Phrenic Nerve Pacing and Diaphragm Pacing
- Although chronic positive-pressure mechanical ventilation is life-preserving, it not only carries the stigma of the ventilator tubing for patients but also leads to posterior lobe atelectasis, pneumonia, barotrauma, and respiratory complications, which are the leading cause of death among spinal cord–injured patients on ventilators and morbidity for all patients.
- Patients requiring long-term ventilator support due to spinal cord injury or congenital central hypoventilation should be offered diaphragm or phrenic nerve pacing.
- Phrenic nerve pacing or diaphragm pacing requires a functional diaphragm and an intact phrenic nerve to be successful. Diaphragm pacing can facilitate recovery of injured nerves.
- Failure to wean from mechanical ventilation is in part due to rapid onset of diaphragm atrophy, barotrauma, posterior lobe atelectasis, and impaired hemodynamics, all of which would be improved by maintaining a more natural negative chest pressure with temporary diaphragm pacing.
- Diaphragm pacing can improve patient’s ventilation with unilateral diaphragm dysfunction and allow recovery of diaphragm function.
Chronic respiratory insufficiency or the inability to independently breathe has a profound impact on the affected individual, his or her family, and the health care community as a whole. The treatment of chronic respiratory insufficiency has been traditionally performed with positive-pressure ventilation through a ventilator. Chronic mechanical ventilation, although life-saving, is expensive, invasive, disruptive, and unreliable at times.
Mechanical ventilation is associated with functional limitations and psychosocial consequences. The tubing of the ventilator hinders mobility by increasing the difficulty of dressing and transferring patients. Patients are limited to spaces and places that can accommodate a portable, electrically driven mechanical ventilator and suction device. Ventilator-assisted individuals need a caregiver who is able to use and troubleshoot these devices throughout the day as well as during transport. Noises from the ventilator can interfere with hearing and concentration. Typical speech on a ventilator has long pauses between phrases, short phrases, and poor voice quality. These changes in voice can make clear communication difficult or stressful. Ventilated patients feel more insecure, helpless, and dependent compared with nonventilated patients. Disruptions of sleep-rest patterns among patients with prolonged mechanical ventilation have been reported as common. In addition, mechanical ventilation increased feelings of isolation for both patients and their caregivers, In the field of spinal cord injury research, it is recognized that “improvements in respiration and elimination of ventilator dependence are extremely important to the quality of life and this topic should be at the forefront of research.”
Inherent complications of mechanical ventilation include infection, tracheal injury, and equipment malfunction. Ventilator-associated pneumonia is a common occurrence among patients with prolonged use of an artificial ventilator, and pneumonia is the most common cause of death after spinal cord injury., Tracheomalacia, tracheal stricture, and tracheal erosion or perforation are potential complications associated with prolonged use of an artificial airway. In some geographic regions, it is difficult to find skilled nursing care for mechanically ventilated patients. As shown during multiple natural disasters, the lack of electricity negatively affects patients on mechanical ventilation, because the batteries last only several hours, whereas the loss of electricity and availability of reliable generators can last months.
Electrical activation of the diaphragm muscle by either direct phrenic nerve stimulation or direct diaphragm motor point stimulation offers an alternative to mechanical ventilation. It can reduce many of the previously described problems associated with mechanical ventilation. The two main clinical indications for phrenic nerve or diaphragm pacing (DP) have been cervical spinal cord injuries and central hypoventilation syndromes. Although both of these conditions manifest in the individual’s inability to independently breathe, spinal cord injury involves the disruption of the signal pathway from the respiratory center in the brain to the respiratory nerves (primarily the phrenic nerves), whereas central hypoventilation syndromes generally involve a decreased respiratory drive. In the latter case, the signal from the respiratory center to the phrenic nerves is not generated or sent, although the conduction pathway to deliver the signal is intact.
The concept of using phrenic nerve stimulation to provide ventilatory support dates back to the 18th century. In the 1940s, Sarnoff and coinvestigators first demonstrated that ventilation could be maintained with percutaneous electrodes in patients with poliomyelitis. In the 1960s, Glenn and coworkers made significant technological advances that led to the development of modern phrenic nerve pacing systems. They developed an implantable electrode/receiver system that could be activated by radiofrequency waves generated by a power source external to the body. These investigators also accumulated a significant clinical experience that defined patient evaluation methods, surgical techniques, and safe parameters of stimulation resulting in optimal diaphragm conditioning via stimulation of the phrenic nerve.
In the 1980s, Mortimer and colleagues showed that the diaphragm could be directly stimulated at the motor point to provide ventilation. By the late 1990s, the device had been refined for the initial human studies. Because muscle motor point electrodes can be used for short periods and then removed, Onders and colleagues began investigations for temporary use in other groups of patients.
For a phrenic nerve or diaphragm pacing device to be effective in recruiting diaphragm muscle that can provide ventilatory support, the phrenic nerve must be able to provide conduction pathways through the muscle. Therefore, both the lower motor neurons in the spinal cord and the phrenic nerve must be intact to avoid muscle denervation and to be able to stimulate the muscle at acceptable levels.
A thorough assessment of phrenic nerve function is performed in all patients for whom phrenic nerve or diaphragm motor point pacing is contemplated. Many patients with tetraplegia have sustained injury to the phrenic motor neurons in the spinal cord and/or phrenic rootlets. If phrenic nerve function is absent or significantly reduced, phrenic nerve or diaphragm pacing is not undertaken. Phrenic nerve function is assessed both by measurements of phrenic nerve conduction times and by fluoroscopic evaluation of diaphragm movement during phrenic nerve stimulation as has been described. In 2021, Onders et al in an observational report reviewing 175 patients with phrenic nerve conduction studies showed that phrenic nerve conduction studies do not adequately predict diaphragm pacing success or failure. Utilizing phrenic nerve conduction studies as a criterion to undergo diaphragm pacing could eliminate patients who would benefit from diaphragm pacing. The most reliable way to verify the integrity of the phrenic nerve lower motor neuron is by direct stimulation at the time of laparoscopy.
In this chapter, the two basic surgical techniques used to provide diaphragm movement, phrenic nerve pacing and diaphragm motor point pacing, are reviewed. The indications and results for appropriate patients with chronic respiratory insufficiency are then reviewed.
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