Lecture 19: Transvascular Diaphragm Pacing Flashcards
What patients are a candidate for temporary assisted ventilation?
critically ill patients in intensive care
patients undergoing surgery under general anesthesia
vs patients with SCI who need it permanently
Could VIDD be Prevented by Pacing the Phrenic Nerves in the ICU? What could be the benefits? How does it assist the heart?
Induce diaphragmatic contractions to
1. maintain diaphragmatic endurance
2. provide exercise and strengthen an already weakened diaphragm
3. provide negative pressure ventilation, thereby replicating a more physiological respiratory pattern
• eliminate VIDD and Ventilator-Induced Lung Injury
- improve clinical outcomes in ICU
- shorten hospital stay
- significantly reduce healthcare costs
- simple to place
- easy to use
- temporary and easily removable
- Protect the diaphragm
- Protect the lungs
- Assist the heart (venous return is assisted by pumping by the diaphragm)
- Reduce nosocomial infections,
pneumonia - Accelerate weaning
- Liberate patients from mechanical ventilation
- Reduce mortality rates
- Improve survivor’s quality of life
base of lungs are better ventilated during paced breaths
What % of patients can wean on and off ventilator?
70% manage to wean
30% don’t manage to wean and become dependent on ventilator
Describe transvascular stimulation
Minimally invasive nerve stimulation method and apparatus: intravenous catheter outfitted with electrodes to pace nearby nerves.
Feed electrodes into left subclavian vein and slightly into superior vena cava to pace both left and right phrenic nerves. Apply bipolar stimulation and adjust field intensity to selectively stimulate phrenic nerve only (no vagal which acts on the heart)
Ensure catheter length is appropriate to reach both nerves but not enter the heart. electrodes are rotated slightly on catheter to account for location of left and right phrenic nerve
How can you tell where the phrenic nerve is?
During surgery, advance a search electrode into the left subclavian vein and stop every cm and stimulate. Observe if there is a twitch in the abdomen and watch the trace of ventilator air flow to see when phrenic nerve activates diaphragm. Measure the minimum value threshold current for phrenic nerve activation and plot against cathode electrode depth into vein (cm).
observe a parabolic curve indicative of proximity to phrenic nerve.
Place electrodes where current is the lowest.
How does diaphragm pacing assist the ventilator when used simultaneously?
mechanical ventilators use positive pressure. this can cause lung injury
diaphragm pacing provides negative pressure to inflate lungs more normally, reducing peak ventilator pressure needed to inflate lungs
timed to pace/stimulate before next breath
you can time the onset of stimulation to start before, at the same time, or after the next ventilator breath
What is the role of the therapist in the use of the lung pacer?
Describe some disturbances to the closed loop system
decide how hard to stimulate diaphragm. has a dial, pick a value (10% effort, 25%, etc.) [input]
can be closed loop as there are sensors [feedback] to measure flow of air in response to diaphragm contraction.
don’t want full blast cause you can fatigue diaphragm and have too much negative pressure. overstimulation –> less and less force
disturbances: change posture of patient,
catheter can jump a bit with heart beat and breathing, effecting pacing, diaphragm fatigue, electrode displacement
Describe all of the components of the lung pacer
- neurostimulation catheter placed into left subclavian vein that can selectively stimulate each phrenic nerve. The lumen can also be used as a central line catheter
- airflow sensor: single use component that connects to the breathing circuit
- therapy control unit: Automatically selects best pacing electrodes. Paces the diaphragm in synchrony with
ventilator-delivered breaths
* Agnostic to ventilator makes and models
How did they measure diaphragm thickness in ICU patients?
What did they find when measuring diaphragm thickness with assisted-control ventilation with pressure-support ventilation?
ultrasonography
5% loss in diaphragm thickness per day with assisted-control ventilation
1.5% increase in diaphragm thickness per day with pressure-support ventilation
pressure support: they breathe a little on their own but with ventilation help
diaphragm thickness declines with assist control ventilation then increases with pressure support ventilation
How did lungpacer prove the following objectives:
1. phrenic nerves could be paced in synchrony with MV
2. ability to reduce peak positive pressure in airway
3. protect diaphragm from disuse atrophy
4. preserve diaphragm endurance
- initial trials in sedated pigs demonstrated this. so did the first in-human trials
- in pigs, they paced every 2nd ventilated breath and measured airway pressure and tidal volume. observed a 20-30% decrease in peak positive pressure while maintaining tidal volume. high peak pressure –> lung injury
- histological comparison showed that pacing reduced ventilator induced muscle fibre atrophy
- performed a tolerance endurance test. showed that all MV + paced pigs enduranced the 8 minute test while 50% of MV only pigs failed test after 8 minutes due to low O2 saturation and high CO2 levels
What did the first in-human clinical studies of lung pacer dmeonstrate?
- successful live catheter insertion and placement
- absence of device or procedure related adverse events
- bilateral phrenic nerve stimulation
- diaphragm contraction in synchrony with mechanical ventilation
- reduction in airway pressure
In the first in-human lung pacer study, some patients’ phrenic nerve(s) could not be stimulated - what was the proposed reason?
Possibly due to a layer of fat surrounding vein not allowing for the phrenic nerve to be stimulated. Perhaps if stimulation amplitude was increased, could stimulate phrenic nerve
Describe the current standard of care with a graph that uses days in ICU as the x axis and diaphragm strength in m(uscle thickness)^2 as the y axis
if you let a person become dependent on ventilator, thickness and strength of muscle declines very quickly within a week of intubation
can decline below minimum strength required for independent breathing (~60?). current standard of care: discontinue sedation and start exercise program - diaphragm will gradually recover strength and endurance for independent breathing
What are the 2 clinical strategies lung pacer could be used for?
- rescue from VIDD - Restore diaphragm strength and endurance by pacing supported exercise in patients who failed to wean in at least two Spontaneous
Breathing Trials (theory: only 30% fail to wean; lets see who fails to wean and use the lung pacer)
* resulted in 11/28 ventilator free days - protect from VIDD - Mitigate diaphragm muscle atrophy and lung injury in adult critical care patients
with Acute Respiratory Failure who are expected to require IMV for at least 96 hours and are at high risk of failing to wean. early pacing before being deemed medically ready to start wean.
* resulted in 18/28 ventilator free days
as compared to vacation from sedation, 3/28 days of ventilation free
Describe the results in the RESCUE 2 trial involving lungpace + standard of care vs SOC alone
Lungpacer therapy improves diaphragm strength by
an average of 246% compared to SoC alone, as measured by improvement in
Maximal Inspiratory Pressure (MIP)
The Lungpacer therapy group also showed a strong positive trend in proportion of MV patients weaned and reduction in average MV duration, as compared to SoC.
