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What is Phrenic Nerve Pacing?

Electrical stimulation of the phrenic nerves results in contraction of the diaphragm. Electrodes may also be connected directly with the diaphragm, although this is a new technique with little experience. Phrenic nerve pacing uses the patient`s own diaphragm as respiratory pump. This resembles as far as possible the normal mode of breathing, because inspiration is induced by negative pressure within the thorax.

 

What are the parts of the pacing system?

The phrenic nerve pacing system consists of three external components (a battery-operated transmitter in connection with two antennas, see fig.1) and of four implants: two radio receivers implanted subcutaneously on both sides of the thorax and two electrodes sutured to the phrenic nerves within the thorax (see fig.2). During active pacing the transmitter creates a train of radiofrequency signals which are converted by the receiver into electrical pulses. The electrical stimulation of the phrenic nerves induces diaphragmatic contraction and inspiration. When the transmitter stops generating signals, the diaphragm relaxes and passive expiration starts. In children bilateral synchronous phrenic nerve pacing is recommended to achieve optimal ventilation.

 

What is necessary to do before implantation?

Before surgical implantation the following diagnostic procedures should be done: chest X-ray, tracheobronchoscopy, transcutaneous stimulation of the phrenic nerve at the neck together with ultrasound of the diaphragm in order to ensure normal function of the diaphragm, and finally careful neuromuscular examination to exclude myopathies.  Contraindications to diaphragm pacing are: severe, chronic pulmonary disease, tracheo-bronchial stenosis, diaphragmatic paralysis, and myopathy.  A relative contraindication is the age below one year.

What are the benefits of phrenic nerve pacing? 
The benefit of phrenic nerve pacing is greatest in patients, who need the ventilatory support 24 hours per day. In these severely affected patients the breathing pacemaker offers freedom from the mechanical ventilator during the day. They use the small and easily portable pacing system during daytime allowing to be mobile and to participate in all daily activities. Toddlers can carry the transmitter in a little rucksack on their back (fig.3).
 During the night they should continue to use a positive pressure ventilaton. Pacing more than 12 – 15 hours per day is not recommended because of the risk of neuromuscular fatigue.
Patients who need ventilatory support only during sleep time benefit also from the smaller pacing device, thus facilitating mobility during vacation, camping with school mates, etc.

Is it possible to perform pacing without tracheostomy?

It is possible to remove the tracheal cannula in older children. In young patients – less than six years of age – pacing in combination with a tracheostomy produces a greater stability of tidal volume, oxygen saturation and end tidal pCO2. Closure of the tracheostomy in this young group might be complicated by a high risk of upper airway collaps during sleep. Between the age of  6  and 12 years successful weaning from the tracheal cannula is more likely, but it should be tried only with careful observation and monitoring in specialized centers. 

 

What are the risks related to the pacing system?

The implantation of  the pacing system needs bilateral thoracotomy (opening of the ribcage), general anaesthesia and postoperative treatment, which implies general risks related to these procedures.
Pacer malfunction is possible and is mainly caused by an elevation of the pacing threshold, which can occur during an infection. Very rarely a local infection around the implanted system can occur.

pacing diaframmatico
What are the most frequent technical problems?

Within a year the external antenna can break, which can be managed by changing the antenna.
A couple of new spare antennas should always be at home.
After ten to fifteen years following implantation a defect of the implants may occur. Most frequently it is a break or an insulation defect of the wire between receiver and electrode. This problem needs a reoperation, which should be performed in a specialized center.

 

What should be monitored at home during pacing?

Continuous monitoring of oxygenation (pulseoximetry, SpO2) is mandatory during sleep. If possible end tidal or transcutaneous pCO2 should also be monitored, especially during respiratory infection. Both parameters should be kept in the normal range (above 95% SpO2 and between 30-45 pCO2 mmHg) with a lower alarm limit for SpO2 of 90% and the upper alarm limit for pCO2 of 50 mm Hg.
Even more important than technical monitoring is the presence of a caregiver ( that may be a nurse, medical student or a highly trained non-medical person) who can help in an alarm situation.
In patients who use the pacer during daytime a periodical control o SpO2 in different states of activity should be done.

 

Does the phrenic pacemaker exclude or interfere with a cardiac pacemaker in the same patient?

Some patients with CCHS may require a cardiac pacemaker in addition to the phrenic pacer. In this situation it is important to implant a bipolar cardiac pacemaker to avoid interference with the monopolar phrenic nerve electrodes.

 

What is essential for successful phrenic pacing?

Essential for successful pacing is a highly qualified surgical technique during implantation and careful setting of the pacing parameters. Therefore surgery and follow up should be performed only in a centre with experience in phrenic nerve pacing. Annual in-hospital checks and evaluation of the pacing parameters are recommended.
The parents, the caregivers, and the patient himself should be trained how to deal with the pacing system. They can easily vary the respiration rate and the tidal volume according to the actual needs of the patient.
The goal should be to minimize the electrical stimulation stress to the phrenic nerves while providing optimal ventilation.

update: 12/01/2012


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