Patient Positioning and Anaesthesia

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PATIENT POSITIONING AND ANAESTHESIA

Anesthesiologists share a critical responsibility for the proper positioning of patientsin the operating room.

Positions deemed optimal for surgery often result in undesirable physiologic changes

1. hypotension from impaired venous return to the heart oxygen

2. desaturation owing to ventilation-perfusion mismatching.

3. peripheral nerve injuries.

During anesthesia care, whenever possible, patients should be placed in a position thatthey would tolerate when awake.

Padded surfaces, lumbar support, and natural joint position are optimal.

The head should remain midline without substantial extension or flexion whenever

possible.

At no time should pressure on the eyes occur.

The duration of more extreme positions, if such are necessary, should be limited as

much as possible.

SUPINE POSITION

The most common position for surgery is the supine, or dorsal decubitus position. Because

the entire body is close to the level of the heart, hemodynamic reserve is best maintained.

Because compensatory mechanisms are blunted by anesthesia, however, even a few degrees

of head-down (Trendelenburg) position or head-up (reverse Trendelenburg) position are

sufficient to cause significant cardiovascular changes.

Physiology

Un-anaesthetised patients

1. Cardiovascular

Complex arterial, venous, and cardiac physiologic responses have evolved to blunt the

effects of positional changes on arterial blood pressure and maintain perfusion to vitalorgans.

As an individual reclines from an erect to a supine position, venous return to the heart

increases as pooled blood from the lower extremities redistributes toward the heart.

Preload, stroke volume, and cardiac output are augmented. The resultant increase in

arterial blood pressure activates afferent baroreceptors from the aorta and within the

carotid sinuses to decrease sympathetic outflow and increase parasympathetic

impulses to the sinoatrial node and myocardium. The result is a compensatory

decrease in heart rate, stroke volume, and cardiac output.

Mechanoreceptors from the atria and ventricle also are activated to decrease

sympathetic outflow to muscle and splanchnic vascular beds. Resulting in lowering of

blood pressure.



Atrial reflexes are activated to regulate renal sympathetic nerve activity, plasma renin,

atrial natriuretic peptide, and arginine vasopressin levels.

As a result, systemic arterial blood pressure is maintained within a narrow range

during postural changes in the unanesthetized setting.

2. Pulmonary

Spontaneous ventilation results from small negative intrathoracic pressure shiftsduring inspiration owing to diaphragmatic displacement and chest wall expansion.

This pressure decrease also promotes venous return to the thorax by reducing the

pressure in the great veins and right atrium compared with the periphery.

Normal distribution of ventilation is determined by the excursion of the diaphragm,

movement of the chest wall, and compliance of the lung.

When an individual shifts from standing to supine, functional residual capacitydecreases owing to cephalad displacement of the diaphragm. The relative contribution

to ventilation of the chest wall compared with the diaphragm decreases from 30% to

10%.

With spontaneous ventilation in either position, diaphragmatic movement is greatest

adjacent to the most dependent portions of the lung.

The preferential perfusion of the dependent portions is dominated by gravity and ismore in the dorsal pulmonary segments. As a result, the ventilation-perfusion

mismatch is corrected.

Anaesthetised patients

1. Cardiovascular. General anesthesia, muscle relaxation, positive-pressure ventilation, and neuraxial

blockade interfere with venous return, arterial tone, and autoregulatory mechanisms,

leading to uncompensated circulatory effects of changes in position.

The use of spinal or epidural anesthesia causes a significant sympathectomy across allaffected dermatomes, independent of the presence of general anesthesia, reducing

preload and potentially blunting cardiac response if the sympathetic output to the

heart is affected.

Positive-pressure ventilation increases mean intrathoracic pressure, diminishing the

venous pressure gradient from peripheral capillaries to the right atrium. Positive end-

expiratory pressure increases mean intrathoracic pressure further, as do conditions

associated with low lung compliance, such as airways disease, obesity, ascites, and

light anesthesia.

For these reasons, arterial blood pressure is often particularly labile immediately after

the initiation of anesthesia and during patient positioning. It is crucial for the

anesthesiologist to anticipate, monitor, and treat these effects, and to assess the safety

of positional changes for each patient. Blood pressure should be measured frequently

after induction of anesthesia or initiation of neuraxial blockade. It is often necessary

to increase intravenous fluid administration, adjust the level of anesthesia, or

administer vasopressors during this hemodynamic transition. Temporary use of head-

down positions may be helpful.Interruptions in monitoring to facilitate positioning or

turning of the operating room table must be minimized during this dynamic period.



2. Pulmonary

Anesthetized patients who are breathing spontaneously have a reduced tidal volumeand functional residual capacity and an increased closing volume compared with the

nonanesthetized state.

Positive-pressure ventilation with muscle relaxation may ameliorate ventilation-perfusion mismatches under general anesthesia by maintaining adequate minute

ventilation and limiting atelectasis.

The diaphragm assumes an abnormal shape, however, owing to the loss of muscletone, and is displaced less in the dependent portions of the lung.This causes

ventilation-perfusion mismatching .

Patients undergoing neuraxial anesthesia lose abdominal and thoracic muscle function

in affected dermatomes, but diaphragmatic function is retained.

Complications

1. Pressure alopecia

resulting from ischemic hair follicles is related to prolonged immobilization of the

head with its full weight falling on a limited area, usually the occiput.

Lumps, such as those caused by monitoring cable connectors, should not be placedunder head padding because they may create focal areas of pressure.

Hypothermia and hypotension during surgery, such as during cardiopulmonary

bypass, may increase the incidence of this complication.

Consequently, it is prudent to cushion the head well, and if possible during prolonged

surgery, periodic rotation of the head to redistribute the weight may be considered.

2. Backache

may occur in the supine position as the normal lumbar lordotic curvature, particularlythe tone of the paraspinous musculature, is lost during general anesthesia with muscle

relaxation or a neuraxial block.

Consequently, patients with extensive kyphosis, scoliosis, or a previous history of back pain may require extra padding of the spine or slight flexion at the hip and knee.

3. Pressure ischaemia

Tissues overlying all bony prominences, such as the heels and sacrum, must be

padded to prevent soft tissue ischemia owing to pressure, especially during prolonged

surgery

4. Peripheral nerve injury

is a complex phenomenon with a multifactorial etiology.

Ulnar neuropathy is the most common lesion.

Although there is no direct evidence that positioning or padding alone can prevent

perioperative ulnar neuropathies, it is recommended, to limit arm abduction in a

supine patient to less than 90 degrees at the shoulder with the hand and forearm either

supinated or kept in a neutral position.



Regardless of the position of the upper extremities, maintaining the head in a

relatively midline position can help minimize the risk of stretch injury to the brachial

plexus.

Arm position in Supine position

One or both arms may be abducted out to the side or adducted (tucked) alongside the

body.

It is recommended that upper extremity abduction be limited to less than 90 degrees to

minimize the likelihood of brachial plexus injury by caudad pressure in the axilla

from the head of the humerus.

The hand and forearm are either supinated or kept in a neutral position with the palm

toward the body to reduce external pressure on the spiral groove of the humerus and

the ulnar nerve

When the arms are adducted, they are usually held alongside the body with a ―drawsheet‖ that passes under the body and over the arm, and is then tucked directly under

the torso to ensure that the arm remains properly placed next to the body. Alternatively, in surgeries in which access to the chest or abdomen is not necessary,

curved arm cradles may be used. In all cases, the arms are placed in a neutral

position.[16]

The elbows and any protruding objects, such as intravenous fluid lines

and stopcocks, are padded

Variations of the Supine Position

1. The lawn chair position

the hips and knees are slightly flexed.

reduces stress on the back, hips, and knees, and is better tolerated by patients who areawake or undergoing monitored anesthesia care.

As the legs are slightly above the heart, venous drainage from the lower extremity is

facilitated.

Also, the xiphoid to pubic distance is decreased, reducing the tension on the ventral

abdominal musculature and easing closure of laparotomy incisions.

2. The frog-leg position

the hips and knees are flexed, and the hips are externally rotated with the soles of the

feet facing each other, allows access to the perineum, medial thighs, genitalia, andrectum

. Care must be taken to minimize stress and postoperative pain in the hips and prevent

dislocation by supporting the knees appropriately.

3. Trendelenburg position

Head low position

often used to increase venous return during hypotension, to improve exposure duringabdominal and laparoscopic surgery, and to prevent air emboli and facilitate

cannulation during central line placement



The Trendelenburg position has significant cardiovascular and respiratory

consequences.

The head-down position increases central venous, intracranial, and intraocular

pressures.

Prolonged head-down position also can lead to swelling of the face, conjunctiva,

larynx, and tongue with an increased potential for postoperative upper airwayobstruction.

The cephalic movement of abdominal viscera against the diaphragm also decreases

functional residual capacity and pulmonary compliance.

In spontaneously ventilating patients, the work of breathing increases. In

mechanically ventilated patients, airway pressures must be higher to ensure adequate

ventilation.

protect the airway from pulmonary aspiration related to reflux and to reduce

atelectasis.

Because of the risk of edema to the trachea and mucosa surrounding the airway during

surgeries in which patients have been in the Trendelenburg position for prolongedperiods, it may be prudent to visualize the larynx before extubation.

4. Reverse Trendelenburg position

head-up tilt

is often employed to facilitate upper abdominal surgery by shifting the abdominal

contents caudad.

Caution is advised to prevent patients from slipping on the table

frequent monitoring of arterial blood pressure may be prudent to detect hypotension

owing to decreased venous return.

In addition, the position of the head above the heart reduces perfusion pressure to thebrain and should be taken into consideration when determining optimal blood

pressure.



LITHOTOMY POSITION

The classic lithotomy position is frequently used during gynecologic, rectal, and

urologic surgeries.

The hips are flexed 80 to 100 degrees from the trunk, and the legs are abducted 30 to

45 degrees from the midline. The knees are flexed until the lower legs are parallel to

the torso, and the legs are held by supports or stirrups. The foot section of the

operating room table is then lowered.

Initiation of the lithotomy position requires coordinated positioning of the lowerextremities by two assistants to avoid torsion of the lumbar spine. Both legs should be

raised together, flexing the hips and knees simultaneously.

The lower extremities should be padded to prevent compression against the stirrups.

After the surgery, the patient must be returned to the supine position in a coordinated

manner.

The hands should be positioned to prevent entrapment in any moving or articulating

sections of the operating room table.

The legs should be removed from the holders simultaneously, knees brought together

in the midline, and the legs slowly straightened and lowered onto the operating room

table.

Physiological changes.(+ those of supine position)

When the legs are elevated, preload increases, causing a transient increase in cardiacoutput and, to a lesser extent, cerebral venous and intracranial pressure in otherwise

healthy patients.

In addition, the lithotomy position causes the abdominal viscera to displace the

diaphragm cephalad, reducing lung compliance and potentially resulting in a

decreased tidal volume.

If obesity or a large abdominal mass is present (tumor, gravid uterus), abdominal

pressure may increase significantly enough to obstruct venous return to the heart.

Lastly, the normal lordotic curvature of the lumbar spine is lost in the lithotomy

position, potentially aggravating any previous lower back pain.

More acute flexion of the knees or hips can threaten to angulate and compress majorvessels at either joint.

hip flexion to greater than 90 degrees on the trunk has been shown to increase stretch

of the inguinal ligaments.

Complications.(+ those of supine position)

Injury to the common peroneal nerve is the most common lower extremity motorneuropathy. A potential cause of the injury was the compression of the nerve between

the lateral head of the fibula and the bar holding the legs. When the candy cane

stirrups are used, special attention must be paid to avoid compression.The injury was



more common with patients who had low body mass index, recent cigarette smoking,

or prolonged duration of surgery.

Paresthesias in the distribution of the obturator, lateral femoral cutaneous, sciatic, andperoneal nerves may occur due to nerve compression.

Lower extremity compartment syndrome is a rare complication associated with the

lithotomy position. It occurs when perfusion to an extremity is inadequate, resulting inischemia, edema, and extensive rhabdomyolysis from increased tissue pressure within

a fascial compartment. Long surgical procedure time was the only distinguishing

characteristic of the surgeries in which patients developed lower extremity

compartment syndromes. It is recommended to lower the legs to the level of the body

periodically if surgery extends beyond several hours.

If the arms are on the operating table alongside the patient, the hands and fingers may

lie near the open edge of the lowered section of the table. When raising the foot of the

table at the end of surgery, strict attention to the position of the hand must be paid to

avoid a potentially disastrous crush injury to the fingers.



LATERAL DECUBITUS POSITION

The lateral decubitus position is used most frequently for surgery involving thethorax, retroperitoneal structures, or hip.

The patient rests on the nonoperative side and is balanced with anterior and posterior

support, such as bedding rolls or a deflatable beanbag, and a flexed dependent leg.

The arms usually are positioned in front of the patient. The dependent arm rests on a

padded arm board perpendicular to the torso. The nondependent arm is often

supported over folded bedding or suspended with an armrest or foam cradle. If

possible, the arm should not be abducted more than 90 degrees.

The patient's head must be kept in a neutral position to prevent excessive lateralrotation of the neck and stretch injuries to the brachial plexus.

The dependent ear should be checked to avoid folding and undue pressure. It isadvised to verify that the eyes are securely taped before repositioning if the patient is

asleep. The dependent eye must be checked frequently for external compression.

To avoid compression injury to the dependent brachial plexus or vascularcompression, an ―axillary roll‖ is frequently placed just caudal to the dependent axilla

This roll should never be placed in the axilla. Its purpose is to ensure that the weight

of the thorax is borne by the chest wall caudal to the axilla and avoid compression of

the axillary contents.

The pulse should be monitored in the dependent arm for early detection of

compression to axillary neurovascular structures. . The act of positioning a patient in the lateral decubitus position requires the

cooperation of the entire operating room staff to prevent potential injuries.

Physiology

1. Circulatory

If the legs are maintained in the long axis of the body, almost no pressure gradients

exist along the great vessels from head to foot. Small hydrostatic differences are

detected between the values when blood pressure is recorded simultaneously on thetwo arms.

If the lower extremities are positioned below the level of the heart, blood pools in the

distensible vessels of the dangling legs because of gravity-induced increases in

venous pressure and resultant venous stasis. Wrapping the legs and thighs in

compressive bandages has been commonly used to combat venous pooling.

Marked flexion of the lower extremities at knees and hips can partially or completely

obstruct venous return to the inferior vena cava either by angulation of vessels at the

popliteal space and inguinal ligament or by thigh compression against an obese

abdomen.

A small support placed just caudad of the down-side axilla can be used to lift thethorax enough to relieve pressure on the axillary neurovascular bundle and prevent

disturbed blood flow to the arm and hand. Any padding should support only the chest



wall and it should be periodically observed to ensure that it doesn't impinge on the

neurovascular structures of the axilla.

If the cervical spine of the patient who is placed in a horizontal lateral decubitusposition is carefully maintained in alignment with the thoracolumbar spine, almost no

gradient occurs between pressures in the mediastinum and those in the head.

However, if the head is not supported and sufficient lateral angulation of the neck occurs in either direction, obstruction of jugular flow may occur.

In the low-pressure pulmonary circuit, hydrostatic gradients occur between the twohemithoraces. Vascular congestion of the dependent lung and the relative

hypoperfusion of the non dependent lung is noted.

2. Respiratory

In the presence of a supple chest, the lateral decubitus position can decrease the

volume of the dependent hemithorax. The weight of the chest forces the rib cage into

a less expanded conformation. Gravity-induced shifts of mediastinal structures toward

the chest wall tend further to reduce the volume of the dependent lung. Abdominal

viscera force the down-side diaphragm cephalad if the long axis of the trunk is

horizontal or head down.

Spontaneous ventilation can partially compensate for the diaphragmatic stretching in

the dependent hemithorax because the contractile efficiency of the elongated

diaphragmatic muscle fibers is increased.

The non dependent hemithorax is much less compressed than the dependent side, and

because the lung lies above the level of the atria, it has less vascular congestion. As a

result, positive-pressure ventilation is directed preferentially to the more compliant

up-side lung. The result can easily be excessive ventilation of the underperfused up-

side lung and hypoventilation of the congested down-side lung. The potential for aclinically significant ventilation – perfusion mismatch is obvious, particularly in the

presence of pulmonary disease.

Complications

1. Eyes and Ears - Injuries to the dependent eye are unlikely if the head is properly

supported during and after the turn from the supine to the lateral position. If the

patient's face turns toward the mattress, however, and the lids are not closed or the

eyes otherwise protected, abrasions of the ocular surface can occur. Direct pressure onthe globe can displace the crystalline lens, increase intraocular pressure or,

particularly if systemic hypotension is present, cause ischemia.In the lateral position,

the weight of the head can press the down-side ear against a rough or wrinkled

supporting surface. Careful padding with a pillow or a foam sponge is usually

sufficient protection against contusion of the ear. The external ear should also be

palpated to ensure that it has not been folded over in the process of placing support

beneath the head.

2. Neck - Lateral flexion of the neck is possible when the head of a patient in the lateral

position is inadequately supported. If the cervical spine is arthritic, postoperative neck

pain can be troublesome. Pain from a symptomatic protrusion of a cervical disk canbe intensified unless the head is carefully positioned so that lateral or ventral flexion,



extension, or rotation is avoided. Patients with unstable cervical spines can be

intubated while awake and turned gently into the operative position while repeated

neurologic checks, with which the patient cooperates and responds, are accomplished

to detect the development of a positioning injury.65

3. Suprascapular Nerve - Ventral circumduction of the dependent shoulder can rotate thesuprascapular notch away from the root of the neck this can stretch the suprascapular

nerve and produce troublesome, diffuse, dull shoulder pain. The diagnosis is

established by blocking the nerve at the notch and producing pain relief. Treatment

may require resecting the ligament over the notch to decompress the nerve. A

supporting pad placed under the thorax just caudad of the axilla and thick enough to

raise the chest off the shoulder should prevent a circumduction stretch injury to the

nerve.

4. Long Thoracic Nerve - Instances of postoperative winging of the scapula have

followed use of the lateral decubitus position. There is a possibility of trauma to the

nerve while establishing the lateral position. Lateral flexion of the neck may stretchthe long thoracic nerve in the obtuse angle of the neck.

5. Nerve - The common peroneal nerve of the dependent side is padded to minimize

compression damage caused by the weight of the legs. A small pad, thick enough to

raise the chest wall and prevent excessive compression of the shoulder or

entrapment/compression of the neurovasclar structures of the axilla, is placed just

caudad to the dependent axilla

6. Vascular - Compression and venous engorgement in the dependent arm may affect

the pulse oximetry reading, and a low saturation reading may be an early warning of compromised circulation. Hypotension measured in the dependent arm may be due to

axillary arterial compression, so it is useful to retain the ability to measure blood

pressure in both arms

Variations of the Lateral Decubitus Positions

1. Semisupine and Semiprone

The semilateral postures are designed to allow the surgeon to reach anterolateral

(semisupine) and posterolateral (semiprone) structures of the trunk.

In the semisupine position, the up-side arm must be carefully supported so that it is

not hyperextended and no traction or compression is applied to the brachial and

axillary neurovascular bundles

Noncompressible padding should be placed under the dorsal torso and hip to prevent

the patient from rolling supine and stretching the anchored extremity.

The pulse of the restrained wrist should be checked to ensure adequate circulation in

the elevated arm.

2. Lateral Jackknife.



The lateral jackknife position places the down-side iliac crest over the hinge between

the back and thigh sections of the table and thetable top is angulated at that point to

flex the thighs on the trunk laterally.

After the patient has been suitably positioned and restrained, the chassis of the table istipped so that the uppermost surface of the patient's flank and thorax becomes

essentially horizontal. As a result, the feet are below the level of the atria, andsignificant amounts of blood may pool in distensible vessels in each leg.

The lateral jackknife position is usually intended to stretch the up-side flank and

widen intercostal spaces as an asset to a thoracotomy incision. However, in terms of

lumbar stress, restriction by the taut flank of up-side costal margin motion, and

pooling of blood in depressed lower extremities, the position imposes a significant

physiologic insult.

3. Kidney.

The kidney position resembles the lateral jackknife position, but it adds the use of

an elevated rest (the kidney rest) under the down-side iliac crest to increase the

amount of lateral flexion and improve access to the up-side kidney under the

overhanging costal margin.

Unlike the lateral jackknife position, the kidney position does not have a useful

alternative for a flank approach to the kidney. Thus, the physiologic insults

associated with the posture need to be limited by vigilant anesthesia and rapid

surgery.

Strict stabilizing precautions should be taken to prevent the patient fromsubsequently shifting caudad on the table in such a manner that the elevated rest

relocates into the down-side flank and becomes a severe impediment to ventilationof the dependent lung.



PRONE POSITION

The prone or ventral decubitus position is used primarily for surgical access to the

posterior fossa of the skull, the posterior spine, the buttocks and perirectal area, and

the lower extremities.

The patient is first intubated on the stretcher, and all intravascular access is obtained

as needed. The endotracheal tube is well secured to prevent dislodgment and

loosening of tape owing to drainage of saliva when prone.

With the coordination of the entire operating room staff, the patient is turned prone

onto the operating room table, keeping the neck in line with the spine during the

move. The anesthesiologist is primarily responsible for coordinating the move and for

repositioning of the head.

It is recommended to disconnect blood pressure cuffs and arterial and venous linesthat are on the side that rotates furthest to avoid dislodgment, although some

clinicians prefer to disconnect all lines and monitors before moving. Pulse oximetry

usually can be maintained if applied to the ―inside‖ arm, and full monitoring should

be reinstituted as rapidly as possible. Endotracheal tube position and adequate

ventilation are reassessed immediately after the move.

Head position is crucial. The patient's head may be turned to the side when prone if neck mobility is adequate. As in the lateral decubitus position, the dependent eye must

be checked frequently for external compression. In addition, in patients with cervical

arthritis or cerebrovascular disease, lateral rotation of the neck may compromise

carotid or vertebral arterial blood flow or jugular venous drainage.

In most cases, the head is kept in a neutral position using a surgical pillow, horseshoeheadrest, or Mayfield head pins.

Pillows are specially designed for the prone position. Most, including disposable foam

versions, support the forehead, malar regions, and the chin, with a cutout for the eyes,

nose, and mouth (see Fig. 36-14 ). The face is not always visible making eye checks

more difficult. Mirror systems are available to facilitate intermittent visual

confirmation that the eyes are unimpinged, although direct visualization or tactile

confirmation of at least the initial appearance is prudent

The horseshoe headrest supports only the forehead and malar regions and allows

excellent access to the airway, but it is more rigid and potentially dangerous if the

head moves . Mayfield rigid pins support the head without any direct pressure on the face, allow

access to the airway, and hold the head firmly in one position that can be finely

adjusted for optimal neurosurgical exposure ( Fig. 36-18 ). Rigid pin fixation is rarely

used outside cranial or cervical spine surgeries.

Regardless of the technique employed to support the head, the eyes, face, and airwaymust be checked periodically to ensure that the weight is borne only by the bony

structures, and that there is no pressure on the eyes.

Careful attention must be paid to the ability of the abdomen to hang free and to movewith respiration.

The thorax is generally supported by firm rolls or bolsters placed along each side from

the clavicle to the iliac crest.



To prevent tissue injury, pendulous structures (e.g., male genitalia and female

breasts) should be clear of compression; the breasts should be placed medial to the

bolsters. The lower portion of each roll or bolster must be placed under its respective

iliac crest to prevent pressure injury to the genitalia and the femoral vasculature.[32]

The prone position presents special risks for morbidly obese patients, whose

respiration is already compromised, and who may be difficult to reposition quickly. The legs should be padded and flexed slightly at the knees and hips.

Both arms may be positioned to the patient's sides and tucked in the neutral position

as described for a supine patient, or placed next to the patient's head on arm boards.

Extra padding under the elbow is needed to prevent compression of the ulnar nerve.

The arms should not be abducted greater than 90 degrees to prevent excessive

stretching of the brachial plexus, especially in patients with the head turned.

Finally, elastic stockings and active compression devices are needed for the lowerextremities to minimize pooling of the blood, especially with any flexion of the body.

Physiology

1. Circulatory

In the prone position, the circulatory dynamics vary according to the postural

modification in use.

If the legs remain essentially horizontal, pressure gradients in the blood vessels areminimal.

If the patient is kneeling, or if the table chassis is rotated head high, significant

pooling of venous blood in distensible dependent vessels is likely to occur. Also as

the head is above the level of the heart, mean vascular pressures are decreased

according to the distance above the heart and conjunctival edema is less evident orabsent, but air entrainment in open veins is possible.

If the head of a prone patient is below the level of the heart, venous congestion of the

face and neck becomes evident. Conjunctival edema is usual and reflects the influence

of gravity on accumulation of extravascular fluid.

With the patient lying on the soft abdominal wall, pressure of compressed viscera is

transmitted to the dorsal surface of the abdominal cavity. Mesenteric and

paravertebral vessels are compressed, causing engorgement of veins within the spinal

canal. Obstruction of the inferior vena cava can produce immediate, visible distention

of vertebral veins.

Turning the patient's head can alter arterial perfusion and venous drainage in both

extracranial and intracranial vessels. No significant changes were detected in mean arterial pressure, right atrial pressure,

or pulmonary artery occlusion pressure.

2. Respiratory

The original areas of compression atelectasis reopen when those parts of the lung

became nondependent, whereas fresh areas of compression atelectasis are formed in

the newly dependent areas of the lung.

No change in oxygenation or shunting when pronation occurred.

If the thorax is supple or compliant, the body weight of an anesthetized, prone patient

compresses the anteroposterior diameter of the relaxed chest. If the essure of the



abdominal viscera is sufficient to force the diaphragm cephalad, the lung is shortened

along its long axis. Hence, the compliance of the compacted prone lung can be

anticipated to decrease.

The result of decreased pulmonary compliance in a poorly positioned, prone,

anesthetized patient is either an increased work of spontaneous ventilation or the need

for higher inflation pressures during positive-pressure ventilation. Proper positioning can retain more nearly normal pulmonary compliance by

minimizing the cephalad shift of the diaphragm caused by compressed abdominal

viscera. If the patient is arranged so that the abdomen hangs free, the loss of

functional residual capacity is less in the prone position than in either the supine or

the lateral position.

Complications

1. Eyes and Ears - The eyes and ears may sustain injury in the prone position. The

eyelids should be closed, and each eye should be protected in some manner so that the

lids cannot be accidentally separated and the cornea scratched. Instillation of

lubrication in the eyes should be considered, although the value of this treatment is

debated. The eyes should also be protected against the head turning medially after

positioning as well as against pressure being exerted on the globe. Conjunctival

edema usually occurs in the eyes of the pronated patient if the head is at or below the

level of the heart. It is usually transient, inconsequential, and requires only

reestablishment of the normal tissue perfusion gradients of the supine position, or of a

slight amount of head-up tilt, to be redistributed.

2. Blindness - Permanent loss of vision can occur after nonocular surgical procedures,

especially those performed in a ventral decubitus position.The occurrence of thisdevastating complication is particularly associated with extensive surgical procedures

done in the prone position, such as reconstructive spine surgery, where there is

associated blood loss, anemia, and hypotension. Causes of significant permanent

postoperative visual loss usually involve compromise of oxygen delivery to elements

of the visual pathway and include ischemic optic neuropathy (anterior or posterior),

retinal artery occlusion (central or branch), and cortical blindness.

3. Neck Problems - Anesthesia impairs reflex muscle spasm that protects the skeleton

against motion that would be painful if the patient were alert. Lateral rotation of the

head and neck of an anesthetized, pronated patient, particularly one with an arthritic

cervical spine, can stretch relaxed skeletal muscles and ligaments and injure

articulations of cervical vertebrae. Postoperative neck pain and limitation of motioncan result. The arthritic neck is usually best managed by keeping the head in the

sagittal plane when the patient is prone.

4. Vascular - Extremes of head and neck rotation can also interfere with flow in either

the ipsilateral or contralateral vessels to and from the head. Excessive head rotation

can reduce flow in both the carotid and vertebral systems.

5. Nerve Injuries - Stretch injuries to the roots of the brachial plexus.The ulnar nerve,

lying in the cubital tunnel is vulnerable to being compressed by the weight of the

elbow Consequently, the medial aspect of the elbow must be well padded and its

weight borne principally on the medial epicondyle.



6. Breast Injuries - The breasts of a pronated woman, if forced laterally by ventral chest

supports, can be stretched and injured along their sternal borders. Medial and

cephalad displacement seems better tolerated. Direct pressure on breasts (particularly

if breast prostheses are present) can cause ischemia to breast tissue and should be

avoided.

7. Abdominal Compression - Compression of the abdomen by the weight of the pronepatient's trunk can cause viscera to force the diaphragm cephalad enough to impair

ventilation. If intra-abdominal pressure approaches or exceeds venous pressure, return

of blood from the pelvis and lower extremities is reduced or obstructed. Because the

vertebral venous plexuses communicate directly with the abdominal veins, increased

intra-abdominal pressure is transmitted to the perivertebral and intraspinal surgical

field in the form of venous distention and increased difficulty with hemostasis. All of

the various supportive pads and frames, when properly used, are designed to remove

pressure from the abdomen and avoid these problems.

8. Knee Injuries - Obese patients, or those who have pathologic conditions of the knees,

can have their knee joints injured in the kneeling position if the supportive ledges are

not heavily padded

Variations of the Ventral Decubitus Position

1. Prone Jackknife

The prone jackknife posture is used to provide access to the sacral, perianal, and

perineal areas as well as to the lower alimentary canal.

The thighs are flexed on the trunk more than is usual in the full prone position, with

the table surface hinges determining the degree of flexion achievable.66

2. Prone Kneeling

Kneeling positions have been used to improve operative conditions in the lumbar and

cervicooccipital areas.If the vertebral column is unstable, kneeling frames are not as useful as

parallel longitudinal supports because kneeling risks application of shearing forces at the

fracture site, with the potential for damage of the contents of the spinal canal. In massively

obese patients who must be operated on in the prone position, kneeling frames tend to prevent

pressure on the abdomen more successfully than longitudinal frames.



Sitting Position

The sitting position offers advantages to the surgeon in approaching the posterior

cervical spine and the posterior fossa.

The main advantages of the sitting position over the prone position for neurosurgical

and cervical spine surgeries are excellent surgical exposure, decreased blood in the

operative field, and, possibly, reduced perioperative blood loss.

The main advantages to the anesthesiologist are superior access to the airway, reduced

facial swelling, and improved ventilation, particularly in obese patients.

The classic sitting position for surgery places the patient in a semi-reclining posture

on an operating table, with the legs elevated to approximately the level of the heart

and the head flexed ventrally on the neck.

The head may be fixed in pins for neurosurgery or taped in place with adequatesupport for other surgeries.

Head flexion should not be sufficient to force the chin into the suprasternal notch.

Elastic stockings or compressive wraps around the legs reduce pooling of blood in the

lower extremities.

Because gravity is pulling the arms caudad, they must be supported to the point of

slight elevation of the shoulders to avoid traction on the shoulder muscles and

potential stretching of upper extremity neurovascular structures.

The knees are usually slightly flexed for balance and to reduce stretching of the sciatic

nerve, and the feet are supported and padded.

Physiology

1. Cardiovascular

The hemodynamic effects of placing a supine patient in the sitting position are

dramatic.

As the head is raised above the level of the heart, pressure gradients develop and

increase with the degree of elevation.

Blood shifts from the upper body toward the feet. Atrial filling pressures decrease,

sympathetic tone increases, parasympathetic tone decreases, the renin-angiotensin-aldosterone system is activated, and fluid and electrolytes are retained by the kidneys.

Because of the pooling of blood into the lower body under general anesthesia patients

are particularly prone to hypotensive episodes. Incremental positioning and the use of

intravenous fluids, vasopressors, and appropriate adjustments of anesthetic depth can

reduce the degree and duration of hypotension. Elastic stockings and active leg

compression devices can help maintain venous return.



2. Respiratory

As the patient becomes more upright in the head-elevated dorsal decubitus position,

the inspiratory stroke of the diaphragm becomes less impeded by the bulk of

abdominal viscera.

Spontaneous chest wall motion requires less effort, and less pressure is needed to

inflate the lungs during passive inspiration. Functional residual capacity increases in

the head-elevated positions.

Complications

Postural Hypotension - In the anesthetized patient, establishing any of the head-

elevated positions is frequently accompanied by some degree of reduction in systemic

blood pressure. The normal protective reflexes are inhibited by drugs used duringanesthesia. Measuring mean arterial pressures at the level of the circle of Willis is

recommended to assess cerebral perfusion pressures more accurately.

Air Embolus - Because of the elevation of the surgical field above the heart, and the

inability of the dural venous sinuses to collapse because of their bony attachments, the

risk of venous air embolism is a constant concern.Air embolization is potentially

lethal. In the bloodstream, air migrates to the heart, where it creates a compressible

foam that destroys the propulsive efficiency of ventricular contraction and irritates the

conduction system. Air can also move into the pulmonary vasculature, where bubbles

obstruct small vessels and compromise gas exchange, or it can cross through a patent

foramen ovale to the left side of the heart and the systemic circulation.The potential

for venous air embolization increases with the degree of elevation of the operative site

above the heart.

Pneumocephalus - When brain mass is decreased by ventricular drainage, steroids,

and diuresis, the space available after dura is opened, to a pneumocephalus is

enlarged. Diffusion of nitrous oxide into the accumulated air, or the warming of

trapped gas, can produce a tension pneumocephalus with signs of increased

intracranial pressure and delayed awakening from anesthesia.

.Ocular Compression - Pressure from a padded head rest on the eyes of a patient who

has been placed in a head-elevated position can dislocate a crystalline lens or render

the globe ischemic.

Edema of the Face, Tongue, and Neck - Severe postoperative macroglossia,

apparently because of venous and lymphatic obstruction, can be caused by prolonged,

marked neck flexion. Extremes of neck flexion, with or without head rotation, have

been widely used to gain access to structures in the posterior fossa and cervical spine,

but their potential for damage should be understood and excessive flexion – rotation

avoided if possible

Midcervical Tetraplegia - This devastating injury occurs after hyperflexion of the

neck, with or without rotation of the head, and is attributed to stretching of the spinal





Peripheral Nerve Injury

Peripheral nerve injury remains a serious peri-operative complication.

Injuries occur when peripheral nerves are subjected to stretch, ischemia, or

compression during surgery.

Because sensation is blocked by unconsciousness or regional anesthesia, early

warning symptoms of pain and the normal spontaneous repositioning are absent.

Ulnar neuropathy is the most frequent site of injury (28%), followed by the brachialplexus (20%), lumbosacral nerve root (16%), and spinal cord (13%).

With the exception of spinal cord injury, the mechanism of nerve injury remains

largely unknown. Most injuries, particularly injuries to nerves of the upper extremity,

such as the ulnar nerve and brachial plexus, occurred in the presence of adequate

positioning and padding.

Padding, positional details andprolonged duration are risk factors.

1. Ulnar Nerve

The etiology of perioperative ulnar neuropathy is complex and incompletely

understood.

Injury was thought to be associated with hyperflexion of the elbow and compression

by the operating room table of the nerve at the condylar groove and the cubital tunnel

against the posterior aspect of the medial epicondyle of the humerus.

The neuropathy, if permanent, results in the inability to abduct or oppose the fifth

finger, diminished sensation in the fourth and fifth fingers, and eventual atrophy of

the intrinsic muscle of the hands creating a claw-like hand.

Perioperative ulnar neuropathy occurred predominantly in men, in an older

population, and with a delayed onset.

The large predominance of ulnar injury in men may be explained by anatomic

differences. Men have a more developed and thickened flexor retinaculum with less

protective adipose tissue and a larger (1.5 ×) tubercle of the coronoid process that can

predispose to nerve compression in the cubital tunnel. Other risk factors are diabetes

mellitus, vitamin deficiency, alcoholism, cigarette smoking, and cancer

2. Brachial Plexus

The brachial plexus is susceptible to injury from stretching or compression because of its long superficial course in the axilla between two points of fixation, the vertebra

and the axillary fascia, in association with the mobile clavicle and humerus

The patient often complains of sensory deficit in the distribution of the ulnar nerve.

Injury is most commonly associated with arm abduction greater than 90 degrees,

lateral rotation of the head, asymmetric retraction of the sternum for internal

mammary artery dissection during cardiac surgery, and direct trauma.

To avoid brachial plexus injury, patients ideally should be positioned with the head

midline, arms kept at the sides, the elbow mildly flexed, and the forearm supinated.

Brachial plexus injuries occurred during a regional block, particularly the axillaryblock.



Brachial plexus injury also is associated with direct compression, particularly with the

use of shoulder braces in patients undergoing surgery in the Trendelenburg position.

The nerves are vulnerable to compression as they pass between the clavicle and the

first rib. Medial placement of the braces can compress the proximal roots, and lateral

placement of the braces can stretch the plexus.

3. Other Upper Extremity Nerves

The radial nerve can be injured from direct pressure as it traverses the spiral groove of the humerus in the lower third of the arm.

The injury often manifests as a wrist drop with an inability to abduct the thumb or

extend the metacarpophalangeal joints.

Isolated median nerve injury most often occurs during the insertion of an intravenous

needle into the antecubital fossa in an anesthetized patient where the nerve is adjacent

to the medial cubital and basilic veins.

Patients with this injury are unable to oppose the first and fifth digits and have

decreased sensation over the palmar surface of the lateral three and a half fingers

4. Lower Extremity Nerves

Injuries to the sciatic and common peroneal nerves occur most often in the lithotomyposition.

Because of its fixation between the sciatic notch and the neck of the fibula, the sciatic

nerve can be stretched with external rotation of the leg. Hyperflexion of the hips or

extension of the knees also can aggravate nerve stretch in this position.

The common peroneal nerve, a branch of the sciatic nerve, can be damaged from the

compression of the nerve between the head of the fibula and the frame of the leg

support. patients who sustain injury complain of a foot drop and the inability to extend the toes

in a dorsal direction or evert the foot.

Injury to the femoral or obturator nerves generally occurs during lower abdominalsurgical procedures with excessive retraction.

The obturator nerve also can be injured during a difficult forceps delivery or by

excessive flexion of the thigh to the groin.

A femoral neuropathy manifests with decreased flexion of the hip, decreased

extension of the knee, or a loss of sensation over the superior aspect of the thigh and

medial/anteromedial side of the leg.

An obturator neuropathy manifests with inability to adduct the leg with decreased

sensation over the medial side of the thigh.

Injury Recommendations for Prevention

Ulnar nerve (25%) Avoid excessive pressure on postcondylar groove of humerus

Keep hand and forearm either supinated or in neutral position

Brachial plexus (19%) Avoid the use of shoulder braces in patients in Trendelenburgposition (use nonsliding mattresses)



Injury Recommendations for Prevention

Avoid excessive lateral rotation of head either in supine or prone

position

Limit abduction of the arm to <90 degrees in supine position

Avoid placement of high axillary roll in decubitus position — keep

roll out of axilla

Use ultrasound to find internal jugular vein for central line

placement

Spinal cord (16%) and

lumbosacral nerve root

(15%)

Be aware that the fraction of spinal cord injuries is increasing,

probably in relation to use of epidural catheters for pain

management

Follow current guidelines for regional anesthesia in anticoagulated

patients *

Sciatic and peroneal

(5%)Minimize time of surgery in lithotomy position

Use two assistants to coordinate simultaneous movement of both

legs to and from lithotomy position

Avoid excessive flexion of hips, extension of knees, or torsion of

lumbar spine

Avoid excessive pressure on peroneal nerve at the fibular head

Median (4%) and

radial (3%)

Be aware that 25% of injuries to the median and radial nerves were

associated with axillary block, and 25% of injuries were associatedwith traumatic insertion or infiltration of an intravenous line

Prevention of Perioperative Peripheral Neuropathies

Preoperative Assessment

When judged appropriate, it is helpful to ascertain that patients can comfortably tolerate

anticipated operative position

Upper Extremity Positioning

Arm abduction should be limited to 90 degrees in supine patients; patients who are positioned

prone may comfortably tolerate arm abduction >90 degrees

Arms should be positioned to decrease pressure on the postcondylar groove of the humerus

(ulnar groove). When arms are tucked at the side, a neutral forearm position is recommended.

When arms are abducted on armboards, either supination or a neutral forearm position is

acceptable

Prolonged pressure on radial nerve in spiral groove of humerus should be avoided

Extension of elbow beyond a comfortable range may stretch median nerve

Lower Extremity Positioning



Lithotomy positions that stretch hamstring muscle group beyond a comfortable range may

stretch sciatic nerve

Prolonged pressure on peroneal nerve at fibular head should be avoided

Neither extension nor flexion of hip increases risk of femoral neuropathy

Protective Padding

Padded armboards may decrease risk of upper extremity neuropathy

Use of chest rolls in laterally positioned patients may decrease risk of upper extremity

neuropathies

Padding at elbow and at fibular head may decrease risk of upper and lower extremity

neuropathies

Equipment

Properly functioning automated blood pressure cuffs on upper arms do not affect risk of

upper extremity neuropathies

Shoulder braces in steep head-down positions may increase risk of brachial plexus

neuropathies

Postoperative Assessment

Simple postoperative assessment of extremity nerve function may lead to early recognition of

peripheral neuropathies

Documentation

Charting specific positioning actions during care of patients may result in improvements of

care by (1) helping practitioners focus attention on relevant aspects of patient positioning, and(2) providing information that continuous improvement processes can use to effect

refinements in patient care

Evaluation and Treatment of Perioperative Neuropathies

When a nerve injury becomes apparent postoperatively, it is essential to perform and

document a directed physical examination to correlate the extent of sensory or motor

deficits with the preoperative examination and any intraoperative events.

Whether or not an etiology is suspected, it is prudent to seek neurologic consultation

to define the neurogenic basis, localize the site of the lesion, and determine the

severity of injury for guiding prognostication.

With proper diagnosis and management, most injuries resolve; however, months to

years may be required.

For motor neuropathy, an electromyogram can be performed to determine the exactlocation of the injury. Abnormalities may point to the affected component within the

motor unit, which consists of the anterior horn cell, its axon and neuromuscular

junctions, and the muscle fibers that it innervates

An electromyogram may distinguish between radiculopathies, plexopathies, andneuropathies.



Nerve conduction studies may be more useful to evaluate potential peripheral nerve

injuries, such as ulnar neuropathy.

Nerve conduction studies permit the assessment of motor and sensory nerves.

To evaluate motor integrity, the nerve is stimulated supramaximally at two points

along its course, and a recording is made of the electrical response of one of the

muscles that it innervates. The size of the muscle action potential provides an estimateof the number of motor axons and muscle fibers that are activated by the stimulus

For sensory conduction studies, the nerve fiber is stimulated supramaximally at one

point, and the sensory nerve action potential is recorded from another point. The

latency of the response can be interpreted as a reflection of the number of functioning

sensory axons.

Nerve conduction studies are useful for several reasons because they may reveal the

presence of a subclinical polyneuropathy that made the individual nerves more

susceptible to injury, and help distinguish between axon loss and demyelination,

which has significant implications regarding course and overall prognosis.

Most sensory neuropathies are generally transient and require only reassurance to thepatient with follow-up, whereas most motor neuropathies include demyelination of

peripheral fibers of a nerve trunk (neurapraxia) and generally take 4 to 6 weeks for

recovery.

Injury to the axon within an intact nerve sheath (axonotmesis) or complete nerve

disruption (neurotmesis) can cause severe pain and disability.

When reversible, recovery often takes 3 to 12 months. Interim physical therapy isrecommended to prevent contractures and muscle atrophy.

No single test can define the etiology of injury.



Perioperative Eye Injury and Visual Loss

Although quite rare, perioperative eye injuries are a source of significant morbidity

and liability

Corneal abrasion is the most common type of perioperative eye injury and is

associated with direct trauma to the cornea from facemasks, surgical drapes, or other

foreign objects. Corneal abrasion also can be associated with decreased basal tear

production or swelling of the dependent eye in patients in the prone position. Patients

complain of pain associated with a foreign body sensation in the eye on awakening

from surgery. This injury also can occur from a dried section of cornea. Symptoms are

generally transient, and treatment comprises supportive care and antibiotic ointment

to prevent bacterial infection.Precautionary measures to reduce the incidence of

corneal abrasion include early and careful taping of the eyelids after induction of

anesthesia, care regarding dangling objects when leaning over patients, and closeobservation as patients awaken. Before they are completely awake, patients often try

to rub their eye or nose with pulse oximeter probes, armboards, and intravenous lines

attached, inadvertently endangering their eyes.

Postoperative visual loss is a devastating complication that has been associated with

specific surgeries and patient risk factors.

Speculated causes of significant permanent postoperative visual loss usually involvecompromise of oxygen delivery to elements of the visual pathway and include

ischemic optic neuropathy (anterior or posterior), retinal artery occlusion (central or

branch), and cortical blindness.

Ischemic optic neuropathy (ION) and central retinal arterial occlusion from direct

retinal pressure are the conditions most sited as potential causes. Perioperative factors associated with an increased risk of ION include prolonged

hypotension, long duration of surgery especially in the prone position, large blood

loss, large crystalloid use, anemia or hemodilution, and increased intraocular or

venous pressure from the prone position

Patient risk factors associated with ION include hypertension, diabetes,

atherosclerosis, morbid obesity, and tobacco use.

Documents

Patient Positioning and Anaesthesia