Module 4: Positioning Injury

How does general anesthesia typically affect the baroreceptor reflex during surgical positioning?

It attenuates the reflex by impairing responsiveness and decreasing sympathetic nervous system tone.

Which two surgical positions are primarily associated with an increase in cardiac preload?

Trendelenburg and lithotomy

Why does the anesthetized patient experience gravity-dependent blood pooling compared to an awake patient?

Protective compensatory mechanisms, such as the baroreceptor reflex, are attenuated by anesthetic agents and positive-pressure ventilation.

(This causes decreased venous return and leads to pooling. The patient lacks the physiological responses to redistribute blood effectively.)

In the context of the Frank-Starling curve, what effect does the sitting position have on a patient's position on the curve?

It shifts the patient's position to the left due to reduced cardiac preload.

What is the primary hemodynamic risk when the patient's brain is positioned higher than the heart?

Cerebral hypoperfusion.

(When the patient's brain is above the heart, it can lead to decreased cerebral blood flow and oxygen delivery, resulting in potential ischemia.)

Where should an arterial line transducer be zeroed when a patient is in the sitting position?

At the level of the external auditory meatus.

How does the Trendelenburg position affect venous hydrostatic pressure in the head and neck?

It increases hydrostatic pressure, leading to edema of the face, eyes, and airway.

(This position redistributes blood flow, causing increased pressure in the veins of the head and neck.)

What is the physiological consequence of Trendelenburg positioning on cerebral venous drainage?

It hinders drainage, potentially increasing intracranial pressure (ICP).

(This position increases venous pressure in the cranial cavity, thereby impairing venous outflow.)

Under what condition can the Trendelenburg position lead to heart failure according to the Frank-Starling relationship?

In patients with poor myocardial function where the volume shift overshoots the peak of the curve.

(This occurs when excessive venous return increases preload beyond the heart's optimal performance capacity.)

Why is hypovolemia often 'unmasked' only after a patient is moved from Trendelenburg back to the supine position?

The head-down tilt artificially maintains central circulation and SV until the gravity-assisted preload is removed.

Compared to the awake state, how does anesthesia affect Functional Residual Capacity (FRC)?

It causes a decrease in FRC.

What change occurs to closing volume in the spontaneously breathing patient upon the induction of anesthesia?

Closing volume increases.

How does the cephalad shift of abdominal viscera in the Trendelenburg position impact pulmonary compliance?

It reduces pulmonary compliance.

(This occurs due to increased abdominal pressure on the diaphragm, limiting its movement.)

Which anatomical direction does the diaphragm move when a patient is placed in a head-up (Reverse Trendelenburg) position?

Caudad

In the lateral decubitus position, which lung serves as the 'dependent' lung?

The lung positioned on the lower side (closest to the table).

How does the V/Q ratio change in the non-dependent region of the lung compared to the dependent region?

The V/Q ratio increases in the non-dependent region.

(This occurs due to the decreased perfusion to that area, leading to a relatively higher ventilation compared to blood flow.)

How does neck flexion specifically affect the position of the Endotracheal Tube tip relative to the carina?

It pushes the tip toward the carina, increasing the risk of endobronchial intubation.

What is the primary airway risk associated with neck extension in an intubated patient?

Inadvertent extubation due to the tip moving toward the vocal cords.

Which intervention should a CRNA perform to assess airway patency before extubating a patient with suspected airway edema?

A leak test (cuff-leak test)

What is the primary mechanism of a stretch injury to the brachial plexus?

The plexus is anatomically fixed at the cervical vertebrae and axillary fascia, making it vulnerable when those points are pulled apart.

The risk of brachial plexus stretch injury is highest when the arm is abducted beyond how many degrees?

> 90 degrees

How does contralateral neck rotation affect the risk of brachial plexus injury in a supine patient?

It increases the risk of stretch injury on the side opposite the rotation.

Which surgical equipment, historically used to prevent sliding in Trendelenburg, is now discouraged due to the risk of brachial plexus compression?

Shoulder braces

If shoulder braces must be used, where is the safest anatomical placement to minimize nerve injury?

At the distal end of each clavicle over the acromion.

What specific positioning error in the lateral decubitus position causes compression of the brachial plexus?

Improper placement of the axillary roll (e.g., placing it directly in the axilla instead of caudad to it).

What is the most commonly injured peripheral nerve in the perioperative period?

The ulnar nerve

Which gender is statistically at higher risk for perioperative ulnar nerve injury?

Male gender

The ulnar nerve emerges from which anatomical structure at the elbow?

The cubital tunnel

What is the classic physical presentation of a chronic ulnar nerve injury?

Claw hand (permanent hyperextension of digits 4 and 5 at rest).

Which forearm position is recommended to protect the ulnar nerve when the arms are abducted on arm boards?

Supination

What are the two common etiologies for a median nerve injury during anesthesia care?

• Traumatic IV placement in the antecubital space

• forced elbow hyperextension

A patient unable to oppose their thumb postoperatively may have an injury to which nerve?

The median nerve.

Chronic median nerve injury leads to what characteristic hand deformity?

Ape hand deformity

The radial nerve passes along which anatomical landmark of the humerus?

The spiral groove

What is the typical motor presentation of a radial nerve injury?

Wrist drop

Which common piece of monitoring equipment can cause radial nerve injury if cycled excessively?

The NIBP cuff

Injury to the long thoracic nerve results in which specific physical exam finding?

Scapular winging

The long thoracic nerve innervates which muscle, responsible for holding the scapula against the chest wall?

The serratus anterior

What is the hallmark symptom of a suprascapular nerve injury?

Dull shoulder pain

In the lateral decubitus position, ventral circumduction of the dependent shoulder can stretch which nerve?

The suprascapular nerve

Excessive flexion of the thigh toward the groin during lithotomy can injure which nerve?

The obturator nerve

What motor deficit is expected in a patient with an obturator nerve injury?

Inability to adduct the leg

Which nerve is most likely injured by excessive traction during lower abdominal surgery, leading to impaired knee extension?

The femoral nerve

Where does a patient typically experience sensory loss if they sustain a saphenous nerve injury?

The anteromedial aspect of the leg

What positioning error in the lithotomy stirrups causes a common peroneal nerve injury?

Pressure on the lateral aspect of the leg at the level of the fibular head.

A patient unable to evert their foot and experiencing 'foot drop' likely has an injury to which nerve?

The common peroneal nerve

Excessive hip flexion in the lithotomy position is the primary cause of injury to which major nerve?

The sciatic nerve

Which nerve is at risk of compression against a perineal post on an orthopedic fracture table?

The pudendal nerve

If a patient's legs remain crossed during a long procedure, which nerve is at risk in the 'top' leg?

The sural nerve.

(This nerve provides sensation to the outer part of the foot and lower leg, and prolonged pressure can lead to numbness or discomfort.)

If a patient's legs remain crossed during a long procedure, which nerve is at risk in the 'bottom' leg?

The superficial peroneal nerve.

In which surgical position is lower extremity compartment syndrome most commonly seen?

The lithotomy position

What is the surgical treatment for a confirmed case of compartment syndrome?

Fasciotomy

What is the primary risk factor regarding 'time' for the development of compartment syndrome in lithotomy?

Surgical time > 2-3 hours

While it can occur in any position, Venous Air Embolism (VAE) is most commonly associated with which position?

The sitting position

How does a Venous Air Embolism (VAE) impact pulmonary dead space?

It increases pulmonary dead space

What is a 'paradoxical' air embolism?

An embolism that moves from the right heart to the left heart (e.g., via a patent foramen ovale), potentially causing a stroke.

Midcervical tetraplegia is most commonly associated with which positioning maneuver in the sitting position?

Hyperflexion of the neck (chin to chest).

Ischemia to which spinal cord level is typically responsible for midcervical tetraplegia?

C5

To prevent midcervical tetraplegia, how much space should be maintained between the chin and the chest?

At least two fingerbreadths

What positioning error in the supine position can lead to paraplegia?

Extreme hyperextension of the lumbar spine (hyperlordosis).

Which surgical table is noted as the best option to preserve normal pulmonary mechanics in the prone position?

The Jackson table

Why is the prone position often used for patients with Acute Respiratory Distress Syndrome (ARDS)?

It provides optimal V/Q matching.

In a patient with an anterior mediastinal mass, what are the three factors that worsen tracheobronchial compression?

• Supine position

• induction of general anesthesia

• loss of spontaneous ventilation

What type of endotracheal tube is recommended when managing a patient with an anterior mediastinal mass?

A reinforced (armored) endotracheal tube

Mnemonic: The four 'T's' for tumors likely to occur in the anterior mediastinum.

Thymoma

Teratoma

Thyroid

'Terrible' lymphoma

How does an anterior mediastinal mass affect the Superior Vena Cava (SVC)?

It can compress the SVC, causing edema of the face, neck, and upper torso.

What is the recommended CRNA intervention if the airway collapses due to a mediastinal mass during surgery?

Reposition the patient laterally or prone to restore airway patency.

Which nerve is most likely compressed by sheets that are too tight when the arms are tucked?

The radial nerve

What is the risk of placing large rolls under a patient's lumbar spine during surgery?

Paraplegia (due to extreme hyperextension).

Which nerve injury presents with impaired sensation of the fourth and fifth digits and inability to abduct the pinky finger?

The ulnar nerve

In the lateral decubitus position, which leg should be flexed to stabilize the patient?

The downside (dependent) leg

What is the risk of using a 'bean bag' positioner that envelopes the shoulders?

Compression injury to the brachial plexus.

Anesthetizing a patient with an anterior mediastinal mass: why is spontaneous ventilation preferred?

Spontaneous ventilation preserves the normal airway distending pressure gradient, preventing tumor-induced collapse.

Under the Frank-Starling curve model, which position shifts the patient toward 'Point B' (reduced preload)?

Reverse Trendelenburg or Sitting