Patient positioning: Common pitfalls, neuropathies, and other problems

Published on 07/02/2015 by admin

Filed under Anesthesiology

Last modified 07/02/2015

Print this page

This article have been viewed 1363 times

Patient positioning: Common pitfalls, neuropathies, and other problems

Mary Ellen Warner, MD

Perioperative neuropathies, vision loss, and positioning-related problems have received increasing attention from the lay press, plaintiffs’ lawyers, the anesthesiology community, and clinical researchers in recent years. This chapter will provide an update of current findings and discuss possible mechanisms of injury for these potentially devastating problems.

Upper-extremity neuropathies

Ulnar neuropathy

Ulnar neuropathy is the most common perioperative neuropathy.

Timing of symptoms

Most symptoms of ulnar neuropathy develop during the postoperative, not the intraoperative, period. Data support the finding that most surgical patients who develop ulnar neuropathy experience their first symptoms at least 48 h postoperatively, suggesting that the mechanism of acute injury occurs primarily outside the operating room. Nonsurgical medical patients also develop ulnar neuropathies during hospitalization.

Impact of elbow flexion

The ulnar nerve is the only major peripheral nerve in the body that always passes on the extensor side of a joint, in this case, the elbow. All other major peripheral nerves primarily pass on the flexion side of joints (e.g., median and femoral nerves). This difference in anatomy may play a role in some perioperative ulnar neuropathies. In general, peripheral nerves begin to lose function and develop foci of ischemia when they are stretched by 5% or more of their resting lengths. Elbow flexion, particularly more than 90 degrees, stretches the ulnar nerve. Prolonged elbow flexion and stretch of the ulnar nerve can result in sufficient ischemia to cause symptoms in awake and sedated patients and potential long-lasting damage in all patients.

Anatomy and elbow flexion

Prolonged elbow flexion of more than 90 degrees increases intrinsic pressure on the nerve and may be as important an etiologic factor as is prolonged extrinsic pressure. The ulnar nerve passes behind the medial epicondyle and then runs under the aponeurosis that holds the two muscle bodies of the flexor carpi ulnaris together. The proximal edge of this aponeurosis is sufficiently thick, especially in men, to be separately named the cubital tunnel retinaculum. This retinaculum stretches from the medial epicondyle to the olecranon. Flexion of the elbow stretches the retinaculum and generates high pressures intrinsically on the nerve as it passes underneath the retinaculum (Figure 244-1).

Figure 244-1 A, The ulnar nerve of the right arm passes distally behind the medial epicondyle and underneath the aponeurosis that holds the two heads of the flexor carpi ulnaris together. The proximal edge of the aponeurosis is sufficiently thick in 80% of men and 20% of women to be distinct anatomically from the remainder of the tissue. It is commonly called the cubital tunnel retinaculum. B, Viewed from behind, the ulnar nerve is intrinsically compressed by the cubital tunnel retinaculum when the elbow is progressively flexed beyond 90 degrees and the distance between the olecranon and the medial epicondyle increases.

Forearm supination and ulnar neuropathy

Supination of the forearm and hand does not, by itself, reduce the risk of ulnar neuropathy. The action of forearm supination occurs distal to the elbow. Supination is typically used when positioning the patient’s arms on armboards or at the patient’s sides because of the impact it has on humerus rotation. That is, supination is uncomfortable for most patients, and they will externally rotate their humerus to increase comfort. It is this external rotation of the humerus that lifts the medial aspect of the elbow, including the ulnar nerve, and prevents it from directly resting on the surface of the table or armboard. This rotation helps reduce extrinsic pressure on the ulnar nerve.

Outcomes of ulnar neuropathy

Approximately 40% of sensory-only ulnar neuropathies resolve within 5 days; 80% resolve within 6 months. Few combined sensorimotor ulnar neuropathies resolve within 5 days; only 20% resolve within 6 months, and most result in permanent motor dysfunction and pain. The motor fibers in the ulnar nerve are primarily located in the middle of the nerve. Injury to these fibers is likely associated with more significant ischemia or pressure insult to all of the ulnar nerve fibers, and recovery may be prolonged or not possible.

Brachial plexopathies

Brachial plexopathies occur most often in patients undergoing sternotomies. The risk for this plexopathy in patients undergoing sternotomy is particularly high in those who undergo mobilization of the internal mammary artery, which is presumed to be associated with excessive concentric retraction on the chest wall and potential compression of the plexus between the clavicle and rib cage or stretch of the plexus. In general, patients in prone and lateral positions have a higher risk of developing this problem than do those in supine positions, except in patients having a sternotomy, as mentioned previously.

Brachial plexus entrapment

Many insults to the plexus can occur in prone and laterally positioned patients. For example, the brachial plexus can become entrapped between compressed clavicles and the rib cage. Special attention should be given to altering any patient positions that might exacerbate this potential problem.

Prone positioning

In prone-positioned patients, it is prudent to tuck their arms at their sides if at all possible; many patients have changes in somatosensory evoked potentials when their arms are abducted (e.g., a “surrender” position).

Anatomy of shoulder abduction

Buy Membership for Anesthesiology Category to continue reading. Learn more here

Related

Fausts Anesthesiology Review Expert Consult 4e