While positive-pressure devices use continuous positive airway pressure (CPAP) to increase functional reserve capacity, negative-pressure devices such as the Exovent simulate natural lung movements and do not require tracheal intubation.
"There are a number of medical reasons why use of negative pressure is beneficial, above and beyond the obvious benefit that the patient does not need to be anesthetized," Dr. Malcolm Coulthard of Newcastle University, UK, told Reuters Health by email. "As it supports a more natural breathing process, the risk of damage to the lungs is reduced and the way that it lifts the chest takes pressure off the heart, allowing the heart to function more effectively."
"While we believe this treatment could benefit many patients," he said, "it could be particularly important for those that are unable to tolerate positive-pressure non-invasive techniques such as CPAP."
"Negative pressure breathing support is not only relevant for COVID but also many other lung diseases," he noted. Because more than 800,000 children under age five die from pneumonia every year, the team is developing a "very low-cost" pediatric system for global distribution in low-and middle-income countries (LMICs).
"A further advantage (for) LMICs is that smaller quantities of oxygen are required to treat patients than conventional positive-pressure alternatives," he added. "A lack of oxygen is a frequent problem in LMICs, and has even been a concern in richer nations, including the UK."
As reported in Anaesthesia, the Exovent chamber consists of a base fitted onto a hospital bed and a removable top that fits over a patient's torso using neck and hip seals. Flexible hoses connect a pump to the base, and a control unit allows pressure adjustment around the torso. A healthcare provider can observe the torso through a window and access it via portholes that seal around the provider's arms.
Using various negative-pressure settings, six healthy development team members tested the device in the supine position, and three tested it in the prone position. Although continuous negative extra-thoracic pressure did not change tidal volumes from baseline levels, participants' functional reserve capacity increased by a mean of 1.1 ml/kg/cm H2O.
The combination of negative-pressure ventilation and negative end-expiratory pressure produced effective ventilation; resting tidal volume was exceeded by applying -4 cm H2O of extra-thoracic negative pressure.
None of the volunteers had ventilator dyssynchrony and all reported that the experience was comfortable. Nurses reported the chamber could be positioned and moved quickly by two people. Dr. C. Nataraj, Director, Villanova Center for Analytics of Dynamic Systems at Villanova University in Pennsylvania, commented in an email to Reuters Health, "There are clearly some advantages to the Exovent system...It is much less complicated than typical forced ventilation systems. The patient can be awake, eat and generally be 'in control.'"
"The noninvasive nature of the proposed system is certainly a significant advantage, provided of course it is equally effective," he said. "Dyssynchrony can be an issue with typical positive-pressure systems (but) is not an issue at all with the Exovent system described. Also, portability seems to be solved here and removes one of the disadvantages of Exovents."
"Weaning the patient off the ventilator is not addressed in the paper," he noted. "This is an issue that has to be handled carefully with modern positive-pressure ventilators, especially when the patient has been on the ventilator for a long time. Given the noninvasive nature of the Exovent, I would presume that this becomes easier."
"In general, the proposed system is potentially a useful innovation which will find niche applications, for example, for patients to use at home," Dr. Nataraj concluded.
The system will likely be available toward the end of 2021 in the UK and probably not until 2022 in the US, after FDA approval, according to Exovent CEO Ian Joesbury.
The Exovent development group is a UK charity formed in response to the COVID-19 pandemic.
SOURCE: https://bit.ly/3sW4oTq Anesthesia, online January 19, 2021
By Marilynn Larkin
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