Patient Positioning and Common Nerve Injuries

Nerve injury

Claims

Ulnar

Brachial plexus

Lumbosacral nerve root

Spinal cord

Sciatic

Median

Radial

Femoral

Table 49.2

Prevention of perioperative peripheral nerve injuries

Preoperative history and physical examination	Ascertain if patients can comfortably tolerate the anticipated operative position
Upper extremity positioning
• Arm abduction: in supine patients, it should be limited to 90°, while prone patients may comfortably tolerate arm abduction greater than 90° • Ulnar nerve: place forearm in supination/neutral position to decrease pressure on the postcondylar groove of the humerus (ulnar groove) • Radial nerve: avoid prolonged pressure in the spiral groove of the humerus • Median nerve: avoid excessive elbow extension • Arms tucked at sides: forearm should be in a neutral position
Lower extremity positioning
• Sciatic nerve: may be stretched by hamstring muscle stretch and by extensive flexion or extension at the hip or knee • Peroneal nerve: avoid prolonged pressure at the fibular head
Protective padding	• Padded arm boards, chest rolls, elbow padding • Padding should be too tight • Avoid using shoulder braces for steep Trendelenburg position
Adequate documentation and postoperative assessment

There are five in vivo mechanisms for perioperative peripheral neuropathies—stretch, compression, generalized ischemia, metabolic derangement, and surgical section. Observational studies have reported postoperative peripheral neuropathies occurring in patients with specific preexisting conditions, such as diabetes mellitus, vascular disease, extremes of body weight, and age.

Evaluation of Perioperative Nerve Injuries

A thorough preoperative history and physical examination is imperative for evaluation of perioperative nerve injuries. When a suspected perioperative nerve injury occurs, a neurologist should be consulted. Sensory neuropathies are more common than motor neuropathies. Also, sensory neuropathies tend to be transient, often less than 5 days, and patient reassurance is appropriate. Motor neuropathies can be evaluated by electromyogram (EMG) to establish the exact location of the injury and also help uncover if the neuropathy was present preoperatively (an EMG done postoperatively will show evidence of nerve injury weeks before the surgery).

Upper Extremity Nerve Injury

Ulnar Nerve Injury

Ulnar nerve injury is the most common perioperative nerve injury. The mechanism of ulnar neuropathy in the perioperative period is unclear. While external nerve compression or excessive stretch from positioning does cause neuropathy, other factors appear to play a role. As stated above, overall peripheral nerve neuropathies occur equally in men and women; however, ulnar nerve neuropathies occur more often in men (less fat, larger tubercle of the ulnar coronoid process in men). Other factors include extremes of body habitus and prolonged hospitalization of greater than 14 days. Also, multiple outcomes have shown that initial symptoms from ulnar neuropathies were noted more than 24 h after the procedure. With this information, there is a consensus that ulnar neuropathies are not always preventable even when taking all precautions. When they do occur, the possible results are decreased sensation along its innervation, a failure to abduct or oppose the fifth finger, and eventual atrophy of the intrinsic muscles of the fourth and fifth finger producing a “claw”-like hand.

Brachial Plexus Injury

Brachial plexus injury is the second most common injury and results from excessive stretching, direct trauma, and compression during surgery. Stretching can result when there is arm abduction greater than 90°. Displacement of the first rib during median sternotomies is a key source of brachial plexus injuries where up to 4.9 % of patients who underwent open heart surgery had this complication. Shoulder braces for steep Trendelenburg position are another risk for injury to the brachial plexus and should be avoided. The use of a nonsliding mattress should be used in place of braces. Further, attention is required when a patient is in steep Trendelenburg, as the patient is at risk of moving cephalad while the arms or shoulders are steadied in place causing stretching of the brachial plexus.

Radial and Median Nerve Injury

Radial and median nerve injuries are rare. The radial nerve can be injured as it wraps around the middle of the humerus laterally in the spiral groove. Injury results in wrist drop, weak thumb abduction, inability to extend the metacarpophalangeal joints, or a sensory deficit. Median nerve injury may be due to trauma while attempting to obtain intravenous access in the antecubital fossa. Another proposed mechanism for median nerve injury occurs in men who have hypertrophied biceps muscles. Under general anesthesia and muscle relaxation, there may be increased stretching at the elbow for these patients. Median nerve injury results in inability to oppose the first and fifth digits.

Lower Extremity Nerve Injury

The lithotomy position is responsible for the majority of lower nerve injuries. According to Warner et al., there are three risk factors associated with increased risk of developing a neuropathy in the lithotomy position, which include surgery time greater than 2 h, thin body habitus, and recent cigarette smoking. The most common lower nerve injury is to the common peroneal nerve. This can occur from the stirrups, which are used to position the patient in lithotomy, compressing the nerve at the head of the fibula. Injury produces foot drop, loss of dorsal extension of toes, and incapability to evert the foot. Sciatic nerve damage can ensue from excessive flexion of the hips or extension of the knees. Insult to this nerve may also cause foot drop and decreased sensation to the foot, except the medial aspect of the ankle and arch. Femoral and obturator nerve injury occur with lower abdominal surgery as a result of excessive retraction. Impairment of these nerves results in loss of hip flexion and knee extension and the inability to adduct the leg with diminished sensation over the medial thigh, respectively. Obturator nerve injury can also follow difficult forceps delivery.

Eye Injury

Corneal abrasions are the most common eye injury. Pressure on the eyes should be avoided throughout the entire procedure using specific pillows or support for the head while in the prone position. Blindness is a devastating complication, most commonly found in anesthetized patients who undergo surgery while in the prone position. This has led to the development of the American Society of Anesthesiologists’ Postoperative Visual Loss Registry. An ASA Task Force on Perioperative Blindness issued a practice advisory stating there are subsets of patients who undergo spine procedures in the prone position that have an increased risk for perioperative visual loss. They include those who undergo procedures that are prolonged, have substantial blood loss, or both. They further advise using colloids with crystalloids to replace intravascular volume in patients who have significant blood loss and also that high-risk patients should be positioned so that their heads are level with or higher than the heart.

A more recent study including patients from the registry supports the advisory recommendations. In addition to the advisories and findings, they identified that the use of Wilson surgical bed frame, which places the patient head down, obesity, decreased percentage of colloid administration, and male sex are associated with ischemic optic neuropathy. Several of the above findings support acute venous congestion of the optic canal as a possible etiology of ischemic optic neuropathy. Cardiopulmonary bypass also has an augmented possibility of perioperative visual loss. New evidence suggests that prolonged steep Trendelenburg may also be a risk for ischemic optic neuropathy.

Patient Positions

Supine Position

The supine position is the most commonly used position for surgical procedures. The patient lies on his/her back with the arms padded and beside the body or abducted less than 90° on padded arm boards (Fig. 49.1a). The patient’s heels should be padded and legs must be uncrossed. The lawn chair position is a variation of the supine where the hips and knees are slightly flexed. This position may provide better comfort for the patient and can be implemented by placing a rolled towel, pillow, or blanket beneath the patient’s knees.

Fig. 49.1

Various patient positions during surgery. (a) supine, (b) Trendelenburg, (c) reverse Trendelenburg, (d) lithotomy, (e) lateral decubitus, (f) lateral jackknife, (g) lateral kidney, (h) prone, (i) sitting

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