UKC

Had this measured today. Never come across it before.

What does it 'explain' (i.e. why are they looking at it)

In reply to ClimberEd: Isnt it percentage of oxygenated blood in your arteries compared to non-oxygenated blood?

In reply to ClimberEd:
like osmosis (iirc) oxgen moves across the gradient. so if your muscles have 50% and your blood 70%, the muscles get oxygen.

if your haemoglobin has been compromised/poisoned by e.g. carbon monoxide, it won't be able to carry oxygen.
I think.

In reply to thin bob:

But as a standard check at hospital (it came off the thingy they clipped to my finger)

In reply to ClimberEd: I had this constantly monitored after my op, and anything less than 95% caused the alarm to go off! I kept dropping to 92%, then they told me to sit up, and that caused me to breathe deeper so the blood oxygen rose.

In reply to ClimberEd:

That was probably a pulse oximeter:
http://en.wikipedia.org/wiki/Pulse_oximetry

In reply to thin bob:


true, Haemoglobin prefers CO to O2 in a simple sense so will bond to it more readily than O2 thus slowly suffocating you

In reply to owlart: It drops at high altitude 85% - 90% although I've seen 80% and below occassionally. This was the reason for the Extreme Everest Study - you can sort of acclimatise to Oxygen levels at extreme altitude which would be intolerable normally - so how the body adapts could be useful for sick patients at sea level.

In reply to m0unt41n: However, my op was done not far off sea level, and they hadn't taken me to altitude first to acclimatise, so anything below 95% was a concern to them.

In reply to ClimberEd: Theya re just checking how well your lungs are working: how much oxygen your blood is carrying, how well you are transfering oxygen to your blood.

In reply to lynda:

Should it be 100%?

In reply to ClimberEd: yes, somewhere between 97 and 100. your normal

In reply to ClimberEd:

>> The closer it is to 99% the happier the medics are.

In reply to ClimberEd:

Yeah when I got HAPE, mine was measuring at about 89% - can't be good!


Chris

In reply to ClimberEd: I've had mine down below 80 regularly when putting some effort in above 5000m. The little electronic ones you finger to measure O2 sats work by measuring light / colour through your blood apparently. V clever.

In reply to ClimberEd:
Falsely low readings may be caused by hypoperfusion of the extremity being used for monitoring (often due to the part being cold or from vasoconstriction secondary to the use of vasopressor agents); incorrect sensor application; highly calloused skin; and movement (such as shivering), especially during hypoperfusion.

When I was in the Khumbu, one of my companions got HAPE bad. We got him to the clinic at Pheriche ably manned by Dr Dubowicz. They took his O2 sat and it was at 53%. They were stunned that he was still concious. They then did an ultrasound scan of his heart and discovered very bad tricuspid regurgitation (ie one of the valves in his heart wasn't doing what it was supposed to). Lots of drugs later, he recovered and managed to cross over a high pass afterwards.

In reply to Chris Ellyatt:

Dunno what altitude you were at... but if you were above 4000m, not acclimatised and you had 89% you probably didn't have HAPE! I'd ask for a refund

In reply to ClimberEd: We use pulse oximetry to give us an idea of how much oxygen is circulating in your blood and therefore how well your organs are being supplied. It is by no means fool proof but it is a very handy gizmo to have. Measures pulse too, again its not a substitute for feeling and counting but it helps keep an overview of a patient's state of perfusion.

In reply to adamtc: Just to complcate matters, the 02 saturation measures how much oxygen is dissolved in your blood, and not how much is being carried by haemoglobin. So if you were anaemic you could have a normal saturation, but not be able to deliver enough oxygen to tissues.

on Aconcagua there are medical stations where it is compulsory to be tested, and if your saturation is not high enough you may be sent down the hill.

In reply to Jack Frost:

I was digging out basecamp tent platforms at 5,100m with Gerald Dubowicz and his wife in 2003. Debby was feeling a bit rough so checked herself with a pulsoximeter - 43%! Rest and some mild medication was all she needed!

In reply to Dean177:

Also watch out for nicotine stained fingers and nail varnish!

In reply to David55:


>Just to complcate matters, the 02 saturation measures how much oxygen is dissolved in your blood, and not how much is being carried by haemoglobin. So if you were anaemic you could have a normal saturation, but not be able to deliver enough oxygen to tissues.

It measures oxygen as a percentage bound to the haemoglobin - oxyhaemaglobin, so you are half right. It doesn't measure carbon monoxide so it can't tell if you have been exposed to a source, even if O2 % is low. There are one or two pulse co-oximiters available which claim to do this. Increase accuracy of any pulse oximiter by covering the probe - its affected by ambient light.

Regards

D

In reply to tony: Used to have a Casio watch that did the same, great for starting a conversation with the laydeez in the bar. Can't get one now....

In reply to Denzil:

This happened to my wife at 7,200 m on Cho Oyu. From memory it was high 30's to low 40's . We gave her 1l/min Oxygen for several hours and she was fine. I dont trust Pulse Oximeters

In reply to ClimberEd:

Was planning on getting one of the little monitors for an attempt on Broad Peak. Was thinking it would give additional information which would distinguish between feeling knackered and having a real problem.

From the posts it seems like these things would put you in the ball park of what % your at. But it depends upon the person, for what % should raise alarm bells for you.

Have I got the right end of the stick?

In reply to jonnyboy: It seems like you've got the right idea - it will give extra info but interpretation will depend on the person. Also worth keeping the pulsox on for a few minutes and looking at how the sats vary over that time. On the 94 Medex trip we noted that as you acclimatised the min/max range over a few minutes reduced - I assumed due to the body's oxygen and CO2 control loops adjusting to the changed conditions.

In reply to Denzil:

Cheers, thanks for your help. I just wasn’t sure if there was even any loose guidance out there to stay within.

Can anybody recommend any particular make and model?

In reply to jonnyboy:

You should not think of going to extreme altitude without one! Yes, the readings vary but the day to day trend will give you a good idea of your acclimatisation. In a medical emergency very handy aid for diagnosing AMS.

They aren't cheap in the UK - mine is a Nonin Onyx, has lasted 5 or 6 years and is well travelled.

In reply to AndyUKC:

can you support that with any sort of evidence?

In reply to AndyUKC:
Sorry Andy, but AMS has nothing to do with your oxygen saturations. And I wouldn't rely on a pulse oximeter (which have a lot of limitations, particularly in cold temps when poor peripheral perfusion is likely to be an issue) to either reassure me or worry me about developing any of AMS, HAPE or HACE or giving me any information about my acclimatisation. In an extreme situation they *may* (and there's still a lot of ifs/ands/buts) tell you that you're totally buggered and you need help fast, but you probably knew that anyway. And just because your sats are "normal" (bear in mind they're not going to be >95% at any altitude that's like to cause you bother anyway, so you'd have to painstakingly compare your sats to the predicted sats for that altitude and barometric pressure to even work out what "normal" is) doesn't mean it's safe for you to crack on.

Can you provide any evidence that oxygen saturations as measured by pulse oximeter correlates with acclimatisation? Most acclimatisation is, AFAIK (and I'm by no means an expert on this), related to improved oxygen uptake/consumption, shift of oxyhaemoglobin dissociation curve, and then (over a longer period) erythropoiesis, none of which would be reflected in a pulse oximeter reading.

Pete.

In reply to Dr.Strangeglove:

Depends which part of what I wrote you are referring to - that %SpO2 is directly related to your level of acclimatisation goes without saying. %SpO2 will vary depending on how much work you are doing / have done, your level of hydration etc. For acclimatisation monitoring you need to try and be consistent with your measurements.

That people with HAPE generally have low and reducing %SpO2 is an easy observation and a couple are made in this thread.

If in doubt... descend.

In reply to PeteH:

I didn't mean to imply the oximeter was a definitive tool for diagnosing AMS, although it will provide additional information. In an emergency, on the other hand, it is very useful for patient monitoring.


Only personal observation made over the years. Go straight to 4000m from sea level and your %SpO2 will probably be in the mid 80s. After a four of five days you should be getting up into the low to mid 90s. Go higher and it will fall again, then gradually increase. But there is a maximum that can be reached with is inversely proportional to altitude. Different for different people.

In reply to AndyUKC:
As an addendum to my comments above, I just realised that I wrote that raised 2,3-DPG and/or shift in the oxyhaemoglobin dissociation curve wouldn't be reflected in the sats - which is of course a bit silly. Although the truth is quite complicated - raised 2,3-DPG, which happens pretty fast at altitude, shifts the curve to the right, which improves O2 uptake by tissues but would actually be expected to reduce arterial saturations, rather than increasing it - which is why I was confused by your assertion that acclimatisation should lead to higher sats.

Just had a quick read around this. The physiology textbooks say that your P50 should be slightly higher after acclimatisation, i.e. lower saturations for a given pressure of oxygen, due to a combination of raised 2,3-DPG and respiratory alkalosis which then corrects due to renal compensation. That's kinda what I thought. However, there is actually some evidence that saturations do improve with acclimatisation, as you've said (http://www.ncbi.nlm.nih.gov/pubmed/8410766 ), although no-one seems to be explaining why... Anyone else able to help us out?

You're right that an oximeter is a useful tool in an emergency, but I'll still say it's not of much use in diagnosing altitude-related illness in general, and certainly not AMS.

Pete.

In reply to PeteH:
its all a good complex field, but one way is by hyperventilating - this drops the partial pressure of CO2 in the lungs and allows a greater partial pressure of oxygen leading to higher PaO2 and hence saturation.

In reply to Dr.Strangeglove:
I thought about that - it's true that hyperventilation will cause a slight increase in alveolar PO2 (by eliminating CO2 and allowing alveolar gas to more closely resemble atmospheric gas), but I thought that would be a fairly rapid response (within hours) and so wouldn't account for saturations gradually increasing sats over days at altitude.

Just had a bit more of a read though - initial hyperventilation is limited by the resultant respiratory alkalosis, and it's only as you get renal compensation for the alkalosis that respiratory rate can continue to rise. So maybe that's it?

I think I need to track down someone who actually knows the field to confirm the above!
Pete.

To the OP:
Er, muchos apologies for blatant thread hijack!

In reply to AndyUKC: As far as AMS diagnosis the standard is the Lake Louise scoring system - how many of the AMS symptoms have you got and how bad are they. See page 14 of the Medex booklet:
http://medex.org.uk//medex_book/about_book.php

In reply to ClimberEd: Having read all the threads for this no doubt some is going to give you the full works on respiratory physiology and an explaination of the alveolar gas equation. Essentially it is a calulated determination of peripheral oxygen satuations and does not replace blood gas analysis. readings from 100% to 90% are ok. However at 90% you are approaching the steep part of the oxygen dissociation curve and thus an small drop in partial pressure of oxygen will cause a large reduction in % oxygen readings. This shape of curve is important for unloading of oxygen and the collection of CO2. Yes the readings can be affected by poor perfusion and other factors outlined and that is why in acute situations it is considered along with other symptoms.
Having said all this it is just possible that the healthcare professional taking your SpO2 was just too lazy to take your pulse (as it gives a pulse reading but gives no information to the quality of the pulse). often healthcare professionals take SpO2 in routine situations when perhaps it is not going to add anything to the clinical picture. As suggested there is a multiple of physiology books and websites get further info.
Cheers
Andy
Andy