Filipe Marchesini

Filipe Marchesini's Comments

How strong is the evidence for hydroxychloroquine?

Gautret et al. 2020° shouldn't be considered a study of hydroxychloroquine efficacy. It should be considered a failed attempt at studying hydroxychloroquine efficacy. Here is why I believe that.

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Coronavirus: Justified Practical Advice Thread

Thanks for the suggestion, ESRogs. I'm adding the shortened version now.

Coronavirus: Justified Practical Advice Thread

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.

Coronavirus: Justified Practical Advice Thread

Should I expect a faster infection rate on my country (Brazil) because most people here use paper money to make trades? Should I recommend people to stop using paper money and instead opt for a contactless card? Most people don't have access to banking services; so is there any option for them?