Spo2 in the mountains

[John111]

Fellow EMTs,

I recently took a trip to Rocky Mountains National Park in CO with my kids. We live at sea level so I was worried they might get altitude sickness from flying in to nearly 8,000 ft and hiking at 9-10k next day. We took all standard precautions like taking it slow, lots of water, being ready to descend on first symptom, etc. But what caught my eye was that some mountaineers routinely use pulse oximeter to predict altitude sickness before it hits. So I got one before the trip.

Kids played with it at home and all of us always were getting 97%-99%. In my ambulance corps we always take and record Spo2 and I've rarely seen anyone below 95%. For the sake of science, I held my breath as long as I could until I almost passed out, and it showed 92%. Once I resumed breathing, it shoot up to 99% in seconds.

On a 3rd day of hiking my daughter tells me - so what about that doohickey which you put on a finger? I completely forgot about it. I got it out of backpack and put it on myself. 76%. Whoa. My daughter had 82%, son 85%. I rechecked on several fingers to be sure - same or very close numbers. We all felt just fine - at ~11,000ft. Back in hotel at 8000ft numbers were higher, but nowhere close to 95%. When we got back home at sea level - all of us were again at 97-99% range.

My findings seem to be in line with published research. What I don't get is how I felt like I was going to pass out at 92% at sea level but was absolutely fine with 76% higher up? What about charts which say that 90% is beginning of hypoxia, and 80% means risk of immediate organ failure? If you live in mountains, do you get to >95% at some point, or you live whole life with 25% of your hemoglobin not carrying oxygen? Do EMS in mountain areas have reference tables to figure out how low Spo2 should get to be a problem?

Looks like this topic hasn't been brought up since the beginning of EMTLife, so I thought I'll give it a try

Thanks,

John

 

[Summit]

Some things to think about disjointed very sorry:

We don't bat an eyelash at 7-9k for a 92% sat up on an acclimated person in hospital who feels fine. We only treat symptomatically or numbers below 90, acclimated or not. We tolerate patients in the 80s all the time when extricating and having limited supplies.

At 11k you guys were in the 70s and 80s on the finger unit... but what was your HR/RR? Notice you had to pee and drink more? Know why? Acclimatization is something to study. Know how you compensate over hours and days vs weeks and months. The primer would probably still be Herb Hultgren's High Altitude Medicine.

But is 80% "risk of immediate organ damage"? Before I ask how and why, what is the context? Someone attempting to oxygenate at sea level at rest with full compensation but unable due to pathology? Ever seen a sleep study on someone with sleep apnea? People can spend most of the night in the 80s and have few symptoms besides feeling tired until they suffer years of that stress (see signature). That's very different from profound hypoxia secondary to organ failure like acute heart failure or a COPD exacerbation etc etc.

Think about supply vs demand: Ever room air challenged a patient who has been on oxygen for days? How often have you measured your pulse ox after athletic exertion? Recovery times at sea level? Then you hike at altitude and exert... again, recovery times? Longer! But what is it that makes you primarily want to breath when you hold your breath? Hypoxia or acidosis? Is it different when you exercise at altitude vs sitting there?

Holding your breath... how long does that take to manifest on a pulse ox? (hint lot longer than you think) and how does the pulse ox calculate the percentage? Over how many seconds does it average data? 8s? 30s? Does your finger unit even tell you? I can have biomed reprogram my ICU monitors and telemetry monitors. Your finger unit is probably 15s averaging. Other things affect the reading... cold fingers? Heck you could have a 3 minute delay in mild hypothermia.

Is a pulse ox a useful predictor for AMS? I think the evidence is mixed. But you were going to turn around at the first symptom... I'd be shocked if anyone didn't have some symptoms. That new apple watch has "afib detect." Can you imagine if the new apple watch had a pulse ox? Panic on all the airplanes once cabin altitude rises to 8k!

Sorry for the disjointed response.

 

[chriscemt]

I'm going to be all amateurish and say that your "about to pass out" is a hypercarbic response, not hypoxic...

Also, next time I'm skiing Keystone (next January if you're jealous) I'm going to bring my own pulse oximeter and give this an n=2...

 

[Summit]

I'm going to be all amateurish and say that your "about to pass out" is a hypercarbic response, not hypoxic...

Also, next time I'm skiing Keystone (next January if you're jealous) I'm going to bring my own pulse oximeter and give this an n=2...

Feeling like you are about to pass out is usually hypocapnea (light headedness associated with alkalosis) but truly feeling that way is probably hypoxia (blacking out).

I'm sitting at 9500ft at the moment and my little finger unit says HR 64 SpO2 95 and I'm breathing about 14 but my Hgb/Hct is something like 19/56. Might need some therapeutic leeches.

 

[NPO]

As has been mentioned, low Spo2 is normal at elevation and you can feel completely normal.

Remember that central Chemoreceptors monitor CO2, not oxygen. It is typically high CO2 that causes a feeling of shortness of breath, and low CO2 that causes light headedness. You could be profoundly hypoxic and your body be unaware.

It is not uncommon to also see this on airlines as well. Airline cabins are pressurized, but not to normal ground level atmospheres. You may see Spo2 as low as 80% while on an airline. Take an Spo2 meter with you next time you fly and pass it around.

 

[sharpe15]

I live at 7500 feet and typically sat at around 92%. If I go down to Denver or Fort Collins (5000) it rises to the high 90s. It was around 80% when we drove up to Pike's Peak (14000) in May. They taught us in EMT class to give oxygen to anybody under 94%, but we typically don't administer O2 above 90 unless it looks like the patient needs it.

 

[Peak]

Another thing to consider is the pulse oximetry monitors can vary greatly in their displayed values compared to the oxygen saturation you would get off a blood gas (this is regardless of type of monitor, these very much affect the monitors in our PICU). While the values are different from different monitors typically they are within 2-3% of your capillary oxygen gas when you are above 90%, the deviation from a blood gas measurement increases substantially the lower your saturation is. Pulse oximetry monitors are affected by a number of variables including florescent lighting, nail polish, perfusion status (including but not limited to hydration, blood pressure, the use of vasoactive medications), medications that can alter hemoglobin's binding sites like nitroprusside, and many others.

If you are becoming dehydrated due to increased demand and respiratory rate, your body is shunting somewhat to compensate, your are getting colder, et cetera I would expected a much lower displayed value than both your first days at altitude as well as compared to your actual saturation.

I would also trust a physical assessment far more than a monitor in determining the effects of altitude sickness on an individual. I have had adults present with classic symptoms of altitude sickness with relatively normal oxygen saturation at 6000 feet and healthy teens/young adults who are visible cyanotic at altitude but are cognitively intact and still capable of exercise at 1400 feet. I worry far more about the first group than the latter.

What I don't get is how I felt like I was going to pass out at 92% at sea level but was absolutely fine with 76% higher up?

This is more likely due to acidosis/hypercapnia than oxygen saturation or pressure.

What about charts which say that 90% is beginning of hypoxia, and 80% means risk of immediate organ failure?

From a physiology perspective you would need to be substantially hypoxic to cause any kind of real damage, we have cardiac babies that live with a saturation of 60% for months or years until surgery (and in some ductal dependent heart diseases purposely keep them hypoxic to prevent closure). In the NICU our goal oxygen on non-cardiac patients is 90-95% when on supplemental oxygen, with the upper limit to prevent retinopathy of prematurity. In the adult world put a pulse ox on one of your drunk patients who doesn't have oxygen on and look at their saturations, 70s and 80s are not uncommon when sleeping/unconsious; there are many adults who have had a few too many and probably had similar saturations at home that night.

On the other side of the argument we know that patients with untreated central or obstructive sleep apnea are at higher risk for dementia and other nerological disease, which is thought to be in at least part due to their lower oxygen saturation during sleep. Respiration/gas exchange is far more complex than just an oxygen saturation measurement.

This is not to say that we shouldn't treat a low oxygen saturation, however it also depends on the individual patient. If a patient is in respiratory distress but has a saturation of 95% that doesn't mean that I'm not going to treat their distress, nor would I withhold oxygen in a (real) trauma patient. In the case of MI or stroke we often give some oxygen to patients with a normal pulse ox (up to 98 or 99%) in order to maximize the amount of oxygen going distal to the point of occlusion, even if it is a very small amount.

If you live in mountains, do you get to >95% at some point, or you live whole life with 25% of your hemoglobin not carrying oxygen?

Depends on the person, although I wouldn't expect a saturation of lower than 90% in 8000 feet or less while awake at altitude in the young healthy adult or school age child; there is probably more definitive literature on this but I gonna be a bit lazy and not look it up. I typically sat around 92% from 5000 to 10000 feet and sit in the high 80s if I go higher in altitude.

Do EMS in mountain areas have reference tables to figure out how low Spo2 should get to be a problem?

Depends on the agency and the mission, but generally speaking protocols state that goal saturation for most patients is greater than 90%. There are of course variances to this for limited resource environments, cardiac/stroke patients, trauma, et cetera.

As an aside NREMT, NCLEX, BCEN, et cetera all write for sea level; let me tell you about the joys of taking a test for an altitude you have never worked or trained at.

 

[John111]

Thanks a lot for very interesting and informative answers, really appreciate you all taking time to explain this in detail!

Research indeed seems to be quite mixed on Spo2's value in predicting altitude sickness. I found more studies saying there is no link than those which did find a link. To add a personal anecdote - none of us got any symptoms up there despite low Spo2 readings. Of course hiking took way more effort than similar distance/difficulty hike at sea level. But no nausea, headache, muscle pain, or dizziness.

Peak's note about sleep apnea being linked to higher rates of dementia got me thinking - what about risk when living in mountains? Quick search took me to several studies which show strong inverse correlation. People living at high altitudes have nearly 50% lower risk of developing dementia!

John

 

[E tank]

Thanks a lot for very interesting and informative answers, really appreciate you all taking time to explain this in detail!

Research indeed seems to be quite mixed on Spo2's value in predicting altitude sickness. I found more studies saying there is no link than those which did find a link. To add a personal anecdote - none of us got any symptoms up there despite low Spo2 readings. Of course hiking took way more effort than similar distance/difficulty hike at sea level. But no nausea, headache, muscle pain, or dizziness.

Peak's note about sleep apnea being linked to higher rates of dementia got me thinking - what about risk when living in mountains? Quick search took me to several studies which show strong inverse correlation. People living at high altitudes have nearly 50% lower risk of developing dementia!

John

Don't forget that a lot of the symptoms of altitude sickness are 2/2 the pulmonary hypertension and RV strain that results. That doesn't happen with everybody.

 

[johnrsemt]

I live and work at 4800' and I am always running around 90-92% room air. My partner even knows if I am getting about 98-99% I am getting ready to crash; (I have been in the ED at 66% on 4 L/m, (freaked out the ED doc).

When I lived in Indianapolis at about 300' I was the same; asthma is a fun thing.

I have never had a pulse ox when I go up to altitude, but one of these days I will take one.


A co-worker went with his wife to base camp at Everest (17,000') a few years ago; and did vital signs I will ask him if they did SPO2 % and what readings they got, and report it when I hear from him.

 

[johnrsemt]

I talked to my co-worker today:

They did an in depth study of people going to Everest; including some MRI's and CT's before and after the trip.

SPO2 usually does drop, but comes back after a couple to a few days; HR increases, but then usually dropped back to normal. Same with BP.

They decided it was the body's way of compensating for lack of oxygen.. To go up to Everest takes weeks; few days at 8,000'; days at 12,000' Week to 10 days at 17,000'. Etc. Shorter coming down, but you have to delay coming down too, otherwise you can have health problems and they don't know why that happens..

 

[NPO]

but you have to delay coming down too, otherwise you can have health problems and they don't know why that happens..

Unless you're sick. Rapid decent is the only treatment for HAPE and HACE.

Just wanted to throw that in there.

 

[johnrsemt]

Rapid descent is the only cure for true altitude illnesses; and it can be a problem.
And it isn't just people that come from sea level and go into the mountains that have altitude issues: We had a Boy Scout a couple of years ago that lives at 5100' and goes hiking and camping a lot with the Scouts and his family up around 7000-7500' That went back packing with his troop last fall up to about 10,000'. They had done some shakedown hikes at that altitude and higher without problems. He told his leaders at dinner and just before bed he had a headache, and they had him drink more, then gave him something for the headache.
When the rest of his troop woke up the next morning he was dead. The ME after autopsy said that it was HACE. Couldn't find anything else or anything that contributed to it. Which was very weird.