Fingertip Pulse ox meter and DCS

[Jayfarmlaw]

My search on the topic only revealed a 2006 thread so I apologize if this has been covered before. I'm putting together an oxygen kit and was wondering if a finger tip pulse ox meter would be of any value. It does not appear that nitrogen in the bloodstream would register on the clip on devices. Will a conscious DCS patient show a reduced blood oxygen level?

The Red Cross recommends reducing oxygen flow or switching to a lower flow delivery device once pulse ox hits 100%. Would this apply to a DCS patient or should they stay on a non rebreather mask at 15lpm until the next level of help is available? If the nitrogen registers as oxygen...I would guess leave the O2 cranked up.....

Thanks in advance for the response.

Jay

 

[doctormike]

I'm not a hyperbaric doc, but oxygen saturation is probably not a reasonable endpoint for pre-chamber treatment of suspected DCS. Reduced O2 sats are generally a sign of lung disease (pneumonia, emphysema, pulmonary edema, drug induced hypoventilation, etc...). With normally functioning lungs, you can easily obtain a sat of 100% with minimal supplemental O2. But that's not what you are doing with surface O2 for a patient with DCS.

Ideally, a conscious patient with suspected DCS who is being transported for medical care should be breathing 100% O2 from a standard regulator, which will maximize the inert gas gradient (no nitrogen in the system at all) and therefore optimize offgassing. Breathing from a nasal cannula or other low flow device will provide enough O2 to give you a 100% saturation, but the patient will still be breathing gas with nitrogen in it, reducing offgassing.

Sometimes, logistics will dictate the mode of O2 delivery. For example, if you have a limited supply of O2 and a long boat ride, it will last longer with a low flow device than with a demand regulator.

The fingertip pulse ox might be helpful with someone who has immersion pulmonary edema or other acute lung issues related to diving.

 

[tbone1004]

@Jayfarmlaw I think the bigger benefit of the pulse-ox is the pulse part to help keep track of that.

obviously not a doctor in this field
That said, in "normal" operation your body is capable of getting to 100% saturation with a ppO2 of .21 and fO2 of .21. I think it is important to remember that O2 saturation of the blood is not that the blood has 100% O2 and thus no inert gas in it, but that it has taken in as much O2 as it can take and there is still a significant amount of inert gas in the blood. When treating DCS you are trying to create a gradient in the body that encourages more and more inert gas to leave that is still in the blood and that is what controls offgasing efficiency which is what we are trying to accomplish by breathing pure O2. We use pure O2 because it's convenient, but the important part is breathing a gas mix that does not include the inert gas you are trying to get rid of. Obviously have to be careful about which other gases those are, but the concept stands.

I'm sure @Duke Dive Medicine can weigh in on this with a bit more authority though

 

[Duke Dive Medicine]

My search on the topic only revealed a 2006 thread so I apologize if this has been covered before. I'm putting together an oxygen kit and was wondering if a finger tip pulse ox meter would be of any value. It does not appear that nitrogen in the bloodstream would register on the clip on devices. Will a conscious DCS patient show a reduced blood oxygen level?

The Red Cross recommends reducing oxygen flow or switching to a lower flow delivery device once pulse ox hits 100%. Would this apply to a DCS patient or should they stay on a non rebreather mask at 15lpm until the next level of help is available? If the nitrogen registers as oxygen...I would guess leave the O2 cranked up.....

Thanks in advance for the response.

Jay

Jay, great question. @doctormike and @tbone1004 pretty much hit the high points. To me as a critical care nurse, a pulse ox is never a bad thing - the more data the better. One has to interpret the data in context though. As @tbone1004 said, one of the things that 100% O2 does is set up a high pressure gradient in the lungs so that nitrogen is eliminated more quickly. I would say that oxygen is more than a convenience for treating DCS though; at higher inspired partial pressures, it penetrates the body better and helps oxygenate tissue that may be ischemic or at risk for ischemia due to DCS bubbles. An SpO2 reading will provide an estimate of hemoglobin oxygen saturation, but it doesn't measure nitrogen at all. It could be useful in cases of actual or suspected pulmonary DCS to help measure gas exchange.

The Red Cross position is based on some data that says that excessively high FiO2 (fraction of inspired oxygen) can worsen outcomes in cardiac arrest patients, the rationale being that the extra O2 can lead to oxidative damage. A diver with DCS is (hopefully) about to get a lot more O2 than that in a hyperbaric chamber so the supplemental O2 that's given pre-treatment is pretty much immaterial from that standpoint.

Hope this helps.

Best regards,
DDM

 

[doctormike]

Right. 100% saturation means that 100% of the binding sites on hemoglobin molecules are bound to O2. It does not mean that there is 100% O2 in the airway.

 

[uncfnp]

I’m with doctormike on this. I don't really see a benefit since a DCS patient needs 100% O2 regardless. And little benefit for tracking pulse too while adding complexity and cost (albeit minimal). And the cheap little finger moniters would not hold up well to environmental exposure.

 

[Duke Dive Medicine]

I think it depends on who's using it and why. For lay individuals who aren't trained to interpret the readings and intervene appropriately, it probably has limited utility. For advanced rescuers caring for critically ill divers it may be more useful.

Best regards,
DDM

 

[fmerkel]

2 bits from a Respiratory Therapist who started using pulse ox when they were the size of a briefcase.
1. Agree with pretty much everything said above.
2. They are a device that takes some understanding of HOW it works, and how to determine if it's being used with any accuracy. The sensor is simply sending a light signal through the fingernail bed and interpreting SaO2 as a function of color: more red=more O2. BUT, if you are having poor peripheral blood flow from cold fingers, not at all unlikely on a wet diver in a stressful situation, the reading you could be getting from the unit has a high probability of being useless.

You are NOT measuring blood O2 level. You are measuring COLOR, and making an interpretation on a known blood O2 saturation curve about what the blood O2 level is.

Interesting side note: CO (carbon monoxide) is an aggressive molecule and binds to hemoglobin with a much higher affinity than O2, approximately 200 times more tightly. It also makes the blood bright red, rendering a pulse ox pretty useless. You can be dying from lack of O2 and the thing would happily interpret that as 100%.

It doesn't take a lot of CO to tie up a significant portion of your hemoglobin molecules rendering them useless for O2 transport. Put that under pressure (contaminated tank) and you have a really bad situation.

 

[tbone1004]

Interesting side note: CO (carbon monoxide) is an aggressive molecule and binds to hemoglobin with a much higher affinity than O2, approximately 200 times more tightly. It also makes the blood bright red, rendering a pulse ox pretty useless. You can be dying from lack of O2 and the thing would happily interpret that as 100%.

It doesn't take a lot of CO to tie up a significant portion of your hemoglobin molecules rendering them useless for O2 transport. Put that under pressure (contaminated tank) and you have a really bad situation.

for funsies, this is how a lot of beef and tuna is made bright red during processing

 

[Akimbo]

@Duke Dive Medicine

Have you found any pulse oximeters that work under pressure/inside dry chambers without modification? If so, how does it affect the calibration? I'm confident one could be designed that would take the pressure (but maybe not Helium), but I'm not sure the numbers would have much value for treating DCS. HBOT or barotrauma patients perhaps?