Week 11 - Positioning Flashcards
Two things that general anesthesia decreases
Cardiac output and BP –> Due to the myocardial depression and vasodilation that these anesthetics cause.
Compensatory mechanisms are blunted due to ____________ ___________ (Increase in HR due to hypotension)
General anesthesia –> This causes the body to be more susceptible to gravitational forces
How does neuromuscular blockade contribute to decreased venous return?
Normal muscle tone is abolished.
What positions are hemodynamics usually unaffected?
Supine and lateral positions
What positions cause a decrease in CO and BP?
Sitting, prone, and flexed lateral positions
Why is hypotension associated with the lateral decubitus position with the kidney rest elevated?
Legs are in a dependent position, which reduces blood flow. Also may contribute to compression of the great vessels
For every inch change in height between the heart and the body region, _________________
MAP increases or decreases by 2 mm Hg
What physiological effects can positioning devices and mechanical ventilation place the patient in?
Decreased CO and hypotension
Where should the kidney rest be positioned in a patient placed in the lateral decubitus position?
Should lie under the dependent iliac crest
Large tidal volumes and increased PEEP causes increased intrathoracic pressure, causing what hemodynamic changes?
Reduction in venous return, right atrial filling, and CO
The combination of what positions can cause a detrimental effect on myocardial function?
Trendelenburg with lithotomy –> Causes increased CVP, PAP, and PAOP, but a decrease in CO
Individuals with poor cardiac function who experience increased central pressures due to position changes (Trendelenburg) cause a shift in which way on the Frank Starling curve?
Right –> This increased volume from positional changes can cause even worse cardiac function
How does prone and trendelenburg positions contribute to facial, pharyngeal, and orbital edema?
Because the veins on the head are valveless, can contribute to greater venous pooling.
Downward displacement of the diaphragm (caudad) generate which type of pressure?
Negative pressure, allows for easier lung expansion
What is a ventilation/perfusion mismatch?
One lung may be getting better perfused while the other lung is being better ventilated –> This can happen in various positions
Lateral positions cause the diaphragm to move in which way?
Cephalad –> Decreases ventilation and lung compliance
In which patient position is ventilation/perfusion matched the best and aids in increased functional residual capacity (FRC)?
Prone position
What effect does the sitting position have on ventilation?
Increases. The more the torso is elevated, the smaller the effect on lung mechanics
Three types of nerve injuries?
Transection, compression and stretch
What is a common component of all peripheral nerve injuries?
Ischemia –> This can be due to reduced neural blood flow due to stretch and compression
Does tissue metabolism continue even after blood flow has been occluded?
Yes
What happens intracellularly when ischemia occurs?
ATP production is stopped –> This causes the Na/K ATPase pump to stop leaving sodium inside the cell –> This causes water to rush into the cell do to the increased osmotic gradient leading to tissue edema
Layers of the nerve?
Describe blood flow within the nerves
Blood vessels in the epineurium run parallel to the nerve and form anastomoses with the perineurium. Collateral connection form within the perineurium and endoneurium which is susceptible to compression
Why can neural edema obstruct blood flow?
The endoneurial space lacks lymphatic vessels so this fluid can’t be easily expelled.
Improper use of positioning devices contributes to
Nerve injuries
Post operative vision loss (POVL), nerve injuries, and compartment syndrome has been associated which surgeries that last longer than ________ hours
4
How can muscle relaxants contribute to nerve injuries?
Allows for an increased mobility of joints –> This can lead to stretch injuries
Neuraxial and peripheral nerve blocks contribute to nerve injury how?
Poor technique –> This contributes to the majority of nerve injuries over improper positioning.
What should be suspected in a patient with a delay in function of an extremity after a block or severe pain of a seemingly adequate block?
Nerve injury
What types of body habitus is correlated with increased incidence of positioning complications?
Extremes –> Anorexia to obesity
Thin patient may be at higher risk of sciatic nerve damage when ____________
The opposite buttock is elevated
What patient population is more likely to develop ulnar nueropathies?
Thin women
How does obesity contribute to morbidity from positioning?
Large tissue masses are exerting more pressure on dependent body parts
What patient population is more susceptible to nerve injuries and preexisting neuropathies?
Diabetics –> Most common metabolic cause of isolated femoral neuropathy
What effect does smoking have on nerves?
Increased risk for damage if patient has smoked 1 month prior to the surgical procedure, as well as delayed healing
What are some positioning devices that have contributed to position related injuries?
What is the most common upper extremity nerve injury after surgery/anesthesia?
Ulnar neuropathy
What manifestations will an ulnar injury present with?
Inability to oppose the fifth finger and diminished sensation to the fourth and fifth finger –> If prolonged, can result in atrophy of these muscle, creating a claw like contracture
Where does the ulnar nerve stem from?
Medial cord of the brachial plexus
What effect does flexing the elbow have in the ulnar nerve?
Causes the cubital tunnel retinaculum to stretch, increasing pressure on the ulnar nerve
Is ulnar neuropathy precipitated immediately?
No, generally has a delayed onset of 3 days after damage
Positioning recommendations to prevent ulnar nerve damage
- Padding with arms in a supine or neutral position
- Abduction of the arms should NOT exceed more than 90 degrees
- If arms are placed by patients side, face palms inward
DO NOT place arms down pronated, this causes increased pressure on this nerve
When is brachial plexus injury the greatest?
When arms are abducted greater than 90 degrees –> This stretches the plexus around the humeral head
What should be avoided in prone positions in regard to the brachial plexus?
Do not allow the shoulders to sag –> causes traction to the plexus
If arms are place above the head in this position it can compress the plexus between the clavicle and first rib
Lateral position interventions to prevent brachial plexus injuries?
Using an axilla roll –> This prevents the dependent should from compression the axilla neuromuscular bundle
Axilla role should be placed just caudal to the dependent axilla to relieve this pressure