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20: Patient Positioning

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CHAPTER 20 Patient Positioning

James Duke, MD, MBA

1 What is the goal of positioning a patient for surgery?

The goal of surgical positioning is to facilitate the surgeon’s technical approach while balancing the risk to the patient. The anesthetized patient cannot make the clinician aware of compromised positions; therefore the positioning of a patient for surgery is critical for a safe outcome. Proper positioning requires that the patient be securely placed on the operating table; all potential pressure areas padded; the eyes protected; no muscles, tendons, or neurovascular bundles stretched; intravenous lines and catheters free flowing and accessible; the endotracheal tube in the proper position; ventilation and circulation uninterrupted; and general patient comfort and safety maintained for the duration of the surgery. It is always advisable to question a patient or ascertain if there is impaired mobility at any joint; never attempt to position patients beyond their limitations.

Throughout the surgical procedure it is also important to reassess the positioning, readjust as needed, and document any positioning actions and reassessments.

2 Review the most common positions used in the operating room

See Figure 20-1.

image image

Figure 20-1 Patient positioning.

(From Martin JT: Positioning in anesthesia and surgery, ed 2, Philadelphia, 1987, WB Saunders.)

3 What physiologic effects are related to change in body position?

An important consideration is the gravitational effects on the cardiovascular and respiratory systems. A change from an erect to a supine position increases cardiac output secondary to improved venous return to the heart, but there is minimal change in blood pressure secondary to reflex decreases in heart rate and contractility. Conditions that increase intra-abdominal pressure in the supine position, including abdominal tumors, ascites, obesity, pregnancy, or carbon dioxide insufflation for laparoscopy, decrease venous return and cardiac output.

The supine position results in decreased functional residual capacity and total lung capacity secondary to the abdominal contents impinging on the diaphragm. Anesthesia and muscular relaxation further diminish these lung volumes. Trendelenburg and lithotomy positions result in further compression of the lung bases, with a subsequent decrease in pulmonary compliance. Although some improvement is achieved with positive-pressure ventilation, the diaphragm is not restored to the awake position. In the supine position spontaneous ventilation to the dependent lung areas increases. Matching of ventilation to perfusion improves because blood flow also increases to dependent areas.

4 Describe the lithotomy position and its common complications

The patient’s hips and knees are flexed, and the patient’s feet are placed in stirrups to gain ready access to the genitalia and perineum. The range of flexion may be modest (low lithotomy) or extreme (high lithotomy). The feet may be suspended on vertical structures known as candy canes or in boots, or the knees may be supported with crutches. With elevation of the legs, pressure is taken off the lower back, and blood is translocated from the lower extremities to the central compartments.

Compression to lower extremity peripheral nerves is the most common injury, occurring in about 1% to 2% of patients placed in the lithotomy position. Neuropathies may be unilateral or bilateral and are a function of the time in this position (especially longer than 2 hours). They are noted soon after surgery, may present with paresthesias and/or motor weakness, and usually resolve completely, although this may require a few months. Before these injuries are attributed to lithotomy positioning, consider if use of neuraxial needles, lower extremity tourniquets, or surgical trauma (e.g., use of retractors) may have contributed.

To prevent dislocation of the hips, at case conclusion both feet should be released from the lithotomy stirrups and lowered simultaneously. When the leg section of the operating table is elevated, ensure that the fingers are clear to avoid crush or amputation injuries.

5 What nerves may be affected from lithotomy positioning?

image Femoral nerve: A reasonable practice is to avoid hip flexion >90 degrees, although it remains a matter of debate whether extreme flexion predisposed the patient to a femoral neuropathy. The femoral nerve is also at risk from pelvic retractors.
image Common peroneal nerve: May be injured when the head of the fibula is insufficiently padded and compressed against the stirrup canes.
image Sciatic nerve: Avoid stretching the hamstring muscle group by avoiding hip flexion >90 degrees.
image Saphenous nerve: May become injured if the medial tibial condyle is compressed.
image Obturator nerve: May be stretched as it exits the obturator foramen during thigh flexion.
image Lateral femoral cutaneous nerve: Would always present with only sensory findings.

6 What are the special concerns for a patient positioned in the lateral decubitus position?

All patients in the lateral position should have an axillary roll positioned to distribute weight to the patient’s rib cage and prevent compression of the neurovascular bundle of the dependent arm. Loss of pulse to the dependent arm suggests excessive compression, but the presence of a pulse does not ensure that the brachial plexus is protected. The arms are usually supported and padded in a position perpendicular to the shoulders. The dependent leg is usually flexed at the hip and knee, with padding between the legs and under the inferior fibular head to reduce pressure on the peroneal nerve. The head position should be in line with the vertebral column to prevent stretching of the brachial plexus of the nondependent arm. Horner’s syndrome has been reported when the head was not supported in a neutral position. Facial structures, breasts, and genitalia should also be protected.

Ventilation-perfusion mismatching is a risk in the lateral position. The dependent lung is underventilated and relatively overperfused. In contrast, the nondependent lung is overventilated because of the increase in compliance. Usually there is some physiologic compensation, and changes in ventilation and perfusion are usually well tolerated, although in a compromised patient they may prove problematic.

7 What are the physiologic effects and risks associated with the Trendelenburg position?

Head down, or Trendelenburg position, further increases translocation of blood to the central compartment. Intracranial and intraocular pressure increase in the Trendelenburg position secondary to decreased cerebral venous drainage. Adverse outcomes in healthy patients have not been noted, although the Trendelenburg position is clearly contraindicated in patients with increased intracranial pressure. Lengthy procedures may result in significant facial and upper airway edema. The likelihood of postextubation airway obstruction should be considered, and the ability of the patient to breathe around the endotracheal tube with the cuff deflated is reassuring, although it does not completely ensure that postextubation airway obstruction will not occur. After prolonged surgery in the Trendelenburg position, particularly when there has been substantial intravenous fluid administration, it may be prudent to leave the patient intubated with the upper torso elevated, allowing time for fluid redistribution to take place. Decreases in pulmonary compliance and functional residual and vital capacity also occur in the Trendelenburg position. Peak airway pressures during mechanical ventilation are also noted. Shoulder braces used to keep the patient from sliding off the surgical table have been associated with brachial plexus injuries.

8 What specific concerns are associated with the prone position?

The prone position results in a cephalad displacement of the diaphragm. Chest rolls are used to decrease abdominal compression, improving diaphragmatic excursion while limiting compression on the aorta and inferior vena cava. Proper padding of all pressure points, including the face, eyes, ears, arms, knees, hips, ankles, breasts, and genitalia, is necessary in this position. The arms should be placed in a neutral position to avoid traction on the brachial plexus, although modest abduction >90 degrees is acceptable. Electrocardiogram electrodes should not be placed so the patient is lying on them.

9 What is the beach chair position?

This position is used to improve access and mobility of the shoulder for surgery. When finally positioned, the anesthesiologist does not have easy access to the head or endotracheal tube; thus these structures must be well secured and in a neutral position before initiation of the surgery. Perfusion pressure must be closely monitored since the head is well above the level of the heart. Special care should also be taken to protect the eyes because the surgeon is working very close to the face and instruments and the like could place pressure on the eyes. Protective plastic eye shields are often used in this instance.

10 When is a sitting position used?

The sitting position is used to gain access to the posterior fossa of the cranium and perform cervical laminectomy. However, these procedures are now often performed with the patient in a prone position, and the use of the sitting position is decreasing.

11 What are the advantages of the sitting position?

image Optimal positioning for surgical exposure with significantly less blood loss, improved surgical field, and perhaps improved resection of the lesion
image Decreased facial swelling
image Relatively easy access to the endotracheal tube
image Less cranial nerve damage

12 List the disadvantages of the sitting position

image Hypotension. Because of decreased venous return, cardiac output may be reduced by as much as 20% but improves with fluid administration and pressors. Consider lower extremity compression hose to improve venous return. Intra-arterial monitoring is essential. Level the transducer at the level of the external auditory meatus to monitor cerebral perfusion pressure.
image Brainstem manipulations resulting in hemodynamic changes.
image Risks of severe neck flexion include spinal cord ischemia and airway obstruction (caused by severe swelling of the tongue or kinking of the endotracheal tube). Two fingerbreadths of space should be allowed between the chin and sternum.
image Venous air embolism (VAE).

13 How does venous air embolism occur? What are the sequelae?

Because the surgical site is above the level of the heart, air entrainment into the venous circulation is a risk. VAE may result in pulmonary air embolism, hypotension, and paradoxic air embolism if an intracardiac shunt is present. Unless massive, VAE usually responds to fluid challenge and pressor therapy. The surgical site must also be flooded with fluid to prevent continued air entrainment.

14 Review the sensitivity and limitations of monitors for detecting venous air embolism

There are numerous monitors for detection of VAE. No single technique is totally reliable; thus the more monitors used, the greater the likelihood for detecting VAE. In decreasing order of sensitivity the monitors are transesophageal echocardiography and Doppler ultrasound > increases in end-tidal nitrogen fraction > decreases in end-tidal carbon dioxide > increases in right atrial pressure > esophageal stethoscope.

A right atrial catheter has the advantage of being able to aspirate intracardiac air. Therefore, of all modalities mentioned it is the only one capable of diagnosis and treatment. Multiorifice catheters are clearly preferable and should be placed high in the right atrium.

15 What are the concerns for positioning a pregnant patient?

The pregnant patient is susceptible to aortocaval compression secondary to the gravid uterus exerting pressure on these vascular structures, potentially decreasing the uteroplacental blood flow and venous return to the heart. Left uterine displacement decreases intra-abdominal pressure and is achieved by placing a pillow or wedge under the right hip.

16 What peripheral neuropathies are associated with cardiac surgery?

The brachial plexus may be injured. Anatomic features of the plexus, including its superficial location, tethering between the intervertebral foramina and investing fascia, and the limited space in its course between the first rib and clavicle, render it vulnerable to injury. Sternal retraction and first rib fractures predispose to this injury. There does not appear to be a significant difference in brachial neuropathy when the arms are tucked against the body vs. when the arms are abducted 90 degrees with elbows elevated and palms up. The best recommendations are to maintain the head in a neutral position, place the sternal rectractor as far caudally as possible, and use asymmetric retractors cautiously.

17 What is the most common perianesthetic neuropathy?

The ulnar nerve is the most frequently injured peripheral nerve, although its incidence is still relatively infrequent. There is a distinct predilection for men older than 50 years of age, and it is not uncommon for there to be a few days’ delay in presentation. Occasionally the neuropathy is bilateral. Of interest, the American Society of Anesthesiologists’ (ASA) Closed Claims Analysis found that 15% of ulnar neuropathies occurred in patients who were sedated and received spinal or epidural anesthesia or monitored anesthesia care. One would presume that, being awake, the patient would readjust their arms if they felt numbness or paresthesias developing during the procedure. Ulnar neuropathies tend to be mild, mostly sensory in nature, and self-limited. Return of function within 6 weeks is reasonable advice for patients so affected, although deficits have been reported to last up to 2 years. There are numerous cases of ulnar neuropathy in which padding to protect the ulnar nerve was undertaken; thus perioperative ulnar neuropathies are clearly multifactorial in nature. Some patients may have a subclinical ulnar neuropathy before recognition after surgery.

18 Review the incidence of brachial plexus injuries

Closed Claims Analysis found that brachial plexus injuries account for 20% of all anesthesia-related nerve injuries. Risk factors include use of shoulder braces in head-down positions, malposition of the arms, and sustained neck extension. Although not a matter of positioning, upper-extremity regional anesthetic techniques may also cause brachial plexus injuries. Of interest, eliciting paresthesias during needle placement or injection of local anesthetics was not a common finding.

19 How might upper extremity neuropathies be prevented through careful positioning?

Arm abduction should be limited to 90 degrees in supine patients. Protective padding is essential to avoid upper extremity neuropathies but does not guarantee against them. The ulnar groove should be padded, and pronation avoided since this places the ulnar nerve in its most vulnerable position. When arms are tucked at the side, a neutral position is preferable. Flexion at the elbow may increase the risk of ulnar neuropathy. Pressure on the spiral groove of the humerus may result in radial neuropathy. Range limitation is not uncommon at the elbow, and overextension may place the median nerve at risk. Properly functioning automated blood pressure cuffs do not alter the risk of upper extremity neuropathy.

KEY POINTS: Patient Positioning image

1. A conscientious attitude toward positioning is required to facilitate the surgical procedure, prevent physiologic embarrassment, and prevent injury to the patient.
2. Postoperative blindness is increasing in frequency, but it is unclear exactly which patients are at risk. Although not a guarantee to prevent this complication, during lengthy spine procedures in the prone position maintain intravascular volume, hematocrit, and perfusion pressure.
3. The most common postoperative nerve injury is ulnar neuropathy. It is most commonly found in men older than 50 years, is delayed in presentation, is not invariably prevented by padding, and is multifactorial in origin.
4. In order of decreasing sensitivity, monitors for detection of VAE are transesophageal echocardiography and Doppler ultrasound > increases in end-tidal nitrogen fraction > decreases in end-tidal carbon dioxide > increases in right atrial pressure > esophageal stethoscope. It should be noted that, of all these monitors, only the right atrial catheter can treat a recognized air embolism.

20 What injuries may occur to the eye?

The most common injury is corneal abrasion, but patients may also develop conjunctivitis, chemical injury, direct trauma, blurred vision, and ischemic optic neuropathy. Symptoms range from discomfort to pain to blindness. The relatively minor injuries are caused by direct pressure on the eye from face masks, surgical drapes, chemicals that touch the eye, and failure to administer ocular protection. Positions other than supine are more commonly associated with eye injuries. Although in the past it was recommended that a corneal abrasion be treated with an eye patch, this appears to delay healing; use of nonsteroidal anti-inflammatory ophthalmic ointments is now recommended by some. Repetitive use of local anesthetic or steroid drops is not recommended.

21 Review the procedures that have been associated with postoperative visual loss

The incidence of blindness after cardiac surgery has been estimated at about 4%. The mechanisms are thought to be embolic, thrombotic, oncotic, and ischemic and related to the surgical procedures themselves. These patients may develop central retinal artery occlusion or ischemic optic neuropathy (ION).

Other surgical procedures that have been associated with postoperative visual loss (POVL) include neck dissections (including when there is ligation of the internal jugular veins), thyroidectomy, major vascular surgery, and craniotomy. It is of concern that the incidence of POVL associated with prone spine surgery seems to be on the increase.

22 What factors may predispose a patient having spine surgery to postoperative visual loss?

The causative factors associated with POVL after spine surgery are not fully understood. The incidence appears to be about 0.2%. The ASA has developed a visual loss registry in an effort to identify predisposing factors and make recommendations to reduce the incidence of this tragic complication. It is thought that there is a subset of patients at high risk for this complication, although it is not always possible to identify before surgery which patients are at high risk. These patients may have a history of hypertension, diabetes mellitus, smoking, other vasculopathies, and morbid obesity.

Longer spine surgeries (longer than 6 hours) with significant blood loss (1 to 2 L or more) are common features in patients who have sustained POVL. It does not appear to be a pressure effect on the globe since many of these patients were placed in Mayfield pins. Deliberate hypotensive anesthetic techniques do not appear to be a factor, although it may be argued that sustained hypotension in the setting of anemia requires therapy. It is interesting that, in this day when transfusion triggers are being pushed downward (to lower hematocrits), long spine cases may not be a subset in which profound anemia is acceptable. It may be that, in spine cases that require both anterior and posterior stabilization, staging the procedure might be advisable. Although the complication is devastating, its incidence remains small, and the patients at risk, the factors that contribute to POVL, and recommendations for preventing POVL remain speculative.

23 What patterns of blindness are noted?

ION is noted in about 90% of cases, and central retinal artery occlusion is noted in the remainder. Posterior ION is more common than anterior ION, and ION is more likely to be bilateral (approximately two thirds of the time), suggesting that the etiologies are different. Substantive recovery of vision is not frequent.

24 How does the head position affect the position of the endotracheal tube with respect to the carina?

Flexion of the head may move the endotracheal tube toward the carina; extension moves it away from the carina. A general rule is that the tip of the endotracheal tube follows the direction of the tip of the patient’s nose. The change in tube position is probably more problematic in a child than in an adult. Sudden increases in airway pressure or oxygen desaturation may be caused by mainstem bronchial intubation.

Website image

http://www.asahq.org

SUGGESTED READINGS

1. ASA Task Force Perioperative Blindness. Practice advisory for perioperative visual loss associated with spine surgery. Anesthesiology. 2006;104:1319-1328.

2. Lee L.A., Roth S., Posner K.L., et al. The American Society of Anesthesiologists postoperative visual loss registry: analysis of 93 spine surgery cases with postoperative visual loss. Anesthesiology. 2006;105:652-659.

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