Week 14 - Nagelhout c. 23 positioning Flashcards
What is the act of positioning a patient for surgery?
A group endeavor that requires knowledge, teamwork, timing, and communication to protect against injury.
What is the goal of patient positioning?
To allow optimal surgical access while minimizing potential risk to the patient.
What is a key consideration regarding surgical positions?
Every surgical position carries some degree of risk that is magnified once an anesthetic is administered.
What must clinicians be knowledgeable about?
Possible hazards associated with various surgical positions.
What happens to cardiac output and blood pressure under general anesthesia?
They are generally decreased in response to myocardial depression and vasodilation induced by anesthetic medications.
What effect does blood pooling have during anesthesia?
It reduces preload and decreases stroke volume.
How do neuromuscular blocking agents affect venous return?
They contribute to decreased venous return.
What is the effect of opioids on heart rate?
They may slow heart rate, further decreasing cardiac output and blood pressure.
How is MAP maintained in healthy patients?
By compensatory increases in heart rate and systemic vascular resistance (SVR).
Who is less adaptive to hemodynamic changes?
Elderly patients and those with preexisting diseases.
What effect do general anesthetics have on compensatory mechanisms?
They blunt these mechanisms, making patients more susceptible to gravitational forces.
What are the hemodynamic changes in supine and lateral positions?
They are usually minimal.
What happens to cardiac output and blood pressure in sitting, prone, and flexed lateral positions?
They decrease.
What occurs to CVP in the prone position?
It increases, but left ventricular volume is reduced due to decreased venous return from increased intrathoracic pressure.
What may happen to blood pressure in the lithotomy position?
It may appear normal or higher due to gravity-dependent central redistribution of blood volume.
How does MAP change with height differences?
Changes by approximately 2 mm Hg per inch in height between the heart and a body region.
What positions may risk hypoperfusion and ischemia?
Head-up, sitting, and lithotomy positions, especially with hypotension.
What is the effect of a 45-degree head-up sitting position on hemodynamic changes?
They are minimal.
What is the decrease in cardiac output in a 90-degree seated position?
Decreases by 20% due to blood pooling in the extremities.
What changes occur in seated position regarding CI, CVP, and SVR?
CI, CVP, and PCWP decrease, while SVR increases.
What monitoring is useful for cerebral perfusion concerns?
Invasive blood pressure monitoring and cerebral oxygen saturation trending.
What can contribute to hypotension during surgery?
Positioning devices and mechanical ventilation.
What can kidney rest in lateral decubitus do?
Compress the vena cava.
What may extreme hip flexion in prone/lithotomy positions occlude?
Femoral vessels, contributing to decreased venous return.
What do large tidal volumes and PEEP do to venous return?
Increase intrathoracic pressure, reducing venous return and cardiac output.
What are methods to attenuate hemodynamic changes?
Slow positioning, nitrous-narcotic technique, lighter anesthesia (<0.5 MAC), gradual deepening of anesthesia, and intravascular volume loading (with caution against overload when returned to supine).
What is the purpose of the Trendelenburg position?
Used to treat hypotension by increasing venous return and mean arterial pressure (MAP).
What happens to cardiovascular parameters in the Trendelenburg position?
CVP and pulmonary artery pressure (PAP) increase; normotensive individuals respond with vasodilation and baroreceptor-induced heart rate decrease.
How do hypotensive individuals respond to Trendelenburg position?
They may not respond similarly to normotensive individuals.
What is the effect of Trendelenburg on intrathoracic blood volume?
It increases by 2%-3%.
What cardiovascular changes may not reflect in CI, SV, or MAP during Trendelenburg?
Increases in CVP, mean PAP, and pulmonary artery occlusion pressure (PAOP).
What can happen to MAP in lithotomy + Trendelenburg?
It can appear normal despite hypovolemia.
What may happen when a patient is returned to horizontal after lithotomy + Trendelenburg?
Hypotension may occur despite seemingly adequate volume replacement.
What is a risk of lithotomy + head-down tilt in CAD patients?
It can harm myocardial function (↑CVP, PAP, PCWP; ↓cardiac output).
What may Trendelenburg do to myocardial work?
It may increase myocardial work via increased central blood volume, cardiac output, and stroke volume.
What is a risk for patients with poor cardiac function in Trendelenburg?
They may have decreased cardiac output due to worsened Frank-Starling position.
What risk do patients with peripheral vascular disease face in lithotomy/Trendelenburg?
They risk lower extremity ischemia due to hypoperfusion.
What does elevation above heart level increase the risk of?
Compartment syndrome.
What risks are associated with prone and Trendelenburg positions?
They increase venous pressure in the head, causing facial, pharyngeal, and orbital swelling.
What can happen to ICP when the head is dependent?
It can increase due to venous pressures transmitted via the jugular system.
What can decrease due to venous congestion?
Cerebral blood flow (CBF).
What may occur postoperatively due to increased ocular venous pressure?
Postoperative visual loss (POVL) due to decreased ocular perfusion pressure.
What are some complications linked to prone/head-down positions?
Facial edema, macroglossia, and airway edema.
How can facial edema be prevented?
By positioning the head level or higher than the heart.
What causes expansion of the thoracic cavity during spontaneous respiration?
Contraction of the diaphragm and intercostal muscles causes expansion of the thoracic cavity in both an anterior-posterior and a lateral direction.
What generates negative intrathoracic pressure?
Downward displacement of the diaphragm generates a negative intrathoracic pressure and allows lung expansion as gas flows inward.
What factors affect lung expansion pressure?
Lung elastance and chest-wall compliance affect the amount of pressure necessary to expand the alveoli for a given change in volume.
How do gravitational factors influence the lungs?
Gravitational factors affect the distribution of ventilation and perfusion within the lung, as well as the shape of the thoracic cavity and movement of the diaphragm and abdominal contents.
What impact do postural changes have on respiratory function?
Postural changes may significantly alter compliance, lung volumes, and the distribution of ventilation and pulmonary blood flow.
How can positioning devices affect respiratory movement?
Positioning devices may cause mechanical interference with movement of the belly wall and abdominal contents, the chest wall, or the diaphragm.
What effect does anesthesia have on ventilation during surgery?
Anesthetic-induced depression of ventilation may be worsened by the majority of surgical positions.
Who may be more susceptible to ventilatory effects of surgical positions?
Individuals with pre-existing diseases that alter respiratory function may be more susceptible to the deleterious ventilatory effects of surgical positions.
What is necessary for effective respiratory gas exchange?
Effective respiratory gas exchange depends on a balance of ventilation and perfusion throughout the lungs.
What creates a gradient favoring perfusion and ventilation in the lungs?
Gravitational forces are theorized to create a gradient that favors perfusion in dependent portions of the lungs and ventilation in nondependent regions.
What pattern of blood flow has been identified in the lungs?
New imaging techniques have identified a concentric pattern of blood flow in the lungs, with central regions receiving a greater proportion of flow than the periphery.
What factors may influence the gradient of blood flow in the lungs?
The diameters and branching patterns of pulmonary vessels and the distance blood must flow to reach a site are possible factors.
What non-gravitational factors affect regional lung perfusion?
Nongravitational factors such as cardiac output, pleural pressures, and lung volumes are also thought to play a factor in regional lung perfusion.
How do positional changes affect ventilation and perfusion?
Positional changes may result in redistribution of ventilation and perfusion.
In which position are changes in ventilation and perfusion less evident?
These changes are evident less in the sitting position and more so in the prone and lateral positions.
What is the effect of the prone position on oxygenation?
In the prone position, changes in ventilation-perfusion (V/Q) ratios have been postulated as the cause of improved oxygenation.
Why are posterior lung segments better ventilated in the prone position?
More lung volume is present posteriorly than anteriorly, where anterior mediastinal structures occupy significant space.
How does the prone position affect V/Q matching?
Ventilation is more uniform, and V/Q matching is better in the prone position than in the supine position due to the alleviation of pressure from the anterior structures on the posterior lung tissue.
What happens to ventilation and perfusion in the lateral decubitus position?
In the lateral decubitus position, both ventilation and perfusion are greater in the dependent lung than in the nondependent lung in awake, spontaneously breathing patients.
What effect does anesthesia have on ventilation in the lateral position?
With the addition of anesthesia, positive pressure ventilation, and paralysis, the upper lung becomes easier to ventilate than the dependent lung, thereby creating a V/Q mismatch.
How does hypoxic pulmonary vasoconstriction affect blood flow?
Hypoxic pulmonary vasoconstriction in the unventilated lung further redistributes blood flow to the dependent lung to improve oxygenation.
What changes occur in the diaphragm and abdomen when shifting positions?
Changes in the elastance and resistance of the diaphragm and abdomen occur when shifting between positions.
How do position changes affect healthy individuals versus those with lung conditions?
These changes have little effect on movement of the chest wall in healthy individuals but may have an effect in persons with conditions that predispose to abnormalities of lung function.
What limits diaphragmatic excursion in the prone position?
In the prone position, diaphragmatic excursion can be limited by the abdominal viscera if the abdomen is compressed by the weight of the body or positioning devices.
How does gravity affect abdominal contents in the prone position?
If the abdomen hangs free, gravity allows the abdominal contents to shift, reducing interference with diaphragmatic movement.
What happens to ventilation in the dependent lung of an anesthetized patient in the lateral position?
In the anesthetized patient in the lateral position, abdominal contents shift cephalad, moving the hemidiaphragm of the dependent lung upward, thereby decreasing ventilation in the dependent lung and reducing its compliance.
How does ventilation in the nondependent lung change in the lateral position?
In the nondependent lung of the anesthetized patient, ventilation is greater and compliance is increased due to the caudal shift of the upper hemidiaphragm allowing unrestricted lung excursion.
What happens to lung capacities with position changes?
Lung capacities are decreased with most position changes.
How does the supine position affect functional residual capacity (FRC)?
In the supine position, functional residual capacity (FRC) and total lung capacity are significantly decreased compared with the sitting position due to the cephalad shift of the diaphragm caused by pressure of the abdominal viscera.
What effect does the prone position have on FRC?
Some investigators have found an increase in FRC with patients in the prone position, when the abdomen hangs free.
What is theorized to improve oxygenation in the prone position?
Theories pose that better matching of ventilation and perfusion, rather than changes in lung volumes or capacities, cause improvements in oxygenation in the prone position.
What is the effect of the lithotomy position on respiratory compliance?
Little effect on the compliance of the respiratory system in healthy, conscious volunteers.
Extreme flexion of the thighs in exaggerated lithotomy compresses the abdomen, shifts the abdominal viscera cephalad, and limits diaphragmatic movement.
What are the consequences of extreme flexion in the lithotomy position?
Compliance and tidal volume are reduced, and airway pressures and dead space/tidal volume ratios are increased.
This effect may be amplified in obese individuals.
How does the sitting position affect ventilation?
More favorable for ventilation and has less effect on lung volumes than other positions.
What happens to lung mechanics as the torso is elevated in the sitting position?
The smaller the effect on lung mechanics.
What are the normal parameters for forced vital capacity and FRC in the seated position?
Forced vital capacity and FRC are within normal parameters in the seated position.
How does the sitting position affect diaphragmatic movement?
Abdominal contents shift caudally and anteriorly, causing less interference with diaphragmatic movement and allowing greater expansion of dependent lung regions.
How does the rib cage contribute to ventilation in the sitting position compared to supine?
In the sitting position, the rib cage contributes more to ventilation than in the supine position.
What can attenuate the respiratory benefits of the sitting position?
Modifications to minimize cardiovascular effects.
What effect does flexion of the lower extremities at the hip have in the sitting position?
Can cause abdominal contents to shift cephalad against the diaphragm, limiting diaphragmatic excursion and decreasing FRC and closing volumes.
What is the effect of the Trendelenburg position on ventilation?
Exacerbates the deleterious ventilatory effects of the various positions.
What happens to the diaphragm in the Trendelenburg position?
The diaphragm is displaced cephalad, and its excursion is limited by shifting of the abdominal contents.
How does FRC change in the Trendelenburg position?
FRC progressively decreases as the degree of Trendelenburg position increases.
What complication may occur with the endotracheal tube in the Trendelenburg position?
Movement of the mediastinum toward the head may result in the tip of the endotracheal tube migrating into the right mainstem bronchus.
What complication may occur upon establishment of pneumoperitoneum?
The diaphragm is displaced in a cephalad direction by pressurized gas.
What are the primary mechanisms responsible for nerve injuries?
Transection, compression, and stretch.
How can nerves be transected?
By surgical maneuvers or by trauma.
What causes compression of nerves?
When a nerve is forced against a bony prominence or a hard surface.
What is an example of nerve compression in the lateral position?
The weight of the superior leg compresses the common peroneal nerve of the dependent leg against the operating table.
What are stretch injuries?
Injuries that occur where nerves have a long course across many structures.
What happens with excessive elongation or stretch of peripheral nerves?
It may cause conduction changes, axonal disruption, or interruption of the nerve’s vascular supply.
What are traction injuries?
Injuries that occur when a peripheral nerve is pulled over or under immovable structures.
What is an example of a traction injury?
The femoral nerve can be kinked under the inguinal ligament when the thighs are flexed on the abdomen.
What is a common component of all peripheral nerve injuries?
Ischemia.
What can compromise intraneural blood flow?
Stretch, compression, or disruption of the nerve tissue itself.
What are other causes of ischemia?
Occlusion of major vessels, emboli, tissue edema, or inhibition of perfusion at the capillary level.
How does pressure applied over a body surface affect venous capillary outflow?
It may limit outflow, causing a rise in venous capillary pressure and a decrease in the hydrostatic pressure gradient.
What occurs as venous capillary pressure rises?
Tissue edema occurs as fluid is sequestered in the cells and interstitial space.
What happens as venous and tissue pressures continue to rise?
Arterial inflow is eventually obstructed, resulting in ischemia.
How can low mean arterial blood pressure affect ischemia?
It may augment the development of ischemic conditions.
What happens to tissue metabolism during ischemia?
Adenosine triphosphate (ATP) production is decreased.
What is the effect of decreased ATP production on cells?
It causes failure of the transmembrane sodium-potassium pump and accumulation of sodium within the cell.
What results from the accumulation of sodium within the cell?
The osmotic pressure gradient favors the movement of water into the cells, leading to tissue edema.
What is the cycle that results from increased tissue pressures?
A vicious cycle of ischemia that prevents the movement of fluid and nutrients from the capillaries into the cells.
What contributes to the susceptibility of peripheral nerves to ischemia?
Their anatomic structure.
What are peripheral nerves composed of?
Bundles of nerve fibers (fascicles) encased in protective connective-tissue coverings.
What covers each nerve fiber?
One or more axons sheathed by Schwann cells (neurolemma).
What is the endoneurium?
A loose connective tissue covering the axons and neurolemma.
What is the function of the perineurium?
It binds the fascicles into identifiable structures.
What does the epineurium consist of?
An inner epineurium that supports the fascicles and an outer epineurium that covers the external surface of the nerve.
How does the quantity of protective tissues vary?
It varies between nerves and even along the same nerve.
What is the function of the loose layer of connective tissue covering the entire nerve trunk?
It allows the nerve to slide across joints and other tissues.
What is the microvascular supply of peripheral nerves like?
Peripheral nerves have an extensive microvascular supply.
How do blood vessels in the epineurium interact with the perineurium?
They run parallel to the nerve and form numerous anastomoses with the perineurium.
What may obstruct microcirculation in the endoneurial space?
Edema and fluid accumulation due to the lack of lymphatic vessels.
What are perioperative peripheral nerve injuries (PPNI) frequently attributed to?
Incorrect surgical positioning
PPNI can result from a combination of factors, but incorrect positioning is a primary cause.
What type of factors contribute to the etiology of PPNI?
Multifactorial involving:
* Patient predisposition
* Precipitating physiologic factors
* Mechanical factors
This complexity suggests that multiple elements contribute to nerve injuries during surgery.
List some perioperative factors that contribute to nerve injuries.
- Ancillary positioning devices
- Prolonged surgical procedures
- Anesthetic technique
These factors can affect nerve integrity during surgery.
What are some patient-related factors that can lead to nerve injuries?
- Gender
- Advanced age
- Extremes in body habitus
- Preexisting medical conditions (e.g., diabetes mellitus, tobacco use, hypertension)
These factors may predispose patients to higher risks of nerve injuries.
Name intraoperative occurrences associated with nerve injury.
- Hypovolemia
- Hypotension
- Induced hypothermia
- Hypoxia
- Electrolyte disturbances
These occurrences can compromise nerve function during surgery.
What is often unclear regarding the mechanism of nerve injury?
The precise mechanism of nerve injury
This uncertainty indicates a need for further investigation into causative factors.
What evidence is largely lacking regarding complications from positioning devices?
Controlled studies of complications related to specific positioning devices
Much of the current knowledge comes from isolated case reports.
How can tight padding or straps used in positioning devices lead to nerve injury?
Can cause skin breakdown or nerve injury if excessively tightened
Proper use of these devices is crucial to avoid complications.
Which nerve is susceptible to injury by tight table straps?
Lateral femoral cutaneous nerve
This nerve’s location makes it vulnerable to compression from positioning.
What common injury is attributed to the improper use of stirrups?
Common peroneal nerve injury
This is a known risk during certain surgical procedures.
What can cause brachial plexus injury during surgery?
- Armboard falling off the OR table
- Improper use of shoulder braces in steep Trendelenburg position
These factors can lead to significant nerve damage.
What type of injury can occur from the intraoperative use of tourniquets?
Compression injury of the radial nerve
This risk highlights the importance of monitoring during surgical procedures.
What issues can arise from prolonged surgical procedures?
- Postoperative positioning complications
- POVL
- Nerve injuries
- Compartment syndrome
- Rhabdomyolysis
- Acute renal failure
Lengthy surgeries pose multiple risks to patient safety.
What is one possible explanation for complications during long procedures?
External compression of dependent tissues and states of low perfusion
This can lead to edema and ischemic injury.
How may anesthetic techniques contribute to position-related injuries?
Patients cannot move in response to painful stimuli due to general anesthesia
This can lead to prolonged exposure to harmful positions.
What effect do neuromuscular blocking drugs have on nerve injuries?
Allow increased mobility of joints, potentially leading to stretch injuries
This can exacerbate nerve damage during surgery.
What should anesthetists be vigilant about regarding nerve injury recognition?
Delayed return of function beyond expected timelines
Symptoms may be misattributed to residual effects of regional blocks.
True or False: Most nerve injuries related to anesthetic techniques are due to positioning.
False
Most injuries are related to poor block technique, hematoma formation, and direct needle trauma.
Fill in the blank: The use of hypotensive techniques during surgery should be balanced against the risk of possible complications resulting from _______.
Decreased perfusion pressures
This is particularly critical in certain patient positions.
What body habitus factors contribute to nerve injuries?
Extremes of body habitus correlate with an increased incidence of positioning complications. Underweight individuals may develop decubiti or nerve damage due to lack of adequate adipose tissue. Obesity increases morbidity from positioning due to pressure on dependent body parts.
How does body habitus affect the risk of ulnar neuropathy?
Thinner women (BMI <22) are more likely to develop ulnar neuropathy. Ulnar neuropathy has also been associated with an increased BMI.
What preexisting conditions increase the risk of nerve injuries?
Hypertension, diabetes mellitus, peripheral vascular disease, peripheral neuropathies, and alcoholism can exacerbate physiologic effects of various positions.
What is the most common metabolic cause of spontaneous isolated femoral neuropathy?
Diabetes mellitus is the most common metabolic cause of spontaneous isolated femoral neuropathy.
What factors are associated with position-related injuries?
Factors include positioning devices, length of procedure (> 4-5 hrs), obesity, malnutrition, bulky musculature, anemia, diabetes mellitus, and smoking.
How does anesthesia affect susceptibility to nerve injuries?
The induction of anesthesia renders a patient unable to optimize position for relief of symptoms, making them more susceptible to injury.
What is ulnar neuropathy?
Ulnar neuropathy is one of the most frequently reported injuries after surgery, resulting in inability to oppose the fifth finger and diminished sensation to the fourth and fifth fingers.
What anatomical features are associated with the ulnar nerve?
The ulnar nerve traverses from the medial cord of the brachial plexus to the hand, passing along the medial head of the triceps and through the cubital tunnel.
What are the associated risk factors for ulnar neuropathy?
Risk factors include excessive flexing of the elbow, male gender, preexisting asymptomatic neuropathy, prolonged hospital stays, and extremes of body habitus.
What are the prevention recommendations for ulnar neuropathy?
Use padding, place arms in a supinated or neutral position, avoid excessive flexion of the elbow, and ensure arms are secured properly.
Is ulnar nerve palsy always preventable?
Evidence supports that ulnar nerve palsy is not always a preventable complication despite careful positioning and padding.
What is the brachial plexus?
The brachial plexus is a network of nerves that is vulnerable to injuries in almost every surgical position, particularly if the arms are abducted or the head is rotated.
What happens in the supine position with arm abduction?
Arm abduction greater than 90° stretches the plexus around the humeral head. Turning the head to the side with arms abducted causes stretching and compression under the clavicle.
What risks are associated with tucking arms next to the body?
Tucking arms next to the body carries risk if the head is turned laterally and shoulders are depressed.
What are the risks of the prone position?
Inadequate shoulder support allows sagging anteriorly causing traction; arms extended overhead may compress the plexus between clavicle and first rib.
What causes injury in the lateral decubitus position?
Injury commonly results from excessive stretching — arm abduction greater than 90°, external rotation, head flexion, and shoulder displacement.
What is the ‘axillary roll’?
The ‘axillary roll’ is placed caudal to the axilla to relieve compression of the axillary neurovascular bundle.
What can cause brachial plexus injuries during surgery?
Injuries may occur from arms slipping off armboards or armboards falling off the table.
What is the risk of steep Trendelenburg position?
Shoulder braces too close to the neck can compress neurovascular structures.
What is the proper shoulder brace placement?
The shoulder brace should be placed on the distal clavicle over the acromioclavicular joint.
What is a complication of cardiac surgery related to the brachial plexus?
Spreading the sternal retractor moves clavicle and rib, pinching the plexus.
What should be avoided during dissection of the internal mammary artery?
It is recommended to avoid excessive, prolonged asymmetric chest wall retraction.
What does ASA closed-claims data show about spinal cord injuries?
Spinal cord injury claims surpassed ulnar nerve claims and are associated with neuraxial blocks in anticoagulated patients and blocks for acute/chronic pain.
What can cause hemiparesis and quadriplegia?
These conditions may occur from sitting and prone positions.
What can midcervical flexion myelopathy result from?
It can result from head flexion compressing the spinal cord.
What factors may decrease spinal cord perfusion?
Increased vertebral venous pressure, lack of valves, and intraabdominal pressure may decrease cord perfusion.
How can hyperflexion of the head be avoided?
By maintaining a two-finger space between the sternum and mandible.
What is recommended for detecting spinal cord injuries?
tceMEP is recommended for detecting spinal cord, brachial plexus, and ulnar nerve injuries.
What are the causes of brachial plexus injuries?
Causes include supine/trendelenburg/lithotomy >90° abduction, arm falls, head lateral flexion, and shoulder braces.
What are the recommendations to prevent brachial plexus injuries?
Do not abduct arms >90°, support head/arms, and place shoulder brace on distal clavicle.
What causes ulnar nerve injuries?
Causes include pronation, elbow flexion >90°, poor padding, and arm extending off the table.
What are the recommendations to prevent ulnar nerve injuries?
Supinate forearm, avoid elbow flexion >90°, pad elbow, and secure arms properly.
What causes radial or circumflex nerve injuries?
Arm pressed against poles or vertical posts.
What is the recommendation for radial or circumflex nerve injuries?
Use padding between arm and surface.
What causes suprascapular nerve injuries?
Lateral position roll over shoulder.
What is the recommendation for suprascapular nerve injuries?
Stabilize position.
What causes sciatic nerve injuries?
Malnourished body and straight legs.
What are the recommendations to prevent sciatic nerve injuries?
Use soft buttock padding and maintain knee flexion.
What causes common peroneal nerve injuries?
Stirrups and fibular head pressure.
What are the recommendations to prevent common peroneal nerve injuries?
Use padding and ensure proper leg position.
What causes posterior tibial, saphenous, obturator, and pudendal nerve injuries?
Stirrups, hip flexion, and perineal post pressure.
What are the recommendations to prevent injuries to these nerves?
Use generous padding, avoid prolonged use, and minimize flexion.
What should be evaluated in the preoperative assessment?
Evaluate history of neurologic symptoms, diabetes, vascular disease, arthritis, and sex.
What are the upper extremity strategies for preventing nerve injuries?
Limit arm abduction in supine to 90°; avoid elbow flexion; assess position periodically.
What are the lower extremity strategies for preventing nerve injuries?
Avoid over-stretching hamstring, assess hip/knee flexion, and avoid pressure at fibular head.
What protective padding should be used?
Use padded armboards, chest rolls, and elbow padding while avoiding overly tight padding.
What equipment should be avoided?
Avoid automated BP cuffs below antecubital fossa and shoulder braces in steep Trendelenburg if possible.
What should be done in the postoperative assessment?
Perform a physical exam of extremity nerve function.
What should be documented?
Record positioning actions for quality improvement.
What is Postoperative Visual Loss (POVL)?
POVL is a rare but devastating complication of nonophthalmic surgery.
What causes visual loss after nonophthalmic surgery?
Visual loss is generally attributable to ischemic optic neuropathy (ION), central retinal artery occlusion (CRAO), central retinal vein occlusion, cortical blindness, and glycine toxicity.
What percentage of POVL cases are accounted for by ION and CRAO?
ION and CRAO accounted for 81% of all cases, with ION accounting for 89% of POVL after prone spinal procedures.
What is Ischemic Optic Neuropathy (ION)?
ION is the result of ischemia in a portion of the optic nerve.
What makes optic nerves susceptible to ischemia?
The central retinal and posterior ciliary arteries are end arteries and lack anastomoses.
What are the two types of ION?
Anterior ION (AION) – injury anterior to the lamina cribrosa and Posterior ION (PION) – injury posterior to the lamina cribrosa.
What are the risk factors for ION?
Risk factors include male sex, obesity, Wilson frame use, longer operative times, greater blood loss, lower colloid:crystalloid ratio, anemia, surgery >5 hours, diabetes, hypertension, vascular disease, smoking, and intraoperative hypotension.
What is the ocular perfusion pressure (OPP)?
OPP = MAP – IOP.
What can increase intraocular pressure (IOP)?
Head-down tilt, increased abdominal and right atrial pressure, and obstruction of jugular venous return can increase IOP.
What causes Central Retinal Artery Occlusion (CRAO)?
CRAO is caused by decreased blood supply to the retina, often due to improper head positioning.
What surgeries are associated with CRAO?
Associated surgeries include prone spine procedures, cardiopulmonary bypass, and head/neck procedures with injections near eyes or nose.
What is the prognosis for CRAO?
Few treatments for CRAO have proven efficacy, and prognosis is poor.
What are the risk factors for Central Retinal Vein Obstruction Syndrome?
Risk factors include hypertension, cardiovascular disease, increased BMI, open-angle glaucoma, and sickle cell anemia.
What is the preferred headrest for avoiding Central Retinal Vein Obstruction Syndrome?
Three-pin headrests are preferred over horseshoe headrests.
What is the ASA Practice Advisory for POVL?
Developed in 2006 and updated in 2012, based on opinions of spine surgeons, neuroophthalmologists, and anesthesiologists.
What should high-risk patients be informed about preoperatively?
High-risk patients should be informed preoperatively about POVL.
What should be monitored intraoperatively to prevent POVL?
Monitor hemoglobin/hematocrit intraoperatively.
What should be avoided in patients with hypertension or risk factors?
Avoid deliberate hypotension.
What position should the head be in to prevent CRAO?
The prone head should be in a neutral position, avoiding excessive flexion, and level/slightly elevated above heart (10° head-up tilt).
What is the least preferred headrest for preventing CRAO?
The horseshoe headrest is least preferred due to pressure risk.
What type of head pillows are preferred?
Foam head pillows with cutouts are preferred.
If a horseshoe headrest is used, how long should it be used?
It should be used for short procedures only.
What are position-related injuries?
Position-related injuries range from minor skin abrasions and backache to events with serious morbidity.
What complications can arise from position-related injuries?
Complications can lead to tissue necrosis, infection, renal failure, paralysis, loss of limbs, and even loss of life.
What is the typical recovery outcome for minor position-related injuries?
Most individuals recover from minor position-related injuries without sequelae.
What impact can serious position-related injuries have?
Serious injuries may prolong a patient’s hospital stay and recovery, cause psychological trauma, and perhaps result in permanent disability.
What should anesthetists consider regarding transient injuries?
Anesthetists must not minimize the physical, psychological, social, and financial impact of transient injuries.
What is compartment syndrome?
Compartment syndrome is a rare but potentially life-threatening complication that causes damage to neural and vascular structures from tissue swelling.
What causes compartment syndrome?
It is caused by increased pressures and decreased tissue perfusion in muscles with tight, fascial borders.
What can precipitate compartment syndrome?
It can be precipitated by intraoperative hypotension in conjunction with leg elevation that causes low-flow states.
What is the distinguishing characteristic of surgeries that may lead to lower extremity compartment syndrome?
Long surgical duration with the patient in lithotomy position.
What is the definitive treatment for compartment syndrome?
Fasciotomy is generally considered the definitive treatment.
What are the potential consequences of untreated compartment syndrome?
It can progress to tissue necrosis with rhabdomyolysis and acute renal failure, and may lead to amputation or death.
What is venous air embolism (VAE)?
VAE is a well-known consequence of surgery performed in the sitting position.
What can happen when air enters the right side of the heart?
It can limit gas exchange in the lungs as it displaces blood in the pulmonary vasculature.
What are the physiologic effects of VAE?
Effects range from no effect for minimal amounts of air to hypotension, arrhythmias, cardiac arrest, and death with larger volumes.
What is paradoxic air embolism (PAE)?
PAE can occur in the patient with a patent foramen ovale (PFO).
What is the incidence of PFO in the general population?
The incidence of PFO can be as high as 35%.
How can air enter the systemic circulation in patients with PFO?
Air can enter when right atrial pressure is greater than left atrial pressure.
What is the gold standard for detecting PFO?
Preoperative transesophageal echocardiograph (TEE) with contrast.
What are the advantages of transcranial Doppler studies?
They are a noninvasive approach with excellent diagnostic capability in detection of right-to-left shunting.
What monitoring techniques are used for detecting air embolism?
TEE, precordial Doppler ultrasonography, capnography (ETCO2), end-tidal nitrogen (ETN2), and pulmonary artery catheterization.
What is a characteristic sound associated with VAE?
A ‘mill-wheel murmur’ can be heard through the esophageal or precordial stethoscope.
How can entrained air emboli be removed from circulation?
By aspiration through a multilorifice central venous catheter.
Where should the CVP catheter be placed for patients undergoing surgery in the sitting position?
In the right atrium at the junction of the superior vena cava.
What must be weighed against the benefits of fluid volume management with a CVP catheter?
The risks of central venous catheter placement, potential for VAE, and cardiopulmonary risks of the sitting position.
What are the airway complications of surgical positions?
Anesthetized patients in various surgical postures are vulnerable to endotracheal tube displacement, airway edema, and passive regurgitation.
What can happen to the endotracheal tube during position changes?
The endotracheal tube may become dislodged, kinked, or disconnected when the patient is moved or upon position change.
What is a potential risk of neck flexion during intubation?
A right mainstem intubation may occur as a result of flexion of the neck or when the patient is placed in steep Trendelenburg position.
How does neck flexion affect the endotracheal tube?
With neck flexion, the endotracheal tube moves downward and may inadvertently enter the right mainstem bronchus.
What effect does the Trendelenburg position have on the diaphragm?
In the Trendelenburg position, pressure of the abdominal contents forces the diaphragm cephalad and may cause a similar occurrence.
What complications can occur after procedures in the prone, head-down, and sitting positions?
Extensive edema of the face, tongue, and oropharyngeal structures has been reported.
What can restrict venous return from the head and neck in certain positions?
In the prone and head-down positions, gravitational forces or increases in hydrostatic pressures may restrict venous return.
What can excessive flexion of the head on the neck cause?
It may obstruct jugular venous return, resulting in macroglossia and airway edema.
What can compress the base of the tongue?
Oral airways, endotracheal tubes, and esophageal stethoscopes may compress the base of the tongue and limit lymphatic drainage.
What may necessitate leaving a patient intubated after surgery?
Macroglossia or upper airway edema may necessitate leaving the patient intubated until the edema subsides.
What should be verified before extubation in suspected patients?
It may be prudent to verify an air leak around the endotracheal tube or examine the larynx via direct laryngoscopy.
What are potential injuries related to the head, eyes, ears, nose, and throat?
Postoperative vision loss, corneal abrasion, facial edema, vocal cord edema.
What cardiovascular injuries can occur during surgery?
Vascular occlusion, deep vein thrombosis, ischemic injuries.
What respiratory complications can arise?
Atelectasis, endobronchial intubation.
What neurologic injuries may occur?
Peripheral neuropathy, quadriplegia, decreased cerebral blood flow, increased intracranial pressure.
What genitourinary complications can arise?
Myoglobinuria, acute renal failure.
What musculoskeletal injuries may occur?
Amputation, backache, compartment syndrome, rhabdomyolysis.
What integumentary injuries can happen?
Abrasion, alopecia, decubiti.
What is the supine position used for?
The supine position is most frequently used for surgical procedures on the abdomen, head, neck, extremities, and chest.
How should the head be positioned in the supine position?
The head should be maintained in a neutral position on a small pillow or donut.
How should the arms be positioned in the supine position?
The arms should be either comfortably positioned and secured alongside the trunk or positioned on padded armboards.
What should be considered for patients with severe arthritis or decreased mobility?
It is best to position using patient preference prior to the induction of anesthesia.
What should be done during prolonged procedures in the supine position?
The head should be repositioned at intervals and the occiput inspected for alopecia due to prolonged pressure.
What can help prevent postoperative backache in the supine position?
Placing a pillow under the knees helps prevent postoperative backache.
What is the purpose of a ‘chair’ position pillow?
It increases patient comfort by flexing the hips and knees and slightly elevating the trunk.
Why should the legs remain uncrossed in the supine position?
To avoid pressure from the superior extremity damaging the superficial peroneal nerve in the dependent leg and the sural nerve in the superior leg.
What should be done to prevent pressure sores during prolonged surgery?
The heels should be elevated off the mattress.
What is a potential risk of tucking the arms?
Ulnar nerve damage may occur if the arms hang over the edge of the operating table.
What position should the hands be in when arms are tucked?
The hands should be placed in a neutral position, the elbow padded, with the palms facing the hip.
What is the risk of pronating the forearm on an armboard?
Pronation may result in compression of the ulnar nerve against the armboard.
What is the Trendelenburg position used for?
It is often used temporarily to increase venous return during episodes of hypotension.
What physiologic alterations occur in the Trendelenburg position?
An increase in central venous, intracranial, and intraocular pressures is observed.
What challenges does robotic-assisted surgery present?
It often requires steep Trendelenburg and presents challenges in positioning.
How can the risk of sliding in the Trendelenburg position be mitigated?
By using antiskid sheeting, lithotomy positioning, or padded cross-strap slings.
What should be avoided in the Trendelenburg position?
Using the least degree of Trendelenburg possible for adequate equipment placement and for the shortest duration of time.
What can happen if shoulder braces are improperly positioned?
They can injure the brachial plexus.
What is the risk of placing braces too laterally in the Trendelenburg position?
It may result in a stretch injury of the brachial plexus.
What is the lithotomy position used for?
It is used for surgical procedures that require access to any perineal structure.
How are the legs positioned in the typical lithotomy position?
The legs are held in flexion and abduction at the level of the torso by a leg-holding device.
What is the difference between low and exaggerated lithotomy positions?
In low lithotomy position, the legs are almost level with the torso; in exaggerated lithotomy position, the legs are suspended with boots or stirrups.
What must be done to avoid crush injuries in the lithotomy position?
Strict attention must be paid to the fingers if the arms are tucked at the sides.
What can happen if legs are raised and lowered separately in the lithotomy position?
It can cause hip dislocation, spinal torsion, or postoperative back pain.
What injuries are frequently associated with the lithotomy position?
Peroneal nerve injury is frequently associated due to its anatomic course.
What should be done to protect the peroneal nerve in the lithotomy position?
Padding should be placed along the lateral aspect of the dependent leg.
What is the lateral decubitus position used for?
It is often used for surgeries involving the thorax and kidneys.
What should be done before positioning the patient in the lateral decubitus position?
Secure the endotracheal tube, breathing circuit, intravenous and monitoring lines.
What is important for body alignment in the lateral position?
The shoulders, hips, head, and legs must be maintained in the same plane.
How should the dependent arm be positioned in the lateral decubitus position?
It should be positioned on a padded armboard perpendicular to the torso and flexed less than 90 degrees at the elbow.
What should be monitored in the dependent arm during the lateral position?
Perfusion should be periodically assessed by palpating the radial artery and checking capillary refill.
What can happen if straps or tape are overly tight in the lateral position?
Soft tissue injury may occur.
What is the sitting position commonly used for?
It is used for procedures where the torso is elevated from the supine position.
What is the modified sitting position?
The torso is elevated 45 degrees, the head is flexed, and the legs are elevated and flexed.
Why do some neurosurgeons favor the sitting position?
It allows excellent visualization of intracranial structures and facilitates drainage of blood and cerebral spinal fluid.
Why do surgeons favor the sitting position for posterior fossa and cervical spine procedures?
It allows excellent visualization of intracranial structures and facilitates drainage of blood and cerebral spinal fluid from the wound.
What is the benefit of the sitting position during shoulder arthroplasty and arthroscopy?
It reduces brachial plexus stretch and aids surgical exposure and manipulation of the arm and shoulder.
What does placement of the patient in the sitting position involve?
Flexion of the OR table, elevation of the backrest and legs, and sometimes head-down rotation.
What device is generally used to secure the head during neurosurgical procedures in the sitting position?
A three-pin head holder.
What complication can occur if the head is excessively flexed on the neck?
Jugular venous obstruction.
How much space should be allowed between the neck and mandible?
At least two fingerbreadths.
What type of headrest is often used for shoulder procedures in the sitting position?
A horseshoe headrest.
What can happen if the head is firmly secured to the headrest during vigorous surgical manipulation?
Excessive traction or stretch can be placed on the neck and brachial plexus.
What risk is associated with loose restraining straps on the head?
The head can become partially or completely dislodged from the headrest, introducing the potential for cervical spine injury.
What serious complications are associated with the sitting position?
VAE, pneumocephalus, quadriplegia, and peripheral nerve injuries.
What reflex may cause profound hypotension and bradycardia during shoulder surgery in the sitting position?
The Bezold-Jarisch reflex.
What is the primary benefit of the prone position?
It provides optimal exposure for various procedures performed on the spine and certain orthopedic procedures.
Why is the prone position advocated for intracranial procedures?
It has a decreased risk of VAE compared with the sitting position.
What must anesthetists become familiar with in the prone position?
The various methods of securing the patient and the potential hazards of each variation or device.
How is the torso typically supported in the prone position?
On a frame or with rolls that extend from the shoulders to the iliac crests.
What must be done to protect pressure points in the prone position?
Care must be taken to pad pressure points at elbows, knees, and ankles.
What is the goal of positioning a patient prone?
To avoid pressure on the abdomen, which can impede venous return and interfere with ventilation.
What can external abdominal pressure affect in the prone position?
It can be transmitted to the vena cava and communicated to the lumbar epidural veins.
What positioning device is associated with greater decreases in inferior vena cava pressures?
Devices that allow the abdomen to hang freely.
What is a complication associated with the prone position that requires attention to eye protection?
Corneal abrasions and POVL.
What is the purpose of closed-claims studies?
To investigate malpractice claims and provide insight into position-related injuries.
What are the major causes of liability identified in the ASA-CCP?
Death (26%), nerve injuries (22%), and permanent brain damage (9%).
What percentage of nerve injury claims were associated with regional anesthesia?
Regional anesthesia was more frequently associated with nerve-injury claims, particularly of the spinal cord and lumbosacral nerve root.
What is a limitation of closed-claims studies?
They are not a random or representative sample because only cases with filed claims are included.
What is a primary goal of anesthesia providers regarding surgical positioning?
To recognize and anticipate complications and prevent position-related injuries.
