Anesthesia for Functional Neurosurgery

Research Article

Austin J Anesthesia and Analgesia.2014;2(3): 1016.

Anesthesia for Functional Neurosurgery

Alex Bekker1,*

Jean Eloy2

Rutgers New Jersey Medical School, USA

*Corresponding author: Alex Bekker, Rutgers New Jersey Medical School, 185 South Orange Ave, MSB E538 Newark, NJ, 0710, USA.

Received: January 30, 2014; Accepted: March 18, 2014; Published: March 20, 2014

Introduction

Functional neurosurgery refers to the surgical management of neurological disorders that lack a gross structural or anatomical marker [1-2]. It produces therapeutic results by modifying or interrupting malfunctioning pathways and altering their underlying physiology. This is in contrast to non-functional neurosurgery also called anatomic or lesional neurosurgery, which refers to the dissection and excision of distinct lesions with the goals of removing these entities and preserving functionality in the remaining tissue[3]. Whereas non-functional neurosurgery is typically used to treat pathologic parenchymal or vascular lesions, the goal of functional neurosurgery is to improve quality of life by providing symptomatic relief to patients with movement disorders, psychiatric disorders, and chronic pain [4].

Awake neurosurgery is performed when patient participation is required to guide the surgical intervention, and may be used for either functional or non-functional procedures [5]. In the case of functional procedures, interaction with the patient allows the surgeon to maximize clinical improvement and minimize untoward side effects. Non-functional procedures are performed awake when the lesion to be excised is close to a vital area of cortex, like the speech or motor cortex commonly referred to as "eloquent" areas. In this case,communication with the patient allows the surgeon to remove the pathological lesion while minimizing damage to the adjacent areas.

This review will focus on the anesthetic considerations for the most commonly performed awake functional procedures; [6-7] specifically,Deep Brain Stimulator (DBS) implantation for the management of Parkinson's Disease (PD) and Spinal Cord Stimulator (SCS) insertion for the management of chronic pain syndromes will be discussed. It should be noted that DBS implantation is also performed for the management of other movement disorders (e.g. dystonia, familial tremor), certain psychiatric conditions, and chronic pain syndromes [8-10].

Deep Brain Stimulation

Background

The most common and well recognized of the movement disorders is Parkinson's disease (PD), but other entities include chorea, dystonia, and tremor [4,7,8]. The common feature of these conditions is a disruption in the patient's ability to control body movements. PD is due to the progressive degeneration of dopaminergic neurons in the basal ganglia and is characterized by tremor, rigidity, bradykinesia, and postural instability. Historically, the surgical management of PD involved the production of lesions in deep brain structures like the thalamus, globus pallidus, or cingular cortex. Although effective, the ablative procedures were associated with high complication rates and were irreversible [9,10]. These drawbacks, combined with the introduction of medical therapy for PD, led to the abandonment of ablative surgical therapy in the late 1960s.

The goal of medical therapy is to restore balance between dopaminergic (inhibitory), and cholinergic (excitatory) tone, and may be achieved by dopaminergic augmentation, cholinergic inhibition, or both.

As the adverse effects of long-term medical management of PD became more apparent, the advent of computer-guided stereotactic surgery and deep-brain stimulator (DBS) technology fostered a renewed interest in the surgical management of PD [11,12]. Stereotactic surgery refers to the use of a computer that correlates external reference points also defined by a headframe applied to the skull with internal structures seen on CT or MRI to guide the optimal approach and trajectory needed to reach a given target. Deep-brain stimulators are implantable devices that consist of electrodes precisely placed at target brain structures connected by wires to a remotely located module [13-15]. A conceptually analogous and more familiar device is the cardiac pacemaker. While the older ablative procedures could only coagulate and destroy targeted regions of the brain, the newer DBS can modulate the function of the same areas without destroying them. In addition, the DBS can be adjusted to deliver different types of stimulation to maximize benefit, or be turned off completely if it produced untoward effects. The ability of the surgeon to employ technological advances that allow precise localization and reversible modulation of deep brain structures represents an enormous advancement in the management of PD [16,-18].

Anesthetic Goals

The anesthesiologist faces many challenges in caring for patients who are undergoing placement of a DBS device. The anesthesiologist's role includes keeping the patient responsive and cooperative, often for a very long period of time. Many of these patients are elderly, presenting with complex medical problems. Moreover, often these patients are on multiple medications, raising the specter of possible anesthesia-drug interactions. All of these issues require constant vigilance to maintain a stable hemodynamic and minimize respiratory depression. In addition, the anesthesiologist should familiarize him/ herself with the potential effects of sedatives on micro recording (see below), because the altered signal may lead to the imprecise placement of the electrode.

When medical therapy fails or produces unacceptable side effects, surgical intervention may be considered [19-21]. The selection of a highly motivated patient is crucial, and the patient must be psychologically prepared for the experience of undergoing an invasive procedure while fully awake [22-24]. During the preoperativeinterview, the anesthesiologist must explain clearly that adequate sedation and analgesia will be provided for the painful portions of the procedure, and that there will be a period during the operation in the patient will be awake, alert, and required to follow instructions. It should be emphasized that the awake portion of the procedure is not painful and that the anesthesiologist will be at the bedside throughout the procedure to administer sedation and analgesia as necessary [25] Premedication, particularly benzodiazepines, is generally avoided as it may precipitate unpredictable responses (e.g. disinhibition) in the elderly.

All patients must follow the standard "nothing by mouth" orders.

Preoperative Considerations

The Preoperative Interview

When medical therapy fails or produces unacceptable side effects, surgical intervention may be considered [19-21]. The selection of a highly motivated patient is crucial, and the patient must be psychologically prepared for the experience of undergoing an invasive procedure while fully awake [22-24]. During the preoperative interview, the anesthesiologist must explain clearly that adequate sedation and analgesia will be provided for the painful portions of the procedure, and that there will be a period during the operation in the patient will be awake, alert, and required to follow instructions. It should be emphasized that the awake portion of the procedure is not painful and that the anesthesiologist will be at the bedside throughout the procedure to administer sedation and analgesia as necessary [25] Premedication, particularly benzodiazepines, is generally avoided as it may precipitate unpredictable responses (e.g. disinhibition) in the elderly.

All patients must follow the standard "nothing by mouth" orders.

Disease-Specific Considerations

In addition to the effects adverse effects caused by the medications used to treat it, PD itself produces systemic manifestations that may interfere with anesthetic management. Generally, these are the result of either autonomic dysfunction or muscle rigidity. Autonomic derangements result in orthostatic hypotension, delayed gastric emptying, excessive salivation, excessive sweating, and bladder disturbances. Muscle rigidity of the upper airway can result in pharyngeal and laryngeal dysfunction, increasing the risk of pulmonary aspiration and laryngospasm, and predisposing for anemia, hypovolemia, and malnutrition due to chronic dysphagia. Respiratory muscle rigidity can decrease inspiratory and/or expiratory flows, producing restrictive, obstructive, or mixed patterns of pulmonary dysfunction. Also seen is an increased perception of dyspnea, which leads to tachypnea and abnormal respiratory patterns [25-27].

Airway Considerations

Because of the inability to use advanced airway management devices during the awake portion of the procedure and the relative inaccessibility of the airway due to the presence for the head frame, a detailed airway evaluation must be performed with specific effort devoted to eliciting any history of obstructive sleep apnea. Options for securing the airway emergently at any point of the procedure must be considered and planned for preoperatively.

The Off-Drug State

To facilitate physiologic mapping and clinical testing, some patients are told to stop taking their usual anti-Parkinson's medication prior to surgery. This may significantly worsen the parkinsonian signs and symptoms described above. In severe cases a compromise may be necessary, with the administration of reduced doses of the usual regimen to partially control the symptoms while still allowing for adequate testing. This must be discussed with the neurosurgical teamand decided upon jointly.

Intraoperative Management

Overview

DBS insertion is a three-part procedure (Table 1). The first part involves attaching the stereotactic headframe and obtaining imaging studies; the second part involves placing and testing the electrodes; the third part entails tunneling the wires and implanting the pulse generator. The first and third portions of the procedure can be intensely stimulating, but the patient only needs to be awake andcooperative during the second portion. This had led to the use of the "asleep-awake-asleep" technique, in which general anesthesia is provided for the first and third parts, and light sedation is given for the second part. The details of the procedure and the "asleep-awakeasleep" anesthetic technique are discussed below [26-28].

Citation: Bekker A, Eloy J. Anesthesia for Functional Neurosurgery. Austin J Anesthesia and Analgesia. 2014;2(3): 1016. ISSN: 2381-893X