Understanding COVID, ARDS, and Mechanical Ventilation
April 7 Update: some research is emerging since I posted this that COVID related ARDS is not typical ARDS. Here’s the medical reference for providers but it’s very early evidence so far we should keep an eye on: COVID-19 Does Not Lead to a “Typical” ARDS. This was further validated by an article in MedScape that previews some emerging peer-reviewed research. Thus while my explanations of ARDS and ventilators is accurate, the ties to COVID-19 are not and new treatment protocols are emerging. Although this is a security blog, this post has absolutely nothing to do with security. No parallels from medicine, no mindset lessons, just some straight-up biology. As many readers know I am a licensed Paramedic. I first certified in the early 1990’s, dropped down to EMT for a while, and bumped back up to full medic two years ago. Recently I became interested in flight and critical care and completed an online critical care and flight medic course from the great team at FlightBridgeED. Paramedics don’t normally work with ventilators – it is an add-on skill specific for flight and critical care (ICU) transports. I’m a neophyte to ventilator management, with online and book training but no practice, but I understand the principles, and thanks to molecular biology back in college, have a decent understanding of cellular processes. COVID-19 dominates all our lives now, and rightfully so. Ventilators are now a national concern and one the technology community is racing to help with. Because of my background I’ve found myself answering a lot of questions on COVID-19, ARDS, and ventilators. While I’m a neophyte at running vents, I’m pretty decent at translating complex technical subjects for non-experts. Here’s my attempt to help everyone understand things a bit better. The TL;DR is that COVID-19 damages the lungs, which for some people triggers the body to overreact with too much inflammation. This extra fluid interferes with gas exchange in the lungs, and oxygen can’t as easily get into the bloodstream. You don’t actually stop breathing, so we use the ventilators to change pressure and oxygen levels, in an attempt to diffuse more oxygen through this barrier and into the lungs without, causing more damage by overinflating them. We start with respiration Before we get into COVID and ventilators we need to understand a little anatomy and physiology. Cells need oxygen to convert fuel into energy. Respiration is the process of getting oxygen into cells and removing waste products – predominantly CO2. We get oxygen from our environment and release CO2 through ventilation: air moving in and out of our lungs. Those gases are moved around in our blood, and the actual gas exchange occurs in super-small capillaries which basically wrap around our cells. The process of getting blood to tissues is called perfusion. Theis is all just some technical terminology to say: our lungs take in oxygen and release carbon dioxide, we move the gases around using our circulatory system, and we exchange gases in and out of cells in super-small capillaries. Pure oxygen is a toxin, and CO2 diffused in blood is an acid, so our bodies have all sorts of mechanisms to keep things running. Everything works thanks to diffusion and a few gas laws (Graham’s, Henry’s, and Dalton’s are the main ones). Our lungs have branches and end in leaves called alveoli. Alveoli are pretty wild – they have super-thin walls to allow gases to pass through, and are surrounded by capillaries to transfer gasses into and out of our blood. They look like clumps of bubbles, because they maximize surface area to facilitate the greatest amount of gas exchange in the smallest amount of space. Healthy alveoli are covered in a thin liquid called surfactant, which keeps them lubricated so they can open and close and slide around each other as we breathe. Want to know one reason smokers and vapers have bad lungs? All those extra chemicals muck up surfactant, thicken cell walls, and cause other damage. In smokers a bunch of the alveoli clump together, losing surface area, in a process called atelectasis (remember that word). Our bodies try to keep things in balance, and have a bunch of tools to nudge things in different directions. The important bit for our discussion today is that ventilation is managed through how much we breathe in for a given breath (tidal volume), and how many times a minute we breathe (respiratory rate). This combination is called our minute ventilation and is normally about 6-8 liters per minute. This is linked to our circulation (cardiac output), which is around 5 liters per minute at rest. The amount of oxygen delivered to our cells is a function of our cardiac output and the amount of oxygen in our blood. We need good gas exchange with our environment, good gas exchange into our bloodstream, and good gas exchange into our cells. COVID-19 screws up the gas exchange in our lungs, and everything falls apart from there. Acute Respiratory Distress Syndrome ARDS is basically your body’s immune system gone haywire. It starts with lung damage – which can be an infection, trauma, or even metabolic. One of the big issues with ventilators is that they can actually cause ARDS with the wrong settings. This triggers an inflammatory response. A key aspect of inflammation is various chemical mediators altering cell walls, especially those capillaries – and then they start leaking fluid. In the lungs this causes a nasty cascade: Fluid leaks from the capillaries and forms a barrier/buffer of liquid between the alveoli and the capillaries, and separates them. This reduces gas exchange. Fluid leaks into the alveoli themselves, further inhibiting gas exchange. The cells are damage by all this inflammation, triggering another stronger immune response. Your body is now in a negative reinforcement cycle and making things worse by trying to make them better. This liquid and a bunch of the inflammation chemicals dilute the surfactant and damage the alveolar walls, causing atelectasis. In later stages of ARDS your
