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.
TL;DR. If you have (slightly) low PaO2, but no trouble breathing, you probably don't need to go to the hospital. And if you have trouble breathing, you should probably go to the hospital whether or not you have low PaO2. So testing for oxygen saturation doesn't add much.
I had an online conversation with an intensive care physician. I sent him a translated version of juliawise's text and he said he didn't think buying the pulse oximeter would help and then sent me a 5 minute audio explaining why. The following text is his audio translated from Portuguese to English, I hope there are no wrong translations and I changed my mind after listening to him. Please also share what you think about his response:
"All pneumonia will desaturate the patient. O2 saturation is related to perfusion (gas exchange). Patient with acute respiratory syndrome (inflammation of the lungs by viral or bacterial infection) may course with poor tissue perfusion, that is, inadequate tissue oxygenation. One way to evaluate this is pulse oximetry, PaO2.
Patients with respiratory discomfort due to lung inflammation may or may not present desaturation. PaO2 < 90 indicates oxygen therapy. But perfusion and ARDS severity should be evaluated by the PaO2/FiO2 ratio (serum O2 concentration/offered amount of O2) to maintain good oxygenation.
What takes the patient to the emergency room is not the oxygen saturation level. You won't see a patient say "I'm feeling bad, let me see my saturation level" and suddenly find 80 or 85. If you start running and put the oximeter on your finger you can easily find 91~92.
What takes the patient to the emergency room is respiratory distress. He will feel shortness of breath and we will evaluate this with the methods of severity assessment, which would be oxygen saturation. And we would see in more severe patients a value below 90%.
The clinical picture of pneumonia is coughing, shortness of breath, respiratory discomfort, pain and by doing an x-ray he will detect a pulmonary opacity. You'll see a white field, where there should be air, there'll be fluid. Then you diagnose pneumonia.
The medical reasoning is this: I think about pneumonia based on the symptoms, I observe the saturation and it correlates with pneumonia, I see the x-ray and it correlates with pneumonia so I start the protocol... actually when I do the physical exam and I think "ah, it's an acute respiratory distress syndrome" I don't even want to know what it is initially, I want to offer oxygen, guarantee the airways, improve the gas exchange and keep the patient alive until finally I can test for coronavirus.
In fact, the saturation will indicate a marker of severity in a dyspneic patient. Not a diagnostic marker. There is no way to observe a patient who is desaturating and give a diagnosis for coronavirus.
Many things change oxygen saturation. Like I told you, oxygen saturation measures the amount of oxygen inside the RBC, right? So if I have a RBC with low hemoglobin inside, like with an anemic patient, it changes the oxygen saturation. If the patient is not doing good gas exchange, it changes the oxygen saturation. For example, lowering of consciousness will give low saturation. Also if he is shocked, hypotensive or hypothermic. Another thing that also changes is the use of enamel on his fingers. "
Then I sent him an audio saying:
Me: "I got it. But let's suppose we were in the following situation: there are 10,000 infected in the city, the government starts to declare quarantine. Suppose you're home with a fever and another symptom like cough. You're left wondering, "Should I go to the hospital and test for coronavirus?" But knowing there is an outbreak and that the hospital is crowded with people with the disease, chances are you will get the disease when you go to the hospital if you don't have it. I am at home, isolated because I have the symptoms of the disease, but I am not sure if I have coronavirus and I do not know if I should really go to the hospital. How do I know if I should really go to the hospital? Should I wait until a respiratory problem like difficulty to breathe starts to appear? Is it possible that I take the measurement with the oximeter and it gives a low oxygen saturation before I even start having a breathing difficulty?
He: "Not under normal conditions. Under normal conditions, a patient with only a cough, fever, runny nose, or an upper airway condition will not change oxygen saturation. That wouldn't make you think about going to the hospital, you'd stay home, like you did every time you had a common flu picture.
Even because you will not change the treatment. You will be treated as supportive therapy like all viral infections: H1N1, etc. But if you stay home without any signs of severity, it will resolve as if nothing had happened and the diagnosis would not be closed, you know? It would be a syndromic diagnosis... a flu picture, a common flu without any complications. What happens is that in the face of the epidemic, people are testing coronavirus for patients with acute respiratory syndrome, respiratory discomfort. Then, for fear of serious evolution, these patients are tested [for coronavirus] for early ventilatory support."
Then I sent him this text message:
Me: "1) Fever → coughs → respiratory discomfort → recommend going to hospital to test for ncov and receive early ventilatory support.
Would the mistake in my reasoning be to assume that there would be low oxygen saturation before even presenting respiratory discomfort?"
He: "Yes."
Thinking about it, now I believe if I have Fever → coughs → respiratory discomfort or shortness of breath → I should go to the hospital.
If I have Fever → coughs → NO respiratory discomfort and NO shortness of breath → check oxymeter and low PaO2 → Do not go to the hospital.
So having the oxymeter wouldn't make me go to the hospital. So I don't need an oxymeter.