New negative pressure ventilator requiring less human resources developed to fight COVID-19

A new negative pressure ventilator that could provide additional treatment options for patients with respiratory failure, including those with COVID-19 – and whose design can be easily adapted to developing countries – was created by a team including anesthesiologists, nurses and engineers. Details of the new exovent system – which is similar in design but much smaller and easier to use than devices used to help treat polio patients in the 1950s – are published in Anesthesia.

Using this system would provide more comfort for patients, who would not need to be asleep or have an artificial airway in place, although the authors make it clear that a clinical trial is needed to test it. completely. After closely monitoring patients early on, the system would also mean less nursing care and could be used anywhere in the hospital, and potentially even at home. Staffing requirements for the new system would generally be much lower than for today’s typical intensive care unit ventilators, and lower than for other non-intensive positive pressure systems for the equivalent severity of illness.

Negative pressure devices lower the pressure outside the body to allow lung tissue to expand and function in a way that resembles normal breathing, while positive pressure devices such as conventional ventilators and Continuous positive airway pressure (CPAP) systems in use today push air into the lungs under positive pressure. Most research on negative pressure devices had been abandoned since the 1950s, as positive pressure devices had become much smaller, cheaper, and more convenient.

The exceptional task force formed in March 2020 in response to the COVID-19 crisis, inspired by UK government calls for rapid innovation to tackle the challenge presented by SARS-CoV-2. The team is made up of anesthesiologists, critical care consultants, nurses, medical clinicians, engineers, academics, scientists and manufacturers. This initiative was not part of the UK Ventilator Challenge, as this project encouraged innovation only for positive pressure devices.

“The exovent team focused on exploring the benefits of negative pressure ventilation, based on lessons learned from almost 100 years of using negative pressure ventilation, especially during the polio epidemic. 1950s, ”says co-author Dr Malcolm Coulthard of the Translational and Clinical Research Institute, Newcastle University, UK.

Using negative pressure is much less intrusive and is much more like normal breathing than positive pressure ventilation through a tube inserted into the trachea, or giving CPAP through a tight fitting face mask. The exovent system is non-invasive, which means that patients do not need to intubate their trachea, so they do not need to be anesthetized and oxygen can be given in the form of a hand mask. normal oxygen or nasal pins rather than a high-flow oxygen machine that pressurizes hospital oxygen supplies Patients remain conscious and can take food and oral medications and talk to loved ones on the phone .

The exovent chamber consists of a base mounted on a standard hospital bed that contains its own mattress section and a removable top that fits over the torso with neck and hip joints (see link to the photos below). A self-contained pump unit is connected to the base by flexible hoses and a control unit allows the pressure to be adjusted around the torso. The subject’s torso can be observed through a window and accessed through portholes that seal around the arms of the healthcare professional. Thin neoprene neck and hip joints are loosely fitted to the person before the chamber is put on and then adjusted.

Tests were performed on six healthy adult volunteers who are members of the development team in the presence of three senior anesthetists. All subjects were tested supine (face up) and tilted slightly up, while three were also tested supine (face down). Various negative pressure settings were tested and spirometry (lung performance) readings recorded. These showed that the exovent was able to provide both increased lung expansion to people breathing spontaneously and powerful ventilation to fully support people’s breathing, using only moderate negative pressures.

Nurses reported that the exovent chamber could be positioned and removed quickly by two people. They noted that the window and portholes would allow them to safely monitor and care for their patients, despite inevitably reduced direct access to their torso. Supine, the subjects’ heads could be positioned easily to allow view of the larynx for tracheal intubation, should it become necessary, without having to remove or adjust the neck seal. For patients progressing to intubation, it probably wouldn’t be necessary to keep them in the exovent (although it would be easy and safe to do so) – and in an emergency intubation, it wouldn’t be necessary. to delay the exovent has been removed.

The volunteers all found the bedroom comfortable, and in particular reported that the neck and hip joints were flexible and easy to adjust, and that they could intentionally break them to stretch their arms or touch their face without affecting significantly the stability of the pressure of the chamber. .

Importantly, all test subjects felt “in control” knowing that they could immediately release the vacuum by opening a large space under one of the joints if they wanted. When the ventilation mode was used, subjects all allowed the exovent to resume breathing without feeling any urge to “fight” it or feel unnatural or uncomfortable, and described the sensation as relaxing; a participant fell asleep within minutes.

“We are really excited to unveil this rescue system which is a cutting edge reinvention of pre-existing technology,” says exovent CEO and article co-author Ian Joesbury. “Since the patient does not need to be sedated, this opens up alternative treatment options that may allow more patients with COVID-19 to be treated outside of intensive care.”

It is estimated that the UK version of the exovent will cost around £ 8,000 GBP (US $ 10,496, € 8,856), which is considerably cheaper than existing positive airway pressure devices, which cost around £ 15,000 for CPAP and over 30,000 £ GBP for intensive care ventilators. It is also estimated that a cheaper global version of the exovent could be produced for less than £ 500 (US $ 652, € 550).

The authors add: “The anticipated advantages of the exovent over positive pressure ventilators, which may be particularly relevant in low- and middle-income countries, include the fewer resources required to ventilate conscious patients and the potential for greater oxygen conservation, since oxygen should only be supplied to patients directly through a face mask or nasal pins when needed, rather than the continuous supply of oxygen required for positive pressure systems. “

They explain that because it is so much less invasive and so much easier to do than PPV, the threshold for exovent use when it becomes available will be much lower, and many more patients will be eligible for therapy. Although hospitals in low- and middle-income countries have conventional ventilation equipment for intensive care, the resources to (a) intubate, paralyze, and sedate them if necessary, and (b) manage them during treatment. unconsciousness, which means intensive care, intravenous or tube nutrition, skin care, etc., are too rare to make intensive care ventilation accessible to a very small number of individuals. The authors explain: “It’s about personnel rather than equipment, and the exovent would be much easier and cheaper to use.”

Thanks to the investment of over £ 1million in volunteer time from the exovent team, rapid development and prototyping by Marshall ADG, and partnership with Warwick Manufacturing Group (WMG) High Value Manufacturing Catapult, the system is now ready for formal assessment and approval. The authors plan to submit the design to the Medicines and Health Products Regulatory Agency (MHRA), which regulates medical devices in the UK, and hope to receive approval by mid-2021.

Provided by AAGBI