Various considerations have led to the development of spinal navigation as a tool for surgery of the spine (1–3). To ensure a practical and accurate spinal navigation technique, a mobile computed tomography (CT) scanner is used during surgery. This procedure allows the correct insertion site for pedicle screws to be determined during surgery, thus avoiding screw misplacement. The procedure, including the setup, has been described in detail elsewhere (4).
The development of this new surgical procedure also has an impact on intraoperative anesthesia management. The anesthetic approach needs to consider the general guidelines for neurosurgery as well as the special environment and tactics of spinal neuronavigation (5). Most of the problems influencing anesthesia in this surgical procedure are associated with patient positioning, the specific construction of the CT examination table, and the movement of the patient through the gantry during the CT scans.
Inspired by the first results of this new technique, we report our experiences in handling the problems encountered and present a step-by-step anesthetic approach that we use in our clinic for cases involving spinal navigation with intraoperative CT.
Approval of the local ethic committee was obtained for this observational study without the requirement for written consent to evaluate anesthesia characteristics after a standardized protocol in patients undergoing spinal surgery using the spinal navigation technique.
In addition to the standard preparations, the preoperative visit also considered any anatomical problems that would make patient positioning during the surgical procedure difficult.
Anesthesia was induced on a regular operating room stretcher and maintained using total IV anesthesia (remifentanil/propofol) or balanced anesthesia (thio-pentone/sufentanil/isoflurane). Muscle relaxation was achieved with rocuronium bromide. The trachea was intubated using a reinforced endotracheal tube with special attention to its fixation. Because of insufficient access to the completely draped patient during the whole procedure, hemodynamic monitoring included electrocardiogram, invasive arterial and central venous blood pressure line, and gastric tube and urinary catheter. A second large-bore peripheral venous cannulation was required for rapid volume replacement. Temperature monitoring and a convective warming system were used in all patients.
Because the patient is moved approximately 100 cm back and forth through the CT gantry opening, monitoring cables, tubing, and IV lines were required to be at least twice the usual length (Fig. 1).
After induction of anesthesia, the patients were positioned prone on the narrow CT examination table for the procedure. During this maneuver, the patients were only clinically monitored and taken off the ventilator for a short period. In patients with surgery performed in the lumbosacral region (L5/S1), a different CT procedure was used. In these cases, the gantry was not positioned next to the anesthesia working environment but was placed at the feet of the patient (Fig. 2, A and B). Intraoperative CT scans were performed in aponic oxygenation (50 s) after ventilating with pure oxygen for 1 min.
We have documented time intervals for the induction, maintenance, and recovery from anesthesia as well as for surgery. Patient data and results are expressed as median and range.
Data of 35 patients, anesthetic regimes, and several anesthetic time intervals are shown in Table 1. Twenty-eight patients had surgery in the thoracic and thoracolumbar region and seven patients in the lumbosacral region with a different CT procedure.
Twenty-nine patients could be transferred in stable condition to the regular neurosurgical postoperative ward, and six patients were admitted to the intensive care unit. Four of these had suffered heavy blood loss, and one had ventilation and oxygenation difficulties. A further autistic patient was transferred to the intensive care unit to ease recovery from anesthesia and postoperative pain management.
The intraoperative fluid replacement and total intraoperative blood loss is shown in Table 1. In 14 patients, we re-transfused the erythrocytes collected in the cell saver 694 mL (226–2400 mL). In 3 of these patients, further transfusion of two to four homologous packed red blood cell units were required to maintain the hematocrit to more than 20%. Acquired intraoperative coagulopathies required additional fresh frozen plasma in six patients.
The intraoperative CT in spinal surgery has specific impact on the anesthetic management. The duration of the surgical procedure and the lack of access to the patient make adequate monitoring essential (1). The long duration of surgery with the patient in the prone position and the large fluid turnover as shown in Table 1 requires invasive hemodynamic monitoring for maintenance of hemodynamic stability and for early detection of significant blood loss and fluid shift. The Australian Incident Monitoring Study of 1993 (6) confirmed the superiority of direct arterial blood pressure monitoring over indirect monitoring techniques for the early detection of intraoperative hypotension. Central venous lines may become an option for certain indications such as hemodynamically unstable patients where catecholamines will be required. The indication for central venous catheterization should be therefore broadened, particularly with respect to improved safety and success with modern cannulation techniques (e.g., ultrasound guided cannulation) (7,8).
Another major concern is the tubing and lines. All tubing and lines used have to be long enough to be moved with the patient during the CT scans. Mishaps might occur if lines get entangled under the moving CT table. Thus, length, fixation, and organization of the equipment are important factors to be checked before surgery.
A crucial step is positioning the patient on the CT table in the prone position. At first, the tubes and lines have to be disconnected and passed through the gantry opening of the CT system. At this point, the anesthesiologist is unable to operate the ventilator and monitor the patient in the usual manner. Before this step is performed, the circulation must be stable, and the patient should be fully relaxed. The turning maneuver should only be performed when at least four persons are available to assist. The anesthesiologist is in charge of the head, shoulders, and the endotracheal tube. The anesthesiology staff should operate the ventilator and the monitoring devices and two operating room attendants turn the pelvis and the legs.
Moving the patient through the CT aperture can only present a problem if the lines and tubing are not long enough. The first movements therefore have to be undertaken very carefully, without scanning, to check the whole setup and allow adjustments. Before CT scanning, the forearms need to be lifted off the cushions and pulled forward towards the anesthesiologist (diving position). This has the disadvantage of having to secure the arms throughout the CT procedure to prevent them from dropping and rubbing against the inside of the CT gantry opening with the possibility of abrasions.
Balanced anesthesia with isoflurane as well as total IV anesthesia with propofol and remifentanil both proved to be adequate anesthetic procedures for spinal neuronavigation without significant differences with respect to recovery from anesthesia. However, in high-risk cases of permanent neurological damage where cortical somatosensory-evoked potentials monitoring is required, total IV anesthesia is preferable, because it does not cause somatosensory-evoked potential amplitude depression (9).
The time required for this surgical procedure was acceptable and comparable to conventional procedures in our hospital. Anesthesia induction and recovery times were also comparable to those of other surgical procedures with extensive monitoring systems and a relatively long duration. We believe that our anesthetic management allows us to perform this surgical procedure with maximal patient safety.
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