Update March 4
I've done an extensive analysis of the disease and Impact of a Pandemic.
http://tinyurl.com/sv5v4vc
I'll excerpt my On Masks Section as I suspect the reasoning contained within will be the most appropriate and interesting to this thread. But there is good stuff throughout, I've built things for lay readability, and am not a technical expert, I would appreciate thoughts and advice. I don't have variables for mask exposure, but I think my reasoning is solid and useful. You can tweet me @qastokes
About N95 Masks
All non-N95 face masks, such as medical masks, (of the dental kind), are relatively useless for self-protection, as they lack a seal. Please donate your excess to medical facilities. These are very useful for containing the spreading of all illness, those who are sick and coughing, regardless of disease, should find and wear these type masks. Containing spread is far more effective than reducing exposure for managing the risks.
Please understand N95 isn't prevention, it's odds increase. When properly fitted and used it reduces exposure, but technically it's only 95% efficient.
An N95 might keep a doctor with constant exposure alive, but won't help Joe who's out shopping much. Wearing a mask could theoretically increase your risk if used wrong, by being a capture of virus that moves along with you and extends your exposure time. It is not generally helpful, compared with handwashing and effective prevention protocols.
It is true there is benefit to be had by using a mask. But it is only significant if you are competent in following the use protocol. It is better by far to learn & to carefully follow all the other higher impact protocols, especially handwashing. By far the greater benefit, for you individually considering your total exposure risk across time regarding the disease and it's spread, around you to managing your personal exposure will be for those managing the disease directly to have the best protection they can. Hence my advice to donate extra masks to those at highest risk.
Think about this along the lines of "the more the disease spreads, the greater your total exposure risk, regardless of managing your personal exposure risks."
Note: For really significant improvement in your exposure chances, I & wearing a mask effectively, you will need to carefully follow the behavior protocol for a disposable full body exposure management system. A protocol which includes gloves, a hooded tyvek particulate suit, and goggles, along with the mask, this is only really applicable in an extremely exposing environment. Additionally, a P100 would be the optimal mask of choice for this situation and protocol.
The biggest risk management benefit comes from one complete set of masks and a full body exposure management system for every one of your loved ones. This allows you the freedom to make one situation optimizing decision in a worst case scenario.
This would look like:
The family is out of food. Healthcare is overburdened to the point the death rate has matched the critical cases rate. You must move with high risk of high exposure.
Alternately, with planning these suits can also be burned one use at a time in a clean room caring for a loved one, allowing for several days of constant and very direct care with low gain viral load & exposure risk for those still without symptoms or as yet uninfected.
Note for completeness: of all the routine contexts to wear a mask, high droplet spray environments are the ones the mask will help in the most, especially if you sanitize your clothes afterwords. I would strongly consider wearing one in a crowded subway, if there is a known outbreak in your city. This would only significantly help if you wear the mask correctly, sanitize clothes, & don't touch your face and are meticulous about hand washing.
Hospitalization and oxygen therapy thresholds
Tl;dr: Not knowing much about this and not a doctor, my current policy is to go to a hospital if SpO2 drops below ~92% and my hospital isn’t completely overrun, unless my SpO2 is naturally low or some other extenuating circumstance. If I was forced to use an oxygen concentrator outside of a hospital, I would target a ~~94-96% SpO2 range, trying very hard to make sure I didn’t hit 99%
If you do have COVID and shortness of breath, when do you go to a hospital?
Hopefully you already have a pulse oximeter as Julia Wise recommends. But sources say anywhere between 90 and 95% SpO2 is the threshold for hospitalization (WHO says <= 93% is classified as severe, ctrl+f “O2”), while other sources say you should threshold on trouble breathing and shortness of breath, not the actual SpO2 number.
It seems to me that using “trouble breathing” as the indicator would track the lung blockages and thus immune response relatively well, while O2 as an indicator would track the danger metric directly (if in fact the primary source of death is insufficient oxygen; if anyone knows this, would be useful).
The benefit of looking at trouble breathing is that it’s an advance indicator. Usually people progress from oxygen therapy to ventilators relatively quickly. If you have naturally low SpO2, your O2 might drop under threshold (say, 93%) in the early stages with mild trouble breathing, but you wouldn’t have much of a dangerous immune response until later. In this case, you’d have wanted to use difficulty breathing as your indicator instead of SpO2.
That being said, having low oxygen seems pretty bad for you, both by common sense and science. For example, 92% or lower is associated with increased morbidity in pneumonia patients; <90% is increased with 36% increased morbidity. Since it’s hard to measure even moderate effects due to the treatment-correlated-with-severity issue, my guess is that there’s some general bodily harm from reduced oxygen even at levels like 95%, though I don’t know how much. So at some SpO2 threshold, I think you want to be supplementing oxygen even if your breathing doesn’t feel that difficult.
Unfortunately, it seems like you can’t supplement oxygen at 95%, because over-oxygenating causes neuronal damage. Standard targets appear to be 94-98% or 92-96%. This study says it seems bad to set your target range during oxygen therapy to greater than 92-96%, because one inevitably exceeds the upper target occasionally. This review/musing muses that it’s a difficult problem, evidence for hyperoxaemia being pretty bad is “comparatively strong”, but not strong enough to warrant especially conservative oxygen titration. Because of these numbers, I think 92-93% is a reasonable threshold to self-hospitalize, since anything above this means they probably shouldn’t be oxygenating you anyways.
If hospitals are overloaded and you have to do oxygen therapy yourself (really try not to do this), I think the targets above are still reasonable, subject to your ability to titrate well with the machine. If you have lots of trouble, of course be conservative. However, you may be able to do better than hospitals: the first study above says that “even in a research setting in the intensive care unit, in which patients receiving mechanical ventilation are closely monitored, most patients who were randomized to an SpO2 target of 90–92% and were receiving supplementary oxygen did not have their inspired oxygen reduced if the SpO2 was 99% or 100%.” So—seems like you could easily do better monitoring than this if you were oxygenating at home. This is why I would probably shoot for 94-96% myself.