Implantation of deep brain stimulators

Deep brain stimulation (DBS) involves the implantation of electrodes into select regions of the brain, allowing for electrical stimulation of the area to modulate brain activity, resulting in attenuation, if not elimination, of the symptoms and signs of a number of disease states (Table 133-1). The specific site of electrode implantation depends on the disorder for which the patient requires treatment (Figure 133-1). Despite the use of DBS for many decades, the exact mechanism or mechanisms accounting for its clinical efficacy are not well understood, but the electric current is believed to somehow modulate abnormal neuronal function, either by acting directly on neuronal action potentials or altering neurotransmitter release. Use of DBS has generally replaced ablative procedures, such as pallidotomy or thalamotomy (i.e., thermal, mechanical, or electrical destruction of a region of the globus pallidus or thalamus, respectively), for the treatment of Parkinson disease. Unlike these earlier procedures, DBS is reversible.

DBS implantation is typically conducted via frame-based stereotactic techniques. In essence, a stereotactic head frame is applied, usually under monitored anesthesia care, and the neurosurgeon injects a local anesthetic agent at the sites where the pins of the head frame will be inserted to immobilize the skull within the head frame, after which the patient undergoes imaging (i.e., computed tomography or magnetic resonance imaging) to localize the deep brain target relative to the stereotactic head frame. An electrode is advanced via a burr hole to the approximate location of the target. Implantation of the electrode into the exact target nucleus is usually facilitated by single-neuron recordings and then confirmed, if possible, by the resolution of symptoms upon stimulation. The nature of various disorders, such as obesity, epilepsy, and obsessive-compulsive disorder, may not allow for immediate confirmation of symptom resolution. Following electrode implantation, the wires are tunneled under the skin to reach a generator, which is typically implanted in the pectoral region.

Generally, electrode implantation is performed with the patient in a semiseated position with monitored anesthesia care with sedatives administered to keep the patient “comfortable” but not so sedated that the surgeon cannot intraoperatively assess and optimize the efficacy of electrode placement. Providing an adequate but not excessive level of sedation can prove to be very challenging because the procedures tend to be of long duration and access to the airway is limited due to the presence of the head frame, which is rigidly fixed to the operating table. A means to rapidly secure the airway (i.e., laryngeal mask airway, fiberoptic bronchoscope) should be readily available. Some sedative drugs (i.e., propofol, benzodiazepines) can inhibit neuronal activity, thus influencing the ability to utilize single-neuron recordings to accurately identify the deep brain target. Short-acting opioids (e.g., fentanyl, remifentanil) and dexmedetomidine have been used successfully to provide sedation for these procedures.

Alternatively, in patients not able to tolerate the procedure with sedation (e.g., children or adults with impaired cognitive or intellectual abilities) implantation of a depth electrode can be conducted with general anesthesia. Drugs used to maintain general anesthesia may significantly impact the ability to identify and monitor neuronal electrical recordings. In these situations, proper placement of the depth electrode is usually dependent on imaging data referenced to the stereotactic head frame; thus, the likelihood of improper or ineffective electrode position may be greater when using general anesthesia.

Clinically consequential venous air embolism has been reported with the implantation of electrodes for deep brain stimulation, and the use of precordial Doppler sonography monitoring should be considered. Of note, electrical impedance from precordial Doppler sonography may impair neuronal electrical recording and may need to be suspended during recording of neuronal activity. Tunneling of electrode leads and implantation of the pulse generator are usually conducted during general anesthesia following removal of the stereotactic head frame.

Cervical denervation for dystonia

Dystonias are a group of disorders in which inappropriate and sustained muscle contractions lead to twisting movements and abnormal postures. The causes are many and types include congenital, idiopathic, trauma-induced, and drug-induced dystonias. Conservative treatment options include antiparkinsonian drugs (such as trihexyphenidyl or the combination of carbidopa and levodopa), antiepileptics, benzodiazepines, and β-adrenergic receptor blocking agents. If these medications do not produce satisfactory results, injection of botulinum toxin into the affected muscles may also provide some improvement and is the most commonly performed invasive procedure. DBS has been approved by the Food and Drug Administration in the United States for treatment of cervical dystonia and is currently under investigation, assessing efficacy compared to other treatment options, for other dystonias.

Refractory cervical dystonia may also be treated with selective peripheral muscular denervation, which involves identifying and transecting the nerves supplying the affected muscles. This procedure is usually conducted under general anesthesia with the patient in either the prone or sitting position. In either case, the surgeon will directly stimulate nerves with an electric current to identify specific muscule innervation; hence, the use of neuromuscular blocking agents is contraindicated during this segment of the procedure. In patients undergoing cervical denervation in the sitting position, techniques used to monitor for (i.e., transesophageal echocardiography, precordial Doppler sonography) and to treat (i.e., central venous catheter) air entrained into the venous system should be considered.

Epilepsy surgery

Epilepsy, or recurrent seizure disorder, affects 50 million people worldwide and occurs in all age groups. Initial management of epilepsy is usually with the use of one or more antiepileptic drugs. Despite this, many patients either continue to experience frequent seizures despite the use of multiple antiepileptic agents or are unable to tolerate the side effects of these drugs, which include somnolence, ataxia, hepatitis, cutaneous reactions, or aplastic anemia. Active epilepsy has a major negative impact on quality of life. For example, patients are unable to drive automobiles, may have work limitations, and also suffer the embarrassment of having seizures in public. In these patients, surgical management should be considered as a treatment option. Although epilepsy surgery was long considered as a last resort, the loss of developmental milestones in children and young adults who continue to experience seizures or have unacceptable side effects with the use of antiepileptic medications has increased the number and decreased the age of those having surgery. There are two major types of epilepsy surgery: (1) resective and (2) nonresective or functional procedures.