmonary bypass surgery
Head/Neck procedures where injections are performed around nose and eyes