Patient positioning for surgery and anesthesia in adults

INTRODUCTION — Positioning the patient for a surgical procedure is a shared responsibility among the surgeon, the anesthesiologist, and the nurses in the operating room. The optimal position may require a compromise between the best position for surgical access and the position the patient can tolerate. The chosen position may result in physiologic changes and can result in soft tissue injury (eg, nerve damage, pressure-induced injury or ulceration, or compartment syndrome).

This topic will discuss the basic principles for positioning and specific concerns for a variety of positions. Postoperative visual loss, which may be related to patient positioning, is discussed separately. (See "Postoperative visual loss after anesthesia for nonocular surgery".)

GENERAL CONSIDERATIONS

Trial positioning — When possible, the position during surgery should be one that would be comfortable with the patient fully awake. Patients should be questioned about limited range of motion and their ability to lie comfortably in the expected position. If questions arise, the patient should be placed in the anticipated position as a trial before sedation or induction of anesthesia.

If the operating table will be tilted either top to bottom, side to side, or moved into the sitting position (eg, during breast reconstruction) during surgery, the anticipated position should be practiced before skin preparation and draping, to make sure supports and straps are secure and that the patient tolerates the position physiologically.

Physiologic changes — All positions used for surgery can cause cardiovascular and pulmonary changes. Both general and neuraxial anesthesia can affect the normal compensatory mechanisms that maintain cardiovascular stability and can cause changes in ventilation and perfusion that can result in hypoxemia. In addition, compression of tissue or vascular structures related to positioning can cause regional ischemia. The physiologic effects of specific positions are discussed individually. (See 'Physiologic effects of supine position' below and 'Physiologic effects of Trendelenburg positioning' below and 'Physiologic effects of reverse Trendelenburg position' below and 'Physiologic effects of lithotomy positioning' below and 'Physiologic effects of lateral decubitus positioning' below and 'Physiologic effects of prone positioning' below and 'Physiologic effects of sitting position' below.)

Nerve injury — Perioperative peripheral nerve injury can result in temporary or permanent sensory or motor deficits, paresthesias, or pain, and in some cases, these injuries are related to patient positioning. General considerations for perioperative nerve injuries are discussed here. Nerve injuries related to specific positions are discussed in subsequent sections.

Incidence of perioperative nerve injury — Nerve injury after anesthesia is a rare event, and the true incidence is unknown. Related literature consists mostly of case reports, retrospective reviews, and malpractice claims data. A review of over 380,000 surgical cases in one institution, using quality assurance, closed claims, and billing code databases, reported an incidence of perioperative nerve injury unrelated to surgery of 0.03 percent [1].

Peripheral nerve injuries are an important medical legal issue. The mechanisms for peripheral nerve injury are incompletely understood, and they may occur despite optimal positioning procedures (see 'Mechanisms of nerve injury' below). In an analysis of the American Society of Anesthesiologists (ASA) Closed Claim Database, nerve injury accounted for 12 percent of malpractice injury claims between 1990 and 2013 for patients who had general anesthesia [2]. Nearly one-half of the claims for nerve injury had no obvious etiology, and 91 percent were thought to be associated with appropriate anesthetic care, compared with 58 percent of other claims. In another analysis of Anesthesia Closed Claims Project database for surgical procedures from 2000 to 2014, spine surgery claims comprised >10 percent of claims, and were associated with severe permanent disability primarily from nerve and eye injuries [3]. Prone positioning and surgical duration ≥4 hours were associated with permanent disabling injuries in patients who underwent spine surgery.

Peripheral nerve injury is a complex phenomenon that may occur during any type of anesthesia, including procedures performed outside of the operating room. Theoretically, patients who are awake or lightly sedated without regional anesthesia should be at lower risk of position-related nerve injury since they would be able to move an uncomfortable extremity. However, upper extremity nerve injury has been reported during neuraxial anesthesia and during monitored anesthesia care [1,4].

Mechanisms of nerve injury — The mechanisms for perioperative nerve injury are incompletely understood and may involve local mechanical insult related to positioning (compression and stretch), ischemia, and/or inflammation. Nerve injury may also be related to preexisting patient factors (eg, preexisting subclinical neuropathy, diabetes, hypertension, body habitus), or as yet undetermined factors. (See "Overview of upper extremity peripheral nerve syndromes", section on 'Etiologies' and "Traumatic peripheral neuropathies", section on 'Traction/stretch' and "Traumatic peripheral neuropathies", section on 'Contusion/compression' and "Overview of lower extremity peripheral nerve syndromes", section on 'Pathogenesis'.)

Some nerves are at particular risk for position-related injury, either because of a superficial course that is vulnerable to compression (eg, peroneal nerve at the fibular head, ulnar nerve in the ulnar groove at the elbow), or because of potential stretch (eg, brachial plexus with the neck rotated).

Risk factors for nerve injury — Risk factors for perioperative peripheral nerve injury unrelated to the surgical procedure include longer surgical procedures, extremes of body weight, older age, smoking, hypertension, and diabetes [1,4,5].

Prevention of nerve injury — Perioperative peripheral nerve injury is difficult to predict and difficult to prevent. In 2018, the ASA issued an updated practice advisory for prevention of perioperative peripheral neuropathies [6]. The task force that created this document based their recommendations on observational studies, case reports, and expert opinion; recommendations emphasize proper padding and positioning, and are summarized in a table (table 1). (See 'Prevention of skin and tissue injury' below.)

Somatosensory evoked potential (SSEP) monitoring is used for early detection of neurologic compromise during surgery, and may detect positioning related nerve ischemia [7,8]. Early detection is appealing, as most perioperative nerve insults are potentially reversible and treatable [2]. Standard SSEP monitoring is logistically challenging, and is not feasible for routine monitoring for peripheral nerve injury, though it may be beneficial for high-risk patients and high-risk surgical procedures (eg, cardiac or shoulder surgery) (see "Neuromonitoring in surgery and anesthesia", section on 'Somatosensory evoked potentials'). Pilot studies involving the use of a novel automated SSEP device during cardiac [9] and shoulder surgery [10] have been promising, but further studies are needed to determine diagnostic accuracy and outcome benefit.

Management — There are limited effective treatment options for peripheral nerve injury. Limited and heterogenous studies in animals and humans suggest that hyperbaric oxygen may be a possible therapy for injuries due to tissue ischemia [11]. Optimal treatment regimens are unknown, and further study is required before suggesting its use. Hyperbaric oxygen therapy has been suggested via animal and human subjects as a possible treatment option.

Skin and tissue injury — Immobilization places patients at risk for skin and underlying tissue injury during anesthesia, particularly during longer surgical procedures. (See "Prevention of pressure-induced skin and soft tissue injury", section on 'Repositioning and frequency'.)

Skin breakdown, pressure-induced injury, and ulceration are possible and, rarely, compartment syndrome. (See "Acute compartment syndrome of the extremities", section on 'Trauma without fracture' and 'Particular concerns with lithotomy position' below.)

Incidence of tissue injury — Pressure-induced injury is common among hospitalized patients in general and among surgical patients in particular. The incidence of these injuries in surgical patients varies widely by clinical setting, and is reported at between 10 and 37 percent during the hospital stay [12-15]. (See "Epidemiology, pathogenesis, and risk assessment of pressure-induced skin and soft tissue injury", section on 'Epidemiology'.)

●In one study, 208 patients who had surgery lasting more than four hours were prospectively followed for the development of pressure ulcers [16]. Effective preventive measures for pressure ulcers were not used, and 21 percent of patients developed pressure ulcers; 53 percent occurred on the heels, and 16 percent occurred in the sacral area.

●In a single institution prospective observational study of 287 patients undergoing elective spine surgery in the prone position, by postoperative day two 24.6 percent of patients developed pressure ulcers, most commonly of the upper extremities [15].

Risk factors for tissue injury — Multiple perioperative risk factors have been identified for development of perioperative pressure injuries, based on retrospective reviews and observational studies. Risk factors include high preoperative Braden scale score (table 2), extremes of body mass index (BMI), older age, total surgery time, hypotension and vasopressor administration, diabetes, high ASA risk score and intraoperative acidosis [12,17]. These risk factors overlap with the risk factors for intraoperative nerve injury.

However, risk factors specifically related to intraoperative management may be different. In a retrospective observational cohort study the electronic anesthesia and medical records of approximately 2700 critically ill surgical patients were reviewed [18]. Pressure injury occurred in 10.7 percent of patients and was associated with intraoperative blood product administration but not with operative case length, hypotension, or use of vasopressors.

Epidural analgesia has rarely been reported to lead to serious heel ulcers, even in young and fit patients without other risk factors, both in the postoperative period [19] and during labor [20]. Motor block associated with overly dense epidural block may restrict lower extremity movement, and sensory block can prevent discomfort related to pressure. For this and other reasons, the lowest effective doses of epidural drugs should be used, patients should be reminded to move their legs, and all care providers should routinely examine pressure points for signs of tissue damage.

Prevention of skin and tissue injury — Pressure redistribution is the most important factor in preventing pressure-induced injuries and may be accomplished by appropriate use of pressure-reducing devices and surfaces, frequent repositioning of the patient's head and limbs as possible, and proper patient positioning. Tissue pressures are greatest over bony prominences where weight-bearing points come in contact with external surfaces (eg, heels, occiput, sacrum, iliac crests, ischial tuberosity), and these sites should be padded or free. In addition, plastic connectors in intravenous tubing, stopcocks, and the wires and connectors of monitoring devices are potential points of pressure injury. All of these devices should be padded where they may press against skin, especially when extremities are wrapped or tucked. (See "Epidemiology, pathogenesis, and risk assessment of pressure-induced skin and soft tissue injury", section on 'Pathogenesis'.)

In the operating room, a variety of padding materials are used to disperse pressure with the goal of avoiding tissue damage (figure 1 and figure 2 and figure 3). It is not clear whether any particular type of padding material is better than others for prevention of tissue injury. High specification reactive or viscoelastic foam (ie, memory foam) and gel pads/supports should be used, rather than standard pads or firm supports (eg, blankets or towels). (See "Prevention of pressure-induced skin and soft tissue injury", section on 'Support surfaces'.)

Egg crate foam may not be as effective as other padding materials, because it compresses over time and under heavy body parts. For short periods of time and under lighter body parts, foam may be as effective as gel or visco-elastic material.

Multilayer soft silicone foam dressing, such as Mepilex border sacral dressings (MöInlycke Health Care), have been shown to reduce pressure ulcers in the critical care setting when placed in particularly susceptible locations [21].

Based on the type of surgery and necessary position, specific bony prominences may be at risk. We often place foam dressings on these particular bony prominences, such as the iliac crests during prone spine surgery.

For prevention of heel ulcers, elevating the leg so that the heel does not contact the mattress is the most effective preventive measure for bedridden patients [22,23] and may be applicable in anesthetized patients as well. This can be accomplished with pillows placed beneath the knees. (See 'Particular concerns with the supine position' below.)

Postoperative visual loss — Postoperative visual loss, usually due to posterior ischemic optic neuropathy, occurs most commonly after spine surgery in the prone position but may also occur after other prolonged procedures, including those performed in the head down position (eg, robotic gynecologic and urologic procedures). (See "Postoperative visual loss after anesthesia for nonocular surgery", section on 'Postoperative posterior ION'.)

Operating tables — Movement of the operating room table while the patient is on it should be avoided. If the table must be moved, the patient should be secured and surrounded by operating room personnel on all sides to avoid having the patient shift or fall. The surgical table weight limits should be strictly followed; weight limit specifications are usually much lower if the table is tilted side to side or top to bottom. In addition, weight limits are lower if the patient is placed on the table in reverse orientation (ie, head placed at the foot of the table) because the patient's weight is no longer centered over the base (figure 4).

SUPINE — In the supine (or dorsal decubitus) position, one or both arms may be abducted out to the side on arm boards or tucked next to the patient's body (figure 5). When the arms are adducted, they may be placed on padded arm supports or tucked using the lift sheet that goes under the patient. (See 'Particular concerns with the supine position' below.)

A true horizontal supine position may place strain on the back, does not put the hips and knees in a neutral position, and may be poorly tolerated by awake patients. Therefore, the hips and knees should be flexed slightly by placing a pillow under the knees or configuring the operating table into a slight beach chair position.

Physiologic effects of supine position — There are minimal horizontal gradients in the vascular system in the supine position. Heart rate (HR) and peripheral vascular resistance are generally lower in the supine position compared with the sitting and prone positions. If the legs are elevated, venous return to the heart and cardiac output increases [24].

The supine position affects pulmonary physiology, primarily related to cranial displacement of the diaphragm by abdominal contents. Changing body position from upright to supine reduces functional residual capacity by 0.8 to 1 L (ie, from approximately 3.5 L to 2.5 L) and induction of anesthesia causes another decrease by 0.4 to 0.5 L [25]. A reduction in lung compliance, airway closure, and atelectasis can result. In addition, ventilation perfusion mismatch may occur during mechanical ventilation. Perfusion increases in dependent lung regions, while ventilation is more evenly distributed. Such changes are usually well tolerated by healthy patients but may be problematic for patients with obesity, pulmonary disease, and older patients. (See "Mechanical ventilation during anesthesia in adults", section on 'Lung protective ventilation during anesthesia' and "Mechanical ventilation during anesthesia in adults", section on 'Goals for lung protective ventilation' and "Anesthesia for the patient with obesity", section on 'Ventilation management'.)

Patients in advanced stages of pregnancy, or with a large mobile abdominal mass, may be at risk for aortocaval compression and hypotension in the supine position and may benefit from leftward tilt with a wedge under the right hip. (See "Anesthesia for cesarean delivery", section on 'Intraoperative positioning'.)

Nerve injuries associated with supine positioning — The arms should be positioned to minimize the chance of brachial plexus and ulnar nerve injuries, recognizing that the majority of perioperative nerve injuries occur despite what is considered optimal positioning. Guidelines for arm positioning are based on anatomical considerations, expert opinion, and equivocal evidence, which mostly consists of case reports and small trials [6]. We agree with generally accepted recommendations that the arms should be abducted less than 90 degrees, to avoid stretching the brachial plexus across the head of the humerus in the axilla.

●Ulnar nerve – The optimal position for the forearm with the arm abducted is unclear, though the goal should be to eliminate or minimize pressure on the ulnar nerve in the ulnar groove at the elbow. This may be accomplished with supination or a neutral arm position and should be individualized based on patient anatomy [6]. In one study of awake volunteers, both supination and the neutral position of the forearm resulted in less pressure over the ulnar nerve than pronation [26].

Arms adducted along the patient's side are usually placed in a neutral position, with the palm facing the patient. Similar to positioning with the arms abducted, no particular forearm position has been shown to reduce nerve injury. When the arms are abducted, the padded arm board should support the upper arm at the same level as the operating table mattress, to avoid impingement at the edge of the mattress. The forearm should be slightly flexed to avoid hyperextension at the elbow (figure 6).

●Radial nerve – The radial nerve is rarely injured but is theoretically at risk for compression as it runs in the spiral groove of the humerus in the posterior upper arm, between the heads of the triceps muscle. Arm board padding should be even with the operating table mattress, without a step that could compress the nerve (figure 6). In addition, intravenous poles and devices attached to the operating table should be positioned away from the patient's upper arm.

●Brachial plexus – Brachial plexus injury has been associated with median sternotomy for cardiac surgery, particularly after asymmetric sternal retraction for dissection of the internal mammary artery [27,28]. The injuries are usually to the lower roots of the brachial plexus, which may be stretched when sternal retraction rotates the first rib. (See "Neurologic complications of cardiac surgery", section on 'Upper extremity'.)

Studies of the effect of arm positioning during sternal retraction on the incidence of brachial plexus injury have yielded conflicting results, and data are insufficient to recommend a particular arm position. Some studies have found that the hands up position (ie, arms abducted 90 degrees, elbows flexed) reduces brachial plexus injury [29,30], compared with arms at the side, and others have found no difference [28,31,32]. Patients positioned with arms at the side may be at increased risk of ulnar nerve compression and injury.

Particular concerns with the supine position

●Pressure points – In the supine position, bony prominences in contact with the operating table mattress, arm boards, and head supports are at risk for skin pressure damage and should be adequately padded. Prolonged pressure on the occiput can cause alopecia, which may be permanent [33], and the heels and sacrum are at risk for pressure sores, especially during longer procedures. Protective measures include the following:

•Pillows can be placed under the lower legs to elevate the heels, or special heel protectors may be used. The feet should be supported without pressure on the Achilles tendon and without the knee hyperextended.

•The head should be supported in a foam or gel donut shaped pad, to eliminate pressure on the occiput (figure 2). When possible, intermittent slight repositioning of the head during anesthesia may relieve pressure on specific areas of the occiput and reduce the risk of alopecia [33]. (See "Prevention of pressure-induced skin and soft tissue injury", section on 'Static positioning'.)

●Arm support – If the arms are abducted on padded arm boards, straps, towels, or blankets used to secure the arms should be loose enough to avoid constriction. Intravenous tubing, plastic connectors, and monitor cables should be padded.

When the arms are adducted, or tucked, they should be secured next to the patient's body using the draw sheet to achieve this goal by tucking the sheet between the bed frame and mattress for stability. Wrinkles should be avoided. The elbows should be slightly flexed with wrists in neutral position and palms facing inward. Bony prominences should be padded to avoid pressure on the ulnar groove (figure 7).

●Backache – Backache may occur after surgery in the supine position, theoretically because of the loss of normal lumbar lordotic curve associated with musculoskeletal relaxation during anesthesia. In patients with known back problems, the planned position should be tested for comfort with the patient awake. Padding under the lumbar spine to maintain the lordotic curve may be beneficial. The lawn chair position, with the operating table flexed slightly at the hips and knees, may reduce strain on the back. Alternatively, a pillow can be placed under the knees to achieve a similar position.

●Extreme head and neck extension – Extension of the neck is often required for thyroid and parathyroid surgery and other procedures on the neck. A roll or inflatable pillow is placed under the patient's shoulders after intubation, to extend the neck and facilitate exposure; the head should not float but rather should be supported under the occiput (figure 8).

The patient's ability to extend the neck should be assessed preoperatively. Excessive neck extension can cause neck pain, vertigo, headache, and postoperative nausea. (See "Thyroidectomy", section on 'Patient position and skin preparation'.)

TRENDELENBURG — The Trendelenburg position is a supine position with the head of the operating table tilted down (figure 9). Trendelenburg positioning improves exposure of pelvic organs during abdominal and laparoscopic surgery and may be used briefly to facilitate central line placement. For steep Trendelenburg positioning, a variety of devices may be used to keep the patient in position on the operating table, including slip-resistant table padding, cross chest taping, knee flexion, bean bag supports, and shoulder supports. (See 'Nerve injuries associated with the Trendelenburg position' below.)

If the arms are abducted on arm boards, they should be secured with padding, straps, or taping to avoid movement during change in position.

We often rehearse the expected maximal degree of head down tilt, prior to skin prep and drape, especially in patients with severe obesity, to make sure the patient doesn't slip and to confirm the ability to ventilate and oxygenate.

Physiologic effects of Trendelenburg positioning — The Trendelenburg position causes greater cardiovascular and pulmonary changes compared with the supine position. Additional physiologic effects can result from the pneumoperitoneum that is often used during surgical procedures in steep Trendelenburg, such as laparoscopic or robotic pelvic surgery.

●Cardiovascular changes – The Trendelenburg position increases venous return, central blood volume, and mean arterial pressure (MAP), compared with the supine position. With progressive tilt within the range used in the operating room (ie, ≤45 degrees), filling pressures progressively increase, without a significant change in cardiac output or MAP [34-36].

One study of the hemodynamic effects of laparoscopy in the Trendelenburg position included 16 patients who underwent laparoscopic radical prostatectomy with 12 mmHg intraabdominal pressure and a 45-degree Trendelenburg position [37]. Central venous pressure, mean pulmonary artery pressure, and pulmonary capillary wedge pressure increased two- to threefold, and mean arterial blood pressure (ABP) increased by 35 percent, without changes in cardiac output, heart rate (HR), or stroke volume. Such changes are generally well tolerated by healthy patients, but in patients with cardiac disease, cardiovascular compromise can occur. (See "Anesthesia for laparoscopic and abdominal robotic surgery in adults", section on 'Cardiovascular changes'.)

●Pulmonary changes – The head down position also causes pulmonary physiologic changes as the cephalic movement of the abdominal viscera against the diaphragm decreases functional residual capacity and pulmonary compliance and may cause atelectasis. The pulmonary effects of Trendelenburg positioning during laparoscopy are discussed separately. (See "Anesthesia for laparoscopic and abdominal robotic surgery in adults", section on 'Pulmonary changes'.)

●Intracranial pressure – The head down position increases intracranial pressure, alone or in combination with pneumoperitoneum, and should be avoided in patients with known intracranial hypertension [38].

●Intraocular pressure – The head down position increases intraocular pressure [39], though the clinical effects of this increase in patients without baseline increased intraocular pressure are unclear. There are reports of visual loss after prolonged surgery in Trendelenburg position, which is most commonly diagnosed as posterior ischemic optic neuropathy. (See "Postoperative visual loss after anesthesia for nonocular surgery", section on 'Postoperative posterior ION'.)

Nerve injuries associated with the Trendelenburg position — In addition to the nerve injuries that can occur with level supine positioning, brachial plexus injury can occur when shoulder supports (eg, shoulder braces or bean bags) are placed at the base of the neck, where they may compress the roots of the brachial plexus. In addition, if the arms are abducted, pressure on the shoulder can theoretically cause injury by stretching the brachial plexus around the head of the humerus. One-half of the brachial plexus injuries in the American Society of Anesthesiologists (ASA) Closed Claims Database were associated with shoulder braces in the Trendelenburg position [40]. We do not use rigid shoulder braces or bean bag shoulder supports, because of the risk of brachial plexus injury. If they are used, supports should be placed laterally, at the acromioclavicular joint, to avoid direct nerve compression.

Airway concerns — Prolonged Trendelenburg positioning, especially with administration of intravenous fluid, can result in edema and swelling of the face, tongue, and laryngeal tissues, which can cause airway compromise after extubation [41]. An extubation strategy should be formulated that includes a plan for reintubation if necessary (eg, placement of an airway exchange catheter prior to intubation). (See "Management of the difficult airway for general anesthesia in adults", section on 'Extubation'.)

The Trendelenburg position may increase the risk of passive regurgitation as the stomach is above the level of the glottis; this factor should be considered when choosing a device for airway management (ie, supraglottic airway versus endotracheal intubation). (See "Airway management for induction of general anesthesia", section on 'Choice of airway device' and "Supraglottic devices (including laryngeal mask airways) for airway management for anesthesia in adults", section on 'Choice of supraglottic airway'.)

REVERSE TRENDELENBURG — Reverse Trendelenburg is supine positioning with the head of the operating table tilted up (figure 10). It is commonly used for upper abdominal surgery, to improve access to upper abdominal organs during laparoscopic or open abdominal surgery. For procedures that require an extreme (eg, 40 to 45 degrees) head up position (eg, laparoscopic cholecystectomy, gastric bypass or sleeve resection), cross table straps may be insufficient to prevent patient movement, and a padded foot board may be required. The arms may be abducted on padded arm boards or tucked at the patient's side.

Physiologic effects of reverse Trendelenburg position

●Cardiovascular changes – Head up tilt, or reverse Trendelenburg positioning, causes pooling of blood in the lower extremities and abdominal vasculature. Central blood volume and cardiac filling fall, resulting in decreases in stroke volume and cardiac output [34,42]. In healthy, un-anesthetized patients, heart rate (HR) and sympathetic tone increase to maintain blood pressure, but these compensatory mechanisms may be blunted during general anesthesia. The magnitude of these changes depends on the degree of head up tilt and, in the extreme, is similar to the effects of the sitting position. (See 'Physiologic effects of sitting position' below.)

Hemodynamic changes can be mitigated by intravenous fluid administration, compression stockings, and gradual, incremental head elevation. In extreme reverse Trendelenburg (eg, 45 degrees head up), blood pressure measurement should be adjusted to reflect the hydrostatic gradient between the blood pressure cuff and the brain. The effects of extreme head up positioning on cerebral perfusion are discussed separately. (See 'Physiologic effects of sitting position' below.)

●Pulmonary changes – The head up position reduces pressure from abdominal contents on the diaphragm and chest and, therefore, increases functional residual capacity and compliance, especially in patients with obesity [43].

Nerve injuries associated with reverse Trendelenburg — Nerve injuries associated with reverse Trendelenburg positioning are similar to those associated with supine level positioning. (See 'Nerve injuries associated with supine positioning' above.)

LITHOTOMY — The lithotomy position is a supine position, with the legs separated and hips and knees flexed to a variable degree (figure 11). The standard lithotomy position is usually used for urological, gynecological, and some rectal procedures and may be combined with some degree of Trendelenburg. The lower extremities are flexed at both the hip and the knees. For standard (high) lithotomy, the hips are flexed approximately 90 degrees, as are the knees (figure 12). Less extreme, or more extreme, flexion is used for specific procedures. A variety of stirrups and slings may be used to support the legs in this position (figure 13). The arms may be abducted on padded arm boards, or tucked at the patient's side, as they would be for level supine positioning.

The hemi-lithotomy position is often used for positioning on an orthopedic trauma table for repair of hip fracture (figure 14).

Physiologic effects of lithotomy positioning — In the lithotomy position, venous return is usually increased compared with the supine position, though this may be a minor and transient effect [44,45]. Other physiologic effects of this position depend on body habitus. Abdominal pressure may increase in lithotomy enough to obstruct venous return to the heart and may cause hypotension, particularly in patients with obesity, or in those with an abdominal mass or gravid uterus.

The diaphragm may be displaced cephalad by abdominal contents, resulting in a reduction in functional residual capacity and lung compliance and increases in inspiratory pressures. These effects are more pronounced in patients with obesity [46] and in exaggerated lithotomy position [47].

Nerve injuries associated with lithotomy position — Several types of lower extremity nerve injuries may be more common with lithotomy positioning, compared with other positions. In an observational study of patients positioned in lithotomy, 1.5 percent of patients experienced transient, sensory lower extremity neuropathy [48].

Lower extremity nerve injuries can also result from surgical injury during procedures that are commonly performed in the lithotomy position (eg, lateral femoral cutaneous nerve or femoral nerve injury during gynecologic surgery) (figure 11 and figure 15). (See "Nerve injury associated with pelvic surgery", section on 'Selected neuropathies' and 'Nerve injury' above.)

●Peroneal nerve – The peroneal nerve (also called the common fibular nerve) is at risk for injury from compression at the level of the fibular head. Thus, the lateral lower leg should be either free or padded when stirrups are used. Superficial peroneal nerve dysfunction has also been associated with lithotomy positioning and results in sensory neuropathy without a motor deficit [48]. The superficial peroneal nerve may be compressed in the lateral calf or may be stretched with plantar flexion of the foot.

●Saphenous nerve – The saphenous nerve can be compressed by contact with the leg brace medially as it courses superficially and horizontally across the medial femoral epicondyle. This bony prominence should be padded.

●Lateral femoral cutaneous and obturator nerves – Lateral femoral cutaneous and obturator nerve injuries have been associated with lithotomy positioning, by an unclear mechanism. Hip flexion beyond 90 degrees has been shown to stretch the inguinal ligaments, and since the lateral femoral cutaneous and obturator nerves pass directly through these ligaments, this extreme angle should be avoided. A cadaver study showed stretch of the obturator nerve with hip flexion [49].

●Sciatic nerve – The sciatic nerve can be stretched at the level of the hip or knee or may be compressed distally in the popliteal fossa. The degree of hip flexion or abduction, or knee extension, that may cause sciatic nerve injury has not been determined. As a general rule, the position of the hips and knees during anesthesia should be limited to those that are comfortable preoperatively. The legs should be positioned without pressure on the popliteal space (figure 15). (See "Nerve injury associated with pelvic surgery".)

Particular concerns with lithotomy position

●Coordinated positioning – The patient's legs should be simultaneously placed in leg supports or stirrups by two attendants, to avoid torsion of the lumbar spine and extension of the hip joint. The legs should be taken out of the lithotomy position in a coordinated manner as well.

●Hand injury – The foot section of the operating table is lowered or removed to allow access to the perineum or pelvis for procedures in the lithotomy position. If the arms are adducted, the hands and fingers may be at risk for injury when the foot section is moved; amputation of fingers has been reported [50]. Thus, safe position of the hands should always be confirmed prior to moving, removing, or replacing the foot of the table.

●Compartment syndrome – Compartment syndrome without an apparent cause is a rare occurrence after surgery and anesthesia and may be more likely when the patient is in the lithotomy position compared with supine. Compartment syndrome can occur in any surgical position and may affect both lower and upper extremities, though most case reports after anesthesia occurred in a lower extremity in patients in lithotomy. A retrospective review of approximately 575,000 anesthetics reported 13 cases of compartment syndrome; 1 of 8720 cases occurred in lithotomy position, compared with 1 of 92,441 cases in the supine position and 1 of 9700 patients in lateral decubitus position [51]. In that review, compartment syndrome was associated with longer surgical procedures (ie, >2 to 3 hours).

The cause of potentially position-related compartment syndrome is unknown, and the pathophysiology of acute compartment syndrome is complex. Ultimately, tissue perfusion and muscle oxygenation are compromised when tissue pressure approaches MAP. (See "Acute compartment syndrome of the extremities", section on 'Pathophysiology'.)

Compartment syndrome has been reported in the nonoperative leg in patients in hemi-lithotomy position on a fracture table [52]. Possible mechanisms for compartment syndrome in this setting include the weight of the extremity on supports, reduced perfusion pressure with the limb elevated, and position-related reduction of the capacity of the affected compartment. Calf pressures in the nonoperative leg may be increased by obesity and the use of calf support rather than heel support, and pressures increase over time during surgery [53]. For patients who have surgery in the hemi-lithotomy position, we avoid intraoperative hypotension and hypovolemia in order to maintain perfusion of the nonoperative leg. We discuss alternative positioning with the surgeon for patients with obesity and for procedures that are likely to go beyond two hours.

●Back pain – The lithotomy position may aggravate radicular pain in patients with a preexisting herniated lumbar disk. This position can also cause back pain in patients without preexisting back problems by removing the normal lordotic curve. In patients with known back or lower extremity radicular pain, the position should be rehearsed with the patient awake to allow modifications, though back or radicular pain may still occur.

LATERAL DECUBITUS — The lateral decubitus position may be used for surgery on the thorax, retroperitoneal structures, or hip. The patient lies with the operative side up, with anterior and posterior supports (eg, blanket or gel rolls, or a bean bag support) to prevent rolling to the supine or prone position during surgery. The legs are slightly flexed, with pillows or foam padding between them. A pad or roll is placed under the chest wall, to alleviate pressure on the neurovascular structures in the axilla. The down arm is padded, and the up arm is supported on pillows or any of a number of arm supports (figure 16).

When the operating table is flexed in the lateral decubitus position, with or without a kidney rest (eg, for thoracotomy or retroperitoneal surgery), the point of flexion should be beneath the iliac crest to minimize compression of the dependent lung and the inferior vena cava.

Physiologic effects of lateral decubitus positioning

●Cardiovascular effects – In the flexed lateral decubitus position, blood may pool in the dependent lower extremities, causing reduced venous return to the central circulation and hypotension. In addition, the inferior venous cava can be partially or completely obstructed by marked flexion at the hips. In one study of 12 patients who underwent nephrectomy, the change from the lateral to flexed lateral (ie, operating table flexed 30 degrees, with kidney rest elevated at iliac crest) resulted in significant reductions in blood pressure, pulmonary artery wedge pressures, cardiac index, and stroke volume, with an increased in systemic vascular resistance [54]. Wrapping the legs in compressive elastic or using sequential compressive devices may decrease this change.

●Pulmonary effects – The lateral decubitus position can result in ventilation perfusion mismatch in anesthetized patients. When anesthetized, mechanically ventilated patients are turned from the supine to lateral position, perfusion of the dependent lung usually increases, while ventilation of the dependent lung decreases, due to reduced functional residual capacity and compliance [55]. At the same time, ventilation increases and perfusion decreases in the nondependent lung. The resultant ventilation perfusion mismatch can cause hypoxemia in patients with reduced pulmonary reserve, and a high fraction of inspired oxygen may be required.

Nerve injuries associated with the lateral decubitus position — The brachial plexus is at risk for injury in the lateral decubitus position if a chest pad or roll is not properly placed. Though this device is often called the axillary roll, it should not be placed in the axilla. Rather, the chest should be supported caudal to the axilla, to free the axillary structures from compression (figure 16). If a deflatable bean bag is used to support the patient, the upper edge should similarly be below the level of the axilla. The radial pulse should be monitored in the dependent arm (eg, by placing pulse oximeter on a finger on the down arm), as an indication of vascular patency (and, presumably, lack of pressure on the brachial plexus).

The brachial plexus and other nerves that arise from cervical nerve roots may be stretched and injured if the neck is flexed laterally. The head should be supported in a neutral position continuously during the positioning process, to avoid such injuries. The table should be flexed slowly, with the head supported, and padding added as necessary to keep the neck in a neutral position [56].

The dependent arm should be placed on a padded arm board, such that the upper arm is abducted no more than 90 degrees to the torso, to avoid stretch of the brachial plexus. The upper portion of the nondependent arm should be parallel to the dependent arm and should be supported on pillows, blankets, or on an arm cradle. Perfusion of the arms should be monitored with palpation of pulses, a blood pressure cuff, and/or continuous pulse oximetry.

If the upper arm needs to be abducted more than 90 degrees (eg, during thoracotomy), the time in this position should be minimized. The fibular head of the down leg should be padded to avoid peroneal injury. The saphenous nerve is at risk for injury, as it courses along the medial femoral condyle, and should be padded.

Particular concerns with lateral decubitus position — The patient is anesthetized and the airway secured in the supine position and then turned to the lateral position. The turning process must be coordinated among operating room care providers, to prevent patient injury and dislodgement of the airway device, intravenous catheters, and/or monitoring devices. The head should be positioned on a foam or gel support, without pressure on the eyes, and with the ears flat to the head. The eyes should be closed and covered with adhesive dressing, tape, or eye protectors (figure 17).

PRONE — The prone position is used for posterior spine procedures, some craniotomies, rectal and buttock procedures, superficial procedures on the back, and surgery on the posterior extremities. Most patients are anesthetized on a stretcher while supine and then rolled prone onto the operating table after intubation. In the prone position the head can be supported on a foam or gel head rest (figure 3 and picture 1) or held in skull pins with the Mayfield apparatus. The torso is supported on a surgical frame, chest rolls, or pillows (figure 18 and figure 19 and picture 2 and picture 3 and figure 20).

In some cases, the patient positions himself or herself prone, and the head is usually turned to the side on a pillow. Examples include procedures on the back or rectum performed with monitored anesthesia care, spinal anesthesia for lumbar disk surgery, and cases in which a supraglottic airway is placed after induction in the prone position. (See "Supraglottic devices (including laryngeal mask airways) for airway management for anesthesia in adults", section on 'Prone position'.)

Arms may be placed with the shoulders and elbows flexed with the hands up (the "prone superman" or "surrender" position) or tucked at the patient's side. The hips and knees are flexed, with the lower leg supported to prevent pressure on the toes.

The jackknife position, a variant of the prone position with the operating table flexed, is usually used to optimally expose the rectum (figure 21).

Physiologic effects of prone positioning — A goal for prone positioning should be to avoid pressure on the abdomen, to minimize compression of the vena cava and abdominal contents, and the associated physiologic changes.

Prone positioning can result in variable effects on cardiovascular physiology. Most commonly, with level prone positioning, there is a reduction in cardiac index, which has been attributed to reduction in venous return to the heart and reduced left ventricular compliance as a result of increased intrathoracic pressure [57]. Abdominal compression in the prone position can cause vena caval compression, reduction in venous return with resultant hypotension, venous stasis, and increased pressure in the epidural venous plexus. (See "Anesthesia for elective spine surgery in adults", section on 'Positioning'.)

Rarely, positioning prone without abdominal support can also cause hypotension, possibly due to pooling in the splanchnic vasculature or kinking of the vena cava. Severe sudden hypotension has been reported in a patient with a pendulous abdomen [58]. If severe hypotension occurs, turning the patient urgently back to the supine position may be necessary. We keep the stretcher in the operating room after turning prone until it is clear that the patient has tolerated the turn.

Dependent legs in the prone jackknife position cause venous pooling that may result in hypotension (figure 21).

In the absence of abdominal compression, the prone position may result in beneficial effects on pulmonary function. In healthy volunteers breathing spontaneously, functional residual capacity increases in this position [59], and the prone position alters the mechanics and physiology of gas exchange to consistently improve oxygenation in mechanically ventilated intensive care patients. Improvement in oxygenation in this position is multifactorial (figure 22 and table 3). (See "Prone ventilation for adult patients with acute respiratory distress syndrome", section on 'Physiologic effects on oxygenation'.)

Abdominal compression in the prone position can cause cephalad displacement of the diaphragm, reduced pulmonary compliance, and increased peak airway pressure [60].

Prone positioning with the patient's face below the level of the heart can result in venous congestion and edema, particularly during long surgical procedures with high blood loss, and may be a factor associated with postoperative visual loss. The use of the Wilson frame has been associated with ischemic optic neuropathy, possibly because it positions the head below the level of the heart (figure 19). (See "Postoperative visual loss after anesthesia for nonocular surgery", section on 'ION associated with spine surgery'.)

Nerve injuries associated with the prone position — The upper extremities are at risk of peripheral nerve injuries in the prone position. They can be placed at the sides or extended along the head on arm boards. If the arms are positioned with the hands up, arms should not be overextended, to avoid stretching or compressing the neurovascular bundles in the axilla, although there are no available data to support a recommendation for the maximal degree of extension at the shoulder joint. The patient's range of motion at the shoulder joint should be tested preoperatively to determine the safe degree of extension.

Chest rolls should not compress the axillary structures. Perfusion of the arms should be monitored with visual inspection, palpation of pulses, a noninvasive blood pressure cuff, and/or a continuous pulse oximeter.

With the arms positioned with hands up, the ulnar nerve at the elbow should be padded or free. The brachial plexus may be stretched when the neck is rotated; the limits of the patient's ability to rotate the head should be determined preoperatively.

Particular concerns with the prone position

●Turning prone – The process of turning the patient prone requires coordination among the anesthesia clinician, the surgeon, and other individuals helping with positioning, whether the patient is anesthetized or awake for the turn. The goals are to avoid patient injury, prevent dislodgement of the airway device, intravenous and monitoring catheters (eg, arterial catheter), and to minimize physiologic effects during the turn.

For general anesthesia, after induction of and intubation, the endotracheal tube should be well secured, the eyes should be closed and taped, a soft bite block or blocks placed, and a nasal or oral temperature probe placed. If the patient's head is to be supported on a foam headrest, the headrest is placed over the patient's face while supine, making sure that the eyes and nose are free in the respective openings in the device, and turned in place (figure 3). Before turning prone, both the operating table and stretcher should be locked and positioned as closely together as possible.

In anticipation of the turn, we administer 100 percent oxygen to prevent desaturation while ventilation is interrupted. Intravenous tubing and arterial line transducer tubing should be positioned along the patient's side to avoid dislodgement while turning. Monitoring cables may be disconnected for the turn but should be replaced as soon as possible. We maintain either pulse oximetry or invasive blood pressure monitoring throughout the turn and positioning whenever possible.

The breathing circuit should be disconnected at the last possible moment prior to turning, when all involved individuals are in place and ready. During the turn, the patient's neck should be kept in a neutral position. The arm over which the patient rolls should be along the patient's side to prevent injury. After the turn, the endotracheal tube should be reconnected and adequate ventilation confirmed, and monitors should be reconnected as quickly as possible.

We keep the stretcher in the operating room after turning prone until it is clear that the patient has tolerated the turn and the airway is secure.

●Torso support – Firm rolls or bolsters that extend from the clavicle to the iliac crests should be placed laterally, to minimize pressure on the abdomen and thorax and the associated physiologic changes. (See 'Physiologic effects of prone positioning' above.)

A number of support devices are available for use in prone positioning. The Wilson frame is one such device, which tends to keep the head below the level of the heart and is associated with development of postoperative visual loss (figure 19). (See "Postoperative visual loss after anesthesia for nonocular surgery", section on 'Risk factors'.)

Other prone positioning frames include the Jackson table and frame, the Andrews frame, and the Relton-Hall frame. Some require placing skull pins to hold the head, while others allow the choice of a head cradle with foam or gel inserts.

Patients should be positioned with the head at or above the level of the heart in the prone position, to avoid venous congestion of the face. The breasts, iliac crests, and genitalia should be positioned to avoid compression and padded as appropriate. If a Foley catheter is placed, it should hang free after positioning without traction on the genitalia.

●Neck position – The neck should be placed in a neutral position, without excessive flexion or extension relative to the torso, or in the natural position for patients with neck deformities. This may require changing the height of the torso or head support, adding or removing padding under the face pillow, or changing the height or angle of the Mayfield apparatus.

The patient's ability to rotate the neck should be tested preoperatively if the head will be turned. Lateral rotation of the head and neck can stretch the roots of the cervical plexus and the neurovascular bundle at the head of the humerus and can compress the nerves and vessels between the clavicle and first rib. Severe head rotation can also obstruct the carotid and vertebral arteries and jugular veins and has rarely led to cerebral infarction [61,62].

●Protecting the face – There are multiple pillows designed with cutouts for the eyes, nose, and mouth. The head is supported on the bony prominences of the face (ie, the forehead and the chin). The horseshoe headrest (picture 4) should be avoided because of close proximity to the eyes and multiple reports of central retinal artery occlusion with its use. (See "Postoperative visual loss after anesthesia for nonocular surgery", section on 'Central retinal artery occlusion'.)

The eyes, nose and endotracheal tube should be checked after positioning and repeatedly during surgery to make sure there is no pressure or traction on the eyes or other facial tissues and that the endotracheal tube remains securely in place. Such checks should be documented in the anesthesia record.

SITTING — The sitting position is usually used for posterior fossa craniotomy, posterior cervical spine surgery (figure 23), and shoulder procedures. The variant of the sitting position that is used for shoulder surgery is often called the beach chair position (figure 24). The head can be elevated to a varying degree, and many shoulder surgeons request 20 degrees of elevation, rather than the 45 degrees that was historically used.

The head is fixed in skull pins for neurosurgical procedures and supported with tape or a face support for shoulder surgery. The arms are supported on padded arm boards or arm supports. Advantages for the surgeon include improved surgical exposure [63] and possibly reduced blood loss during neurosurgical procedures [64], and access to the shoulder with improved mobility of the joint, and less blood in the surgical field for orthopedic surgeries.

Physiologic effects of sitting position

●Cardiovascular effects – Cardiovascular changes are the most important physiologic effects of the sitting position. Venous pooling in the lower extremities, along with the vasodilation and myocardial depression that accompany general anesthesia, can produce a decrease in cardiac preload, stroke volume, mean arterial pressure (MAP), and cerebral perfusion pressure [65]. Hemodynamic changes can be mitigated by intravenous fluid administration, positioning with the hips flexed and the legs elevated, compression stockings, and gradual, incremental head elevation.

●Cerebral perfusion – A number of cases of stroke, ischemic brain injury, spinal cord injury, and death have been reported in patients who had shoulder surgery in the beach chair position [66,67]. The incidence of catastrophic neurologic injury in this setting is unknown and appears to be very low [68,69]. The incidence of more minor neurologic injury is also unknown.

Efforts to prevent neurologic injury in the beach chair position have focused on the maintenance of cerebral perfusion and oxygenation. The effects of the sitting position on cerebral perfusion and oxygenation are complex and are not completely understood. As the head is raised above the heart in unanesthetized patients, cerebral perfusion pressure decreases by approximately 15 percent, and systemic vascular resistance increases by 50 to 80 percent to compensate [70]. General anesthesia usually blunts such compensatory mechanisms, and cerebral hypoperfusion can result [35,65]. Hypocapnia associated with mechanical ventilation results in cerebral vasoconstriction and may further reduce cerebral perfusion [71]. (See "Anesthesia for craniotomy in adults", section on 'Ventilation'.)

•Cerebral autoregulation – It has been traditionally thought that cerebral autoregulation should maintain cerebral blood flow constant between MAP from 50 to 150 mmHg. However, there is wide individual variation in the range of autoregulation [72], among surgical patients in general, and in patients in the beach chair position in particular [73]. In some patients (eg, patients with chronic hypertension, older patients) the set point for autoregulation is increased [74]. Thus, a MAP significantly higher than 50 mmHg may be required to prevent cerebral ischemia in the sitting position, and without definitive evidence to support a specific goal blood pressure, we maintain a MAP >70 mmHg for patients in this position. (See "Evaluation and management of elevated intracranial pressure in adults", section on 'Autoregulation'.)

•Cerebral oxygenation – Cerebral oxygen desaturation events may be more common in patients in the beach chair position compared with other positions for surgery. Several studies have reported a high incidence of cerebral desaturation, measured by near infrared spectroscopy, in patients placed in the beach chair position for shoulder surgery [75-78]. In one study, cerebral oxygen saturation (SctO2) was measured in 140 patients who underwent shoulder surgery, one-half in the beach chair position and one-half in the lateral decubitus position. Cerebral desaturation events, defined as ≥20 percent decrease from baseline or absolute value ≤55 percent) occurred in 80 percent of patients in the beach chair position compared with 0 percent in the patients in lateral decubitus position [78]. There were no difference is hemodynamic variables.

Management of ventilation during anesthesia is known to affect cerebral blood flow and may affect cerebral oxygenation in the beach chair position. In one study including 56 anesthetized patients in the beach chair position, increasing end tidal carbon dioxide (CO₂) from 30 to 45 mmHg, combined with increasing the fraction of inspired oxygen from 0.3 to 1.0, resulted in an increase in regional cerebral oxygenation from 68 to 75 percent [77].

The clinical implications of cerebral desaturation events are unclear, and cerebral desaturation events have not been correlated with neurologic injury. One prospective observational study of patients who had intravenous general anesthesia for shoulder surgery found that cerebral desaturation events were associated with worse scores on two of three neurobehavioral tests at 24 hours after surgery [79]. Postoperative cognitive function, measured with the Mini Mental State Examination, was similar between groups. Further study is required before recommending the routine measurement of cerebral oximetry for patients in the beach chair position.

•Goal blood pressure – Definitive, evidence-based guidelines for management of blood pressure, with the goal of maintaining adequate cerebral perfusion in the sitting position, have not been established. This issue is particularly important when surgeons request induced hypotension to improve surgical conditions. We suggest correcting MAP measurements for the hydrostatic difference between the blood pressure cuff and the brain for patients in the sitting position, and we aggressively treat blood pressure values below 80 percent of the preoperative resting values, while maintaining a MAP >70 mmHg. We aim for the patient's baseline blood pressure for older patients, hypertensive patients, and others at risk for cerebrovascular disease.

It is widely accepted that blood pressure should be measured at the level of the brain (ie, the transducer zeroed at the external auditory meatus) when intraarterial pressure monitoring is used and that noninvasive blood pressure should be corrected for the difference in hydrostatic pressure between the cuff and the brain. This would mean that for every 1 cm difference between the cuff and the auditory meatus, MAP would be 0.77 mmHg lower at the brain than measured by the cuff (ie, 1 mmHg for every 1.25 cm). Using this calculation, a patient in the beach chair position with the external auditory meatus 30 cm above the midpoint of the blood pressure cuff, MAP at the brain would be unacceptably low, at approximately 47 mmHg, with a MAP of 70 mmHg as measured by the cuff.

•Effect of anesthetic technique – Cerebral desaturation events may be less likely during regional anesthesia in the beach chair position compared with general anesthesia [80-82]. In one observation study, cerebral desaturation (ie, SctO2 decrease >20 percent from baseline) occurred in 58 percent of patients who had general anesthesia in the beach chair position, compared with no desaturation events if regional anesthesia was used [83]. The reasons for less cerebral desaturation with regional anesthesia are unclear but may include better preservation of blood pressure and higher partial pressure of carbon dioxide (PaCO₂) during regional anesthesia. Cerebral desaturation with general anesthesia may be unrelated to effects on blood flow. In one study, cerebral blood flow was measured by carotid Doppler in 40 patients randomly assigned to general or regional anesthesia for shoulder surgery [84]. MAP was maintained at >70 mmHg, and there was no difference in cerebral blood flow between the two groups.

We prefer to use regional anesthesia when possible for shoulder surgery in the beach chair position. In addition to any physiologic benefits, regional anesthesia allows the clinician to monitor the patient's neurologic status by assessing arousability and ability to communicate.

●Pulmonary effects – Functional residual capacity and lung compliance increase in the sitting position, compared with supine, lateral and prone positions, as the abdominal contents fall away from the diaphragm [59]. The ultimate effect on oxygenation depends on cardiac output, which tends to fall in the sitting position, and may negate the beneficial effects of improved respiratory function [65].

Nerve injuries associated with the sitting position — The brachial plexus is at risk for stretch if the arms are inadequately supported. The ulnar nerve may be compressed at the elbow and should be padded. The hips should be flexed no more than 90 degrees, and the knees should be slightly flexed, to prevent stretch injury of the sciatic nerve. Thin patients may benefit from extra seat padding as they may be at higher risk of sciatic nerve compression where it exits the pelvis.

Neck flexion that may be used during craniotomy has been implicated in rare cases of quadriplegia [85,86]. Preexisting cervical spinal stenosis may be at higher risk of such injury.

Position specific concerns — Neck flexion in the sitting position (or other positions) can also cause vascular obstruction in the neck, kinking or obstruction of the endotracheal tube or supraglottic airway, and tongue and oropharyngeal swelling [87]. We maintain two finger breadths of space between the mandible and the sternum when positioning the head, to avoid these complications.

The sitting position for craniotomy is associated with a higher risk of venous air embolism and supratentorial pneumocephalus than other surgical positions. These issues are discussed separately (table 4). (See "Intraoperative venous air embolism during neurosurgery" and "Anesthesia for craniotomy in adults", section on 'Positioning'.)

Patients in the sitting position are at risk for pressure injury over the ischial tuberosity. The seat or operating table should be well padded, and the patient should be well supported to avoid slipping and shear injury.

SUMMARY AND RECOMMENDATIONS

●General considerations – Positioning the patient during anesthesia is a shared responsibility among the care providers in the operating room or procedure room. When possible, the position should be one that is comfortable for the patient awake. If questions arise, the position should be rehearsed with the patient awake. (See 'Trial positioning' above.)

●Physiologic changes – All positions can cause cardiovascular and pulmonary physiologic changes, which may be exacerbated by anesthesia. Such changes may be poorly tolerated by older patients and patients with cardiac disease. (See 'Physiologic changes' above.)

●Nerve injury – Perioperative peripheral nerve injury is a complex phenomenon that may occur during any type of anesthesia. Goals for positioning should include avoidance of compression and stretch of neurovascular structures, to minimize the risk of nerve injury. (See 'Nerve injury' above.)

●Skin injury – Immobilization places patients at risk for skin and underlying tissue injury during anesthesia. Pressure redistribution is the most important factor in preventing pressure induced injury and may be accomplished by the use of pressure-reducing surfaces and padding, particularly over bony prominences. (See 'Skin and tissue injury' above.)

●Supine position – In the supine position, we suggest that the arms should be abducted ≤90 degrees and should be placed in a neutral or supinated without pressure on the ulnar groove at the elbow (figure 5) (Grade 2C). (See 'Nerve injuries associated with supine positioning' above.)

The arms, sacrum, and occiput should be positioned and padded with gel or viscoelastic material to avoid pressure-induced injury for patients in any of the supine positions (ie, supine, Trendelenburg, reverse Trendelenburg, lithotomy) (figure 6). Heels should be supported such that there is no contact with the operating table mattress. (See 'Particular concerns with the supine position' above.)

•The Trendelenburg position causes increased intracranial pressure and increased intraocular pressure. Prolonged steep Trendelenburg can cause edema of the face and airway structures and can cause airway obstruction after extubation. (See 'Physiologic effects of Trendelenburg positioning' above and 'Airway concerns' above.)

We do not use shoulder supports for patients in the Trendelenburg position, to avoid injury to the brachial plexus. If they are used, shoulder supports should be placed laterally, at the acromioclavicular joint (figure 9). (See 'Nerve injuries associated with supine positioning' above.)

•In the reverse Trendelenburg position, cross table straps may be insufficient to prevent patient movement, and a padded foot board may be required (figure 10). The cardiovascular effects of extreme reverse Trendelenburg positioning may be similar to the effects of the sitting position. (See 'Physiologic effects of reverse Trendelenburg position' above.)

●Lithotomy position – In the lithotomy position, the peroneal nerve, saphenous nerve, lateral femoral cutaneous, obturator, and sciatic nerves are at risk for injury from compression or stretch. The legs should be positioned without hyperextension or flexion, and bony prominences should be padded (figure 11). The legs should be raised into position simultaneously by two attendants and taken out of the lithotomy position in the same way. (See 'Nerve injuries associated with lithotomy position' above.)

Compartment syndrome has rarely occurred during anesthesia and is more common in the lithotomy position. Compartment syndrome may occur in the nonoperative leg when placed in the hemi-lithotomy position on the fracture table. For patients in the hemi-lithotomy position, we avoid hypotension and hypovolemia, and we discuss alternate positioning with the surgeon for patients with obesity and for procedures that are expected to go beyond two hours. (See 'Particular concerns with lithotomy position' above.)

●Lateral decubitus position – For the lateral decubitus position, the patient should be supported with rolls or bolsters to prevent rolling into the supine or prone position (figure 16). The chest support (ie, axillary roll) should be placed caudal to the axilla to avoid compression of neurovascular structures. The head should be supported in a neutral position, and the dependent arm should be abducted ≤90 degrees. (See 'Nerve injuries associated with the lateral decubitus position' above.)

For the flexed lateral decubitus position, the table should be flexed at the iliac crest, rather than at the flank, to minimize compression of the vena cave and thoracic structures (figure 17). (See 'Physiologic effects of lateral decubitus positioning' above.)

●Prone position – The turning process for the prone position should be coordinated among the care providers in the operating room (figure 18). The goals are to avoid patient injury; prevent dislodgement of the airway device, intravenous catheters, and monitoring catheters; and to minimize physiologic effects during the turn. (See 'Particular concerns with the prone position' above.)

The torso should be supported on firm rolls or bolsters that extend from the clavicle to the iliac crests, placed laterally to avoid abdominal compression. Breasts and genitalia should not be compressed, and the neck should be in a neutral position. The eyes and nose should be free from pressure and should be checked regularly during surgery. The head should be positioned at or above the level of the heart. Rare cases of postoperative visual loss have occurred in patients in the prone position. (See 'Postoperative visual loss' above and 'Particular concerns with the prone position' above and "Postoperative visual loss after anesthesia for nonocular surgery", section on 'Risk factors'.)

●Sitting position – Cardiovascular effects are the most important physiologic changes associated with the sitting position (figure 23). Venous pooling in the lower extremities, along with the vasodilation and myocardial depression due to general anesthesia, can produce a decrease in cardiac preload, stroke volume, and mean arterial pressure (MAP). (See 'Physiologic effects of sitting position' above.)

Rare cases of stroke, ischemic brain injury, and spinal cord injury have been reported in patients who underwent shoulder surgery in the beach chair position. Cerebral perfusion and oxygenation should be maintained, to minimize the risk of such injuries. We suggest the following strategy for patients who have shoulder surgery in the beach chair position:

•Correct blood pressure measurement for the hydrostatic difference between the blood pressure cuff and the brain.

For every 1 cm difference between the cuff and the auditory meatus, MAP would be 0.77 mmHg lower at the brain than measured by the cuff (ie, 1 mmHg for every 1.25 cm).

When invasive blood pressure monitoring is used, the transducer should be zeroed at the level of the auditory meatus.

•Maintain MAP within 20 percent of baseline preoperative resting value and ≥70 mmHg (Grade 2C).

We prefer to use regional anesthesia when possible for patients who have shoulder surgery in the beach chair position, rather than general anesthesia.