Patient Positioning and Anesthesia

By Ronald Ombaka Esq.

Preamble

• Patient positioning is a major responsibility that is shared by the entire operating room team. A balance between optimal surgical positioning and patient well-being is sometimes required.

• It is prudent to adapt optimal positioning as it can pre-empt adverse outcomes.

Why Bother????

• Many patient positions that are used for surgery result in undesirable physiologic consequences e.g.– significant cardiovascular and respiratory

compromise.• Anesthetics blunt natural compensatory

mechanisms , rendering surgical patients vulnerable to positional changes.

• Anesthesiologists play a critical role for the proper positioning of patients in the operating room. – Primarily because positions deemed optimal for

surgery often result in undesirable physiologic changes putting surgical intervention at cross purposes with patient safety.

• The TeamAnaesthe-siologist

NursesSurgeon

• The goal (ideally)

– Whenever possible, patients should be placed in a position that they would tolerate when awake.

• Surgeons wish to have optimal exposure, and positions may be maintained for long periods.

• The duration of more extreme positions, if such are necessary, should be limited as much as possible.

• Expected tilting of the operating room table during surgery should be anticipated before draping, and the patient should be secured accordingly.

• Use of safety straps and prevention of a patient fall are fundamental.

Cardiovascular Concerns

• Complex arterial, venous, and cardiac physiologic responses have evolved to blunt the effects of positional changes on arterial blood pressure and maintain perfusion to vital organs.

– This is particularly important for humans who maintain an upright posture, owing to the vertical distance from the heart to the brain and its need for constant perfusion.

• Normally, 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 ↑– cardiac output ↑

• Increase in arterial blood pressure activates afferent baroreceptors– aorta – carotid sinuses

• Resulting in – decreased sympathetic outflow – increase parasympathetic impulses

• Ultimately = compensatory– decrease in heart rate– stroke volume– cardiac output

• Mechanoreceptors from the atria and ventricle also are activated to decrease sympathetic outflow to muscle and splanchnic vascular beds.

• 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.

• General anesthesia, muscle relaxation, positive-pressure ventilation, and neuraxial blockade interfere with autoregulatory mechanisms, rendering patients under anesthesia especially vulnerable to relatively uncompensated circulatory effects of changes in position.

• Positive-pressure ventilation – ↑ mean intrathoracic pressure, – ↓ venous return– ↓ cardiac output

• Positive end-expiratory pressure increases mean intrathoracic pressure further, as do conditions associated with low lung compliance, such as – Airways disease– Obesity– Ascites– Light anesthesia.

• As such , arterial blood pressure is often particularly labile at induction 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.)

• Interruptions in monitoring to facilitate positioning or turning of the operating room table must be minimized during this dynamic period.

• Patient positioning is always secondary to patient safety.

Pulmonary Concerns

• Anesthetized patients who are breathing spontaneously have;– ↓ tidal volume – ↓functional residual capacity – ↑ closing volume

(Positive-pressure ventilation with muscle relaxation may ameliorate ventilation-perfusion mismatches )

• Any position that limits movement of the diaphragm, chest wall, or abdomen may increase atelectasis and intrapulmonary shunt.

• For instance when an individual shifts from standing to supine, – functional residual capacity decreases 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%.

• The preferential perfusion of the dependent portions of lung is dominated by gravity.

Specific Positions

Supine(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.

Associated Arm Position• In a supine patient, 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

• The elbows and any protruding objects, such as intravenous fluid lines and stopcocks, are padded.

Arm position on arm board. Abduction of arm should be limited to less than 90 degrees whenever possible. The arm is supinated, and the elbow is padded.

• Variations of the Supine Position– Lawn chair position

Trendelenburg position and reverse Trendelenburg position. Shoulder braces should be avoided to prevent brachial plexus compression injurie

Tilting a supine patient head down, the Trendelenburg position, is often used to increase venous return during hypotension, to improve exposure during abdominal and laparoscopic surgery, and to prevent air emboli and facilitate cannulation during central line placement.

Nonsliding mattresses are recommendedto prevent the patient from sliding cephalad. Shoulder braces are not recommended because of considerable risk of compressioninjury to the brachial plexus

• 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 airway obstruction. • 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. • The stomach also lies above the glottis. Endotracheal intubation is often

preferred to 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 prolonged periods, it may be prudent to verify an air leak around the endotracheal tube or visualize the larynx before extubation.

• Reverse Trendelenburg position (head-up tilt) is often employed to facilitate upper abdominal surgery by shifting the abdominal contents caudad.

• This position is increasingly popular because of the growing number of laparoscopic surgeries.

• Caution is advised to prevent patients from slipping on the table, and more 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 the brain and should be taken into consideration when determining optimal blood pressure.

(In all positions in which the head is at a different level than the heart, the effect of the hydrostatic gradient on cerebral arterial and venous pressures should be carefully considered in terms of cerebral perfusion pressure. Careful documentation of any potential arterial pressure gradients is especially prudent.)

• The Lawn chair position– It better tolerated by patients who are awake

or undergoing monitored anesthesia care.

• In addition, because 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.

• The frog-leg position– allows access to the perineum, medial thighs,

genitalia,and rectum.• Care must be taken to minimize stress and

postoperative pain in the hips and prevent dislocation by supporting the knees appropriately.

Complications(Supine position and its analogues)

• Pressure alopecia(Lumps, such as those caused by monitoring cable connectors, should not be placed under head padding because they may create focal areas of pressure.)

• Backache (as the normal lumbar lordotic curvature, particularly the tone of the paraspinous musculature, is lost during general anesthesia with muscle relaxation or a neuraxial block.)

• 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.

• Peripheral nerve injury (Ulnar neuropathy is the most common lesion.) – 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.

NB: When patients are very heavy, caution is advised when placing them in reverse axis on the operating room table.

• Lithotomy

• The classic lithotomy position is frequently used during gynecologic, rectal, and urologic surgeries.

• Initiation of the lithotomy position requires coordinated positioning of the lower extremities 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.

(In essence an exact reversal of the initial positioning process)

Improper position of arms in lithotomy position with fingers at risk for compression when the lower section of the bed is raised.

Complications• When the legs are elevated, preload increases, causing a transient

increase in cardiac output 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.

• Lower extremity compartment syndrome

• Lateral Decubitus

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

• The patient’s head must be kept in a neutral position to prevent excessive lateral rotation of the neck and stretch injuries to the brachial plexus.

(Additional head support may be required )• The dependent ear should be checked to avoid folding and undue pressure.• It is advised 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. • Watch for compression of the dependent axillary structures. (Regardless of the technique, the pulse should be monitored in the dependent arm for early detection of compression to axillary neurovascular structures.)• 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.

• When a kidney rest is used, it must be properly placed under the dependent iliac crest to prevent inadvertent compression of the inferior vena cava.

• Finally, a pillow or other padding is generally placedbetween the knees with the dependent leg flexed to minimizeexcessive pressure on bony prominences and stretch of lowextremity nerves.

• The lateral decubitus position also is associated with pulmonary compromise. In a patient who is mechanically ventilated,– lateral weight of the mediastinum– disproportionate cephalad pressure of abdominal contents on the

dependent lung favors overventilation of the nondependent lung– pulmonary blood flow to the underventilated,dependent lung

increases owing to the effect of gravity.– ventilation-perfusion matching worsens

NB:Patients may be flexed while in the lateral position tospread the ribs during thoracotomies or improve exposure of theretroperitoneum for renal surgeries. The point of flexion, and thekidney rest if raised, should lie under the iliac crest rather thanthe flank or ribcage to minimize compression of the dependentlung

• This position is often accompanied by a component of reverse Trendelenburg positioning, creating the potential for venous pooling in the lower body

• Prone(ventral decubitus position)

• used primarily for surgical access to the posterior fossa of the skull, the posterior spine, the buttocks and perirectal area, and the lower extremities.

• As with the supine position, if the legs are in plane with the torso, hemodynamic reserve is maintained

• Pulmonary function may be superior to the supine or lateral decubitus positions if there is no significant abdominal pressure and the patient is properly positioned.

• The legs should be padded and flexed slightly at the knees and hips. The head may be supported face-down with its weight borne by the bony structuresor turned to the side.

• Both arms may be positioned to the patient’s sides and tucked in the neutral position or placed next to the patient’s head on arm boards—sometimes called the prone “superman” position.

• 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.

• Finally, elastic stockings and active compressiondevices are needed for the lower extremities to minimize pooling of the blood, especially with any flexion of the body.

• When general anesthesia is planned, 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(minimum of 5), 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 forrepositioning of the head.

• It is recommended to disconnect blood pressure cuffs and arterial and venous lines that are on the side that rotates furthest to avoid dislodgment.

• Full monitoring should be reinstituted as rapidly as possible.

• Endotracheal tube position and adequate ventilation are reassessed immediately after the move.

• Patients with cervical arthritis or cerebrovascular disease, lateral rotation of the neck may compromise carotid or vertebral arterial blood flow or jugular venous drainage.

• Regardless of the technique employed to support the head, the eyes, face, and airway must be checked periodically to ensure that the weight is borne only by the bony structures, and that there is no pressure on the eyes.

• Proper position is verified frequently and noted in the anesthetic record.

• Because the abdominal wall is easily displaced, external pressure on the abdomen may elevate intra-abdominal pressure in the prone position.

• External pressure on the abdomen may push the diaphragm cephalad, decreasing functional residual capacity and pulmonary compliance, and increasing peak airway pressure.

• Abdominal pressure also may impede venous return through compression of the inferior vena cava

• As such careful attention must be paid to the ability of the abdomen to hang free and to move with respiration.

• 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 prone position presents special risks for morbidly obese patients, whose respiration is already compromised, and who may be difficult to reposition quickly.

• Sometimes it may be necessary to discuss alternative positioning options with the surgeon to ensure patient safety.

• Sitting position

• The sitting position( although infrequently used because of the perception of risk from venous and paradoxical air embolism, 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– reduced perioperative blood loss. – superior access to the airway, reduced facial swelling, and

improved ventilation, particularly in obese patients.(to the anesthesiologist)

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

• arms 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.

• Because of the pooling of blood into the lower body under general anesthesia patients are particularly prone to hypotensive episodes.

• Head and neck position has been associated with complications during surgery to the posterior spine or skull in the sitting position.

• Excessive cervical flexion has numerous adverse consequences.

– It can impede arterial and venous blood flow, causing hypoperfusion or venous congestion of the brain.

– It may impede normal respiratory excursion. – Excessive flexion also can obstruct the endotracheal tube and place

significant pressure on the tongue, leading to macroglossia.

(Generally, maintaining at least two fingers’ distance between the mandible and the sternum is recommended for a normal-sized adult, and patients should not be positioned at the extreme of their range of motion.)

• 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.

• Arrhythmia, desaturation, pulmonary hypertension, circulatory compromise, or cardiac arrest may occur if sufficient quantities are entrained.

THE END