Diaphragm Pacing by Phrenic Nerve Stimulation

Diaphragm Pacing by Phrenic Nerve Stimulation

Iris A. Perez, MD, FAAP, Sheila S. Kun, RN, BSN, MS, and

Thomas G. Keens, MD, FAAP

Introduction

•Diaphragm pacing is a mode of ventilatory support in which the patient’s own diaphragm acts as the respiratory pump.

•It is an alternative method of ventilating patients with congenital central hypoventilation syndrome, as well as those with high spinal cord (C1-C2) injury.

•It provides daytime ventilatory support for those who are dependent on a ventilator 24 hours a day, which allows for mobility and independence from the ventilator during the day.

•It can be the sole ventilatory support for stable patients who are ventilator dependent only during sleep, which permits tracheostomy decannulation.

•Although diaphragm pacing is only available at a few specialized centers, the primary care clinician should be aware of potential patients where pacing may be useful.

Components

•A diaphragm pacer system involves the following 4 components (Figure 117-1):

—Electrodes that are surgically implanted bilaterally on the phrenic nerves

—Receivers that are surgically implanted bilaterally on the abdomen or chest

—Antennae

—External battery-operated portable transmitter

• The external transmitter generates electric energy similar to radio frequency via an external antenna, which is placed on the skin over the receiver.

•The receiver converts the energy to electric current, which is then conducted to the phrenic nerve, stimulating diaphragm contraction.

Figure 117-1. Diaphragm pacer components are shown. An electrode is implanted on the phrenic nerve, which is connected via lead wire to a receiver implanted subcutaneously in the upper abdomen, with an external transmitter connected to an external antenna taped over the receiver. Note that these components are bilateral. From Kasi A, Perez IA, Kun SS, Keens TG. Congenital central hypoventilation syndrome: diagnostic and management challenges. Pediatric Health, Medicine, and Therapeutics. 2016;7:99–107.

Indications and Eligibility

•Because diaphragm pacing uses the patient’s own diaphragm as the ventilator pump, an ideal candidate must have intact phrenic nerves, normal diaphragm function, and little or no lung disease.

•Diaphragm pacing is contraindicated in those with phrenic nerve injury, diaphragm paralysis, obesity, and patients with conditions that require magnetic resonance imaging. Patients with a C3-C5 spinal cord injury may not be candidates if the phrenic nerve bodies have been injured.

•In obese patients, the high amount of adipose tissue increases the distance between the antenna and the receiver of the diaphragm pacer, resulting in increased variability in the signal received by the receiver.

•In 1 center, the mean age at diaphragm pacer implantation surgery is 9.6 years. For those who are dependent on a ventilator 24 hours a day, the diaphragm pacers can be considered in the toddler age range to allow for mobility.

Surgical Implantation

•Diaphragm pacers are surgically implanted on the phrenic nerves thoracoscopically.

•The pacers are tested intraoperatively, so neuromuscular blocking agents are not administered for the surgery.

•The diaphragm pacers are not used right away; therefore, the patients go back on their previous mode of ventilatory support after surgery.

Risks and Complications of Surgery

•Immediate postoperative complications after a diaphragm pacer implantation surgery are uncommon.

•The risk of atelectasis and pneumonia occurs because the lungs are collapsed during thoracoscopic implantation of the phrenic nerve electrodes. During the postoperative period, these risks can be reduced by optimizing airway clearance and upsizing the tracheostomy tube to minimize leak from the stoma and provide adequate tidal breaths.

•Most patients have the chest tubes removed at the conclusion of the surgery. However, persistent pneumothoraces that require the retention of chest tubes in the immediate postoperative period can occur in some patients.

•Patients undergoing the diaphragm pacer surgery are usually treated intraoperatively with antibiotics to decrease the risk of infection.

•The perioperative period is a vulnerable time for patients with congenital central hypoventilation syndrome (CCHS). They are extremely sensitive to the effects of central nervous system depressants and general anesthesia. When patients with CCHS receive sedating medications in the preoperative and postoperative periods, they must be connected to their ventilator.

•In 1 center, the mean hospital stay after diaphragm pacer implantation surgery is 5.7 days (maximum, 9 days), and the mean intensive care unit stay is 4.3 days (maximum, 9 days).

Initiation of Diaphragm Pacing

•At 1 center, diaphragm pacing is started 6–8 weeks after surgery to allow for healing. However, this timing may vary from center to center. Patients are admitted to the hospital to initiate pacing, where the settings are established and adjusted. Some centers may initiate pacing on an outpatient basis.

•On the night of pacing initiation, the pacers are turned on both sides, whether the patient is awake or asleep, with the goal of beginning to train the diaphragm. The patient is not receiving ventilation during diaphragm pacing.

• The patient is connected to continuous pulse oximetry and end-tidal CO₂ monitoring; the diaphragm pacer settings are adjusted to maintain oxygen saturation at pulse oximetry (SpO₂₎ in the desired range—for example, SpO₂ ≥95% and pulse oximetry and end-tidal CO₂ <40 mm Hg (the target range may vary among centers).

•Pacing is initially used for only 1–1½ hours during the night. After this time period, the patient goes back on the usual ventilatory support.

•The time on pacers is gradually increased by 30–60 minutes each week to train the diaphragm and prevent fatigue. This is usually done at home.

•In general, full pacing during sleep requires 2–3 months to establish. Once on full-night pacing with the tracheostomy open, if the patient does well for 3 months, a plan for decannulation can be considered.

Diaphragm Pacing Without Tracheostomy

•With proper patient selection, diaphragm pacing without tracheostomy can be achieved in patients with CCHS who require ventilatory support only during sleep. Sample criteria for diaphragm pacing without tracheostomy are listed in Box 117-1.

•A suggested protocol for tracheostomy decannulation is outlined in Figure 117-2 and Box 117-2.

Troubleshooting for Patients and Families

•If the diaphragm pacer malfunctions suddenly, this is most commonly unilateral.

•Most sudden unilateral pacer malfunction is caused by an external equipment problem.

•Be sure the battery on the nonworking side is good (this is shown by the battery power indicator on the pacer transmitter); if in doubt, change the batteries.

Box 117-1. Criteria for Pacing Without Tracheostomy

CCHS necessitates ventilatory support only during sleep .

The patient does not require daytime naps .

A stable medical course requires infrequent hospitalizations .

The patient does not require full-time ventilatory support during minor, acute respiratory illnesses .

The patient accepts that diaphragm pacing is not as secure a method of ventilation, and intubation may be required for serious illness .

CCHS, congenital central hypoventilation syndrome . From Diep B, Wang A, Kun S, et al . Diaphragm pacing without tracheostomy in congenital central hypoventilation syndrome patients . Respiration. 2015;89(6):534–538 . Copyright © 2015 Karger Publishers, Basel, Switzerland .

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