What are some causes of nerve injury?
- inadequate positioning
- preexisting conditions
- GA
- extremes of body habit us
- procedures >2hrs
What are some mechanisms of nerve injury?
- transaction
- compression
- stretching
- kinking
All = ischemia
Group of nerves running from neck, through shoulder, axilla, and arm
Brachial Plexus
What are the divisions of the the brachial plexus?
- Roots: 5
- Trunks: 3
- Divisions: 3 anterior, 3 posterior
- Cords: 3
- Branches: 5
Randy Travis Drinks Cold Beer
What are the 5 roots of the brachial plexus?
C5, C6, C7, C8, T1
In C-spine, roots come from above vertebrae, after T1, come from below - this is why there is a C8
Name the 5 peripheral branches of the brachial plexus
- musculocutaneous
- axillary
- radial
- median
- ulnar
*only radial, median and ulnar make it to the hand
Where is the lumbar plexus?
Runs along front of leg.
Femoral and saphenous are major branches
Where is the Sacral Plexus?
- Runs along back of the leg
- sciatic nerve is a major branch
Where is the “end-point” of the dermatomes?
The coccyx, not the feet
In the anesthetized pt, describe ventilation and perfusion of lungs: dependent vs non-dependent
- dependent lung has best perfusion
- non-dependent lung has best ventilation
*creates a V/Q mismatch
How does GA create postural hypotension?
-blunts compensatory sympathetic nervous system response with abrupt position changes
Treatment
- temporarily delay further posting changes
- reduce agent
- IVF to increase volume
- pressors
Supine position is also called what?
Dorsal Recumbent
Cardiac and respiratory considerations of supine position
Cardiac
- minimal
- pressures from head to foot approximate mean pressure at level of the heart
Respiratory
- FRC and total lung capacity are reduced bc ABD contents being pushed up
- spontaneous ventilation favors posterior lung (dependent) while controlled ventilation favors anterior (non-dependent) lung
Pressure may change by _____mmHg for each ______cm that a given point varies in vertical height below or above the reference point of the heart
2 mmHg
2.5 cm
CV, Respiratory and Neuro consideration of trendelenburg positoin
Cardiovascular
- activation of baroreceptors
- decrease CO
- decrease in peripheral vascular resistance
- decrease in HR and BP
Respiratory
- diaphragm displaced cephalad and ABD contents decreases FRC
- movement of mediastinum towards head moves carina closer to ETT and can result in tube moving into right mainstem
- increased V/Q mismatch
Neuro
- increased ICP and decrease cerebral blood flow
- increased intraocular pressure in pts with clay come
Consideration with reverse trendelenburg position
Cardiovascular
-decrease in preload, CO, and arterial pressures
Baroreceptors mediated increase in sympathetic tone, HR< and BP
Respiratory
- FRC increased
- easier to ventilate
Neuro
-CPP and blood flow decrease
Consideration for lithotomy position
Cardiovascular
- auto transfusion from elevation of legs above the trunk causes central blood volume to increase
- returning legs to supine has the opposite effect decreasing volume and preload
- effects on BP and CO depend of volume status
Respiratory
-FRC decreases
Considerations with lateral positions
Cardiovascular
- minimal changes
- pulse ox on dependent had to assure adequate perfusion
Respiratory
- decreased ventilation dependent lung
- increased perfusion dependent lung
- V/Q mismatch may manifest as unexpected arterial hypoxemia
Consideration for sitting position
Cardiovascular
- pooling of blood in lower extremities
- venous air embolism
Respiratory
-more flavorful ventilation with less effect on lung volumes
Neuro
-decrease in cerebral blood flow and CPP
Consideration with prone position
Cardiovascular
- devices that increase ABD pressure or impede venous return via vena cava and femoral veins can contribute to decreased CO, may decrease preload, and BP
- can cause increased difficulty with hemostasis bc vertebral venous plexuses communicate directly with ABD veins
Respiratory
-compression of ABD and thorax decreases compliance and increases work of breathing. Minimized if ABD can hang free
Neuro
-extreme rotation of head my decrease cerebral venous drainage and cerebral blood flow
What do you do if pt has air embolism?
-place them in left lateral trendelenburg and try to aspirate if they have a central line
What are types of vision damage that may occur generally due to compromise of O2 delivery to the visual pathway?
- Ischemic optic neuropathy
- Retinal artery occlusion
- cortical blindness
What are potential causes of blindness due to surgery?
- pressure on globe
- intra-op hypotension
- massive blood loss
- venous congestion due to prone position
- prolonged surgical procedure
- massive fluid replacement
What is thoracic outlet syndrome?
-compression of brachial plexus or subclavian vessels or both due to inadequate passageway thru the thoracic outlet between the base of neck and armpit
*All pts scheduled for a prone case should be asked about their ability to work or sleep with their arms overhead
