What trade-offs to make in a low-cost ventilator design? Ask the doctor.

Working with doctors, a team from MIT has added a mechanical arm to an Ambu-bag, eliminating the need for a manual operator. The goal: a low-cost emergency ventilator.
Working with doctors, a team from MIT has added a mechanical arm to an Ambu-bag, eliminating the need for a manual operator. The goal: a low-cost emergency ventilator. (MIT)

In the wake of a growing number of Covid-19 hospitalizations, health care facilities will be facing a critical shortage of ventilators. In response, some of the world’s most gifted, competent engineers at MIT, the University of Minnesota, and Vanderbilt University are pursuing the development of open-source, low-cost ventilators that can be brought to market quickly. The idea is to make the designs available to the public so that anyone can build them.

In essence, the concept for the designs came from a common starting point: Take a simple design—a manually-operated bag-valve mask (known as a BVM or Ambu-bag) and figure out a way to automate it.

MIT’s team, called MIT E-Vent, is using as its reference a design detailed in a 2010 paper, presented at the Design of Medical Devices Conference, titled “Design and Prototyping of a Low-cost Portable Mechanical Ventilator.” The low-cost design is based on a conventional bag-valve mask, employing a mechanical cam arm to eliminate the need for a manual operator.

A team at the University of Minnesota is pursuing a design, called the Coventor, based on a bag-valve mask that uses an electric motor that turns a crank that pushes a piston up and down. Two weeks ago, a prototype proved successful in a trial run.

Vanderbilt University’s design similarly involves an Ambu-bag, retrofitted with a mechanism to apply the necessary squeezing action. The first prototype consisted of nylon webbing wrapped around an Ambu-bag attached to the crank arm of a windshield wiper motor to apply the repetitive squeezing force

In all three cases, the basic engineering challenge is to take a low-cost design and figure out an economical way to eliminate the need for an operator.

But that’s not the end of the story: A low-cost ventilator will ultimately need specific performance characteristics and features—the very blueprint of any product design—to be safely used in a clinical setting. And determining what those are will require the practical, real-world experience and medical know-how of doctors.

To that end, the three teams consist of a mix of engineers and doctors, bringing together the best technical and medical expertise to bear on the issue.  

MIT Mechanical Engineering Professor Alexander Slocum, one of the authors of the MIT paper on a low-cost mechanical ventilator, stressed that no engineering team can come up with a low-cost ventilator design without specific performance requirements (other than cost) and be effective. “Which is why we work with doctors on the problem and where we post [to the website MIT E-Vent] as we learn,” he noted in an email response.

From that learning is emerging a more detailed set of specifications, which the team is sharing with others who may be seeking to manufacture a low-cost emergency ventilator.

For example, the website states that, “Any low-cost ventilator system must take great care regarding providing clinicians with the ability to closely control and monitor tidal volume, inspiratory pressure, bpm (breaths per minute), and I/E ratio, and be able to provide additional support in the form of PEEP, PIP monitoring, filtration, and adaptation to individual patient parameters. We recognize and would like to highlight for anyone seeking to manufacture a low-cost emergency ventilator, that failing to properly consider these factors can result in serious long-term injury or death.”

In a press release on Vanderbilt University’s website, Robert Webster, Professor of Mechanical Engineering, described why his colleagues added sensors and controls to the design. “This was the result of a lot of conversations with doctors where it became clear that a pressure sensor with an alarm on it for too-high or too-low pressure was essential to the design,” noted Webster. “This is something we would not have known without having many Vanderbilt physicians involved in the project.”

The teams anticipate it will be an iterative process and the concepts will evolve, as doctor’s feedback from early tests is incorporated into the designs.

Many engineers with specific areas of expertise may be interested and wondering how they can contribute to these efforts. Slocumb offered some very good advice: “Stay isolated and do not spread it. And when you see a design on-line, offer constructive peer review.“

Some areas seeking input:

MIT Emergency Ventilator

GitHub open-source ventilator project

Easily manufactured, open source, low-cost ventilator prototype for COVID-19 patients (Reddit post)