NEUROANESTHESIA

A social emphasis on the importance of treating patients with chronic pain has led to the increase in the number of practitioners performing procedures requiring anesthesia. Neurosurgeons, anesthesiologists, physiatrists, orthopedic surgeons, and neurologists now perform these procedures. Regardless of the practitioner involved, the anesthetic issues are important to achieve a stable course.
Spinal cord stimulation. This procedure is most commonly performed for pain involving the extremities. Recent expansion of indications includes pelvic pain, occipital neuralgia, angina, and pancreatitis. The procedure is often separated into stages.
The percutaneous trial. In either the operating room or radiology suite, a temporary stimulation system may be placed under the guidance of a fluoroscope. Anesthesia is difficult because many of these patients have taken oral opioids for long periods and are tolerant to this class of drugs. These patients may require sedation to place the lead in either the lumbar or cervical region but should remain alert and responsive to avoid nerve root injury. The patients also need to be cognitively functional for the computer screening, which involves connecting the epidural lead to the handheld computer and electrically stimulating the nerve tissue to obtain a paresthesia. This requirement for varying levels of sedation makes propofol and remifentanil attractive choices in this group of patients. Regional anesthesia should be avoided. In patients who are stoic, the procedure may be performed under local anesthesia; however, the patient selection for this technique should be very stringent.
The surgical lead. A surgical lead must be placed in some patients with more anatomically difficult spines or in whom a percutaneous lead has failed. This procedure usually requires a wake-up period so the patient can discuss the perception of stimulation. This may lead to a more difficult task because the procedure itself requires a hemilaminectomy. Some surgeons request a general anesthetic with evoked potential testing for this procedure. NSAIDs should be avoided in this population because of the increased risk of bleeding.
The permanent lead. In most cases, the permanent implant involves the placement of both the lead and generator. The permanent implant requires the use of a complex anesthetic because the patient needs to be conversing during the lead placement and more sedated for tunneling and pocket placement. In some cases, the lead placed for the trial procedure is used as a permanent lead. If that is the case, the patient is brought back to the operating room 1 to 4 weeks later for the connection to a permanent generator. This procedure is most often performed under monitored anesthesia care or general anesthesia. This stage requires no period of discussion. Thus, the anesthetic is much less complex. In either method, the placement of the generator pocket determines the patient's positioning. If the generator is placed in a different body area, repositioning and draping may be required, affecting the anesthetic level required.
  Intrathecal and epidural drug infusion systems. The use of neuroaxial infusions to treat pain that is unresponsive to oral or transdermal medications is becoming more common. Catheters may be tunneled and connected to an external infusion source or may be connected to an implantable system that is placed in the subcutaneous tissue.
Totally implantable infusion systems. Placing an intrathecal or epidural pump in the subcutaneous tissue involves two steps. First, a catheter must be placed in the epidural or intrathecal space. Once this has been successfully completed, the catheter can be connected to an infusion source. Anesthesia for these procedures might consist of sedation with local infiltration, subarachnoid or epidural block at the time of catheter placement, or general anesthesia. Each method has its risks and benefits. With general anesthesia, the patient is less likely to move, and the risk of nerve injury may be diminished. In the nonresponsive patient, the risk of nerve injury may be increased, however, if the patient cannot respond to development of parasthesia. The spinal or epidural technique avoids the general anesthetic, which may be advantageous for someone at high risk for pulmonary or cardiac complications. Use of sedation with local anesthetic infiltration reduces the risk of undiagnosed nerve injury at the time of catheter insertion. In some patients, the stimulation involved in the tunneling and pocketing component of the procedure might not be successfully blunted with sedation and local infiltration alone, and a conversion to general anesthesia might be required during the course of the procedure.

Externalized infusion systems. In patients in whom the need for infusion is short term or in those with a life expectancy of <3 months, an externalized system is often selected. The need for general anesthesia in this population is rare because of the lack of pocket creation. Although this procedure could be completed under neuroaxial blockade or general anesthesia, the more common scenario is to use monitored anesthesia care with local infiltration.

Radiofrequency nerve ablation. The cost-effectiveness of radiofrequency ablation has led to a vast increase in the number of procedures performed annually in the United States and Europe. Pulsed radiofrequency ablation is a new technique that has shown promise in treating peripheral nerve processes without larger procedures. This technique is also being utilized more commonly in ablating the sympathetic nervous system and selected peripheral nerves. The anesthetic in these cases is inherently difficult. The patient must be sufficiently sedated to permit the placement of a large radiofrequency cannula and then allowed to awaken rapidly to be able to answer important stimulation questions involving sensory, motor, and nociceptive input. The risks of nerve injury greatly increase in the patient who is not able to fully discern the computer stimulation pattern. Because of these issues, the infusion or injection of fast-acting and rapidly-waning drugs is often utilized. Options include propofol, midazolam, fentanyl, or local anesthetic as a sole agent.
Spinal endoscopy. In 1997, the United States Food and Drug Administration (FDA) approved the use of spinal endoscopy. In this method, the physician uses a fiberoptic scope to visualize and treat disease processes of the spine by an epidural route. This procedure is stimulating and requires sedation to be tolerated in most cases. The use of general anesthesia should be avoided because of the risks of nerve damage in the patient who is unable to report paresthesia.
Minimally invasive disc procedures. The use of new percutaneous techniques to treat contained disc herniations and leaks of the annulus are valuable options in patients who would like to avoid more invasive techniques such as fusion or artificial disc replacement. In these cases, there is a need to converse with the patient at all times. Anesthesia should be with local anesthesia with or without mild sedation.