CRNA 560- Positioning

what happens to patients cardiovascular system when patients are in the sitting or flexed lateral positions

decrease CO and BP

what happens to patients cardiovascular system when patients are proned

decrease CO, BP, left ventricular volume
-due to decrease venous return and inc intrathoracic pressure

increase CVP

what 4 body positions are associated with a higher incidence of hemodynamic instability under GA

reverse T, sitting, flexed lateral, prone

what occurs to the lungs when in the lateral decubitis position when under GA

upper lungs becomes easier to ventilate than dependent lung leading to V/Q mismatch

what can increase risk of endobronchial intubation

neck flexion (tube goes where the nose goes)
trendelenburg
-ABD shift towards head pushing diaphragm towards ETT

what can increase risk of inadvertent extubation

neck extension (tube goes where the nose goes)

what positions can cause edema of face, tongue, and pharynx
what causes this to occur

prone and trendelenburg
-increase hydrostatic pressure--> inc edema

sitting position
-neck flexion impairs venous drainage from head--> inc edema

arm positions while supine
-key things to not

abducted- less than 90 degrees minimize brachial plexus injury
adducted- securely placed next to body
one of each

hands- supinated or pam towards body
pad bony prominence, lines, equipment

what should be supported in the frog leg position

the knees to prevent dislocation and pain in hip

what occurs to the lungs when in the trendelenburg position when under GA

decrease FRC
-gravitational pull of diaphragm superior

when in lateral position poor SpO2 signal in the dependent arm can indicate

neurovascular compression
-axillary rolls to be placed inferior to axilla

when is brachial plexus at highest risk for stretch injury

arm abducted >90 and head rotated to other side

how do compression injury occur for brachial plexus

compressed between clavicle and 1st rib (shoulder braces)
axillary rolls improperly placed

what improper positions can cause ulnar nerve damage

arm pronated on armboard
-needs to be supine and padded

elbow flexed >90
-keep elbow flexion <90

inadequate elbow padding

elbow extending over table edge
-draw sheet should extend above elbow and tucked between patient and the mattress

how do ulnar nerve injuries present

impaired sensation to 4 & 5 finger
inability to abduct or oppose pinky
chronic injury- claw hand

what can cause radial nerve injury

arm compressed by a pole
excessive NIBP cycling
upper extremity tourniquets
sheets that are too tight when arms are tucked

how do radial nerve injuries present

wrist drop- inability to extend hand at wrist

what can cause common peroneal nerve injury

lithotomy- fibular neck rest against stirrup bar
-pad well between leg and stirrup

lithotomy- knees extended, legs externally rotated
-keep knees flex with minimal external rotation

lateral position- pressure on downside leg
-pad under fibular head

how do common peroneal nerve injuries present

from deep fibular
-foot drop
-inability to extend toes

from superficial fibular
-inability to evert foot

what can cause posterior tibial nerve injury

lithotomy- knee cradle stirrups can compress nerve
-generally pad under knee & avoid use of knee cradle stirrups for prolonged procedures

what can cause femoral nerve injury

excessive traction during lower abdomen surgery

how do femoral nerve injuries present

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

what can cause obturator nerve injury

lithotomy- excessive flexion of hip
excessive traction during lower abdominal surgery
forceps delivery

how do obturator nerve injuries present

inability to adduct leg
reduced sensation over medial thigh

what can cause pudendal nerve injury

nerve compressed again perineal post on orthopedic fracture tables
-needs adequate padding between post and pt

how do pudendal nerve injuries present

loss of perineal sensation

what can cause postoperative visual loss

ischemic optic neuropathy
central retinal artery occlusion
central retinal vein occlusion
cortical blindness
glycine toxicity

what are risk factors for ischemic optic neuropathy

male sex
obesity
wilson frame use
longer operative times
greater blood loss
lower colloid to crystalloid ration in nonblood fluid administration

what is the most common cause of central retinal artery occlusion

improper head positioning resulting in external pressure on eye

what perioperative factors can lead to central retinal artery occlusion

prone spine surgeries
CABG
head and neck procedures using injections around eyes

how does central retinal artery occlusion present

unilateral vision loss immediately after surgery

what is glycine toxicity

large amounts that are absorbed can lead to central nervous system toxicity including transient blindness, encephalopathy and ammonia toxicity (metabolite)

which position is most likely to cause venous air embolism

sitting position
positions that cause negative pressure gradient between RA and veins of operative site

how can air embolism be removed

aspiration though CVC