Surgical Details
A surgical procedure is required to place the implanted electrode on the phrenic nerve and the implanted receiver just under the surface of the skin. This procedure can take place at the neck (cervically) or in the chest (thoracically). Usually patients receive two sets of implants, one on each side, unless their condition is limited to only one side.
Surgery is usually performed at hospital close to the patient's home by a surgeon of their choosing. The procedure averages 2-4 hours in length, and the patient is typically discharged from the hospital 1-2 days later. Some procedures can be performed on an outpatient basis.
The decision as to what approach is appropriate for a given patient is made by the surgeon performing the procedure.
Thoracic Approach
The thoracic approach involves a small (5-7 cm) incision made between a pair of ribs so that the phrenic nerve can be isolated alongside the heart. The surgeon places the electrode around the nerve and sutures it in place. The receiver is then placed just under the skin, usually from within the same incision.
A surgeon can perform a thoracic implant using thoracoscopic intruments. This approach is minimally invasive and involves the use of three small (5-10 mm) incisions instead of one larger incision. Through these incisions, a camera and specially designed instruments are used to visualize the nerve and place the electrode.
Thoracoscopic procedures can be performed with standard endoscopic instruments or by use of a surgical robot.
This approach is commonly chosen for the youngest pediatric patients since the anatomy of the neck is not sufficiently developed in these cases. It is also a common approach for patients who are suspected of having nerve damage so that the stimulation can occur below the presumed injury.
Cervical Approach
The cervical approach is also considered minimally invasive since it does not require a thoracotomy, or chest procedure.
It uses a small (3-5 cm) incision made in the area where the neck meets the torso. The phrenic nerve is isolated where it is most superficial, which is under the scalenus anticus muscle. The surgeon places the electrode around the nerve and sutures it in place.
The receiver is then placed just under the skin, usually within a small pocket made on the upper part of the chest.
This approach is commonly chosen for older pediatric patients and adult patients who are known to have good phrenic nerve conduction. In addition to avoiding a thoracotomy, this approach has the advantage that it can be performed on an outpatient basis for some patients.
Intraoperative Evaluation
Intraoperatively, diaphragm function can be confirmed via a number of methods including: visual observation of chest wall, palpation of the costal margin, observation of CO2 changes as measured by anesthesia equipment, and rarely, fluoroscopy.
The primary purpose of intraoperative testing is to confirm that electrode has been correctly placed on the phrenic nerve. Additionally, preliminary threshold and amplitude settings can be assessed. These numbers can provide a baseline from which pacing can be established once healing is complete.
The thoracoscopic surgical technique is unique in that the camera allows for direct visualization of the diaphragm while under stimulation.
Nerve Grafting
For patients whose phrenic nerve(s) no longer conduct due to direct trauma, nerve grafting may be an option. Any grafting procedure would likely need to be performed within 9-12 months of the original trauma before a process, called Wallerian degeneration, occurs and the loss of conduction is irreversible.
The established nerve grafting technique is called an intercostal-to phrenic nerve anastomosis. This procedure involves using an intercostal nerve (from in between the patient's ribs) to reenervate the damaged phrenic nerve.
For this procedure, the intercostal muscle and nerve are cut and brought close to the point where the phrenic nerve enters the diaphragm. The phrenic nerve is then cut, and the two ends are attached using a microsurgical technique. The electrode is then placed between the graft site and the diaphragm.
Since nerves grow at approximately 1 mm per day, it takes several months for the diaphragm to be reenervated. Pacing is begun about six months post-operatively.
Recent advances have led to a new grafting technique using spinal accessory nerves to perform the anastomosis cervically. While the amount of time needed for the graft to grow would increase substantially, this approach will have the advantage of being no more invasive than a standard cervical implant. For additional information on nerve repair techniques, contact the Institute for Advanced Reconstruction.
Upon request, ABD may be able to provide a referral to an experienced surgeon depending on the patient's age, diagnosis, and geographical location.
Detailed instructions on the cervical and thoracic approaches are provided in the Instruction Manual. The thoracoscopic approaches and nerve grafting techniques are discussed in a number of peer-reviewed journal articles. An information packet — containing a manual and reprints of these articles — may be obtained by filling out an information request.