For a more secure and fixed position, Mayfield traction tongs may be applied (Fig. 5.4). However, Mayfield traction should be used carefully in patients with conditions (such as tumors, osteoporosis, hemopathies, etc.) that cause fragility in the skull.

First, the skin is cleansed by an iodine or alcohol solution. The authors do not perform shaving before the application of the Mayfield pins. However, if the surgical area extends to the upper cervical segments, hair should be shaved at least 24 h before the procedure (Fig. 5.5). One pin is placed above the ear, as a reference (Fig. 5.6), and the other two pins are placed at the same level with it on the contralateral side. When placing the pins on this side, attention must be paid as the pin that is located on the temporal bone may cause temporal perforation. Mayfield tongs are squeezed together to make sure that the single contacts the skull. Then the screw is tightened until the pressure gauge shows between 60 and 80 lb (Fig. 5.7).

Because the surgical wound is above the heart level producing a subatmospheric pressure in the open veins, the risk of venous air embolism should be kept in mind. The fixating devices on the skull must be always removed in the supine position to avoid venous air embolism. During the entire operation procedure, the patient should be monitored for venous air embolism until all potential sites for air entry into the blood circulation have been closed [4]. Rigid support is essential for the neck (Fig. 5.3. The spinal processes should be well supported against pressure since considerable force may be applied on cervical spinal bodies (during graft insertion, screwing, etc.)

To determine the midline, sternal notch may be marked with a skin marker. A wide area as much as possible should be draped open, in order to let the surgeon orient for the overall position and the alignment of the patient (Fig. 5.8).

Neuromonitoring protocols depend on the patient, surgeon, and institution and should be individualized accordingly. Both motor-evoked potentials (MEPs) and somatosensoryevoked potentials (SSEPs) may be used during surgical procedures. Communication with the anesthesia team is essential because inhaled agents and paralytic drugs must be avoided. Following the prepositioning, baseline values are obtained, then the patient’s head and neck are extended, and the shoulders are taped inferiorly. MEPs and SSEPs are then retested to ensure no deviation from baseline [5, 6]. For neuromonitoring, neuromuscular blockade must be minimized or avoided. As a result, each stimulation will produce movement of limb and axial muscles. The amount of movement can be minimized by using a threshold-level stimulation protocol that is based on determining the lowest stimulus intensity that produces consistent muscle activation [7]. The variable that is used for monitoring for this technique is the change in threshold needed to elicit muscle activation. Even with this technique, however, it is necessary to warn the surgeon when a stimulus train is going to be delivered to minimize the risk of movement during a critical part of the surgery. In addition, MEP recording introduces constraints into choice of anesthetic agents (vide infra).