Why can’t a Resmed ASV BiPAP be used as a ventilator?



I use an adaptoservo ventilator at night, which really is just a BiPAP with different software. In fact, the machine looks identical to Resmed CPAPs, making me believe it’s just software differences.

Thousands of Americans use these devices.

It is designed to detect a lapse in breathing (in central sleep apnea, your brain forgets to tell you to breathe), and give you a puff to trigger your breathing reflex.

Couldn’t these be modified to function as vents?

In: Engineering

It depends very heavily on how the PAP is designed, and depending on its hardware, the answer is probably not.

A PAP is designed to provide, as you know, Positive Airway Pressure. So its whole job is to keep the pressure in your throat and trachea above standard atmospheric pressure. This helps keep the airway open and in operation. CPAPs maintain a single pressure, while BiPAPs have two pressure settings, one for inhaling and one for exhaling.

While PAPs are a member of the ventilator family, they’re not the same as an inpatient ventilator. The vents used in a hospital setting are designed to take over a patient’s breathing when, for whatever reason, the patient cannot breathe him- or herself. To do that, the machine needs to be able to deliver enough pressure to fill the lungs, not so much that it damages the lungs, and be adjustable to every patient’s lung volume and oxygen requirements (pressure and rate). Consequently, the hardware used to apply air pressure is different, and the firmware controlling the device is very different from that found in a PAP.

Could PAPs help people having difficulty breathing? Absolutely; they do it every day. Could they be used as mechanical ventilation to take over breathing from a patient in respiratory arrest? No. Not as they’re designed, and the modifications would be extensive, requiring a complete rewrite of the software, and even then the hardware isn’t really up to it.

So I suspect you actually asked the wrong question. The other answer here addressed the question you asked pretty well so I’ll leave that alone.

The question you probably wanted to ask is something like:
“Could a Resmed ASV BiPAP be used to supplement the number of available ventilators in the COVID crisis”
To which the answer is: No. PAP machines can aerosolize the virus, posing a risk for spreading the disease to others in the environment, which would be a bad thing.

Back in the days of poliomyelitis, respirators were in high demand. The type in use at the time was called a Drinker Respirator or an “Iron Lung”. This was a cabinet that encompassed anything from the chest to the whole body (save the head) and had an associated mechanism to control the pressure inside. By lowering the pressure, the patient was induced to inhale. Interestingly, this is much more in line with how the body naturally breathes and these machines did not and do not cause the kind of injury a positive-pressure machine can.

But of interest to the topic at hand, they can be constructed comparatively easily compared to a positive-pressure device because of this lack of potential for injury; an Australian named Both invented a field-expedient device that enabled his country to meet Polio head-on, and I distinctly recall seeing plans in *Popular Mechanics* or similar for an expedient respirator. People need to look for these sort of plans again if there is worry of insufficient capacity for medical respirators.

These machines declined because they were very large, comparatively, and the patient had to be lying down. So they can become obnoxious for people who need them all the time, but they’re non-invasive and there are still a few people out there who never recovered the ability to breathe unaided and continue to use an “iron lung”.