Implementing diaphragm pacing involves a multi-step process.
- Health Care Funding Approval
- Surgical Procedure
- Initiating Pacing
Health Care Funding Approval
The hardware for diaphragm pacing alone is expensive. Many insurance companies or government health care funding agencies are not familiar with diaphragm pacing, its indications, or its advantages. Therefore, the program must usually negotiate with funders before the process of pacing can begin. The length of time required is variable, but it can take several months. Once funding is approved, implementing diaphragm pacing can begin.
The Surgical Procedure
The first step is surgical implantation of the phrenic nerve electrodes and diaphragm pacer receivers. Phrenic nerve electrodes are implanted on both the right and left phrenic nerves. This surgery is delicate. To successfully implant these electrodes, our program has enjoyed collaboration between the Divisions of Neurosurgery and Pediatric Surgery since the program began in 1981. Phrenic nerve electrodes are implanted intrathoracically. They are connected by lead wires to receivers, which are implanted bilaterally just under the skin on the upper abdomen.
The Division of Pulmonology collaborates closely with the Divisions of Pediatric Surgery and Neurosurgery for this procedure.
Our pediatric surgeons perform a procedure that implants receivers in the chest thoracoscopically. The capability to perform the procedure thoracoscopically has increased the number of patients wanting this procedure performed at our hospital.
The surgery involves:
Step 1: Deflation of each lobe of the lung
Step 2: Placement of the electrode on the phrenic nerve
Step 3: Securing the electrode into the tissue
Step 4: Testing the diaphragm pacer equipment intraoperatively to be sure that it is functional.
Step 5: Implanting the receiver and connecting it to the electrode lead wire.
Standard Procedure Time
The standard surgical procedure for implanting diaphragm pacer electrodes and receivers takes about 5 hours.
The hospital stay for recovery usually is 4-7 days long.
The diaphragm pacer equipment is tested during the surgical operation. Once we know that the equipment is fully functional, there is no need to test the equipment again until we are ready to begin the pacing initiation process.
After surgery, tissue reaction (scar tissue) forms around the electrodes. This thickness of the scar tissue determines, in part, the amount of voltage that will be required to stimulate the phrenic nerve. Therefore, we wait for approximately 6-8 weeks after surgery before bringing patients back to our hospital to start the pacing.
The child is brought back into Children's Hospital Los Angeles for a 3-day, 2-night admission.
Diaphragm pacing is first initiated with the child awake. The reason is that the sensation of diaphragm pacing is not something the child has ever experienced. It is not painful, as we have several patients who use this everyday when they are awake, and they do not report pain or discomfort. However, it is unusual, and we want children to experience this initially as a positive experience in a supportive setting (with parents, their doctors, etc.).
Pacing is started with each side separately, and then both sides are paced together. Settings are adjusted to approximate the voltage and rate that will be required to assure adequate gas exchange.
We are not able to begin full pacing immediately. Usually, a child will be able to pace for 60-90 minutes before we observe a dramatic drop in diaphragm contraction at the same voltage (fatigue). Therefore, we pace the child each of the two nights for 60-90 minutes, as tolerated, and adjust the settings to optimize comfort and oxygenation.
Although children with congenital central hypoventilation syndrome use their diaphragms during spontaneous breathing, the electrical profile of the diaphragm pacer breath is different than natural phrenic nerve impulses. Therefore, the diaphragm must adapt to the new voltage profile, very much like someone who wants to run the Los Angeles Marathon must gradually increase their distance run (training). Patients increase their pacing time at home by about 30-minutes each week until they reach four-hours/night, and then by 60-minutes per week until full pacing is achieved. This progress is monitored in the outpatient setting by Pediatric Pulmonologists. From start to finish, the pacing process typically takes approximately three months before a child is able to use pacing for a full night of sleep.
For those children in whom we anticipate removing the tracheostomy, we want the child to be ventilated fully by pacing with an open tracheostomy for at least three-months. Then, a sleep study is performed with the tracheostomy capped. If we can achieve adequate gas exchange, then the tracheostomy can be removed. For these patients, the average length of time from pacer surgical implantation to tracheostomy removal is 10-12 months.