Anesthesiology

Patient Positioning During Anesthesia: Supine Position

Patient transfer

Prior to achieving any surgical position, the patient must be transferred onto the operating room table. The final position of the patient is of the utmost importance, but achieving these positions requires careful planning and coordination by the operating room team. The overall plan for each patient transfer should be discussed prior to any movement.

Frequently, the patient can assist in positioning prior to induction of anesthesia. However, under general anesthesia, the operating room team must carefully move and position each patient.

Pertinent patient comorbidities should be reviewed. For example, patients with morbid obesity or unstable spine fractures will require additional staff for transfer and positioning. When the patient is moved after the induction of general anesthesia, the anesthesiologist must be aware of any blood pressure alterations and ensure a safe systemic blood pressure prior to any patient movement.

All monitors, intravenous lines, and the endotracheal tube need to be carefully managed when moving a patient. The eyes should be taped to avoid corneal abrasion. With excellent communication, patients can be safely and successfully transferred within the operating room.

Supine position

The supine or dorsal decubitus position is the most common position used in the operating room. Typically, the head is rested on a foam pillow, keeping the neck in a neutral position. The patient’s arms are either tucked at their side or abducted to less than 90 degrees on padded arm boards. If the arms are tucked, a bed sheet is typically used to secure the arms. This sheet is placed under the body of the patient, brought above and around the arm, and then tucked under the body of the patient.

Preformed arm cradles or "sleds" can be used to hold the adducted arms after tucking with a sheet or as the primary securing device. All pressure points should be checked and padded. The arms should always be maintained in a neutral thumb-up or supinated position. The legs are often positioned with the knees slightly flexed resting on pillows to alleviate strain on the lumbar spine. Ultimately, the proper position of the supine patient is a shared responsibility between the anesthesia, surgery, and intraoperative nursing teams.

What common procedures are performed in this position?

The supine position provides excellent surgical access for intracranial procedures, most otorhinolaryngology procedures, and surgery on the anterior cervical spine. The supine position also is used during cardiac and abdominal surgery, as well as procedures on the lower extremity including hip, knee, ankle, and foot.

What are the common variations of this position?

Alterations of the supine position typically include tilting the patient in various planes. This includes the Trendelenburg, reverse Trendelenburg, and left or right tilt. Other variations include the lawn chair position, in which the patient’s hips and knees are flexed to relieve strain on the lumbar spine. This is often used for patient comfort during monitored anesthesia care (MAC) or awake procedures. The frog-leg position can be used for access to the perineum and for Foley catheter placement. In this variation, the patient’s knees are flexed and the hips are externally rotated. The plantar surface of each foot are placed together.

What are the physiologic changes when placing a patient in this position?

Respiratory

When the patient is placed from the upright to the supine position, the intra-abdominal contents and diaphragm shift cephalad, compressing the adjacent lung tissue. This leads to a decrease in functional residual capacity (FRC) when going from standing to the supine position. In an awake patient placed supine, FRC decreases by 24%. During general anesthesia in the supine position, FRC decreases by 44%. Anesthesia and neuromuscular blockade do not appear to be additive in decreasing FRC.

Closing capacity is the lung capacity at which small airways begin to collapse. In a healthy, spontaneously breathing patient, normal tidal breathing is typically above closing capacity and thus small airways remain open. This changes with age, as closing capacity increases and approaches FRC. By age 45, normal tidal breathing causes airway collapse in the supine position and by age 65 in the upright position. Closing capacity is minimally affected by posture or anesthesia. However, in the anesthetized patient, the decrease in FRC seen in the supine position could place normal tidal breathing at or below closing capacity, allowing airway collapse with normal ventilation leading to atelectasis and intrapulmonary shunt.

Cardiovascular

Placing a patient supine from an erect position increases venous return to the heart through redistribution of blood from the lower extremities. This leads to an increase in cardiac output via preload augmentation. Heart rate, stroke volume, and contractility are reflexively decreased through baroreceptors from the aorta via the vagus nerve and from the carotid sinus via the glossopharyngeal nerve to maintain a constant blood pressure. Downstream alterations in sympathetic flow to splanchnic and renal vasculature continue to augment the circulatory system during postural changes, maintaining a strictly controlled systemic blood pressure.

This synchronized and well-controlled system to maintain a relatively constant blood pressure is altered with the addition of general anesthesia, neuraxial anesthesia, neuromuscular blockade, and the initiation of positive pressure ventilation.

During anesthesia, systemic vascular resistance (SVR) and return of venous blood to the heart decrease. With derailed mechanisms to compensate for changes in position, the systemic blood pressure under anesthesia is more labile.

Placing the patient in the Trendelenburg or reverse Trendelenburg position will have greater effects of systemic blood pressure in a supine patient under general anesthesia than an awake spontaneously breathing patient.

In the parturient, the gravid uterus in the supine position can cause aortocaval compression leading to a supine hypotension syndrome and uteroplacental insufficiency.

The pregnant patient at term should rarely, if ever, be placed in a true supine position in order to maintain placental perfusion. Classic teaching for cesarean section mandates the maintenance of 15 degrees of left lateral tilt to offload the pressure of the gravid uterus on the inferior vena cava (IVC) to decrease venous obstruction.

However, recent reports suggest that a minimum of 30 degrees of left lateral tilt might be needed to improve IVC obstruction and truly improve placental perfusion. However, the ability to perform a cesarean section in 30 degrees of left lateral tilt does not seem optimal for the patient or surgeon and future research needs to evaluate the best intraoperative position for cesarean section. When the left lateral tilt position is used, the pregnant patient must be secured to the table to prevent fall and injury.

What are the options for anesthetic management?

Nearly all anesthetic techniques are employed in the supine position. These range from awake techniques for carotid endarterectomy to general anesthesia with tracheal intubation for cardiac procedures. Other options include MAC or general anesthesia with a laryngeal mask airway (LMA). Regional and neuraxial anesthesia are readily used to provide anesthesia and analgesia in the supine position.

What complications are associated with this position?

The supine position is related to several potential complications including peripheral nerve injury. The importance of perioperative nerve injuries is emphasized by the findings of the American Society of Anesthesiologists (ASA) closed claims database. Among all adverse outcomes, peripheral nerve injury was the second most common event, present in 22% of all claims.

Although the mechanism of nerve injury is not always clear, internal and external compression, stretch, ischemia, metabolic derangement, direct trauma, and direct nerve laceration can all lead to postoperative nerve injury. In theory perioperative neuropathies are preventable through proper positioning and padding. In reality, nerve injuries will continue to rarely occur. Nerve injuries potentially related to patient positioning must be understood to mitigate any risk of injury and limit overall occurrence.

Historically, the ulnar nerve was the most common nerve injured in the perioperative setting, followed by the brachial plexus and lumbosacral roots.

Symptoms of ulnar neuropathy include paresthesia and weakness of the fourth and fifth digits of the affected hand, and pain of the medial forearm and hand. Classically, ulnar neuropathy was blamed on malposition of the elbow and compression of the ulnar nerve in various positions including the supine position.

Although the exact mechanism of ulnar neuropathy is not completely understood, certain factors, including male gender, prolonged hospitalization, and either thin or obese body habitus increase the overall risk. Additionally, ulnar nerve injury is more common following cardiac surgery compared to noncardiac surgery. Studies report the range of incidence of postoperative ulnar neuropathy at 0.04% to 0.5%. The ulnar nerve, originating from the C8-T1 nerve roots, travels within the superficial condylar groove of the elbow. This position places the ulnar nerve at risk for nerve entrapment in patients with anatomic variations at the elbow.

In male patients, the elbow has a lower fat content compared to women, possibly providing less cushion to protect the ulnar nerve and increasing the risk of neuropathy. Additionally, the coronoid tubercle of the ulna is 50% larger in male patients compared to female. During the natural movement of ulna, this creates internal pressure on the ulnar nerve potentially leading to clinical significant ischemia. Overall, the etiology of perioperative ulnar neuropathies appears to be a combination of anatomic variations and pre-existing subclinical nerve injury accompanied by a period of time in the supine position, either intraoperatively or in the postoperative period.

By recent accounts in the ASA closed claims database, the brachial plexus is now the most commonly injured nerve in the perioperative period. The brachial plexus is the combination of the C5-T1 nerve roots forming trunks, divisions, cords, and then branches to create the ulnar, radial, median, axillary, and musculocutaneous nerves.

Position-related injuries to the brachial plexus are characterized by painless motor dysfunction. In the supine position, the brachial plexus is at risk from stretch more than compression, especially when the patient is not properly positioned. Generally, recovery after perioperative brachial plexus injury is promising.

In addition, several other complications are associated with the supine position. These include pressure alopecia due to pressure on the back of the head during prolonged procedures. Further areas of pressure-related injury and necrosis include the heel, sacrum, and other bony prominences. Additionally, postoperative back pain due to loss of the natural lordotic curvature of supine has been reported, especially in patients with pre-existing back pain or kyphoscoliosis.

What strategies can be used to decrease the risk of injury in this position?

Prevention of injury in the supine position begins with proper positioning and constant surveillance of the patient. Certain operations require deviations from the standard supine position. The risk and benefit of any alteration of the standard supine position must be assessed prior to positioning the patient. For example, thyroidectomy or radical neck dissection often requires extension of the head and neck. In this situation, the head is rested on a low-profile circular foam or gel headrest. Although extended, the weight of the head should still rest on the headrest and not hang above the operating room table.

Additionally, rotation of the head is often needed for carotid endarterectomy or intracranial procedures. However, the risk of extreme head rotation should be weighed against the benefits of adequate surgical exposure.

If the head must be rotated, contralateral arm abduction should be avoided to limit injury risk to the brachial plexus. In this situation, optimal arm position would be tucked at the side of the patient.

In the operating room, prolonged surgery in the supine position places the ulnar nerve at risk when not appropriately positioned. Placement of the arm should either be tucked at the patient's side in the thumbs-up position or abducted to less than 90 degrees with the forearm supinated. Supination of the forearm in the abducted position puts the least amount of pressure on the ulnar nerve, decreasing the risk of compression related injury. Flexion of the elbow to greater than 90 degrees should be avoided because this limits the space of the cubital tunnel via ligament tightening and compresses the ulnar nerve.

No clear evidence exists about the benefit of additional padding at the elbow. In high-risk patients as described above, extra padding could be attempted. However, even in clearly documented cases of an adequately positioned and padded ulnar nerve, neuropathies still occurred. In fact, the standard of care in terms of positioning, padding, and evaluation was achieved in 63% of all neuropathies reported in the ASA closed claims database. The anesthesiologist should attempt to limit the risk of ulnar neuropathy through careful attention to arm position and padding, but understand that even providing the standard of care might not prevent all cases of ulnar neuropathy.

In order to limit the risk of injury to the brachial plexus, abduction of the arm should be limited to less than 90 degrees. Dorsal extension of the arm onto a low or malpositioned arm board should be avoided, attempting to keep the arm level with the chest.

When the arm is abducted, contralateral head rotation stretches the brachial plexus and should be avoided whenever possible.

The Trendelenburg position, used during gynecologic surgery, has been linked to brachial plexus injury, especially when using shoulder braces to stabilize the patient on the operating room table.

Also, care must be taken when the patient is placed in the Trendelenburg without shoulder braces. The patient may shift cephalad, but if the arms are secured with arm straps, the resultant downward force on the shoulder puts the upper trunk of the brachial plexus at risk.

Overall, to reduce the risk of brachial plexus injury in the supine position, the arm should not be placed in extremes of abduction, extension, or external rotation. However, even with proper standard of care, rare nerve injuries will still occur.

What's the Evidence?

Cassorla, L, Lee, JW. "Patient positioning and associated risks". Miller’s Anesthesia. vol. 41. 2015. pp. 1240-65.

(Book chapter on patient positioning in the operating room.)

Cheney, FW, Domino, KB, Caplan, RA, Posner, KL. "Nerve Injury Associated with Anesthesia". Anesthesiology. vol. 90. 1999. pp. 1062-69.

(Closed claims database evaluation of anesthesia-related nerve injury.)

Coonan, TJ, Hope, CE. "Cardio-respiratory effects of change of body position". Can Anaesth Soc J. vol. 30. 1983. pp. 424-37.

(Basic physiology of many common surgical positions.)

Dunn, PF. "Physiology of the lateral decubitus position and one-lung ventilation". Int Anesthesiol Clin. vol. 38. 2000. pp. 25-53.

(A detailed description of ventilation and perfusion mismatch in the lateral decubitus position.)

Edgecombe, H, Carter, K, Yarrow, S. "Anaesthesia in the prone position". Br J Anaesth. vol. 100. 2008. pp. 165-83.

(Comprehensive and in depth review of the prone position.)

Gale, T, Leslie, K. "Anaesthesia for neurosurgery in the sitting position". J Clin Neurosci. vol. 11. 2004. pp. 693-6.

(Review of the sitting position and discussion of venous air embolism.)

Higuchi, H, Takagi, S, Zhang, K, Furui, I, Ozaki, M. "Effect of lateral tilt angle on the volume of the abdominal aorta and inferior vena cava in pregnant and nonpregnant women determined by magnetic resonance imaging". Anesthesiology. vol. 122. 2015. pp. 286-93.

(Discussion of aortocaval compression in the parturient and the effects of various degrees of left lateral tilt in the supine position.)

Knight, DJW, Mahajan, RP. "Patient position in anaesthesia. Continuing Education in Anaesthesia". Critical Care & Pain. vol. 4. 2004. pp. 160-3.

(Brief overview of patient position during anesthesia.)

Koh, JL, Levin, SD, Chehab, EL, Murphy, GS. "Neer Award 2012: Cerebral oxygenation in the beach chair position: a prospective study on the effect of general anesthesia compared with regional anesthesia and sedation". J Shoulder Elbow Surg. vol. 22. 2013. pp. 1325-31.

(A prospective study suggesting the possible benefits of avoidance of general anesthesia in the BCP.)

Lee, JR. "Anesthetic considerations for robotic surgery". Korean J Anesthesiol. vol. 66. 2014. pp. 3-11.

(An update and review of robotic surgery including a detailed discussion on the anesthetic implications of many common robotic surgeries.)

Lohser, J. "Evidence-based management of one-lung ventilation". Anesthesiol Clin. vol. 26. 2008. pp. 241-72.

(Ventilation and perfusion in the lateral decubitus position with further discussion of one-lung ventilation management.)

Murphy, GS, Szokol, JW. "Blood pressure management during beach chair position shoulder surgery: what do we know?". Can J Anesth. vol. 58. 2011. pp. 977-82.

(Brief discussion of the beach chair position and intraoperative blood pressure management.)

Picton, P, Dering, A, Alexander, A, Neff, M, Miller, BS, Shanks, A, Housey, M, Mashour, GA. "Influence of ventilation strategies and anesthetic techniques on regional cerebral oximetry in the beach chair position". Anesthesiology. vol. 123. 2015. pp. 765-74.

(Prospective study showing that increasing the inspired oxygen fraction and end-tidal carbon dioxide during general anesthesia increases regional cerebral oxygenation in the BCP.)

Prielipp, RC, Morell, RC, Butterworth, J. "Ulnar nerve injury and perioperative arm positioning". Anesthesiol Clin NA. vol. 20. 2002. pp. 589-603.

(Review of perioperative ulnar neuropathy including anatomy, risk factors, and legal implications.)

Rains, DD, Rooke, GA, Wahl, CJ. "Pathomechanisms and complications related to patient positioning and anesthesia during shoulder arthroscopy". Arthroscopy. vol. 27. 2011. pp. 532-41.

(Discussion of anesthetic options and positioning during shoulder arthroscopy.)

Roth, S. "Perioperative visual loss: what do we know, what can we do?". Br J Anaesth. vol. 103. 2009. pp. i31-i40.

(Review of perioperative visual loss including updates on risks factors and preventative recommendations.)

Washington, SJ, Smurthwaite, GJ. "Positioning the surgical patient". Anaesth Intens Care. vol. 10. 2009. pp. 476-9.

(Brief overview of patient position during anesthesia.)

Winfree, CJ, Kline, DG. "Intraoperative positioning nerve injuries". Surg Neurol. vol. 63. 2005. pp. 5-18.

(Comprehensive review of position related nerve injuries.)
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