To facilitate the intraoperative neurophysiologic mapping (MER) and/or clinical testing of the patient, most DBS procedures are performed with local anesthesia and monitored care or with conscious sedation during parts of the procedure when testing is not performed. However, general anesthesia may be needed for specific groups of patients who have an irrational fear of awake surgery, chronic pain syndromes, severe “off-medication” movements, severe dystonia or choreoathetosis, and the young pediatric population. The second stage of the procedure (internalization) is usually performed with general anesthesia. The airway may be secured with an endotracheal tube, because access to the airway is restricted with tunneling of the cable on the side of the neck. During this procedure, there are no concerns with specific anesthetic drugs because no testing is performed.
The stereotactic frame is usually placed on the patient's skull with the use of local anesthesia for the pin sites, which is followed by MRI for localization and tabulating of the variables for DBS insertion. Some patients may require sedation for frame placement and/or for MRI. If conscious sedation or general anesthesia is to be started in the radiology suite, the anesthesiologist must have adequate equipment and support to care for the patient in this potentially “remote” site. Also, if anesthesia is required for MRI, all safety concerns for anesthesia in an MRI suite must be adhered to.
Ideally, airway management (endotracheal tube and laryngeal mask airway [LMA]) should precede placement of the stereotactic frame. However, if general anesthesia needs to be induced with the frame in place, conventional laryngoscopy may be difficult. Other options of securing the airway such as fiberoptic endotracheal intubation or an LMA may be used. If an LMA is used, one needs to be aware of the increased risk of regurgitation and aspiration, especially in patients with Parkinson disease.
Local anesthesia is used as a subcutaneous infiltration at the pin sites and at the site of incision(s) for the bur hole(s) for electrode insertion. Supraorbital and greater occipital nerve blocks are an alternative because they have been shown to be less painful than subcutaneous infiltration, although they did not result in any difference in pain at the time of pin placement or during surgery.45 The local anesthetic drugs frequently used include bupivacaine, ropivacaine, and lidocaine with and without epinephrine.46 Complications of local anesthesia may include toxic blood levels resulting in seizures and respiratory and cardiac arrest. If the procedure has been long, additional infiltration may be required for closure.
Standard anesthesia monitors include an electrocardiogram, noninvasive arterial blood pressure, oxygen saturation, and end-tidal CO2. Invasive blood pressure monitoring may be indicated for blood pressure control. Monitoring may be technically difficult in some patients with severe movement disorders and spasticity. Omission of the urinary catheter will be more comfortable for the awake patient, but fluid administration needs to be monitored carefully to avoid hypovolemia. Supplemental oxygen is delivered through nasal prongs or a mask with an outlet for end-tidal CO2 and respiratory rate monitoring. Proper positioning of patients on the operating table is an important step to ensure maximal comfort and cooperativeness, especially for awake patients. The head and neck should be positioned with some degree of flexion at the lower cervical spine and extension at the atlantooccipital junction. This helps to make the patient's airway patent and make it possible for the anesthesiologist to secure the airway in an emergency. The legs should be flexed and supported under the knees to maintain stability when the head and back are elevated to a sitting position. To aid in positioning, special treatment modalities have been used such as physiotherapy, small doses of levodopa, and intrathecal hydromorphone.47,48 Patients with obstructive sleep apnea may need continuous positive airway pressure therapy intraoperatively. In these patients, the facemask needs to be placed before the head frame, and the patient's continuous positive airway pressure machine should be readily available. The use of clear plastic drapes will make it easy for the anesthesiologist to maintain verbal and eye contact with the patient throughout the case.
In some institutions and/or for some patients, conscious sedation is used for DBS insertion, especially during the opening and closure of the procedure. Frequently used drugs include midazolam, propofol, opioids such as fentanyl or remifentanil, and dexmedetomidine.5–7,25,26,49,50 However, there are concerns with the use of all these drugs as discussed above. The advantages and disadvantages of various drugs used for conscious sedation are shown in Table 3. Generally, the use of benzodiazepines is discouraged.51 Propofol has been widely used, most frequently as a continuous infusion, alone, or combined with remifentanil. The mean infusion rates of propofol reported in the literature are approximately 50 μg/kg/min.7,48,52 However, one needs to be aware, if using target-controlled infusion devices, that the pharmacokinetic behavior of propofol in patients with Parkinson disease may differ from the general population for which the model was developed.53 Dexmedetomidine with low-dose infusion rates (0.3–0.6 μg/kg/h) may be a better choice because of its non–GABA-mediated mechanism of action allowing for MER, hemodynamic stability, and analgesic properties.6,25,26 Optimal conditions for MER or stimulation testing can be obtained with the use of conscious sedation as long as short-acting drugs are used and stopped before the recordings and testing.
The use of depth of anesthesia monitors to titrate sedation and the state of arousal during DBS insertion would be ideal; however, studies have shown conflicting results. The reliability of bispectral index (BIS) monitoring during MER is questionable because the effects of anesthetics are heterogeneous across the different regions of the brain, and there is dissociation between the neocortical and subcortical effects of IV and inhaled drugs.20 Schulz et al.54 found that the use of BIS did not offer any advantages regarding the time to arousal, total propofol consumption, and cardiopulmonary stability. However, they did not study the effect of the anesthetics on MER. A study by Elias et al.26 showed a positive result for the use of BIS monitoring for titrating dexmedetomidine sedation. They found that the subthalamic MER signals were equivalent to the awake state when sedation was titrated to an easily arousable state (BIS value >80) in patients with Parkinson disease. However, deep sedation (BIS <80) suppressed MER signals.
General anesthesia may provide a higher level of acceptance for DBS surgery by some patients and a possible enlargement of the group of patients that can be treated. Intraoperative mapping and stimulation testing will be difficult under general anesthesia. There are no prospective, randomized, blinded studies to compare the clinical outcome with that of an awake technique. There are few reports in the literature on the use of general anesthesia for DBS insertion.4,27,28,29,55 Yamada et al.27 found that general anesthesia in 15 patients with Parkinson disease did not adversely affect postoperative improvements in motor and daily activity scores, except for “off-medication” bradykinesia, when compared with 10 patients under local anesthesia. In another study with 10 patients, Lin et al.29 found that desflurane anesthesia allowed for adequate MERs for successful DBS insertion. Thus, DBS insertion under general anesthesia is possible with careful titration of anesthetics and with the use of limited electrophysiologic mapping. Randomized controlled studies are needed to compare the long-term clinical benefits of patients undergoing DBS insertion under general anesthesia with that of local anesthesia.
The insertion of a DBS is not without the potential for perioperative complications, which demands vigilance in rapid recognition and treatment of these events by the anesthesiologist. Overall, intraprocedure complications have been reported to occur in 12% to 16% of patients.5,7 Intraoperative respiratory complications are of great concern, occurring in 1.6% to 2.2% of patients.5,7 In the awake patient, they may result from oversedation or intracranial events such as seizures or hemorrhage leading to a decreased level of consciousness. Acute airway obstruction may occur in a restless awake patient as the body shifts but the head remains fixed to the bed.5 All appropriate airway equipment should be readily available because managing the airway in a patient with a rigid head frame poses a great challenge. The frame restricts neck movement and covers some or all the patient's mouth and nose. Ideally, if possible, one should attempt to secure the airway without the removal of the patient's head frame, so the surgery could be continued if indicated. Releasing the frame from the table may take time, and in an emergency securing, the airway with an LMA may be the most appropriate option.
Other respiratory complications relate to the patients’ diseases. Patients with Parkinson disease may have restrictive pulmonary dysfunction from poor respiratory muscle function resulting in reduced forced vital capacity and reduced baseline arterial oxygen saturation, upper airway obstruction, dysarthria, and obstructive sleep apnea.7,38,51,56,57 Respiratory insufficiency caused by the absence of anti-Parkinson medications in the postoperative period may also occur.
Cardiovascular complications can lead to devastating outcomes. Hypertension has been associated with increased risk of intracerebral hemorrhages.58,59 This may be more problematic in the awake patient who becomes agitated and anxious. Arterial blood pressure must be controlled before the insertion of the electrode to prevent intracranial hemorrhages. Frequently used drugs include labetalol, hydralazine, nitroglycerine, sodium nitroprusside, and esmolol. The optimal level of blood pressure is not well defined; one may use a systolic blood pressure of <140 mm Hg or a 20% increase of the patient's usual range.59 Orthostatic hypotension may result from anti-Parkinson medications or might be further aggravated by the vasodilating effects of anesthetics, perioperative hypovolemia, and autonomic dysfunction. Glossop and Dobbs60 reported on 2 patients who experienced chest pain, tachycardia, hypertension, and oxygen desaturation during insertion of a DBS under local anesthesia. This was accompanied with ST segment changes and increased troponins, although further testing showed normal coronary arteries. They attributed the symptoms to abnormal vasoactive responses resulting in coronary vasospasm. Animal studies have shown that stimulation of the paraventricular region in the hypothalamus can cause either hypertension or hypotension.61
The use of a DBS has and will continue to increase in popularity for the treatment of many functional neurologic disorders. This is especially true for an increasing elderly population ratio within the rapidly changing population demographics worldwide. DBS use has been shown to be safe, and new indications will continue to emerge. The role of the anesthesiologist in the care of these patients will also continue to evolve. New developments in surgical and imaging technology and a better understanding of the effects of drugs on the MER will lessen the difficulties and complications of these procedures. Even though the anesthetic techniques will continue to differ among various centers and may include monitored anesthesia care, conscious sedation, and general anesthesia, the general principles of anesthesia care remain the same. The anesthesiologist needs to be aware of the unique requirements of these patients and of these procedures. Continuous monitoring and extreme vigilance are vital to early diagnosis and rapid treatment of complications.
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