Measuring Blood Pressure

[DaveReading]

I recently had the misfortune to spend several days in hospital. I would like to know what is the obsession with measuring blood pressure every few hours? To be woken up in the middle of the night (and it's difficult enough to get to sleep in hospital) to have your blood pressure checked is designed to elevate it. Is it the (relatively) new electronic gadgets that make it too easy? If you had to get a doctor with a mercury manometer to do it I'm sure it would not be done very often (if at all). Note: I was not in for anything related to the heart or high/low blood pressure.

I thought that too.

That is, until I was in hospital a couple of years ago. After a week or so of 4-hourly BP readings, it was decided that I needed to be hooked up to a continuous BP monitor. That involved a somewhat surreal and disturbing spell in ICU, not because I needed their care, but because only they had the required kit, and it took 20 painful minutes for a junior doctor to manoeuvre a probe into my wrist while the ICU nurses looked on with amusement.

I was relieved to get back on the ward next day, despite the 4-hourly checks.

[millimole]

Jonathan,
It wasn't just me everybody on the ward got tested (very regularly) and for blood O2 (I wonder how accurate these little LED devices are as it always seems to come out 98% or greater) .

The finger oxygen saturation monitors seem to work well.
Their accuracy* is (in my mind) questionable, but probably 'good enough' to tell if someone is hypoxic (My wife's was 47% when she drowned & had her MI last month as measured by the lifeguards, which I can believe) .

I'd guess the precision* of these devices on a single given individual is much higher and much more useful in that they will give an early warning of a major change in someone's condition.
I'd suggest that the skin colour, skin thickness and dirt will be a major variable factor between individuals.

Skin saturation monitors are far better than the definitive way of measuring oxygen saturation which is to use arterial blood sampling which is difficult and unpleasant.

Yes, I have previous in this field.

*Accuracy = actual value measured against a gold standard method. Precision = repeatability of result.

[Jdsk]

It wasn't just me everybody on the ward got tested (very regularly) and for blood O2 (I wonder how accurate these little LED devices are as it always seems to come out 98% or greater) .

The finger oxygen saturation monitors seem to work well.
Their accuracy* is (in my mind) questionable, but probably 'good enough' to tell if someone is hypoxic (My wife's was 47% when she drowned & had her MI last month as measured by the lifeguards, which I can believe) .

I'd guess the precision* of these devices on a single given individual is much higher and much more useful in that they will give an early warning of a major change in someone's condition.
I'd suggest that the skin colour, skin thickness and dirt will be a major variable factor between individuals.

Skin saturation monitors are far better than the definitive way of measuring oxygen saturation which is to use arterial blood sampling which is difficult and unpleasant.

Yes, I have previous in this field.

*Accuracy = actual value measured against a gold standard method. Precision = repeatability of result.

Yes: within-individual trend can work much better than comparison to population reference values. (And this is particularly important in using other investigations to monitor chronic conditions, and it often isn't done well.)

Yes: for pulse oximeters there is a problem of bias with skin pigmentation and with race. Here's a convenient paper, and the FDA are looking at it, but I don't know the outcome:
https://www.nejm.org/doi/full/10.1056/NEJMc2029240

Yes: pulse oximetry vs blood gas analysis on arterial blood. As in the old saw: "Investigations need to be cheap, quick and accurate, which two do you want?".

Jonathan

From that paper:

[simonineaston]

As in the old saw: "Investigations need to be cheap, quick and accurate, which two do you want?".

The motto matches the cycle engineer's: "Components need to be strong, light and inexpensive..."

[Jdsk]

Me neither... the difference between the guidence linked by Jonathan and what I had at my local medical centre is quite large!

...
I'd guess the precision* of these (pulse oximetry) devices on a single given individual is much higher and much more useful in that they will give an early warning of a major change in someone's condition.
I'd suggest that the skin colour, skin thickness and dirt will be a major variable factor between individuals.
...

Thanks, millimole. That made me think about bias in measurement of blood pressure. And that reminded me of simonineaston's observation about following guidelines.

I knew about ethnicity and hypertension, both in prevalence and choice of treatment, But not about this. Off to do some reading and so far I've found this:

"Blood Pressure Measurement Biases in Clinical Settings, Alabama, 2010–2011":
https://www.cdc.gov/pcd/issues/2016/15_0348.htm

Jonathan

[Jdsk]

As in the old saw: "Investigations need to be cheap, quick and accurate, which two do you want?".

The motto matches the cycle engineer's: "Components need to be strong, light and inexpensive..."

: - )

Don't we like triads?

Jonathan

[djnotts]

" for blood O2 (I wonder how accurate these little LED devices are as it always seems to come out 98% or greater)

I wish mine still always showed 98%! It did on my gadget and the professionals' for some years despite the COPD.Fell to 92/93 while covid positive, which has clearly done some longer term harm as recovered to only 96/97.
I view the device as a cheap, easy to use and pretty accurate early warning aid.

[Jdsk]

" for blood O2 (I wonder how accurate these little LED devices are as it always seems to come out 98% or greater)

I wish mine still always showed 98%! It did on my gadget and the professionals' for some years despite the COPD.Fell to 92/93 while covid positive, which has clearly done some longer term harm as recovered to only 96/97.
I view the device as a cheap, easy to use and pretty accurate early warning aid.

Me too.

And if many show unremarkable readings in any particular group of people that does not mean that they aren't valuable in that early warning rôle.

Jonathan

[Mick F]

Chilled out ....... as usual in the evening .............. 115 over 57.
I'll get back on this tomorrow morning and a "chilled out" reading will be MUCH higher.

Prediction eh?
Based on experience of me.

[Bsteel]

Table from a 2009 paper titled.
The Importance of Accurate Blood Pressure Measurement
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2911816/

[simonineaston]

I would so love to see a continuous trace of bp over a 24 hour period, taken say from an ordinary individual with no otherwise obvious medical conditions - I bet it goes up & down like a fiddler's elbow...

[Mick F]

Chilled out ....... as usual in the evening .............. 115 over 57.
I'll get back on this tomorrow morning and a "chilled out" reading will be MUCH higher.

Prediction eh?
Based on experience of me.

139 over 73 at 8.45 this morning.
I expected higher.

Just done it again 10.54 ....................159 over 98

[Bsteel]

I would so love to see a continuous trace of bp over a 24 hour period, taken say from an ordinary individual with no otherwise obvious medical conditions - I bet it goes up & down like a fiddler's elbow...

Something like this, taken from "Decoding White Coat Hypertension".
https://www.researchgate.net/publicatio ... pertension

[simonineaston]

Thanks so much!

[Mick F]

BP as measured is a "sreenshot" of it.
It's up and down - with me - horrendously.

No-one has ever told me what my BP actually is.
Even me, measuring it, doesn't know because it varies so much minute by minute.
Go to the doc/nurse/whatever, and they measure it, write it down, and they put me on meds!

They don't take it into account that I've walked there, or cycled there, and sat down in the waiting room clock-watching and getting stressed out.