# Are Finger Pulse Oximetry Devices reliable?



## Noel (Jan 21, 2016)

I recently bought my finger ox from amazon by a brand called accU-rate which was a CMS 500 DL and was having second thoughts if these devices were reliable in charting PT VS. Obviously for spo2 and HR. I don't want to seem reliant on technology to do my job due to already having skills to acquire VS, but it'd be nice having a little help w/charting VS on such short PT transports.


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## ThadeusJ (Jan 21, 2016)

I have been to many international trade shows where these things can be stacked like packs of gum and sold for a few dollars.  Technically they should be calibrated for accuracy, however as licensed medical devices they should be considered accurate enough to rely on.  That being said, technology is only as good as the person using it (and who recognizes those limitations).  Whether its accurate enough to obtain a signal when you need it the most or whether the output will change the way you treat a patient is another matter altogether.


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## Aprz (Jan 21, 2016)

I would consider it reliable if it fits the patient's presentation. Use multiple methods to confirm it is correct.


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## Flying (Jan 21, 2016)

Pulse oximeters are quite reliable no matter what you buy. By design they are increasingly less precise at readings below mid-80%, but at that point we can usually accept that there is a problem from just the gross examination and/or history of the patient and act on it (or not at all).

As Aprz said, confirm your readings with the patient first. Correlate the plethysmograph with the patient's pulse. If your device does not have a pleth, you're better off just timing the palpated pulse in the first place.


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## Qulevrius (Jan 22, 2016)

Noel said:


> I recently bought my finger ox from amazon by a brand called accU-rate which was a CMS 500 DL and was having second thoughts if these devices were reliable in charting PT VS. Obviously for spo2 and HR. I don't want to seem reliant on technology to do my job due to already having skills to acquire VS, but it'd be nice having a little help w/charting VS on such short PT transports.



Always ask the sending facility for baseline v/s, then take your own initial v/s on scene (your partner is an ideal candidate to do that while you get the verbal and handle the rest of the paperwork), followed by another immediately prior to transport. If pt is stable and transport time is shorter than 15 min, take your last v/s @ the receiving facility. That's plenty of data to populate the PCR and you don't kill yourself over it. As far as pulse ox devices go, they're helpful with baseline O2 sat readings and HR but since they don't show the hemoglobin count, it can be quite dangerous in certain situations. I would suggest not blindly relying on SpO2 reading but supplement the readouts with pt's presentation and general impression.


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## ThadeusJ (Jan 22, 2016)

If you've never used one, heed those words stated by our esteemed colleagues above.  I don't know how many times I've seen HR recorded as 300 bpm when the patient has the shakes or as 25 when there's lousy circulation.  I actually had to come right out and tell someone that if they recorded 300 I'd report them (just because they insisted that they record what the machine tells them).


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## joshrunkle35 (Jan 23, 2016)

I put it on my own finger and take my pulse at the beginning of my shift. I am good with about a 5% difference in pulse rate. (Also, finger vs radial technically could be slightly different). Pulse ox can be unreliable for things like CO poisoning. 

Never forget what I'm sure everyone learned on day one of EMT school: treat the patient, not the monitor. Go with your general impression of the patient rather than what your gear tells you. Until we're all doing echocardiograms, ultrasounds, MRIs, lab values, etc...gear is a tool to help you. Not a definitive piece of diagnostic equipment.


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## NomadicMedic (Jan 23, 2016)

Really? A monitor isn't a price of diagnostic equipment? 

Tell me again where you're a medic, so I never go there.


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## Underoath87 (Jan 23, 2016)

I don't know whether you're questioning the reliability of a cheap pulse-ox, or the efficacy of pulse oximetry in general.  However, I can say that I've used dozens of different $30 CVS pulse oximeters, and they read the same as one connected to any expensive monitor.  

You just need to be aware of the factors that can cause a false-low reading.  I've never seen one read falsely high (though I know it would for CO poisoning).  So long as the pleth is reading well, the pulse rate should be accurate.


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## Qulevrius (Jan 23, 2016)

> I've never seen one read falsely high (though I know it would for CO poisoning).



It's more about the SpO2 reading which is never reliable. Can easily be 80% O2 with 15% CO2 but the meter will show a solid 95%. No bueno.


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## joshrunkle35 (Jan 23, 2016)

DEmedic said:


> Really? A monitor isn't a price of diagnostic equipment?
> 
> Tell me again where you're a medic, so I never go there.



I'll note that you changed my wording, and therefore my context. I said "Definitive". I never stated that it wasn't a piece of diagnostic equipment. Taking something out of context and then jumping down someone's throat for it is silly.


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## NomadicMedic (Jan 23, 2016)

joshrunkle35 said:


> I'll note that you changed my wording, and therefore my context. I said "Definitive". I never stated that it wasn't a piece of diagnostic equipment. Taking something out of context and then jumping down someone's throat for it is silly.



So  with rapid pulse rate you don't use that monitor to definitively diagnose VT, Afib or SVT? You don't use that glucometer to determine hypoglycemia in an altered patient?

I'd say that using technology to definitively diagnose and start a treatment pathway is pretty important. 

Making statements like "treat the patient, not the monitor" is pretty shortsighted. How about you treat the patient _and_ the monitor and leave the EMS "pearls of wisdom" where they belong... In the past.


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## Underoath87 (Jan 23, 2016)

Qulevrius said:


> It's more about the SpO2 reading which is never reliable. Can easily be 80% O2 with 15% CO2 but the meter will show a solid 95%. No bueno.



I don't think you understand how a pulse oximeter works (or even RBC's)...


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## gotbeerz001 (Jan 23, 2016)

.....


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## joshrunkle35 (Jan 23, 2016)

DEmedic said:


> So  with rapid pulse rate you don't use that monitor to definitively diagnose VT, Afib or SVT? You don't use that glucometer to determine hypoglycemia in an altered patient?
> 
> I'd say that using technology to definitively diagnose and start a treatment pathway is pretty important.
> 
> Making statements like "treat the patient, not the monitor" is pretty shortsighted. How about you treat the patient _and_ the monitor and leave the EMS "pearls of wisdom" where they belong... In the past.



Something being "indicative of" vs "definative" are separate things. A monitor can indicate V-Fib, and yet you can have artifact, loose wires, etc...hence why we treat the patient not the monitor first. I'm not going to shock someone who's alert and oriented and talking to me if the monitor indicates V-Fib. Additionally, electrophysiology is way more complicated than the few weeks of schooling we paramedics have on it. That's why doctors who are specialists in those areas exist. Just because the monitor "absolutely" says they have one thing, even after I check the leads and confirm in more than one lead...I have an indication, which informs me of how to most appropriately begin treatment as best as I understand it at the time. However, it is way more complicated than that, and my best indication is not the same thing as a definitive diagnosis. In the same way, a pulse oximeter is a tool, also used to indicate findings, but it is not definitive. If it were, there wouldn't be doctors who specialize in placing arterial IVs to read capnography, arterial pressures, etc. We wouldn't bother with blood gases or CBCs if pulse oximetry was definitive. 

Indicative is not definitive!


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## joshrunkle35 (Jan 23, 2016)

Qulevrius said:


> It's more about the SpO2 reading which is never reliable. Can easily be 80% O2 with 15% CO2 but the meter will show a solid 95%. No bueno.



CO2 and CO are not the same thing.


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## Qulevrius (Jan 24, 2016)

Underoath87 said:


> I don't think you understand how a pulse oximeter works (or even RBC's)...



Ok mate, so which part do you think I do not understand ? The one where RBCs carry hemoglobin that O2, CO and CO2 bind to or the one where a pulse oximeter doesn’t tell you if pt is retaining CO2 or has CO in his/her blood ?


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## Run with scissors (Jan 24, 2016)

it's as reliable as a parachute. it's supposed to work, if you use it right. but some times. you have to pull out your back up method.


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## Flying (Jan 24, 2016)

Qulevrius said:


> Ok mate, so which part do you think I do not understand ? The one where RBCs carry hemoglobin that O2, CO and CO2 bind to or the one where a pulse oximeter doesn’t tell you if pt is retaining CO2 or has CO in his/her blood ?


Pulse oximetry works by measuring the amount of red/near-red light reflected by activated heme (hemoglobin carrying something).

First, the major problem is that the ability of CO2 to form a stable complex with hemoglobin is far inferior to CO. So we are not worried so much about CO2 messing with the reading.
Second, it doesn't matter whether or not a pulse oximeter can differentiate between CO2 and O2 because the majority of CO2 in the body is in the form of bicarbonate ion.
Third, the HbCO2 complex does not reflect red light and is in fact blue, contributing to the trademark colour of deoxygenated blood.

Pulse oximetry has been around for a few decades now. Its simplicity and the ubiquity of the electronics has made the tool very reliable.



Run with scissors said:


> it's as reliable as a parachute. it's supposed to work, if you use it right. but some times. you have to pull out your back up method.


This statement is too general to take anything useful from.


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## Flying (Jan 24, 2016)

Addendum:
By "trademark colour", I mean darkish brown/red blood, not blue venous blood.

One could argue that the 10-20% of CO2 bound to hemoglobin in the blood might-maybe-sort-of mess with the SpO2 reading, but we're waaay past that in the 21st century. The wavelengths of light that are being used in current devices take this into account and they have been pretty much set in stone since the 90s.


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## 18G (Jan 24, 2016)

I have read that these cheap $30 pulse oximetry units from China do not reflect changes in saturation values as quickly as more expensive models. I also have to question their efficacy during critically low perfusion states. 

A Masimo or Nelcore pulse oximeter can cost upwards of $800-$1,000. All of that surely isnt in a name. You get what you pay for. I prefer to use a clinically tested piece of diagnostic equipment.


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## meatanchor (Jan 24, 2016)

I'm sure it depends on the application.  For volunteer SAR teams like ours, we wouldn't be able to justify the cost of a hospital-quality unit that would get used 2-3 times per year.  While they probably aren't as good, the cheap (nearly disposable it seems) finger-sized units are now in the hands of a lot of mountain climbers, SAR folks and remote providers that wouldn't have had them before.


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## Qulevrius (Jan 24, 2016)

Flying said:


> Pulse oximetry works by measuring the amount of red/near-red light reflected by activated heme (hemoglobin carrying something).
> 
> First, the major problem is that the ability of CO2 to form a stable complex with hemoglobin is far inferior to CO. So we are not worried so much about CO2 messing with the reading.
> Second, it doesn't matter whether or not a pulse oximeter can differentiate between CO2 and O2 because the majority of CO2 in the body is in the form of bicarbonate ion.
> Third, the HbCO2 complex does not reflect red light and is in fact blue, contributing to the trademark colour of deoxygenated blood.



You're absolutely right. You just forgot to add that the device measures the peripheral saturation without the actual hemoglobin count, so whilst the readings can be reassuring, the actual amount of RBCs carrying O2 could be extremely low. And the other thing you did not mention is that if a pt retains CO/CO2,  the device won't show it and the sat readings could seem quite normal. Therefore, pulse ox devices provide just a brief glimpse into pulmonary function. For anything more substantial, there's the ABG lab.


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## Flying (Jan 24, 2016)

The point is that CO will show up and provide a false positive reading, while CO2 won't show at all. Both molecules have very different optical characteristics when bound.

None of this translates to what you originally posted:


Qulevrius said:


> It's more about the SpO2 reading which is never reliable. Can easily be 80% O2 with 15% CO2 but the meter will show a solid 95%. No bueno.


In no case will the red light read by pulse oximeter be appreciably affected by that 15% of CO2. You will just end up with 80% SpO2.

Sure pulse oximetry has its limitations, but no one here is trying to claim otherwise. This also does not mean it is "unreliable".


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## Carlos Danger (Jan 24, 2016)

Qulevrius said:


> You're absolutely right. You just forgot to add that the device measures the peripheral saturation without the actual hemoglobin count, so whilst the readings can be reassuring, the actual amount of RBCs carrying O2 could be extremely low.



Pulse oximetry is even _more_ important in a patient with a low hgb. These people have little oxygen carrying capacity, so it must be ensured that the carrying capacity they do have is maximized. The difference between an Sp02 of of 95% and 100% is meaningless in a person with a normal hgb, but it represents a relatively large difference in Ca02 in someone who is anemic.

The scenarios where Sp02 is unreliable are relatively few. In the vast majority of patients, it is a really valuable piece of information.


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## ThadeusJ (Jan 25, 2016)

I have seen a false high reading with a great pleth on an ICU monitor.  I used it to decrease the FiO2 on the vent until I was at 21% before I questioned the accuracy.  I checked the probe on the fingertip and found it to be almost right off the finger.  Somehow it was getting the pleth but because the light source and the sensor had no flesh between then, it read 100%.  Most bizarre but it did happen.

Please note that something as simple as nail polish can affect the reading.


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## COmedic17 (Jan 26, 2016)

I feel like everyone is over complicating this. 


A spo2 reading WILL tell you the percentage of hemoglobin that is saturated. 

A SPO2 reading WILL NOT tell you what the hemoglobin is saturated with (be it oxygen, CO, etc), or how much hemoglobin is actually present. 

If your wanting a more accurate depiction of whether someone is taking in oxygen and offloading carbon dioxide, use a capno reading along with pulse oximetry and basic skin vitals. 

If someone is mentating appropriately, has normal skin vitals, and is having no difficulty breathing, and the spo2 reading is 98%, it's a safe assumption the patient has adequate oxygen saturation and the reading is probably pretty accurate. 

A lot of monitors also have CO detectors as well......


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## joshrunkle35 (Jan 26, 2016)

COmedic17 said:


> I feel like everyone is over complicating this.
> 
> 
> A spo2 reading WILL tell you the percentage of hemoglobin that is saturated.
> ...


Well said!


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## ThadeusJ (Jan 27, 2016)

Or we can all watch this...


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