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
Why should shoulder braces be avoided?
Can cause brachial plexus compression is used incorrectly.
If you HAVE to use them, place distally on the clavicle over the acromioclavicular joint
Which device during cardiac surgery can contribute to brachial plexus injuries?
Sternal retractor –> Causes the clavicle to move posteriorly and pushes the first rib upward, this compresses the brachial plexus
This can be avoided with caudal placement of the sternal retractor and avoidance of excessive and prolonged asymmetric retraction
Common nerve injuries and etiologies/preventions
What are spinal cord injuries most often associated with?
Neuraxial blocks with anti coagulated patients and blocks for acute and chronic pain management
What may occur if a patients head is flexed on the neck in the sitting or prone positions?
Midcervical flexion myopathy –> This occurs with temporary or permanent quadriplegia
How can the spinal cord be related to a rubber band?
With stretch it becomes thinner, and blood supply can become reduced
Congestion of the veins draining the spinal cord with hypotension may result in what?
Decreased spinal cord perfusion from compression of these vessels or lack of blood flow, onset of new neurological deficits may occur.
How can hyperflexion of the neck be avoided?
Allowing a minimum of 2 finger breadths between the mandible and the sternum
What are the two most common causes of post operative vision loss?
Ischemic optic neuropathy (ION) and central retinal artery occlusion (CRAO) –> These account for 89% of POVL after surgery
What is a “watershed” region?
A region which receives dual blood supply, but from the most distal branches of two different arteries –> These regions are especially susceptible to ischemia, which is present in the eye.
Steep trendelenburg positions and using beds such as a Wilson frame has what effect on the patients eyes?
Increase venous congestion causing an increase in intraocular pressure (IOP) –> As IOP approaches MAP, Ocular perfusion pressure will decrease (OPP)
Central retinal artery occlusion etiology?
Caused by a decreased blood supply to the entire retina –> Improper head positioning that increases external pressure on the eye.
Central retinal artery occlusion patient presentation
Severe unilateral vision loss immediately following surgery –> Few treatments and prognosis is poor
Patients at high risk for developing POVL?
Patients undergoing lengthy procedures in a steep trendelenburg or prone positions, with a significant amount of blood loss.
How can central retinal artery occlusion (CRAO) be avoided in the intra operative period?
- Avoidance of direct pressure of the eye
- Prone patients head should be in a neutral position and level with or slightly elevated above the heart when possible
- Use foam head pillows with cutouts
What is compartment syndrome?
Damage to neural and vascular structures from tissue swelling as a result of increased pressures and decreased perfusion.
Ischemia occurs first from increased pressures –> When blood flow is restored this region begins to swell from the damage, also called reperfusion injury
How can compartment syndrome occur in the intra operative period?
Hypotension with extremity elevation that causes low flow states.
What has been a distinguishing characteristic of patients who develop compartment syndrome?
Long surgical duration with patients in the lithotomy position –> Patients develop lower extremity compartment syndrome
Other positions can cause this such as trendelenburg
Interventions that can be taken to reduce the risk of compartment syndrome?
If surgeries are longer than 2-3 hours, extremities need to be periodically lowered, if elevated, to the level of the heart.
Treatment of compartment syndrome?
Fasciotomy –> This is really the only treatment method available to release constricted compartments.
How can a patient develop a venous air embolism (VAE) in the intraoperative period?
A patient in any position where a negative pressure gradient is created between the right atrium and the veins of the operative site.
This creates a vacuum, pulling air into the vein
Patient presentation with venous air embolism
No effects for minimal amounts of air to hypotension, arrhythmias, cardiac arrest, and death with larger volumes of air.
What type of air embolism generally occurs in patients with a PFO? How?
Paradoxical air embolism (PAE), air can enter systemic circulation when right atrial pressure is greater than left atrial pressure.
What test is the gold standard for detecting a PFO?
TEE with contrast, this is the most sensitive –> although a less invasive technique can be transcranial doppler, which can detect right to left shunting.
What is the most sensitive test for detecting a venous air embolism (VAE)?
TEE, this is invasive and associated with increased costs.
The more frequently used method is precordial doppler when patients are placed in a sitting position. This method is cheaper and less invasive
How should a precordial doppler be positioned when assessing a patient for a venous air embolism?
Placed over the third to sixth intercostal spaces of the right sternum.
What sound would be heard when using a precordial or esophageal stethoscope in a patient experiencing a venous air embolism?
Mill wheel murmur –> Swooshing sound
Later signs of venous air embolism?
EKG changes, hypoxia, and an increased PAP
How can a venous air emboli be removed?
Place patient on their left side, aspirate via a central venous catheter.
Also can do compression on the patients chest to break up the emboli
The ET tube follows the ________
Nose –> Extension pulls ET tube toward the vocal cords whereas flexion pushes it toward the bronchi
What effect can a steep trendelenburg position or flexion of the neck have on the ET tube?
Right main stem intubation
What effect will a sitting position with extensive flexion at the neck have on the patient?
Macroglossia and airway edema –> This can obstruct the jugular veins, impeding blood return.
What intervention may need to be taken in a patient with macroglossia or upper airway edema post operatively?
Keeping the patient intubated until the edema subsides
If the patient presents with severe arthritis, decreased mobility of the joints or neuropathies, how should the patient be positioned?
It is best to allow these patients to position themselves per preference prior to anesthesia if feasible for the surgery.
True or False
Crossing the legs during surgery is recommended?
False –> This can cause nerve damage of the sural nerve in the superior leg and common peroneal nerve injury in the dependent leg.
When the patients arms are tucked, why must the elbows not be hanging off the table?
This can lead to ulnar nerve damage
Should arms be pronated and tucked to the sides or on an arm board during surgery?
NEVER –> Don’t pronate the arms as this can cause ulnar nerve damage. Arms should always be supinated (palm up) or facing inward toward the patients thigh.
Why should the arms never be abducted more than 90 degrees?
This can cause a brachial plexus stretch injury.
How can the risk of sliding be mitigated in a patient positioned in a steep trendelenburg position?
- Antiskid bedding
- Lithotomy positioning
- Padded cross torso straps
Regardless of the safety equipment used, what is the best way to prevent injury in a patient in a trendelenburg position?
Using the least degree possible and for the shortest duration possible
Why shouldn’t shoulder braces be used in a patient placed in a trendelenburg position?
Because even if these devices are placed correctly they can compress/stretch the brachial plexus causing injury
Proper positioning of a shoulder brace
Over the acromioclavicular joint –> Should still be avoided if possible because proper placement still places the patient at risk for a brachial plexus injury
What are some potential complications from a steep reverse trendelenburg (head up) position?
This position can reduce perfusion pressure of the brain and needs to be monitored.
Lower extremity neuropathies have also been associated with this position from excessively tight table straps preventing the patient from sliding –> The use of a foot board is recommended to over zealous tightening.
When is the lithotomy position preferred?
Any surgery requiring perineal access –> Legs are held in flexion and abduction over the level of the torso by leg holding devices
What must be paid close attention to in the lithotomy position if the arms are tucked at the sides?
The fingers –> Disastrous crush injuries can occur leading to amputation if they become trapped when the foot section is raised.
How should the legs be moved in a patient placed in a lithotomy position?
Should be elevated and lower simultaneously –> doing legs separately can result in hip dislocation, spinal torsion, or post operative back pain.
Why shouldn’t the hips be flexed beyond 90 degrees in a lithotomy position?
Can lead to nerve damage –> Stretching of the sciatic and obturator nerves
What nerve is most often injured in patients placed in a lithotomy position?
The common peroneal nerve –> Because this nerve wraps around the fibular head before its descent, it runs along the outermost part of the leg. The leg holder bars can rest against the leg causing this injury.
Where can the saphenous nerve be found?
Medial aspect of the lower leg –> Can also be injured from compression in the lithotomy position of the leg holder devices.
When is the lateral decubitus position used?
For thorax and kidney surgeries when the supine position doesn’t provide adequate exposure.
How should the patient be placed on the kidney rest in the lateral decubitus position?
Kidney rest should rest beneath the dependent iliac crest.
How should the head and neck be positioned in the lateral decubitus position?
Remain aligned with the spine in a neutral position
How can the eyes and ears be free of pressure in the lateral decubitus position?
Through the use of a gel donut
When should the patient be positioned in the lateral decubitus position?
After induction of anesthesia
How should the legs be positioned in the lateral decubitus position?
Dependent leg flexed stabilizing the patient and the non dependent leg straight –> Pillows need to be used in between, prevent bony prominences from resting on each other
What precautions need to be taken to the upper extremities in the lateral decubitus position?
Perfusion needs to be assessed, especially on the dependent arm. Check radial pulses and capillary refill
A small axilla roll is also placed under the dependent thorax, slightly caudad of the patients armpit –> Prevents compression of the brachial plexus and vasculature
Why should blood pressure cuffs be placed on the nondependent arm of a patient in a lateral decubitus position?
Because the cuff can cause neurovascular compression on the dependent extremity
How would you describe the beach chair position?
Modified sitting position in which the torso is elevated 45 degrees, head is flexed, and the legs are elevated and flexed
What can occur in the sitting position if the head is excessively flexed?
Jugular vein obstruction –> At least 2 finger breadths need to be allowed between the neck and sternum
Why is the sitting position falling out of favor?
Due to the increased and most feared risk of venous air embolism. Pneumocephalus, quadriplegia, and peripheral nerve injuries are also possible
What complication may occur when a patient is placed in a sitting position for a shoulder surgery and an interscalene block is utilized?
Profound hypotension and bradycardia from the activation of the Bezold-Jarisch reflex
Why is the prone position becoming more favorible?
Because it has a decreased risk of a venous air embolism compared to the sitting position
After a patient has been induced, are they disconnected from the ventilator prior to positioning them in a prone position?
Yes –> Prevents accidental extubation
How is a patient placed in a prone position?
Log rolled maintaining good body alignment
How should the hands and forearms be positioned in the prone position?
Lower than the shoulders
What needs to occur to the patients shoulders when placed in a prone position?
Adequate padding to prevent sagging which can cause stretching of the brachial plexus
How should the abdomen be positioned in a prone position?
Hang freely –> Decreases IVC pressures
Avoid pressure on the abdomen in this position as i can occlude vessels
How should the head be positioned in a prone position?
Neutral position –> Hyperextension or lateral rotation can compromise spinal cord blood flow
The prone position is associated with what eye complications?
POVL from compression or corneal abrasions –> Make sure eyes are protected from pressure and taped!
When is a sitting position preferred?
Posterior fossa and cervical spine procedures –> Allows good visualization and promotes drainage of blood and CSF through the wound.
What disease process has been observed in patients after being placed in a lateral decubitus position?
Rhabdomyolysis –> Ensure the OR table is adequately padded and positioning devices are used correctly. Prevent prolonged hypotension which decreases tissue perfusion
