Diaphragm Pacing Periprocedural Care

Updated: Aug 14, 2017
  • Author: Shabir Bhimji, MD, PhD; Chief Editor: Zab Mosenifar, MD, FACP, FCCP  more...
  • Print
Periprocedural Care

Preprocedural Planning

Unlike stimulation of the heart, stimulation of the diaphragm is a long process that requires training of the muscle. A single stimulus usually is not sufficient to produce a contraction: a series of stimuli (ie, a pulse train) is needed to produce a summed contraction. Key aspects of pulse-train stimulation that must be coordinated include the number of pulse trains delivered per minute (rate) and their duration, as well as pulse amplitude, width, interval, and frequency. The muscle contractions usually last only for the duration of the pulse train.

Research in the laboratory has shown that pulse-train stimulation of the diaphragm for weeks to months can result in an orderly sequence of positive ultrastructural and biochemical changes. The muscles slowly develop increased blood supply; enzyme efficiency improves; and mitochondrial capacity for oxidative phosphorylation is enhanced. These changes reflect the transformation of fast glycolytic and slow oxidative muscle fibers to entirely slow fibers, which allows the oxidative muscle fibers to perform sustained mechanical work for prolonged periods.

This conditioning is essential to prevent fatigue in skeletal muscle. Although with normal respiration, the diaphragm is at work every second, 24 hours a day, the pattern of recruitment of individual nerve fascicles and motor units (usually hundreds of fibers) is such that not all motor units are active during an individual breathing cycle; this pattern allows the fatigued muscles to recover. With pulse-train stimulation of the diaphragm, it is likely that most nerve fibers and muscle groups are stimulated strongly during each breath.

These adaptive changes are required for successful acceptance of pulse-train stimulation. However, it should be remembered that in individuals with quadriplegia, the diaphragm may have atrophied from disuse during mechanical ventilation, in which case it must be gradually restored to a functional state. This may not be possible in some patients. [1, 2, 3]

Next:

Equipment

Both the Synapse Biomedical NeuRx DPS RA/4 and the Avery Biomedical Mark IV Breathing Pacemaker devices are available for use in the United States. The key major difference between the two is that the Mark IV Breathing Pacemaker simulates the phrenic nerve and the NeuRx DPS stimulates the diaphragm. The latter is only available for humanitarian use in patients with ALS, and the cost may not reimbursed by Medicaid or Medicaid services. The Avery device is approved and reimbursed by Medicaid and Medicare services.

The diaphragmatic pacing systems have both external and internal components:

  • The internal electrode is not placed on the phrenic nerve but either around it or just adjacent to it. The electrode is then hooked to a small receiver that is inserted under the skin of the upper chest.
  • The external transmitter box connects to an antenna that is anchored on the skin surface, just above the implanted receiver.
  • The transmitter is battery operated and has adjustments for respiratory rate, pulse-train duration, pulse duration, amplitude of current, and pulse frequency. In the majority of patients, the surgeon or pulmonologist will only adjust the respiration rate of current amplitude.

The electrode is only half-cuffed and is applied only to one side of the nerve. To prevent injury to or entrapment of the nerve, circumferential application of the electrode around the nerve is not recommended. So far, no difference in nerve activation has been observed between placing an electrode on the side and placing it circumferentially.

Previous
Next:

Patient Preparation

Before the procedure is begun, it is essential to check the viability of the phrenic nerve at least 12 weeks after the injury. This can be done by stimulating the phrenic nerve in the neck and assessing diaphragmatic movements either with ultrasound or fluoroscopy. If there is weak diaphragmatic response to phrenic nerve stimulation or if there is unilateral movements, the procedure may not be indicated.

 

Previous