Diaphragm Pacing in Children: Update Course 2017
With Dr. Raymond Onders · StayCurrentMD
Educational content from recorded physician discussions — not medical advice. Talk to your (or your child's) care team about your situation.
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What the experts said
The diaphragm muscle atrophies faster than any other muscle; within 12 hours of mechanical ventilation, 50% of diaphragm muscle mass is lost and converts to type 2B (fastest) muscle fiber.
In the United States, 120,000 tracheostomies are performed annually for failure to wean in non-spinal cord injured patients, costing $64 billion per year for long-term mechanical ventilation.
75% of cervical spinal cord injuries require intubation at initial trauma, nearly 20% require tracheostomy, and 53% of trauma patients go to rehab on a ventilator.
Home mechanical ventilation costs approximately $170,000 per year per patient and requires two ventilators plus a backup generator.
The intramuscular electrode system places two electrodes in each hemidiaphragm (anterior and posterior) to achieve diaphragm contraction and breathing.
An intact phrenic nerve and phrenic motor neurons are required; if a nerve is cut, the muscle will die off (similar to brachial plexus injury causing hand atrophy).
The device is percutaneous (not fully implantable) due to cost constraints, uses a 500-hour battery life, and can be programmed to measure tidal volume (target 5–7 cc/kg per breath).
The system modulates the breath with a gradual ramp-up to mimic natural diaphragm contraction, preventing aspiration from sudden hiccup-like breaths seen with direct phrenic nerve pacing.
In the first 20 pediatric patients (ages 2–17, average 9 years on ventilator), 50% achieved full-time pacing (24 hours/day), 4 patients pace only during daytime, and some are still weaning.
Two unrelated deaths occurred (recurrent sepsis after brain stem tumor recurrence, heat stroke in a child with autonomic dysfunction), and two patients discontinued pacing (brittle bone disease with recurrent rib fractures, chronic skin reactions).
If diaphragm stimulation fails at surgery, the child will never get off the ventilator using accessory muscles alone.
In a multi-center adult trauma trial, early implantation (rather than waiting one year) achieved 82% complete ventilator independence.
The implanted electrodes can read diaphragm EMG, allowing detection of burst activity (spontaneous breathing effort) and differential muscle fiber types to monitor recovery.
Functional electrical stimulation (FES) may have a trophic effect on injured spinal cord recovery; distal muscle stimulation sends signals to the brainstem that may facilitate neuroplasticity.
36% of early-implant patients had electrodes removed after recovering natural breathing, demonstrated by EMG burst activity.
The 16-year-old wrestler case was implanted at day 22 post-injury and extubated at day 24 without tracheostomy.
In Pompe disease, enzyme replacement therapy corrects muscle pathology but many children cannot wean from ventilators due to brainstem respiratory drive deficit (lack of diaphragm burst activity on EMG).
Diaphragm pacing in Pompe disease patients restores natural breathing by correcting abnormal neuro-respiratory neuroplasticity; patients on ventilators develop reliance on accessory muscles, and pacing retrains the brainstem.
SMA type 2 patients have intact phrenic motor neurons despite being considered a primary lower motor neuron disease; most become NIV-dependent by late teens/early twenties.
An SMA type 2 patient who aspirated during outpatient dental anesthesia and became trach-vented was weaned off the ventilator within one week with diaphragm pacing.
A second SMA type 2 patient completely dependent on NIV with PCO2 in the 60s is now off NIV with normal PCO2 after diaphragm pacing (now uses pacer only at night).
Early diaphragm pacing may eliminate the need for tracheostomy in appropriate patient groups.
In adult ICU trauma, identifying inability to pace the diaphragm prompts a shift from low tidal volume to high tidal volume ventilation, shortening ICU stay by stopping futile weaning attempts.
Minute ventilation is the primary parameter used to titrate pacing; tissue CO2 monitors exist but are not routinely used. One adult Ondine's curse patient over-ventilated to PCO2 of 20 after implantation.
Electrode removal is possible when patients recover natural breathing through neuroplasticity: multiple pathways exist from cerebral cortex and brainstem to phrenic motor neurons, and one pathway may recover function after spinal cord injury.
Electrical stimulation accelerates nerve recovery; there is a spinal cord device that flows electricity to promote faster nerve recovery.
Most ventilated patients, especially elderly, lose respiratory drive (abnormal neuroplasticity); diaphragm rehabilitation can restore this drive.
When phrenic motor neurons below a spinal cord injury are stimulated, muscle fiber converts from type 2B to type 1, motor neurons change size, and synaptic connections may re-establish (based on animal models).
Current implant centers include Gainesville, Cleveland (Onders), Mayo Clinic (one implant) in the US; internationally Vancouver Children's, sites in Germany, Spain, Israel, and Saudi Arabia.
Limited adoption is due to rarity of the condition and lack of advertising (nonprofit company with no marketing budget).
The older phrenic nerve stimulator (Avery system, available since 1969) has only been used in about 2% of eligible patients, with only two US sites (LA and Yale) still implanting children.
Percutaneous diaphragm pacing is possible via NOTES approach (electrodes placed through stomach at time of PEG) or under ultrasound guidance using a pleural effusion as an acoustic window.
Temporary electrode placement at time of open heart surgery (like temporary cardiac pacing wires) has been studied in an FDA IDE trial and received CE mark approval in Europe; FDA negotiations ongoing for approximately one year.
Temporary pacing has been used in 16 post-cardiac surgery patients for failure to wean, presented at Central Surgical meeting.
Future research includes injectable microprocessors in the carotid body to stimulate the brainstem and drive ventilation, similar to sympathetic/parasympathetic modulation.