Fingertip Pulse ox meter and DCS

[fmerkel]

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

If it isn't illegal, it must be OK to do, no matter how stupid it is........
Seems some people will do ANYTHING to make a buck.

 

[Duke Dive Medicine]

@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?

We use them in the chamber at Duke but they're not stand-alone pulse ox units, they're part of a monitor package. We also have transcutaneous oxygen monitoring (TCOM) capability - a lot of hyperbaric facilities use that to measure O2 delivery to tissue. That unit sits outside the chamber and the cable goes through a penetrator.

Best regards,
DDM

 

[doctormike]

And since some people get HBOT treatment for CO poisoning / smoke inhalation, it's important to note that pulse oximetry overestimates actual SAO2 when compared to the gold standard (arterial blood gas analysis).

 

[Duke Dive Medicine]

And somebody with CO poisoning is going to get CO-oximetry drawn to track COHgb level along with other ABG values.

 

[Akimbo]

We use them in the chamber at Duke but they're not stand-alone pulse ox units, they're part of a monitor package...

Do you know if there is special calibration required? Does it ever read over 100%? Do they work in your deep sat chambers or just the HBOT? I guess I'm the most curious about how they calibrate variances in those two waves of light to compensate for the super-oxygenation.

I have to come back there one day so you can show me all your cool toys!

 

[doctormike]

And somebody with CO poisoning is going to get CO-oximetry drawn to track COHgb level along with other ABG values.

Arterial line, right? I remember those, from the days before I specialized in ear wax...

 

[Duke Dive Medicine]

Do you know if there is special calibration required? Does it ever read over 100%? Do they work in your deep sat chambers or just the HBOT? I guess I'm the most curious about how they calibrate variances in those two waves of light to compensate for the super-oxygenation.

I have to come back there one day so you can show me all your cool toys!

Nope, no calibration. Pressure doesn't affect the machine, and hemoglobin saturation doesn't go over 100% no matter how much O2 you give someone. The partial pressure of O2 dissolved in the plasma does increase significantly though; we have a specially modified ABG machine that can read arterial O2 partial pressures up to 2000 mmHg (normal on room air at the surface is 80-100 mmHg). And you're welcome any time! @doctormike , yes, we draw through an arterial line at pressure and lock the ABG syringe out through the medical lock. It has to be on ice and done quickly after reaching the surface because the dissolved gas will come out of solution quickly.

Best regards,
DDM

 

[Akimbo]

Nope, no calibration. Pressure doesn't affect the machine, and hemoglobin saturation doesn't go over 100% no matter how much O2 you give someone.

Interesting because the device isn't measuring hemoglobin saturation, it is measuring changes in two light frequencies passing through tissues that happen to vary in close relationship to hemoglobin saturation. What surprises me is the added gasses in the tissues under pressure, Oxygen and diluent, doesn't change the light frequencies enough matter.

Have you, or anyone else, ever seen work being done using light-waves to detect diluent in tissues or the blood stream? Heck, I'd stand in line for an implanted sensor that could measure it. Now that would be a true decompression computer! While they are at it, they could include a pressure transducer to replace those primitive blood pressure cuffs.

Thanks.

 

[Duke Dive Medicine]

Interesting because the device isn't measuring hemoglobin saturation, it is measuring changes in two light frequencies passing through tissues that happen to vary in close relationship to hemoglobin saturation. What surprises me is the added gasses in the tissues under pressure, Oxygen and diluent, doesn't change the light frequencies enough matter.

Have you, or anyone else, ever seen work being done using light-waves to detect diluent in tissues or the blood stream? Heck, I'd stand in line for an implanted sensor that could measure it. Now that would be a true decompression computer! While they are at it, they could include a pressure transducer to replace those primitive blood pressure cuffs.

Thanks.

The light frequencies are only altered when hemoglobin becomes bound. Do you get Faceplate? Drs. Moon and Lance from Duke, and Dennis Gallagher from NSWC in Panama City have been working on a workable, wearable pulse oximeter for CCR diving.

http://www.navsea.navy.mil/Portals/...e_September2018.pdf?ver=2018-08-28-120041-260

I don't know that there's any current technology that can measure amount of diluent (He or N2) in tissue besides physically removing a sample and using gas chromatography.

Best regards,
DDM

 

[TrimixToo]

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.

And, those logistics raise an interesting question. Is the patient better off with the maximum gradient for as long as possible, or a reduced gradient for a longer period of time? I can see arguments both ways.