Are Finger Pulse Oximetry Devices reliable?

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.
 
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.
 
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.
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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.
 
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.
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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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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.
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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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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.
 
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......
 
COmedic17 said:
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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Well said!
 
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