End tidal CO2 Monitoring

[Duke Dive Medicine]

There are monitors, since everyone likes to use intubated patients as examples, the two main types of anesthetic scrubbers both have a blue dye that appears when the scrubber is spent.

The Sodasorb dye is not necessarily a good indicator that the absorbent material is spent. We used indicating Sodasorb in our hyperbaric patient recirculators for a number of years, and even though it would turn purple after one dive in some patients, the CO2 in the patient head tents remained well within our specified limits. We used the canisters for a total of three 2-hour dry hyperbaric dives. We've since switched to the high-performance Sodasorb.
Also, the Navy stopped using the indicating Sodasorb in rebreathers in the late 1990's due to problems with odors - I remember switching to Sofnolime for the Mk-16s at that time. http://archive.rubicon-foundation.org/dspace/handle/123456789/4972

 

[kodak88]

Yeah, I remember someone at the Navy EDU telling me something about that. I guess there will be some controversy regarding what I would call IN-UNIT-Loop CO2 monitoring and its true value in maintaining a safe unit environment.

BTW say Hi to Dr Monk and Dr Wheldon for me!!

 

[Duke Dive Medicine]

Yeah, I remember someone at the Navy EDU telling me something about that. I guess there will be some controversy regarding what I would call IN-UNIT-Loop CO2 monitoring and its true value in maintaining a safe unit environment.

Probably so. This is an old thread but I guess there might be some value for CO2 monitoring downstream of the canister since that would be elevated at least a short time before the diver became hypercapnic. I can see the concern about "riding" it, so to speak, and pushing the canister duration but it could also detect channeling in a hastily packed canister or failure in a bad batch of absorbent material. The civilian rebreather divers I know are a pretty careful bunch so don't know what the likelihood of either of those would be.

BTW say Hi to Dr Monk and Dr Wheldon for me!!

I'd be happy to but I don't know who they are and nobody here has heard of them. Were they only here for a short time?

 

[kodak88]

Dr Monk - BLood sustitute research, anesthesia
Dr Weldon - PICU, Anesthesia
They have been there for the last five years

 

[Duke Dive Medicine]

Ah, rgr, we don't deal with that area of the hospital too much. I knew one of the trauma surgeons who was helping with blood substitute research but have very limited contact with the PICU.

 

[drdirt]

Getting back on topic - CO2 measurement would be useful to detect scrubber breakthrough. This is a feature that I would welcome if/when it becomes practical/affordable.

There are known reliability issues with a monitor for CO2 scrubber breakthrough. I'm aware of some. Can anyone identify others?

1. Sensor performance in high humidity -
2. Precision/Sensitivity - a sensor needs to detect an increase from about 300 ppmv to 500 ppmv to be effective at depth.
3. Response time - the diver needs time to respond to the detection - critical at moderate depth since 1% is not safe at 5 atm.
4. Reliability - even O2 sensors are used in triplicate to provide reliability needed for CCR life support...

I see engineering design solutions to #2, #3, #4. These scrubber design factors are not included in the Meg, APV models, or the Titan - so it would take some development and testing.

Does anyone know where I can get performance specs for CO2 sensors on the market?

Thanks for any and all assistance...
DrDirt

 

[Brad_Horn]

I see engineering design solutions to #2, #3, #4. These scrubber design factors are not included in the Meg, APV models, or the Titan - so it would take some development and testing.

See Deep Life Ltd: Functional Safety Design Services for some of the engineering design solutions your after for end tidal CO2 monitoring in a rebreather as DL have designed that feature into 3 different rebreathers. See the applicable reports for details of the development and testing.

Does anyone know where I can get performance specs for CO2 sensors on the market?

Try Gas Sensing Solutions
http://www.gassensing.co.uk/edit/files/brochures/GSS C20 Data Sheet.pdf

Regards
Brad

 

[Gene_Hobbs]

Dr Monk - BLood sustitute research, anesthesia
Dr Weldon - PICU, Anesthesia
They have been there for the last five years

Done, saw Craig earlier today...

As for etCO2 in the loop, you guys might enjoys some posts by Dave and Simon on another board talking about the Deep Life solution (this was the shorter of the threads).

For scrubber duration, the temperature sticks have proven to be a good method (Warkander et al, 2007 - Sorry I don't have his more recent work in the database yet).

ONR and NAVSEA have funded some work on a couple of other CO2 monitors but none have made it into operational use yet.

 

[PeCeDiver]

On this link you'll find an inteview with Dr. Simon Mitchell about the subject: Submerge Productions : HD Dive Videos - Videos

 

[Brad_Horn]

As its on topic, some aspects of this Fault Study: CO2 bypass in Rebreather Mouthpieces that DL have just released might be of interest http://www.deeplife.co.uk/or_files/Fault_Study_CO2_Bypass_110105.pdf

The report also gives some detail about the end tidal CO2 monitoring.

Regards
Brad