Prone positioning - Printable Version

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Prone positioning - BostonCard - 06-18-2020

Having patients lie face down (prone) has been talked about in the past as a way to prevent patients from needing to be intubated and placed on a mechanical ventilator.  This is the first (small) study I've seen:

https://jamanetwork.com/journals/jamainternalmedicine/fullarticle/2767575

The data looks significant.



However, there are a number of issues.  There was no comparator group, so you don't know what would have happened to patients who stayed supine (face up).  Also, they were quick to intubate patients (using a fairly high threshold of 95%).  And obviously we have no long-term data; this is not useful if 30 minutes later, oxygen levels tank.  But still, this is a promising measure that I'd like to see researched a bit more closely.

BC

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RE: Prone positioning - M T - 06-18-2020

(06-18-2020, 08:53 AM)BostonCard Wrote:  However, there are a number of issues.  There was no comparator group, so you don't know what would have happened to patients who stayed supine (face up).  Also, they were quick to intubate patients (using a fairly high threshold of 95%).  And obviously we have no long-term data; this is not useful if 30 minutes later, oxygen levels tank.  But still, this is a promising measure that I'd like to see researched a bit more closely.

It wasn't just a threshold of <=93%, it was also the 30 respirations a minute plus being on what I believe to be a fairly strong flow of oxygen.  I'd guess that if the doctors thought this was stable, the patient probably was ok, but they were taking it as a sign that he patient was going downhill and it was better to insure better airflow now rather than wait to a time when it would be an emergency procedure.

For all we can tell, this improvement is simply the result of laying still (and being left alone?) for an hour, after having the anxiety of being told of a diagnosis with severe hypoxemic respiratory failure and the need to be intubated.  I would have been interested to see heart rate & BP to get a sense of anxiety or activity.  I would also like to have seen respiratory rate reported at the end of the hour. 

I wonder why data wasn't presented for the first hour of prone position (after some hours of supine) on the 2nd day? (Average time prone was less than 6 hours in the first day.)

It seems the patients were given the choice to lie prone or be intubated.  Those that didn't lie prone were intubated.  Apparently none of the patients was allowed (or, at least, chose) to say no to both.  However, some patients only lay prone for only an hour in their first day and, at least an hour, on the 2nd day.

The text part didn't mention that those that were eventually intubated spent (ie, tolerated) more time on average in the prone position on the first day than those that didn't.   It isn't clear whether this is because some were out of distress or whether all were still in distress through that first day.

I see no mention of whether prone means horizontal or not but I would presume so.  If not, the patient would tend to slide down the bed.
Usually if you are on your back in a hospital bed, your head is at a (adjustably) different level than your feet and you have some bend at your hips.  Often your head is on a pillow.  I find being totally flat on my back to be uncomfortable.   Horizontal supine could be similar to horizontal prone.  Or straight (no bend) supine could be similar to (no bend) prone.  Or bent supine (horizontal/slanted torso) could be similar to bent prone (horizontal/slanted torso).  And, as mentioned, no testing was done of laying on one side or the other (heart up or down).

After turning from supine to prone, the opposite side of the patient is on the side of the bed where the wires attach.  The sensors might be moved to different fingers. Were the "before" measurements taken before moving to prone (and perhaps measured on different fingers) or after moving to prone.  My different fingers give different SpO2 measurements.  (I have no idea whether this occurs in other people, or whether there is any pattern to this across people.  But when I was in the hospital for pneumonia and a nurse mentioned they wanted my SpO2 to be 95% before they'd let me out, I pointed out that we should simply move the sensor from my right index finger to my left index finger.  I knew of that difference from playing with a home sensor about 15 years before.)

I presume the SpO2 measurements were done at the fingers.  The body position could impact how much of the freshly oxygenated blood gets to the various parts of the body (specifically, torso, arms/fingers, legs, brain).  Reducing flow to another area could perhaps result in higher readings at the fingers. (A diving reflex would reduce SpO2 at the fingers. Perhaps the prone position reduces a diving reflex resulting from lower O2 because of pneumonia, and so is not helping at all.)

I'm hopeful that moving to prone position does improve outcome.  I hope they can try to isolate what it is that improves the measured SpO2.

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RE: Prone positioning - BostonCard - 06-18-2020

There is a theoretical reason that prone positioning might work, based on a phenomenon called ventilation/perfusion (VQ) mismatch.  Basically, the normal lung is very good at matching blood flow (perfusion) to areas of the lung that are getting oxygen (ventilation), but a diseased lung often has trouble.  The result is that sometimes blood flows to areas where no air is getting to due to damage to the lung (from a pneumonia or ARDS).  This is especially true in the dependent (towards the back, when you are lying on your back) portions of the lung, where gravity enhances blood flow.  If you start with bad VQ mismatch, you may be able to improve the VQ matching by turning around and lying prone so that gravity now enhances blood flow to the anterior (front) of the lungs where ventilation may be better.

BC

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RE: Prone positioning - Mick - 06-18-2020

I was talking with my employee who came down with COVID-19.  She said she was most comfortable in a position where she could sleep leaning forward at a 45 degree angle.  I've had fluid on my lungs, I've done the same.  It was the most comfortable position I could have.

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RE: Prone positioning - fullmetal - 06-18-2020

I had originally heard the theory that there was more tissue mass ventral-side of the lungs (vs. dorsal of the lungs) and thus proning would allow the patient to breathe easier without as much tissue mass resting on top. (Seems too simplistic to be true, no?)  The VQ mismatch theory is more interesting.  Proning has been anecdotally very helpful since early March iirc.

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