Avoidance of Complications in Neurosurgery

Supine Positioning

Exposure, bleeding, and complications such as air embolism depend on the angle of the head relative to the operative site and the patient’s heart. Overflexing the neck may lead to kinking of the endotracheal tube in the pharynx or obstruction of the jugular vein, which may increase venous pressure in the head and cause increased bleeding or decreased perfusion. The heels, gluteal area, shoulders, and head need to be sufficiently padded. Preferably, rolls are placed under both knees so that they are slightly flexed, and the feet should be suspended by padding under the calves. This position prevents heel pressure ulcers and compression on the Achilles tendon. If the arms are to be secured at the patient’s side, adequate padding of the elbow and wrist and any points of contact with monitoring devices need to be verified before the procedure starts.

Prone Positioning

Nerve palsies and compression injuries are the most frequent complications seen and the most easily preventable. Radial and ulnar neuropathies can occur as a result of positioning the patient in the prone position with the arms extended if padding is inadequate or an inappropriate position is used. Keeping the arms in a mildly flexed position prevents excessive traction in either direction. Padding may be in the form of sheets or blankets placed under the elbows and forearms, or egg-crate foam padding can be used. Brachial plexus injuries can occur with rostral or caudal traction on the shoulders and is frequently seen in the prone position when the arms are extended in the cruciate position or too far above the head. Downward traction, such as when the shoulders need to be pulled down for x-ray localization in the low cervical or cervicothoracic junction, can also cause brachial plexus injury. If possible, any tension placed on the patient’s shoulders during radiography should be removed after the x-ray film has been obtained. There are newer traction devices available that can be fastened to the patient during positioning and apply traction only during fluoroscopy use. Neurophysiologic monitoring of the ulnar nerve with somatosensory evoked potentials during spinal procedures has been shown to be effective in correcting and preventing position-related stretch injuries to the brachial plexus. ^, Another common peripheral neuropathy associated with the prone position is inadequate padding of the anterior superior iliac crest, which can lead to pain or numbness in the distribution of the lateral femoral cutaneous nerve. A rare complication is obstruction of the external iliac artery or femoral artery from prolonged compression in the inguinal region. ^,

Starting at the top, the face and head should be gently suspended without any compression on any one area (discussed later in the chapter in further detail). If the patient is being placed on chest rolls or chest bolsters, the ideal position is to have the shoulders slightly overhanging the chest rolls. Breasts should be tucked between the two rolls to prevent excessive pressure. Prone positioning on a spinal table (e.g., Jackson table [Orthopedic Systems]) requires placement of the hip pads (of a size appropriate for the patient) so that the top of the pads is at the anterior superior iliac crest. The thigh pads are placed just below the hip pads. The ankles should be allowed to dangle off the edge of the leg supports, if possible. Inadequate padding of the anterior superior iliac crest can cause pressure necrosis of the overlying skin. Male genitalia should be examined to verify that they are not being compressed between the thighs or gluteal folds and that a Foley catheter, if present, is not causing undue traction on the penis. The knees need to be padded, and a padded roll should be placed underneath the ankles so that the feet hang suspended.

The abdomen should be hanging suspended to prevent venous compression and improve venous return to the heart. This point is critical because excessive venous compression can lead to significant intraoperative bleeding secondary to epidural venous hypertension. If the abdomen cannot be adequately suspended, the three-quarter prone position can be used instead (discussed later), particularly in morbidly obese patients, who may not fit on any chest bolstering system, such as the Kamden frame, the four-post Relton frame, or chest rolls. This position allows the abdomen to remain free while the surgeon works from behind, but the position also makes intraoperative radiography very difficult.

Another difficulty with positioning for spine surgery is the difference between the ideal position for a decompressive procedure, with the spine and hips flexed, and that for spinal fusion, with the spine in a more lordotic position and the hips and spine in neutral positions. Many patients have been subjected to iatrogenic flat-back syndrome because of improper position during a fusion procedure.

Surgeons must be aware of the potential for unilateral or bilateral blindness after prolonged prone surgery. Causes have been hypothesized to be occlusion of the retinal artery or vein, direct trauma, orbital compartment syndrome, posterior reversible encephalopathy, and ischemic optic neuropathy. Although rare, devastating complications have been described even when no direct trauma occurred, and therefore patients’ eyes should be checked frequently during the procedure. Minimizing blood loss and hypotensive episodes and maintaining a slightly elevated head of the bed may reduce the chance for this complication. If orbital compartment syndrome is suspected, emergency orbital decompression offers the best chance for recovery.

Lateral Positioning

The lateral or three-quarters lateral decubitus position carries with it specific risks for peripheral nerve injuries. Stretch on the brachial plexus can be prevented by placement of an axillary roll slightly thicker than the diameter of the upper part of the arm. This roll should be placed approximately four fingerbreadths below the armpit to prevent compression of the long thoracic nerve. Failure to place an adequately sized roll may lead to excessive stretch of the brachial plexus, with the greatest effects on the C5 and C6 nerve roots. The upper extremities need to be supported in relatively neutral positions to prevent ulnar neuropathies. Horner syndrome can occur when the head is inadequately padded and allowed to hang laterally in such a manner that excessive tension is placed on the superior cervical ganglion. Excessive traction on the lateral femoral cutaneous nerve can be caused by undue extension of the upper part of the leg at the hip while bending the dependent leg. Compression of the common peroneal nerve can occur as a result of inadequate padding laterally under the knee.

Intraoperative Monitoring

Various electrophysiologic modalities can be used to detect subtle signs of neurological compromise before they become fixed deficits. The use of intraoperative monitoring can reduce the likelihood of significant neurological deficits in the appropriate circumstances. Some positioning complications can be avoided with the concomitant use of intraoperative monitoring. ^, At our institution we use motor evoked potentials or somatosensory evoked potentials before and after positioning that may result in injury to the cervical cord. We have found excellent correlation between the lack of changes in evoked potentials and patient outcome. Monitoring is not necessary or indicated in all cases because it is time-consuming, can cause inappropriate movement of the patient, results in bleeding, and has the potential for needlestick injury to the operating room staff. However, in procedures with a potential for significant risk to the cord or neural structures, neurological monitoring is a helpful adjunct to the surgeon.

Electrophysiologic neurological monitoring can consist of somatosensory evoked potentials, motor evoked potentials, intraoperative electromyographic responses, nerve action potential monitoring, direct spinal cord stimulation, and other methods. ^{, ,} The information gleaned from these modalities can be used to determine whether manipulation of the neural elements is compromising conduction. Numerous authors have published series in which the surgeon has changed some portion of the procedure as a reaction to changes in electrophysiologic monitoring. ^{, , , ,} Changes in ulnar nerve somatosensory evoked potentials can also indicate traction injury to the brachial plexus and is increasingly being used to monitor positioning, even with lumbar and thoracic procedures. ^{, ,}

Although not appropriate to monitor for positioning-related changes, direct epidural electrode motor evoked potential monitoring (D-wave monitoring) enables real-time evaluation of the spinal motor tracts and allows quantification of the measured output. This technique may be used during intramedullary spinal cord tumor resection and has been suggested to be helpful in minimizing injury during intramedullary resection.

Cranial Fixation Complications

Positioning of the head for cranial fixation is a frequent source of complications ( Box 22.2 ). In sacral, lumbar, and midthoracic surgery performed with the patient in the prone position, the head does not need to remain immobile, nor does the cervical spine need to be kept straight. In these circumstances, the head is positioned on loose foam padding (with a cutout for the airway and no compression on the eyes), or the head is turned to the side on loose padding. The objective is to prevent compression on the eyes, face, and forehead. However, for many types of cranial, craniocervical, cervical, or cervicothoracic surgery, it is necessary to firmly immobilize the head and prevent unwanted motion of the neck. Several devices can be used to immobilize the head, the most effective of which is the Mayfield head clamp. This clamp involves three-point pin fixation into the skull so that the skull and neck are rigid relative to the table and, assuming that the body is adequately secured to the table, rigid relative to the body. Because it is more difficult to correct spine deformities after the head is secured in this manner, if part of the goal is to reconstitute cervical lordosis, this issue needs to be considered when positioning. Placing the patient in traction with Gardner-Wells tongs, for example, may be more appropriate for this situation.

Cranial fixation pin site complications include lacerations, skull fractures, associated intracranial hemorrhage (i.e., epidural, subdural, or subarachnoid hemorrhages), and infections that can lead to osteomyelitis. Lacerations can be prevented by making sure that the two-pin arm swivels freely so that the force is evenly distributed between the two pins without one pin being shielded from tension, which can potentially result in pivoting on the other pin. If the pins are placed into muscle, it is wise to recheck tension on the single pin to make sure that the muscle has not settled and reduced the pressure. The three pins should be centered slightly below the center of gravity of the head when it is in final position to prevent gravity or personnel from pulling the head down and out of the pins. Ideally, the pins should not be placed directly into the coronal suture or temporal squamosal bone because these bones are most prone to fracture. Pins should be tightened to 60 to 80 pounds in adults and 40 to 60 pounds in children younger than 15 years. Pins are generally avoided in children younger than 2 years; however, some skull clamp systems do exist for these patients for procedures in which they are required. Pivoting within the pins by one of these methods or by inadequately locking the clamp before positioning the patient can result in changes in neck position (which can cause cervical spinal cord injury), lacerations, or compression on the eyes and subsequent blindness. These complications can also occur with Gardner-Wells–type tong traction.

Other forms of head support include the horseshoe headrest and the four-cup headrest. Because the horseshoe headrest is not a rigid form of fixation, the head may shift during the procedure, and thus it is imperative that the anesthesiologist continuously observe for any signs of movement. The four-cup headrest is an excellent alternative to the horseshoe, although blindness, skin and scalp compression, and abnormal cervical motion are possible with either support. Alopecia has been reported as a result of scalp compression.