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Diaphragm pacing is a unique treatment used to provide chronic ventilatory support for selected children who require mechanical ventilation. Diaphragm pacing is for patients with Congenital Central Hypoventilation Syndrome (CCHS). Children's Hospital Los Angeles is one of the three largest centers for Diaphragm Pacing.
As opposed to a traditional mechanical ventilator, diaphragm pacing uses the child’s own diaphragm as the “ventilator." Electrodes are surgically implanted on the phrenic nerves, and these are stimulated by a small battery-operated transmitter outside the body, causing the diaphragm to contract and the child to take a breath.
Diaphragm pacing can significantly enhance the quality of life for children diagnosed with congenital central hypoventilation syndrome as well as some children who have suffered a cervical spinal cord injury.
Diaphragm pacing is an attractive treatment option for two reasons:
For many young patients, the freedom from the ventilator is wonderful, and the increased mobility or ability to remove the tracheostomy tube are huge improvements in their quality of life. Notable improvements in the quality of life are made for adolescents who are considerably more affected by perceptions about being or looking different than their peers.
For those patients who use pacing as their sole mode of ventilatory support during sleep, pacing can improve the quality of life for family members who want to live more active lives and enjoy travelling or overnight stays away from their homes. Equipment for mechanical ventilation is typically large, cumbersome, and complicated. Packing up a ventilation system for a few nights away from home can be difficult.
The diaphragm pacer system, on the other hand, is portable. If the child does not have a tracheostomy, then tracheostomy supplies, suction equipment, etc., need not be brought with the child after pacing has been successfully implemented.
For more information regarding our Diaphragm Pacing Program or if you will like to know if your child is a candidate for Diaphragm Pacing surgery please contact Sheila Kun, RN in our pulmonary center at 323-361-2287.
The goal of diaphragm pacing in children diagnosed with CCHS is often to remove the tracheostomy while still providing ventilatory support. Ideal candidates for diaphragm pacing under this category are those with a confirmed diagnosis of CCHS by PHOX2B polyalanine expansion mutation analysis. Though less common, children with other types of central hypoventilation syndrome may also be candidates. There should be evidence from the referring physician that the child breathes adequately while awake, and that he or she requires ventilatory support only during sleep. The child should not require full-time ventilatory support during acute respiratory infections. Because there is no synchronous contraction of the upper airway skeletal muscles during inspiration with diaphragm pacing, there is a risk of obstructive apnea. It is generally not possible to successfully remove the tracheostomy for pacing in children under five-years of age. Therefore, we will not generally perform pacing for this indication on children less than four-years of age.
The goal of diaphragm pacing in this group of patients is to permit children to be mobile while receiving ventilatory support. Because the diaphragm pacer transmitter is small and battery operated, children can wear this in a back-pack or fanny-pack, and participate in school and other activities while receiving assisted ventilation, without being tethered to short ventilator tubing. Ideal candidates for diaphragm pacing under this category are those with a confirmed diagnosis of CCHS by PHOX2B polyalanine expansion mutation analysis. Though less common, children with other types of central hypoventilation syndrome may also be candidates. There should be evidence from the referring physician that the child can not breathe adequately while awake or asleep. As diaphragm pacing can only be used ~12-14 hours per day. The tracheostomy will usually not be removed, because the child continues to require assisted ventilation via conventional ventilator and tracheostomy while sleeping. Once it is clear that the child requires full-time ventilatory support, diaphragm pacing can be implemented at any age in order to improve the mobility and quality of life while awake.
Children with high spinal cord injury (C1-C2) are paralyzed below the neck, and this includes the diaphragm and other ventilatory muscles. However, the phrenic nerves may still be viable, though “disconnected” from the brainstem. If the phrenic nerve is functional, diaphragm pacing is possible. The problem is knowing whether or not the phrenic nerve is viable. If the spinal cord injury is above C-2, the phrenic nerve is probably viable. If it is below C-5, the phrenic nerve should work and be connected to the brainstem, and diaphragm pacing is not necessary. Attempting to measure phrenic nerve conduction time is desirable, but difficult, and many centers cannot perform this test. In the absence of the ability to test the nerve preoperatively, one can test the nerve intra-operatively, before actually implanting the hardware. It may be possible to use pacing as the sole source of ventilatory support in adolescents and older children by pacing unilaterally for 12-hours per day on each side. However, a tracheostomy will probably still be required.
Diaphragm pacing is not useful in children who are ventilator dependent because of muscle disease (such as muscular dystrophy) or motor neuron disease (such as spinal muscular atrophy or polio). This is because the diaphragm muscle and phrenic nerves must be functional for diaphragm pacing to work.
Implementing diaphragm pacing involves a multi-step process.
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 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.
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.
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.
Our hospital's Division of Pediatric Pulmonology began its diaphragm pacing program in 1981. Drs. Thomas Keens and J. Gordon McComb developed the program. Since that time, it has expanded. We have now performed diaphragm pacing in nearly 30 children, the majority of whom are diagnosed with congenital central hypoventilation syndrome (CCHS).
In 1995, doctors pioneered a thoracoscopic technique for implantation of the phrenic nerve electrodes. This requires only a few small incisions, rather than the traditional large bilateral thoracotomy incisions. Our surgeons were the first to perform this successfully in the world, and we remain one of the few institutions who can perform this procedure.
A number of children have come to our hospital for this procedure from around the United States and from Japan. Our hospital is one of the three largest diaphragm pacer programs in the world. Since 1990, we have implanted 27% of all diaphragm pacers in children with CCHS in the world.
The Diaphragm Pacing Program requires the collaboration of several disciplines including:
Chen, M.L., M.A. Tablizo, S. Kun, and T.G. Keens. Diaphragm pacers as a treatment for congenital central hypoventilation syndrome. Expert Review of Medical Devices, 2: 577-585, 2005.
Chen, M.L., and T.G. Keens. Congenital central hypoventilation syndrome: not just another rare disorder. Paediatric Respiratory Reviews, 5/3: 182-189, 2004.
Shaul, D.B., P.D. Danielson, J.G. McComb, and T.G. Keens. Thoracoscopic placement of phrenic nerve electrodes for diaphragmatic pacing in children. Journal of Pediatric Surgery, 37: 974-978, 2002.