Anesthetic Considerations for Deep Brain Stimulation

History

• The foundation of DBS is based on the principle of stimulating neural structures, a concept first demonstrated in the motor cortex of dogs.¹
  Eventually, human cortical stimulation and cortical mapping were developed; however, it wasn’t until human stereotaxic devices were developed that deeper brain structures could be stimulated.¹
• The initial focus was on the positive effects of neurostimulation, but in the 1960s it was demonstrated that specific ventrolateral thalamic stimulation could reduce tremor.
• In the 1970s came the idea of using neurostimulation to treat pain, movement disorders, and epilepsy.¹
• The first notable studies demonstrating the application of this technique focused on patients with cerebral palsy and on symptom management through chronic transcutaneous cerebellar stimulation.¹
• In the 1990s, true long-term DBS therapy was developed by combining cardiac pacemaker technology with deep-brain electrodes.¹

Clinical Indications

DBS has been approved for:

• Movement disorders (Essential tremor, dystonia, Tourette’s syndrome, and Parkinson’s disease).¹
• Psychiatric disorders, including refractory obsessive-compulsive disorder and refractory depression.¹
• Phantom limb pain, cluster headaches, neuropathic pain, and thalamic pain syndrome.¹

Disease Processes and Corresponding Electrode Placement

Proposed Mechanisms

Macro Mechanism

• DBS works by placement of electrodes in a targeted area of the brain.²
• These electrodes are connected by a wire to a pulse generator in the chest wall that is controlled by a remote (as mentioned above, this technology was made possible from adaptations to pacemakers).²

Inhibition Hypothesis

• This hypothesis is based on the observation that neurons surrounding implanted electrodes exhibit reduced firing rates, and that, in abnormally firing neurons, these reduced firing rates may be responsible for the beneficial effects observed in the symptoms of movement disorders.⁴
• The underlying mechanism by which DBS inhibits neurons is debated but may involve inactivation of voltage-gated currents and activation of inhibitory afferents, such as GABAergic afferents.⁴

Excitation Hypothesis

• This is based on observations that DBS antidromically excites afferent neural pathways and thereby reaches the original problematic region.⁴

Anesthetic Considerations for DBS Placement

Positioning

• The patient is typically fitted with a stereotactic head frame for immobilization.⁵

Anesthesia Type

• DBS placement can be performed under local anesthesia alone, local anesthesia with sedation, or general anesthesia (GA), depending on patient factors and surgeon preference.⁵

Local Anesthesia Combined with Sedation

• This was the anesthetic technique used historically.⁵ It involves the injection of local anesthetic into the pin sites of the stereotactic head frame and skin incisions.⁵
• The primary advantage of this approach is the avoidance of interference with microelectrode recordings (MERs), which are electrical firing patterns/rates used to identify distinct brain regions and to confirm electrode placement.⁵
• It is also advantageous when interaction with the patient is required to assess their response to test stimuli.⁵
• Local anesthesia can be applied directly to the pin sites or to areas specifically targeting the greater occipital or supraorbital nerves.⁵
• Depth of sedation can be varied throughout the procedure based on the step of the procedure being performed as well as patient tolerance.⁵
• Typically, deeper sedation is required during pin application, skin incision, and burr hole drilling.⁵

GA

• The primary advantage of GA is the greater comfort it provides the patient during the procedure.⁵
• The primary disadvantages of GA are interference with MER and the inability to evaluate intraoperative patient responses to test stimuli.⁵
• The clinical implications of the commonly used anesthetic induction agents are listed in Table 2.

Considerations for Patients with DBS

Underlying Medical Conditions That Warranted DBS

• Patients with Parkinson’s disease, epilepsy, and dystonia may have unique anesthetic considerations.⁶
• For example, patients with Parkinson’s disease may have autonomic dysfunction, respiratory dysfunction, and gastrointestinal dysfunction that may put them at higher risk of aspiration.⁷

Device Damage

• Electromagnetic interference from electrocautery or magnetic resonance imaging (MRI) can damage the device and lead to overstimulation or suppression of its function.⁶
• Anesthesia providers should consider the type of electrocautery being used, as monopolar electrocautery has a higher risk of current passing through the device compared to bipolar cautery.⁶

Tissue Damage

• Current passing through leads can generate heat in electrodes and cause brain tissue damage near these electrodes.⁶
• Notably, this can still occur when the device is turned off, owing to the metallic case surrounding the deep-brain stimulator.⁶

Interference with Regional Anesthesia

• The use of peripheral nerve stimulators at the DBS site is contraindicated due to concerns about electrical interaction.⁶
• Using ultrasound to visualize anatomy is preferred.⁶

Contraindications for DBS Placement

DBS is relatively contraindicated in patients at increased operative risk, in patients at risk for device malfunction, or with limited device effectiveness.

Some specific contraindications to consider include:

• • Patients with increased bleeding risk.⁸
  • Patients who will likely be exposed to MRI.⁸
  • Patients with pre-existing dementia or cognitive disorders.⁸
  • Patients who are unable to operate the neurostimulator.⁸
  • Patients with unsuccessful test stimulation.⁸
  • Older patients who may experience only mild symptomatic improvement and are at increased risk of cognitive dysfunction after DBS.⁸