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AAOS Now

Published 1/1/2013
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Sarah Gerken, MD

Preventing Positioning Injuries: An Anesthesiologist’s Perspectives

Every member of the operating room team faces both individual and group challenges when caring for patients. A common concern is proper positioning of patients to prevent injury.

Patient injuries due to surgical positioning can take many forms, from end organ damage due to hypoxia or hypotension to direct nerve injury due to compression or traction. This article discusses various forms of positioning injuries incurred by patients in common orthopaedic surgical positions and illustrates the spectrum of complications that may occur.

When considering positioning injuries, it is important to be aware of patients who are at higher risk. Patients at increased risk of positioning injuries, specifically peripheral nerve injury, include obese patients and those with diabetes, peripheral vascular disease, hereditary peripheral neuropathy, or an anatomic variable (eg, cervical rib). Thin patients may also have an increased risk of sustaining peripheral nerve injury during surgery.

Peripheral nerves appear to be particularly vulnerable to injury during positioning. According to information from the American Society of Anesthesiologists (ASA) Closed Claims Database, a significant number of anesthesia-related claims involve nerve damage. Of more than 1,500 claims reviewed, 15 percent were for anesthesia-related nerve injury.

Ulnar nerve, brachial plexus, spinal cord, and lumbosacral nerve root injuries were the major categories of nerve injury resulting in a medical liability claim against an anesthesiologist. Each position can expose various nerves to potential for injury and it is important to be aware of them while positioning the patient.

Supine position risks
The supine position, the most commonly used position for all surgical procedures, is generally the safest position and not associated with dramatic or catastrophic positioning injuries. Even this position, however, can lead to postoperative ulnar neuropathy, the most common position-related nerve injury.

Ulnar neuropathy accounts for approximately one third of post-positioning nerve injuries and is more common in men. The larger tubercle of the ulnar coronoid process in men may compromise the resistance of the ulnar nerve to injury. Pronation of the forearm exerts more pressure on the ulnar nerve, while supination decreases pressure.

The ASA has developed a Practice Advisory for the Prevention of Perioperative Peripheral Neuropathies that includes recommendations for positioning the upper extremity in the supine position (see sidebar). In general, the recommendations cover the use of padded armboards, limiting arm abduction to 90 degrees, and keeping the forearm in a neutral or supinated position.

Hip arthroscopies, which are generally performed in a supine position with traction, have increased in numbers over the years. The unique positioning requirements for hip arthroscopy, aspects of which are similar to positioning on the hip fracture table, may result in injuries typically not encountered in other orthopaedic procedures.

The mechanical traction necessary for surgical exposure leads to the most commonly reported complications of hip arthroscopy. Injuries associated with traction of the operative extremity as well as those secondary to counter-traction against the perineal post have been reported.

Compression injury may include edema, hematoma, and pressure necrosis to the scrotum/labia majora, as well as neurapraxia of the pudendal nerve. Limiting the duration of traction to less than 2 hours and generous padding of the perineal post to more than 9 cm in diameter have been recommended to help decrease the incidence of perineal injury during hip arthroscopy.

Beyond physical injury, patients, particularly morbidly obese patients, can decompensate in the supine position. Fatal cardiorespiratory problems, known as Obesity Supine Death Syndrome, can develop in morbidly obese patients who are placed in the supine position. Moving an obese patient from a semi-sitting or sitting position to a supine position can result in increases in oxygen consumption, cardiac output, and pulmonary artery pressure that push the limits of the patient’s cardiac reserve. It is therefore necessary to be conscientious of positioning the obese patient, even in the supine position.

Beach Chair position risks
Shoulder surgery presents risks for significant injury whether the patient is in the lateral decubitus or beach chair position. The beach chair position has risks associated with the negative pressure gradient between the surgical site and the heart. This situation predisposes the patient to a rare, but potentially fatal, venous air embolism; if a significant amount of air is entrained in the venous circulation, sudden and complete cardiovascular collapse can occur.

The upright position can also lead to potential cerebral injury due to hypotension. Consider a scenario where a blood pressure cuff is placed on either the arm or, even worse, the leg. When the patient is in an upright position, pressure measurements should be performed at the level of the brain, because a large hydrostatic gradient exists between the brain and the site of blood pressure measurement.

For each inch of height difference between the blood pressure cuff and the brain, there is a corresponding drop in blood pressure of approximately 2 mm Hg (10). When this is taken into consideration, it is easy to see that a mean arterial blood pressure measurement taken at the upper arm, or more dramatically at the lower leg, does not accurately reflect the mean arterial pressure at the level of the brain.

If, for example, a surgeon requests hypotension to be induced to aid in visualization, the end result may be inadvertent cerebral hypoxia. A safer solution is to control bleeding by raising the arthroscopic pump pressure.

Studies have demonstrated that a 49 mm Hg difference between the systolic blood pressure and the pressure within the subacromial space can provide a safe and clear operative field. This can be achieved by either raising the arthroscopic pump pressure or inducing hypotension. Whether intentional or not, hypotension in the beach chair position has the consequence of decreased cerebral blood flow and all of the associated potential damage, including ischemic brain damage and possible vision loss.

Less serious, but still concerning, are positioning injuries secondary to incorrect head positioning in the beach chair position. Case reports of cutaneous neurapraxias involving the lesser occipital and greater auricular nerves have been attributed to direct compression of the nerves from the head rest holder. It is not uncommon practice for the anesthesia team to place protective goggles over the eyes of the patients undergoing shoulder surgery; pressure on the supraorbital nerve, either from goggles or restraints, could result in injury to this nerve, resulting in eye pain, forehead numbness, and photophobia.

Sarah Gerken, MD, is an assistant professor in the Department of Anesthesiology at the University of Toledo Medical Center.

Editor’s Note: This is the first of two articles on preventing injuries due to positioning during orthopaedic surgery. This article covers risks for the supine and beach chair positions; the next article will cover the lateral and prone positions.

Recommendations from the ASA
II. Specific Positioning Strategies for the Upper Extremities

  • Arm abduction in supine patients should be limited to 90°.
  • Patients who are positioned prone may comfortably tolerate arm abduction greater than 90°.

Supine Patient with Arm on an Arm Board

  • The upper extremity should be positioned to decrease pressure on the postcondylar groove of the humerus (ulnar groove).
  • Either supination or the neutral forearm positions facilitates this action.

Supine Patient with Arms Tucked at Side

  • The forearm should be in a neutral position.
  • Flexion of the elbow may increase the risk of ulnar neuropathy, but there is no consensus on an acceptable degree of flexion during the perioperative period.
  • Prolonged pressure on the radial nerve in the spiral groove of the humerus should be avoided.
  • Extension of the elbow beyond the range that is comfortable during the preoperative assessment may stretch the median nerve.
  • Periodic perioperative assessments may ensure maintenance of the desired position.

Excerpted with permission from American Society of Anesthesiologists Task Force on Prevention of Perioperative Peripheral Neuropathies. Practice Advisory for the Prevention of Perioperative Peripheral Neuropathies. Anesthesiology 2011;114:1–1.

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