How to understand the Pulse Oximeter?

B

Bravo

Pre-takeoff checklist
Joined
Feb 9, 2014
Messages
138
Location
Maryland
Display Name
Display name:
Bravo
I have one of those ones you put on your finger and it gives you the digital readings. I would like to know how to make the most out of that information. How low are you at risk of hypoxia? I'm not looking for answers like if it's below 90% you should be on oxygen. I'm looking for any hard data that could be helpful to me or my passengers.

Example 1: I am flying along at 10k and check my 4 year old. What numbers would indicate a serious problem. What ranges are safe? What is good?

Example 2: my wife checks it and asks how low is ok for her? What is good?

Both of these came up on a recent flight while I opted to be on oxygen at night and I wasn't sure of the answer.
 
Check your pulse ox on the ground and note what it is - remember there is an ever increasing degradation below 90-92ish i.e the difference between 88 and 90 is huge, the difference between 90 and 92 not as much.

I would want mine to stay over 92 the whole time or get on O2...
 
If it's below 90% you should be on O2. :D

If you're a smoker and your pax isn't then go on oxygen when they do.
 
Looking for hard data, huh...

Well, the pulse oximeter is subject to errors. Certain conditions such as carbon monoxide poisoning will cause it to read incorrectly; google will easily generate a list of such conditions.

90% or greater is generally considered good, safe, choose your adjective. Continuing a flight with readings less than 90% will typically result in symptoms of hypoxemia; again, a list of these symptoms may be generated by google. Search for oxyhemoglobin disassociation curve. This curve explains why 90% is an important number. Below 90% the amount of oxygen carried in the blood decreases rapidly.

In all honesty it sounds like you are asking if less than 90% is acceptable, good, safe, etc. Google hypoxemia symptoms and risks. Typically mild hypoxemia generates mild symptoms, typically... An O2 setup can be relatively cheap to buy and use; you need not buy an aviation O2 setup... If you are concerned about saturation, you would likely benefit from exploring a cheap O2 setup.
 
Bravo said:
I have one of those ones you put on your finger and it gives you the digital readings. I would like to know how to make the most out of that information. How low are you at risk of hypoxia? I'm not looking for answers like if it's below 90% you should be on oxygen. I'm looking for any hard data that could be helpful to me or my passengers.

Example 1: I am flying along at 10k and check my 4 year old. What numbers would indicate a serious problem. What ranges are safe? What is good?

Example 2: my wife checks it and asks how low is ok for her? What is good?

Both of these came up on a recent flight while I opted to be on oxygen at night and I wasn't sure of the answer.
Click to expand...

See here. What is non-obvious is the "oscillation" effect, which depends on your breathing rhythm. You must be aware of that to use this device properly.
 
I own a 2006 Turbo 182T and have on-board oxygen. Do not need another oxygen setup nor am I looking to do anything dangerous. I personally use oxygen above 10k during the day and above 7k at night. I would feel much more comfortable knowing what levels my passengers are safe without oxygen which is the primary intent of this post.
 
Keep the pax over 90 ,unless you want a sleepy passenger. As I get older I would go on ox above 10 k ft. ,of course I was once a smoker. My usual pulse ox is 94-95.
 
Bravo said:
Thanks for the link.
Click to expand...

My pleasure. AFAIK Dr. Brent Blue is the foremost expert on pulse oximeters in aviation, and is the first to have discovered and explained that oscillatory effect.
 
Bravo said:
I own a 2006 Turbo 182T and have on-board oxygen. Do not need another oxygen setup nor am I looking to do anything dangerous. I personally use oxygen above 10k during the day and above 7k at night. I would feel much more comfortable knowing what levels my passengers are safe without oxygen which is the primary intent of this post.
Click to expand...
It would be difficult (or impossible) to know what levels your passengers will be safe. Generally the healthy will tolerate greater insults. Generally a saturation of 90% or better is safe. The reality though is every time you take someone to altitude you are conducting a stress test. Here is a little more information on altitude sickness.
http://emedicine.medscape.com/article/768478-overview
 
It sounds like there are two competing issues - pax safety and pax comfort. You don't want your paxs to have to wear the 02 masks or whatever your airplane is equipped with. Since you're on the East Coast (according to your profile, Maryland), why not just fly lower when you have the paxs on board. The TAS penalty between 9k and 10k feet isn't going to be that substantial...
 
Seems to me we have an anesthesiologist hanging around here (Gary F maybe?) -- that would probably be the best person to ask your specific questions about what constitutes a dangerously low O2 saturation level in a 4-year-old or your wife. Of course, that is going to be a significantly lower level than the levels where your flying abilities are adversely affected.
 
Be careful of too much O2. We had a glider pilot that religiously used his O2 above 10K, but he did not have a good meter and would have headaches at the end of a long flight at altitude. Then he got a pulse ox meter and found his numbers on O2 was running 98%. He dialed back his use to keep it closer to 94% and felt much better at the end of a long day at altitude.

Hydration counts too, hours at altitude can dehydrate. Dehydration leads to problems with decision making and leads to landing accidents or problems. Mild O2 deprivation at altitude many times goes unnoticed. You have a sense that all is ok when it is not.
 
BillTIZ said:
Be careful of too much O2. We had a glider pilot that religiously used his O2 above 10K, but he did not have a good meter and would have headaches at the end of a long flight at altitude. Then he got a pulse ox meter and found his numbers on O2 was running 98%. He dialed back his use to keep it closer to 94% and felt much better at the end of a long day at altitude.

Hydration counts too, hours at altitude can dehydrate. Dehydration leads to problems with decision making and leads to landing accidents or problems. Mild O2 deprivation at altitude many times goes unnoticed. You have a sense that all is ok when it is not.
Click to expand...

Hard to believe too much 02 could be a bad thing. Any chance he was using bad air?
 
BillTIZ said:
Be careful of too much O2. We had a glider pilot that religiously used his O2 above 10K, but he did not have a good meter and would have headaches at the end of a long flight at altitude. Then he got a pulse ox meter and found his numbers on O2 was running 98%. He dialed back his use to keep it closer to 94% and felt much better at the end of a long day at altitude.

Hydration counts too, hours at altitude can dehydrate. Dehydration leads to problems with decision making and leads to landing accidents or problems. Mild O2 deprivation at altitude many times goes unnoticed. You have a sense that all is ok when it is not.
Click to expand...

I dont think you have have too much 02, more than likely he was dehydrated by the excess 02. I normally run 98%, at least that is what my meter tells me when I am on the ground. 1500' MSL.
 
BillTIZ said:
Hydration counts too, hours at altitude can dehydrate. Dehydration leads to problems with decision making and leads to landing accidents or problems.
Click to expand...
I think dehydration negatively impacts more pilots' performance, more often, than we are aware of.

We are frequently motivated to maintain a certain level of dehydration to limit urination. It's easy to unknowingly overdue it.

Stress can exacerbate the effects and do so in some non-obvious ways.

My soaring experiences led me to focus on staying comfortably hydrated in all conditions and to stop trying to limit urination while flying. The former is particularly challenging on some days in some cockpits, the latter takes a lot more work as I've aged.

Is there something like a pulse oximeter and 90% for hydration? I don't think the NTSB has any criteria for determining possible dehydration effects on pilots in accidents.
 
Dehydration is what probably caused the headaches.
 
Bravo said:
Hard to believe too much 02 could be a bad thing. Any chance he was using bad air?
Click to expand...

Well you do have Oxygen Toxicity above about 1.5 Bar, but that only affects divers especially tech divers.
 
ARFlyer said:
Well you do have Oxygen Toxicity above about 1.5 Bar, but that only affects divers especially tech divers.
Click to expand...
Oxygen toxicity may occur outside of diving also. Breathing 100% FiO2 may cause atelectasis, cell damage, vision changes including permanent damage, and more. That said, a cannula or even a mask is not capable of 100% FiO2. As such the risk for pilots is esoteric.

Best course of action for the OP would be to administer O2 when the SaO2 reading of his pulse oximeter is less than 90% or when any of his passengers exhibit symptoms of hypoxemia. Most of us have or will tolerate readings less than 90% but at the cost of being symptomatic. Oxygen can be inexpensive; we might as well use it when indicated.
 
ARFlyer said:
Well you do have Oxygen Toxicity above about 1.5 Bar, but that only affects divers especially tech divers.
Click to expand...

Yeah, it takes a hell of a pressurization system to get a 1.6 (you can go 1.8 and even 2.5 at rest if you take air breaks) PPO2.:lol:;) BTW, that's a Partial Pressure figure that happens above 7 Bar ambient pressure, that's over 100 psi pressurization with air.

Although on pure O2 you could get a CNS hit with 28 psi pressurization.
 
Last edited:
You must log in or register to reply here.
Back
Top