EDUCATION CORNER

Loss of The Airway During a Deep Brain Stimulation Procedure – A Case Report 

Sofia Geralemou, M.D. & Angele Theard, M.D.

Sofia Geralemou, M.D.
Assistant Professor, Interim Chief of Neuroanesthesia

Eman Nada, M.D.
Anesthesiology Department Stony Brook University

Introduction

Deep brain stimulation (DBS) is a surgical procedure in which electrodes are implanted to stimulate areas of the brain responsible for the disease it treats.   It has five FDA-approved indications in the  United States, including   Parkinson’s Disease, essential tremors, drug-resistant epilepsy, dystonia, and obsessive-compulsive disorder. ¹ Off-label/experimental indications are epilepsy, depression, Tourette syndrome, headache, obesity, Alzheimer’s disease, and the minimally conscious state. ²

Treatment:

DBS surgery is a two-stage procedure. In the first stage, the electrodes are implanted in the brain. In the second stage, an internal pulse generator (IPG) is implanted and connected to the electrodes.

The success of DBS surgery depends on precision and accurate electrode insertion. Using a stereotactic frame is a common method to find the target coordinates with the assistance of magnetic resonance imaging or computed tomography using computer software. The patient’s frame is then attached to the operating room table and a geometric arc is placed to allow the target to be achieved from any angle given a stable radius. However, a frameless stereotaxy is available and is increasingly used.  It has the advantage of reduced surgical procedure time and less patient discomfort and provides better airway access. ³

When the coordinates are identified, a skin incision and a burr hole are made. The dura is then opened, and the electrode is introduced. At this point, the process of microelectrode recording is started (MER), and the patient’s feedback is used to monitor the effect of stimulation. Electrodes are implanted in the treatment target area and then connected to an internal pulse generator implanted subcutaneously in the upper chest.

 Case description:

A 56-year-old patient with Parkinson’s disease (PD) was scheduled for (MER) for insertion of DBS. The past medical history was significant for hypertension, obesity, and obstructive sleep apnea (OSA).  We opted for an Asleep Awake Asleep (AAA) technique for this procedure. The patient was induced, and the airway was secured with a laryngeal mask airway (LMA). The surgeon made a burr hole and started introducing the electrodes. The anesthetic was then discontinued. When the patient began to emerge, the LMA was removed. The patient started following commands, and the microelectrode recording (MER) was initiated. Minutes later, the patient began moving his arms in discomfort.  Several small boluses of fentanyl were given.  Minutes later, the patient started to obstruct and desaturate. We applied a jaw thrust and a trial of positive pressure ventilation, but both failed. The airway was then resecured with an LMA after the administration of a propofol bolus. A nasal airway was inserted, and a dexmedetomidine bolus followed by an infusion was started.  Another attempt to emerge the patient was made. The LMA was removed successfully, and the patient remained calm for the duration of the procedure.  After the electrode placement was completed, the patient was sedated for closure, and the procedure concluded uneventfully.

 Discussion:

Deep brain stimulation

The therapeutic success of DBS surgery depends on the precise localization of electrodes to the target subthalamic nucleus.  Several methods are used, including stereotactic frame-based imaging, intraoperative MER, stimulation testing of an awake patient, or the use of intraoperative magnetic resonance imaging (MRI).

MER is spontaneous and stimulus-evoked neuronal discharges that are recorded via a microelectrode as it is advanced toward the target nuclei. MER is an electrophysiological guidance method to localize the target nuclei. In stimulation testing, the implanted DBS electrodes are used to stimulate the target nucleus briefly in an awake patient to confirm the improvement in symptoms such as tremors and rigidity without causing side effects.

Awakening the patient during MER will facilitate the process. MER can be successful under light sedation as well as under general anesthesia (based on anatomical coordinates).

Anesthetic Management:

Preoperative preparation: The patient’s long-term disease-specific medications are usually discontinued so that the symptoms become more apparent for intraoperative testing.    All antiparkinsonian medications are withdrawn 12 hours before the surgery.  Hypotension is a common side effect in patients with antiparkinson drugs. By withholding antiparkinsonian medications, hypertension may result.  Additionally, beta blockers are held in movement disorders. To minimize the risks of intracranial hemorrhage, anesthesia providers should screen patients for preoperative uncontrolled hypertension and coagulopathy.  The routine discontinuation of angiotensin-converting enzyme inhibitors (ACEI) or angiotensin receptor blockers (ARB) in this particular procedure may be avoided as it is considered an independent predictor of hypertension requiring more aggressive intraoperative therapy. ⁴Benzodiazepines are direct GABA agonists that can abolish the recording. If midazolam is needed, a single small dose is recommended a few hours before MER to facilitate the placement of the stereotactic frame. However, propofol is preferred because of its extra short duration ⁵.

A stereotactic head frame is usually placed under local anesthetic infiltration or by using scalp blocks while the patient is awake. The frame is a fixed, rigid metal that is placed parallel to the anterior commissure–posterior commissure line.  It extends from the lateral canthus/orbital floor to the tragus. The head should be centered so that the midline lies within the center of the head frame system.

Intraoperative Management: Anesthesia ranges from monitored anesthetic care (MAC) and asleep-awake-asleep (AAA) to general anesthesia (GA). ⁶ GA is indicated in pediatric and uncooperative patients. Localization of STN using intraoperative MER is possible and showed no difference with a variety of inhalational and intravenous anesthetic agents. ⁷ Scalp blocks were shown to be superior to local anesthetic infiltration in terms of better intraoperative hemodynamics and less need for antihypertensive medications during surgery. ⁸

In the AAA technique, GA with a protected airway is used in the asleep part. This is needed for the scalp incision, burr hole, and dural opening. A laryngeal mask airway (LMA) is usually used to maintain the airway as it is easy to remove when the patient is wakened before the MER.  During the MER, the patient is either kept completely awake by turning off all the medications 15 minutes before or lightly sedated using low doses of dexmedetomidine, remifentanil, or propofol infusions. Then, after the localization of the target areas, the patient is induced once again, and an LMA is inserted for closure.

Effect of Anesthetics on MER: Anesthetics such as benzodiazepines, barbiturates, propofol, etomidate, and volatile agents can potentiate the inhibitory actions of GABA within the basal ganglia and can worsen or abolish MER. ⁹  Although propofol and remifentanil can inhibit MER significantly and propofol can induce sneezing, MER was successful under low-dose propofol and remifentanil.  Using the proper dose of the medication is more important to facilitate the MER.    Using target-controlled analgesia, a plasma concentration of 0.8–2 mg/ml provided enough sedation and did not inhibit MER. ¹⁰

Dexmedetomidine is becoming increasingly utilized for this procedure for its sedative, analgesic, and anxiolytic effects without significant effects on MER. It was found that dexmedetomidine at low doses (< 0.5 μg/kg/h) does not significantly impact the quality of MER in either the GPi or STN. ¹¹ One possible drawback of dexmedetomidine is hypotension which can be magnified in patients with PD and rebound hypertension once the infusions are discontinued. Paradoxical agitation is another drawback, especially with the higher infusion doses. ¹²

Airway Management: The airway can be challenging in these cases for several reasons. Patients with PD can have upper airway dysfunction due to uncoordinated involuntary movements of the pharyngeal, glottic, and supraglottic structures resulting in the retention of secretions, intermittent upper airway obstruction, and aspiration. ¹³ The operating room table is also usually turned 180 degrees away from the anesthesia provider, which adds to the difficulty. Also, if a stereotactic frame is placed, the standard adult anesthesia circuit face mask cannot be utilized. To prevent obstruction of the airway, Scharpf et al.¹⁴ described using a tourniquet around the chin and face to provide a hand-free chin-lift to prevent airway obstruction or inserting a nasopharyngeal airway.

In an emergency airway situation, the use of a pediatric face mask or laryngeal mask airway can be utilized. ¹⁵ Also, tools to remove the stereotactic frame should be immediately available.

Hemodynamic Management: Intracranial hemorrhage due to uncontrolled hypertension during surgery is a devastating complication that can result in a permanent neurological deficit. A target systolic blood pressure of 140 mmHg is usually used as an endpoint for the prevention of intracerebral hemorrhage. Comfortable patient positioning, pain control (i.e., scalp nerve blocks ¹⁶), temperature control, prevention of bladder distension, and avoidance of excessive fluid administration may help to control blood pressure.

Second Stage: The second stage of DBS is performed by tunneling the electrodes and connecting the extension cable through the scalp subcutaneously on the side of the neck to an infraclavicular area where it is connected to the pulse generator.  This can be done on the same day or on another day. This second stage is usually done under GA. If done on the same day, there may be difficulty maintaining adequate cerebral perfusion after the use of intraoperative antihypertensive medications ¹⁷

 Complications of Anesthesia during DBS:

Venous air embolism and seizures are possible complications. ¹⁸ Anesthesia providers should also be aware of the possibility of an akinetic crisis typically found in patients with severe PD disease, in which the patient is alert and conscious but unable to communicate. ¹⁹

Acknowledgment: I would like to thank Sergio Bergese, MD, and Charles Mickell II for reviewing this manuscript.

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