Breathe again: Diaphragm stimulation after prolonged mechanical ventilation

For the past two years, the Greifswald University Medical Center has been collaborating in an international study in which a therapy using electrostimulation of the diaphragm is designed to wean patients off artificial respiration. The innovative system aims to achieve faster independence from the ventilator.

Prof. Ralf Ewert, head of the Pneumology, Infectious Diseases and Weaning Center at Greifswald University Medical Center tells MEDICA-tradefair.com how the system works.

Prof. Ewert, which patients benefit from diaphragmatic stimulation and why?

Prof. Ralf Ewert: The process is aimed at patients in intensive care who need respiratory support – minimally invasive or non-invasive ventilation. This means, the device mechanically supports the patient’s respiratory function. While this is a life-sustaining treatment, the drawback is respiratory muscle weakness due to lack of training. As a result, the diaphragm loses strength and functionality, which is a common problem with patients undergoing mechanical ventilation. The longer patients are ventilated, the more training they need to restore independent breathing.

How can the AeroPace neurostimulation system help in this setting?

Ewert: We are testing a diaphragmatic stimulator device, also called diaphragm pacing system. It comprises a console that sends electrical impulses and a catheter that transmits the pulse through the vascular part of the lungs to the nerves that activate the diaphragm contraction. This trains the diaphragm, our largest muscle of respiration. Many people might know the system from their workouts because it somewhat resembles EMS training devices. The only difference is that the current is not delivered via electrodes on the skin, but through the catheter that delivers the current as it is inserted into a large vessel in the thorax. The phrenic nerves are stimulated via a catheter in the vessel. That is the basic principle.

Do you know what the stimulation feels like?

Ewert: In fact, we know precisely what it feels like because we typically train the patients after they regain consciousness. That means we can ask them if they experience any discomfort. Besides, you can actually see the applied impulse and the subsequent diaphragm contraction. You can feel it when you place your hand on the thorax. And you can also see it on the ventilator. The tidal volume of each breath increases significantly as the electrical stimulation causes the diaphragm muscles to contract, prompting maximum deep inspiration. That is the goal of stimulation. The person who trains feels the muscle contraction and not the actual current flow. He or she feels a slight pull. However, if this gets too uncomfortable, we can reduce the stimulation intensity.

How have you helped patients to regain unassisted breathing in the past?

Ewert: Through respiratory physiotherapy. We have a special ward that’s dedicated to assist with this process. We call it the Weaning Center. Patients are trained to breathe on their own for extended periods of time – predominantly by gradually reducing assisted ventilation. The idea is to not be completely exhausted by the effort, which means we train patients until their diaphragm is strengthened again. In the first few days, patients might only breathe on their own for a minute or two, but these time intervals gradually increase over weeks and months of training. Thanks to diaphragm stimulation, we can intensify this training and wean patients off the ventilator much faster.

How much faster?

Ewert: This is not the focal point of the current scientific study, although statistics already suggest a decrease of 1.4 ventilator days for all people tested worldwide. On our ward here in Greifswald, long-term ventilation patients typically take 35-40 days to be weaned off from mechanical ventilation. We believe we actually gain several days through this intensive breathing muscle training, meaning more than the statistical 1.4 days. Diaphragm stimulation therapy is particularly effective in our patients, many of whom have been COVID-19 affected. That is why we treat as many of them as possible in our group.

You have been involved since the worldwide testing began two years ago. From your perspective, what are the advantages of the Canadian AeroPace neurostimulation system?

Ewert: For one, it affords us the technical possibility to intensify our training. It adds another valuable component to our overall concept of respiratory physiotherapy and mobilization measures. By collaborating with the manufacturer over the different stages of the research, we achieved several technical improvements, enhanced the device, and made it more practical. The catheter can now be placed by means of a connected ECG, eliminating the need for a chest X-ray. Whereas previously the catheter could "only" stimulate the diaphragm, it is now also suitable for infusing drugs and fluids in intensive care patients. The control unit has many automated functions that make it easier for medical staff to use AeroPace in a targeted and swift manner.

What are your hopes and goals for the future?

Ewert: Worldwide, the examination data of 175 ventilator patients have been recorded and evaluated in the study so far, 39 of them from Greifswald. Even though we are a small city near the Polish border, Greifswald University Medical Center is the leading study center worldwide for this new procedure. We have been able to gain extensive experience with electrostimulation of the diaphragm. From our perspective, the results to date are very promising. As we are currently in phase three of the clinical study necessary to receive medical device approval, I hope we will soon achieve clinical adoption of the approved system.