Principles of Surgical Positioning

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Chapter 4 Principles of Surgical Positioning

Surgical positioning is one of the first obligatory steps in adequate surgical planning. Proper patient positioning is a critical part of every operation: it allows the surgeon the ability to comfortably gain access to the surgical site while avoiding potential complications. Positioning is particularly important in neurosurgery because procedures are often lengthy and many different trajectories can be used to access a single lesion. Neurosurgical positioning can vary greatly depending on the indication for surgery, the patient’s body habitus, and the surgeon’s preference. Several general principles of patient positioning must be understood in order to avoid potentially devastating complications. In this chapter the main neurosurgical positions, potential complications related to each position, and important considerations to decrease morbidity associated with each position are discussed in detail.

General Principles of Patient Positioning

Positioning the neurosurgical patient is a critical part of the procedure, perhaps more so than in any other surgical subspecialty. Appropriate patient positioning is not only important for the safety of the patient, but it also plays a key role in optimizing surgical exposure, ensuring adequate and safe anesthesia, and allowing the surgeon to comfortably operate during long procedures.

A thorough preoperative assessment by the anesthesia and nursing staff is necessary, as is a general understanding of the indications, advantages, disadvantages, and potential complications that may arise from commonly utilized neurosurgical patient positions. The final position of the patient should be conveyed to the entire team as early as possible by the surgeon so that appropriate equipment is readily available and to ensure optimal selection and placement of the endotracheal tube, intravenous and arterial lines, noninvasive equipment, and monitors.14

Typically, patient positioning occurs subsequent to the induction of general anesthesia, intubation, acquisition of vascular access, and bladder catheterization. Neurophysiological monitoring leads are placed at various stages throughout the perioperative period. Unlike other surgical subspecialties, the planar rotation of the operative table varies depending on the planned surgical approach. The table can be neutral, turned 90 degrees, or often positioned at 180 degrees to allow adequate space and optimal placement of equipment required during complex neurosurgical procedures. This equipment may include the operating microscope, image guidance equipment, C-arm, endoscope tower, headlight sources, and occasionally intraoperative magnetic resonance imaging (MRI) or computed tomography (CT).1

During table rotation and patient positioning, it is often necessary to disconnect the ventilator and monitors temporarily. All members of the team should pay special attention to the duration of this period in order to avoid hypoxic insult to the patient. Eye protection with lubrication and tape provides a barrier that prevents corneal abrasion and introduction of caustic material into the eyes during positioning, intubation, and patient preparation and draping.2

Principles of padding, taping, and positioning of the patient’s extremities are based on the Summary of Task Force Consensus on the Prevention of Perioperative Peripheral Neuropathies Relevant to Positioning for Neurosurgery (Box 4.1).5 In general, maintaining the patient’s arms and legs in an anatomically neutral and relaxed position with soft protective barriers over areas with associated bony prominences helps prevent neurovascular compression, muscle damage, and cutaneous pressure injuries. A combination of gel pads, foam cushions, pillows, and padded arm rests are used for these purposes. For thoracoabdominal and pelvic protection and positioning, large gel rolls or specially designed frames and operative tables provide padding while simultaneously allowing relaxation of this region, aiding in both ventilation and venous return (Fig. 4.1). Such devices include but are not limited to the Wilson frame, Relton-Hall frame, Andrews frame, and Jackson table and frame.3,4,5

BOX 4.1 Summary of Task Force Consensus on the Prevention of Perioperative Peripheral Neuropathies Relevant to Positioning for Neurosurgery

From American Society of Anesthesiologists Task Force on the Prevention of Perioperative Peripheral Neuropathies: Practice Advisory for the Prevention of Perioperative Peripheral Neuropathies. Anesthesiology 2000;92:1168-1182.

Cranial surgeries and occasionally posterior cervical surgeries require rigid skull fixation. Historically the use of stereotactic navigation universally required skull fixation; however, the development of electromagnetic systems has allowed the head to be mobile during a stereotactic procedure, obviating the need for pins. If rigid fixation is not required, the head may be placed on a gel or foam doughnut (Fig. 4.2) or in a padded horseshoe. The Mayfield frame (Fig. 4.3) is a three-pin device that is typically used for rigid skull fixation.1,2 Both radiolucent and metal versions exist depending on the need for intraoperative x-ray. In cases in which spinal distraction and reduction may be necessary, Gardner-Wells tongs or a halo ring with attached weights are used. For prone positioning the head can be maintained in the Mayfield frame or placed on a foam pillow that is usually precut with openings for the eyes, nose, and endotracheal tube (Fig. 4.4).1 Lateral positioning requires the use of specially positioned arm rests and usually an axillary roll to prevent brachial plexus compression.5 More detailed requirements for the various positions are discussed in the respective sections later in this chapter.

In positions other than prone, placement of the Mayfield frame is carried out on the operative table prior to patient positioning. In the prone position, the pins are usually inserted on the hospital bed prior to transferring the patient to the operative table. In adults pins are placed under 60 pounds per square inch (psi) of pressure.1 Inserting and tightening the pins has a profoundly stimulating effect on the patient that usually leads to an increase in heart rate and blood pressure. This hemodynamic change may incur potential complications, for example, in patients with unsecured aneurysms or intracerebral hemorrhage. The timing of pin insertion should be clearly communicated between the surgeon and anesthesiologist so that the depth of anesthesia can be increased with additional bolus administration of an agent such as propofol (Diprivan). The patient’s vital signs should be closely monitored during this time. This assumes that appropriate invasive and noninvasive forms of monitoring are in place and functioning prior to this step. Additionally, antibiotic ointment should be applied to each of the pins prior to their percutaneous insertion as a bacterial barrier and to avert air embolism, particularly in the sitting position.2,6

Head and neck configuration is perhaps the most important aspect of neurosurgical patient positioning. Final orientation of the head and neck is based on the planned surgical approach and exposure. There are several basic cranial approaches that determine head and neck positioning. The head can be safely rotated approximately 45 degrees in the supine position in healthy individuals. Access to the skull beyond 45 degrees requires manipulation and rotation of the patient’s body into any of the specific positions described later in the chapter.2 Various degrees of anteroposterior and lateral flexion and extension of the neck provide additional modification to the surgical trajectory.1

Avoidance of neurovascular complications during head and neck positioning requires vigilance on the part of the surgeon and the anesthesiologist. Hyperflexion beyond approximately 2 to 3 fingerbreadths between the mandibular protuberance and the manubrium is considered the upper limit of safe neck flexion. Hyperflexion of the neck in both the anteroposterior and lateral planes may lead to a series of complications. These complications include decreased cranial venous return and lymphatic outflow leading to facial swelling, macroglossia, and raised intracranial pressure, compression of the vertebral arteries leading to ischemia, and increased airway pressures affecting ventilation and oxygenation. Awareness of the distance between the patient’s chin and the edge of the operative table is also important. In the prone position if the patient shifts downward on the table, the chin can press against the edge, leading to skin necrosis.1,2,7

The same basic principles and guidelines of patient positioning in general surgery also apply to the neurosurgical patient. However, a number of important considerations should be given to this subset of patients. Each patient position has its own indication and benefit but also carries a set of unique risks and potential complications that can be avoided with a thorough understanding of the use of the position.

Supine Position

The supine position (Fig. 4.5) is perhaps the most commonly used patient position in neurosurgery and across all surgical specialties. Because it is a familiar position, it is arguably the safest with the fewest number of associated complications. As an additional advantage, no special equipment is required.

In the supine position, the patient’s head can be free on a padded doughnut or horseshoe, rigidly fixed in the Mayfield clamp, or in traction with Gardner-Wells tongs or a halo ring. The elbows, wrists, and heels are appropriately padded with gel or foam cushions. The knees are maintained in a slightly flexed position over a pillow. The arms are generally maintained at the patient’s side on padded arm rests.3 The head can safely be turned 45 degrees, as previously mentioned. Additional rotation can be achieved by placing a roll or bolster under the shoulder ipsilateral to the surgical side. If pins are not used and the head is turned, the ear and contralateral scalp should be protected with a gel doughnut or foam pad to avoid compressive injury to the pinna and to prevent pressure alopecia.2 If a shoulder roll is used, the contralateral or dependent arm is often placed in a slightly abducted position on an arm rest. The ipsilateral arm is either placed in a flexed position across the abdomen or maintained at the side on an arm rest, depending on the degree of patient rotation and whether access to the abdomen is desired (e.g., for ventriculoperitoneal shunt or if abdominal fat graft is desired).1 Arms should not be abducted more than 90 degrees at the shoulder and supination of the forearm is recommended in order to minimize ulnar nerve injury.5

In addition to patient position, bed configuration plays an important role in the supine patient. In anterior spinal procedures and endarterectomies, the bed is maintained in the horizontal position. In cranial procedures in which both venous drainage from the brain and venous return from the legs are desired, the lawn chair position is preferable. Maximal venous drainage from the head is achieved with either the Fowler or reverse Trendelenburg position, both of which help to minimize venous bleeding and to reduce cerebral swelling.1,2

The supine position is a familiar position that is commonly used, is easily achieved, and requires no special equipment. The very few complications that are associated with this position can be avoided by using basic principles of patient positioning.