Phrenic Nerve Stimulation

Phrenic Nerve Stimulation (=electrophrenic respiration, = diaphragm pacing), is the rhythmic stimulation of the diaphragm via electrical impulses, resulting in respiration for patients who would otherwise be dependent on a mechanical ventilator.

Phrenic Nerve

The phrenic nerve is a nerve arising from the cervical region of the spinal cord that supplies movement to the diaphragm and some sensation to the chest and upper abdomen. The major function of the phrenic nerve is to contract the diaphragm, a crucial step in the respiratory process. The left and a right phrenic nerves follow different paths, though they both begin in the C3, C4, and C5 segments of the spinal cord.

Indications for Phrenic Nerve Stimulation

Phrenic nerve stimulators are indicated in patients with “partial or complete respiratory insufficiency” and work only in a patient having “an intact phrenic nerve and diaphragm”. If the spinal cord is not functioning; i.e., the cell body is dead, then a phrenic electrical stimulator is not effective. Thus, the stimulation of the phrenic nerve can not contract the diaphragm. If the C3-C5 area of the spinal cord is intact, the phrenic nerve may often be stimulated to contract the diaphragm. Thus, common indications for phrenic nerve stimulation include patients with spinal cord injury, central sleep apnea (ie, Ondine's curse), and diaphragm paralysis.

Surgical Technique

The surgery is performed by placing an electrode around the phrenic nerve, either in the neck, or in the chest. This electrode is connected to a radiofrequency receiver which is implanted just under the skin. An external transmitter sends radio signals to the device by an antenna which is worn over the receiver.
For the cervical placement, the phrenic nerve is approached via an incision slightly above, and midline to, the clavicle. The phrenic nerve is then isolated under the scalenus anticus muscle. For the thoracic surgical technique, an incision is made over the 2nd or 3rd intercostal space. The electrodes are placed around the phrenic nerves alongside the pericardium.

The Devices

There are currently two commercially distributed phrenic nerve stimulators made by Avery Biomedical Devices, Inc. (USA) and Atrotech OY (Finland). The Avery device (“Mark IV Breathing Pacemaker”) is distributed worldwide.

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