Vagal Nerve Stimulator

Surgical indications The vagus nerve is one of the twelve cranial nerves.  The nerve originates in the brainstem from several collections of neurons (nerve cells) called “nuclei”. 

 The nuclei of the vagus nerve send axons (extensions of nerve cells) out of the brainstem, through the subarachnoid space, out a hole in the base of the skull called the jugular foramen, and then alongside the carotid artery in the neck, as the “vagus nerve”.  

Because of its proximity to other neurons in the brainstem that have axons that communicate with other areas of the brainstem, thalamus, cerebral cortex, etc. stimulation of the vagal nuclei can produce reactions in many parts of the brain.  Some of these other brain areas are involved in seizure activity.  

Electrical current applied to the vagal nerve in the neck travels back along the axons into the nucleus where it can then exert influences on other parts of the brain (including those that control seizures).  A vagal stimulator is a device with electrodes that are surgically wrapped around the vagus nerve in the neck.  

The electrodes get their electric current from a generator placed below the skin over the chest mucles at about the level of armpit (axilla).  Wires run under the skin from the generator to the stimulating electrodes.

Surgical objectives The objective of vagal nerve stimulator insertion is to safely and efficiently place electrodes around the vagus nerve in the neck as well as a generator below the skin of the chest with as little trauma to the nerve and surrounding tissues as possible.

Alternative procedures Temporal lobectomy is another surgical procedure for the control of epileptic seizures.

Lesion considerations The vagus nerve is located with the internal jugular vein and carotid artery within a fibrous tissue “sheath”.   The jugular vein has many small branches that are easy to tear resulting in blood in the wound that interferes with vision and makes surgery more difficult and dangerous.

The vagus nerve is small and must be handled with care.  Injury to the vagus could result in scarring that would make it unsuitable for stimulation.

Approach Exposure of the vagus nerve requires opening a space between the sternocleidomastoid and the muscles running up and down the front of the neck.  

The with the muscles retracted the jugular vein is exposed and then moved toward the midline exposing the vagus nerve underneath.  

Exposure  A few centimeters of the vagus nerve must be exposed in order to allow placement of the stimulator electrodes.   

Landmarks The stimulator coils are placed along the vagus nerve approximately halfway between the upper (mastoid) and lower (sternal) ends of the stenoclastoid muscle.  

The neck incision is made in the neck skin crease closest to the sternocleidomastoid midpoint.  The incision measures approximately 3cm in front of and behind the anterior border of the sternocleidomastoid.  

Hazards Structures encountered in the course of exposing the vagus nerve include the internal jugular vein as well as the carotid artery.

The branch to the recurrent laryngeal nerve can be  injured.

Instruments Vagal nerve stimulation is done with a general soft tissue dissection kit.  No instruments for bone work (craniotome, drill, perforator, etc.) are required.    

A rigid hollow tube for creating a subcutaneous tract through which the stimulator wires pulled between the neck and chest wounds.  

The stimulator system includes a generator (in the chest), wires (run under the skin from the generator in the chest to the stimulator electrodes in the neck), and stimulating electrodes (wrapped around the vagus nerve).

Anesthesia Placement of a vagal stimulator is done with the patient under general anesthesia.

Monitoring No special physiologic monitoring (such as electroencephalography [EEG]) is required during  placement of a vagal nerve stimulator.  

After it is connected to the far end of the wires to the stimulating electrodes but before it is implanted in the patient the generator’s impedance is measured by a hand-help sensor wand held over the generator.  The generator is “interrogated” by a computer attached to the wand (this same system is used later in the outpatient clinic to make generator adjustments).

Position The patient is placed in the supine position with the face turned to the right.  Sometimes a pillow is placed under the left shoulder to prop it up a little.

Prep and drape The hair over the neck or chest incisions is shaved.

The skin is scrubbed with an iodine detergent and then painted with betadine solution.  

Drapes are placed to define the surgical field of the neck, shoulder, and chest.  

Incision The neck incision is made along the anterior border of the sternocleidomastoid muscle about halfway between the mastoid process (the bony prominence low and behind the ear) and the clavicle (breast bone) where it ends at the junction of the chest and neck.

The chest incision is variable: the simplest is a straight line incision parallel to the clavicle about half way between this bone and the nipple.   For cosmetic or other considerations the surgeon and patient may elect to put the incision (and therefore the generator as well) in a different location.

The patient is positioned supine for vagal nerve stimulator insertion.  Neck and chest incisions have been marked.

Dissection A metal tube with blunt end is used to open a “tunnel” in the space below the skin and above the muscle fascia of the neck and chest.  After the electrodes are placed the wires that will connect it to the generator are fed through the tunnel.  A “pocket” large enough to accomodate the generator (approximately 4 by 4 by 2 inches, 1/4 pound) is made.  
A tunneling tube tube has been placed under the skin between the neck and chest wounds.
Target manipulation Silicone covered electrodes are wrapped around the vagus nerve with a microscope that magnifies approximately 5 times.
The far end of the electrode wires is inserted into the generator prior to its implantation under the skin of the chest.  The neck wound has been irrigated (rinsed) and is being sutured closed.

Problems Cutting into the jugular vein or one of its branches can result in bleeding that makes the remainder of the dissection and placement of the stimulator electrode coils around the vagus more difficult.

Hemostasis It is essential to keep the surgical field as dry as possible throughout the neck dissection, jugular  retraction, and vagus nerve manipulation.   Blood makes it difficult to see small delicate structures like the vagus nerve which is therefore more liable to injury when hemostasis is inadequate.

The jugular vein may be difficult to pull away from the vagus enough to give room to wrap coils around it.  In order to avoid tearing it by pulling too hard, it may be necessary to ligate (tie) and cut the jugular vein.  Enough blood is drained from other neck veins around it that the left jugular vein can be taken in most patients with no consequence whatsoever. 

Closure Both incisions are closed with sutures to the deep tissue layers, staplels, tape, or glue can be used to close the skin.  

Duration Vagal nerve insertion takes approximately two hours:  dissection through the neck down to the vagus nerve takes about an hour.   The coils are wrapped around the nerve under the microscope in less than 15 minutes.  Testing the generator prior to implanting it and then closing neck and chest wounds is usually done in half to three quarter’s of an hour.

Post Op The patient is taken to the recovery room post operatively and can usually go home the next day.  Overnight observation in the Intensive Care Unit is not necessary in most cases.-

Recovery Most patients can return to work after an uncomplicated vagal nerve stimulator placement within two weeks.

Neck pain.

Follow up Follow up with the surgeon should occur approximately one week after surgery at which time strips, staples, or sutures can be removed.  

Infection can manifest as swelling, redness, or pain along the incisions or over the wires that travel under the skin from the chest into the neck.

Reoperation The battery in the generator has a life of three to five years (approximately) depending on the year the device was made (battery life gets longer with each new generation).  When the battery runs down the generator must be replaced — requires another surgery to reopen the chest incision.

Risks & complications Risks and complications vagal nerve stimulator placementinclude:  injury to the vagus nerve, carotid artery, or jugular vein.  Neck swelling (with or without hematoma) hoarseness, equipment failure, and generator migration, as well as infection.