#KYJ-Oxygen Saturations and Deep breaths.
Do you ask your patient to take a few deep breaths when the sats are being recorded?
You know the patient I'm talking about. Old mate, lying there restfully in the bed, sats sitting at 91%, and you don't want to write that number on the colour coded obs chart; so you lean over, give him a nudge, and say...
"Mate, take 5 deep breaths for me"
....
Well stop it.
...
It doesn't work, its dishonest and it demonstrates that you believe that it puts more oxygen into the blood which is plain wrong.
... have I got your attention?
Read on:
The patient taking deep or fast breaths is breathing the same air you are breathing. The same air they were breathing 2 minutes before you woke him for obs.
21% or a fraction of inspired oxygen (fiO2) of 0.21.
This translates to roughly 100mmHg in his lungs, which diffused into his blood to saturate his haemoglobin. Here’s the vid
You cant increase blood oxygen unless you increase the concentration (fiO2) he is breathing. So take 5 breaths or 50 breaths, and it makes zero difference to his oxygenation.
So what does it do?
Why do you see the sats go up 1-2%?
Well takes few deep breaths, and you blow off CO2. In fact, the faster and deeper you breathe the more CO2 you rid from your blood. This does three things:
One: it raises your pH making your blood slightly alkalotic.
Alkalotic red blood cells (haemoglobin) binds to oxygen more readily raising the saturation. It is temporary and lasts only 20-70 seconds. Before you finish the next patient's obs, old mate has desaturated right back to where he was at the beginning.
Two: Bohr's principle suggests that when decreasing
CO2 bound in Red Blood cells, there is more room temporarily to transport more oxygen... again it it very very short lived.
Three: Taking deep breaths recruits more alveoli (the gas exchange air sacs).
This optimises ( not increases) diffusion. Here again it is temporary, and unless old mate continues to stay awake and rapidly deep breathe, his sats will base line out back at that number you didn't want to write in the chart.
So... what to do ?
Assess your patient. Is he distressed? Does he have any other symptoms that could indicate respiratory discourse?
Triangulate your vital signs and talk to the patient. Normal is anything over 90% (93-96% ideal) when breathing room air. Chronic lung disease patients may have an acceptable lower limit of normal for them (often 88-92%). But all of us when resting or sleeping drop, not just our sats, but also our resp rates, so take the data in context, investigate your patient, and stop bugging them to deep breathe just so your graph looks good.
Final word on deep breathing- its good to get all your patients to do this every hour. It prevents DVTs, pressure area ulcers, atelectasis/pneumonia, and helps clear pooled secretions in de-recruited lungs.
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Thanks Rob. Remember seeing this pop up on my newsfeed a while back. Had a student today in ED who asked "old mate" to "take a few deep breaths" and I remembered this KYJ. I've just printed this off for her to read and hopefully it will change her practice the way it changed mine.
ReplyDeleteCheers Nicki Edwards
This is interesting but doesn't necessarily address the underlying reasons why a nurse may get "old mate" to do deep breaths. The cut-off for a medical review is usually an SpO2 of 95%. It is likely that old mate is fine saturating at 93% with no distress or other respiratory issues. Supplemental oxygen is probably unnecessary and potentially harmful. This is not always the case and an SpO2 of 93%
ReplyDeletemay represent a critical warning sign of a deteriorating patient. Two isses: 1) in the era of colour-coded chart, nurses have no say in which patients should or should not be reviwed; 2) altering calling criteria involves additional personal responsibility for the medical officer involved, despite the alteration often being reasonable and appropriate.
I suspect nurses keenly understand that getting "old mate" to do deep breaths will only have a temporary impact on his SpO2. Rather they are attempting to navigate systemic problems and inflexibibilities involved in review systems. While this review of the pathophysiology is interesting we should also look at the underlying system problems.
3 times in the last year 1/2 I was admitted to hospital for ops etc. This happened on all 3 occasions. It set alarms ringing for me and I went off to get tested- oops moderate sleep apnoea. Maybe could have picked it up earlier if we looked at why it was happening at the first admission instead of just getting me to breathe deep please.
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