Sarah Constantin: Oxygen Supplementation 101

by habryka1 min read20th Mar 20204 comments


Covid-19Fact posts

New post by Sarah on oxygen supplementation. Excerpt: 

COVID-19 causes shortness of breath and in severe cases requires artificial ventilation. There is a shortage of mechanical ventilators in hospitals, and a shortage of medical personnel to treat patients with severe COVID-19, so there’s widespread interest in contributing to open source ventilation projects. For these efforts to be effective, though, we need to understand what COVID-19 patients need in terms of ventilators and other supplemental oxygen sources.

COVID-19 Symptoms and Clinical Guidelines

Most patients who go to a hospital for COVID-19 have pneumonia or infection of the lungs, which is visible on a chest X-ray.  A large fraction (41.3%) receive supplemental oxygen therapy; a smaller fraction (5%) needed to be admitted to the ICU, and 6.1% needed mechanical ventilation.[1] 

ARDS  Severe cases of COVID-19 result in developing Acute Respiratory Distress Syndrome (ARDS). Fluid builds up in the lungs; the lungs may collapse; blood oxygen drops; and mechanical ventilation is required. Merely providing air with a higher oxygen content than room air isn’t enough; pressure needs to be administered to keep the alveoli open.  

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Some notes/highlights (but it's not that long and you should read the whole thing)*:

  • Generally thought to be more helpful if you can get both oxygen and pressure (pressure helps keep alveoli open)
  • At least several oxygen supplementation methods will aerosolize the virus and increase contagiousness nearby, and are not allowed in a healthcare setting as a result. Perhaps particularly methods involving pressure.
    • This is not, or is less of a problem, for low-pressure oxygen (ex: (non-rebreather) oxygen masks). These oxygen masks are probably what is meant by standard oxygen therapy.
    • This is a problem for CPAP machines
    • (Deleted a somewhat-incorrect/confused bullet-point)
    • (Personal thought: Is this part of why hospital outbreaks were so nasty with SARS-1?)

suppose you’re a person with respiratory failure, but you have an oxygen mask, CPAP, BIPAP, or high-flow nasal cannula at home. 40% of the time or so, your noninvasive home equipment is going to fail and you’ll need to be intubated. Usually this happens quite urgently; if you need to take an ambulance to get to the hospital it might be too late.

  • Invasive intubation tends to be be urgent, and is a very seek-a-medical-professional do-not-do-this-at-home procedure
  • From ~300 pneumonia cases: From the set [oxygen mask (rebreather), high-flow nasal cannula, non-invasive ventillator], high-flow nasal cannulas have the best outcomes associated with them (much better 90-day mortality rates). But for all of them, 30-40% ended up needing invasive intubation within 4 days.
  • Given the frequency with which people go on to need invasive intubation, hospitals are probably better than at-home with NIV unless you really can't access the hospital (ex: overun). The rates for needing intubation are still high (~30%-40%).
    • But see also: NIV seems better than standard oxygen therapy (oxygen mask), in the follow-up post

Many of these [open-source ventillators] are automated bag masks, or CPAPs, which aren’t recommended for use in hospitals because they spread COVID-19; and they won’t work on the more severe cases of respiratory distress anyway. Only two projects that I found, the Pandemic Ventilator and the Flometrics project, are explicitly trying to match the specifications of the type of mechanical ventilators found in ICUs.

The follow-up post on non-invasive ventillation (NIV)

  • Lot more data surveyed, but across several ventillators and conditions (ex: COPD (definitely helps), pulmonary edema (somewhat less consistently)).
  • NIV does seem to improve outcomes by quite a lot, including in pneumonia.
    • Strong results on intubation there (60% changed to 15-20%), but only 136 total pneumonia samples across 2 studies. And one of them noted no difference in mortality.
  • NIV makes a pretty big difference on the overall intubation rate, changing 30% to 15%

This means that, in a world where ICUs are overrun, there’s a good chance that a home non-invasive ventilation device could save lives for people with COVID-19.

* Also, I'm not likely to sync this as it updates, I may be out-of-date, errors in bullet-points are mine, etc. etc.

Most potential at-home oxygen supplementation methods will aerosolize the virus and increase contagiousness nearby, and are not allowed in a healthcare setting as a result. Default to assuming this applies.

I don't think this is correct; (almost) all at-home devices will be oxygen concentrators providing supplemental oxygen at low flow rates (majority 1-6L/min) via (low flow) nasal prongs or masks (not the non-rebreather style mask mentioned later). Clinically significant aerosolization of respiratory droplets requires higher flow - like the high flow nasal prongs (30-70L/min flow), CPAP/BiPAP machines (NIV), or high respiratory tract flows (shouting/heavy coughing/puffing from shortness of breath etc).

Part of the problem with this outbreak is that deterioration from requiring supplemental O2 to requiring intubation can be sudden, so while home oxygen would potentially free up a lot of beds/space/workload, lack of monitoring for deterioration and travel time back to the hospital would probably worsen mortality in that subgroup. I'm unsure how this risk/benefit equation would play out overall.

Ah. Then that is an error on my part because I had no prior knowledge on this topic, and assumed that rebreather oxygen masks were the default form of oxygen masks.

Thanks for the correction!

I've tried to update the relevant bullet-points towards what you described.