Can you really hack a ventilator?

“What did Elon Musk say this time?”: COVID-19 Edition

A few weeks ago, Elon Musk promised to purchase and send ventilators to hospitals experiencing equipment shortages. He faced backlash from the media after one of the hardest-hit hospitals in Queens, New York, tweeted a picture featuring one of the “ventilators” he sent – actually a BIPAP machine. Media outlets and Twitter users criticized him for sending these non-invasive devices rather than the life-support ventilators that hospitals desperately need. Was it a rookie mistake? Maybe. Let’s go over the differences among these medical devices that all interact with the respiratory system! 

You probably know someone who uses a CPAP (Continuous Positive Airway Pressure) or BIPAP (Bilevel Positive Airway Pressure) machine. Folks who have sleep apnea use them to sleep more safely and comfortably. When I was younger and would spend nights at my grandparents’ house, I was terrified of the CPAP mask that my grandfather wore at night, and the noises it made. Eventually, after scrutinizing the face mask and hose connected to the machine, I convinced myself that he looked like an elephant. I love elephants. CPAP machine fear: conquered.

CPAP Machine

BIPAP and CPAP machines are both non-invasive types of ventilators, not the type that are normally used in hospitals for patients that are oxygen-compromised. When we inhale, our diaphragms contract and flatten down towards our pelvis, allowing our lungs to expand and increase in volume. Throwing it back to high school physics – when the volume of a container increases, its pressure decreases. Air follows a gradient of high to low pressure, so when our lungs expand, the higher pressure air outside of our body rushes into our lungs. Ventilators generally help facilitate this process when patients need more oxygen in their systems, or their airways are compromised. CPAPs and BIPAPs deliver a constant stream of positive air pressure through the mouth and nose to keep airways open. Their main users, obstructive sleep apnea patients, need them to prevent the throat muscles from relaxing too much during sleep, so the airways can remain unobstructed. 

CPAPs can only be set to one level of pressure or slowly advance to a maximum pressure overnight, whereas BIPAP machines are a little fancier and customizable to provide support for users who need more oxygen saturation support, and higher air pressure. BIPAPs have two pressure settings – a higher one for inhaling, and a lower one for exhaling, because exhaling against a high, continuous pressure can be difficult and uncomfortable. 

Both of these assistive devices consist of a face mask covering the nose and mouth with a hose that attaches to the machine that performs all of the work. It is possible for patients with less acute cases of respiratory distress to use BIPAPs in hospitals, especially when ventilators are few and far between (more on why later), which is why Musk likely chose to send BIPAPs, rather than wait for more complex machines to be manufactured. However, CPAP and BIPAP machines can be dangerous for healthcare providers right now – leaky face masks can expose them to airborne virus particles, though it may be possible to mediate that risk by using some new innovations. 

Life-support ventilators are more invasive and complex. They have many moving parts, settings, and even customizable software, making them powerful enough to meet the demands of different conditions for patients with severely compromised lung function. Size and frequency of breaths can be monitored to manage a patient’s specific needs at all times. Slow, medium sized breaths are more beneficial for stabilizing respiratory distress than deep and slow, or rapid and shallow breaths. They also generate air pressures that are strong enough to hold open bronchioles, the small branched airways in your lungs, that can collapse under inflammation or fluid build-up – all complications of COVID-19. 

Patients who need ventilators are anesthetized while an endotracheal breathing tube is carefully inserted through the mouth and down the trachea (the windpipe), and a cuff is inflated around the breathing tube in the trachea to form a seal (like when you get your blood pressure taken). This is particularly important for COVID-19, as the cuff prevents virus particles from leaving the airway and exposing healthcare providers to the virus. Physicians must decide who gets a ventilator and who gets a CPAP or BIPAP based on the severity of a patients’ case. But, why do they even have to make that decision in the first place?

Ventilator

We are experiencing a global ventilator shortage due to a variety of factors, including significant disruption to global manufacturing supply chains (the resources and companies needed to manufacture products) as a result of the pandemic, and prior market demand. In 2019, before COVID-19, the entire world only needed 77,000 new ventilators a year. Now, manufacturers would need to increase their rate of production by 500-1000% percent in order to meet the demands of this public health crisis. Manufacturers have only been able to increase their production by about 30-50%. Life-support ventilators are incredibly complex and expensive machines; they require more than 700 parts that are often sourced from all over the world, and they cost about $50,000 each. Manufacturing plant size and supply chain disruptions prevent this process from accelerating to meet our needs. 

In order to combat the ventilator shortage, the FDA released new guidelines on March 22nd to allow hospitals to be more flexible with this life-saving equipment to meet the influx of cases of COVID-19 related respiratory distress. The guidelines allow small modifications in materials, software, or functionality to be made to pre-existing or newly manufactured ventilators without FDA approval. The guidelines also allow CPAP and BIPAP machines to be used for less-severe COVID-19 cases, with careful monitoring. The FDA specifies flexibility with materials for breathing tubes, which are now difficult to obtain, and ventilator motors, to increase the capability of less-powerful machines. 

Normally, these changes would need to pass through the FDA’s 510(k) pre-market approval for medical devices, a fast-tracked process that allows newly developed devices that are “substantially equivalent” to previously cleared devices to get approved quickly, without clinical trials. Now, manufacturers and hospitals have the flexibility to use modified devices without clearance for emergencies. The FDA emphasizes that the use of FDA-approved devices should be prioritized over the use of modified CPAP and BIPAP machines. In particular, they encourage the development of filters to protect healthcare providers from aerosolized virus particles when using CPAP and BIPAP machines for less severe cases, and new software to encourage remote monitoring of patients to prevent exposure. 

One example of this innovation is a group at UC Berkeley working to fit CPAP machines with endotracheal tubes and filters, eliminating the need for face masks and significantly reducing the risk of viral exposure. Ultimately, Elon Musk did the right thing here – he provided extra resources to hospitals in need. In fact, after the media backlash, Musk said that the hospitals confirmed that they had a critical need for BIPAP machines for less severe cases. Musk has also pledged to dedicate Tesla factories to manufacturing ventilators. Hopefully he and others can help refit BIPAP machines for safer use! 

Rendering of a sleep apnea device retrofitted to help COVID-19 patients. (Grace O’Connell image)

https://engineering.berkeley.edu/news/2020/04/turning-sleep-apnea-machines-into-ventilators/

What we talk about when we talk about diagnostics.

After spending the last few weeks talking with students, journalists, neighbors and family members, I’ve decided that there might be some value in discussing some of the terminology that we use when talking about diagnostic testing.

Science communication and media relations folks always discourage “jargon” when describing scientific concepts to laypeople. However, technical terminology can be a key part of scientific discussions, especially when it’s important to be precise. Now, in the setting of a global pandemic, precision is particularly important, and I believe people can handle more complexity than the scientific community often gives them credit for. Increasing scientific literacy can empower people to better understand and digest current events. So, here are some of those definitions.

First off, is reagent. In general, a reagent is any substance that is a starting material for a chemical reaction. Do you remember finding the “limiting reagent” in high school chemistry class? That’s the chemical that runs out first; thus, limiting the amount of product that can be made by the reaction. Many outlets have reported that one of the reagents failed in the initial test that the CDC distributed for COVID-19. It is still unclear which reagent did not perform as expected, but the reagent was one of the parts of the test reaction that the CDC shipped out to labs around the country. This problem has now been fixed, and all of the CDC test components are working well. 

Negative and positive screening test cassette strips.

The next term is assay. Assay is just the word we use for “test.” Anytime you hear someone say they are running an assay or assaying for something, they are simply running a test. 

Controls and control material also come up often when discussing test design. Controls are needed to make sure that the test you are running is valid. Basically, controls are parallel experiments that you run alongside your testing to make sure that you didn’t make a mistake while running the test. We science folks are always skeptical and are always checking to make sure we didn’t make a mistake! A positive control, in the context of COVID-19 testing, is when we put some material in the reaction that we know will make the test come up positive. If that reaction does not come up positive, we know that we made a mistake someplace, or that some of our other reagents are not working properly. A negative control is when we set up a test that does not contain a sample or additional material, that we expect to come up negative. If a negative control comes up positive, then we know that we have some kind of contamination, or that something we did not expect is happening in our reaction. If this happens, we need to start over, and figure out what went wrong. In both cases, controls that do not work as expected render any test result invalid. These results are not reliable and should not be reported. 

Now, we need to cover sensitivity and specificity. These guys are a bit more complex. Sensitivity measures how little of the virus you can detect using a particular test in a particular sample. A super-sensitive test can detect very small amounts of the virus. Sensitivity goes hand in hand with the concept of a false negative. A test that is not sensitive enough might come out negative for someone who is infected with the virus, but does not have a viral load high enough to make the test read positive. It is also possible that a false negative can arise from a swab being taken improperly. 

Specificity is a measure of how well the test detects the COVID-19 virus, and not other things that might confuse the test. A very specific test is good at detecting COVID-19 and will not detect other closely related viruses. Specificity goes hand in hand with false positive rates. If a test is not very specific, it might show a positive result when someone is not infected with COVID-19, but with something else like a flu virus. 

Both false positives and false negatives make it difficult for healthcare providers to interpret test results in the context of care. Low rates of false positives and false negatives make a test more trustworthy. 

Now you know the basics of test design and metrics! We hope that this makes reading some of the science reporting a little more clear.