Oxygen Toxicity...

[Saturation]

A safe minimum surface interval between dives is 1 hour for offgassing. You may choose to follow the recreational nitrox clock thereafter to limit your pp02 exposure after a reason for VENTID are found, other than the nitrox being breathed at depth.

One should not dive until its clear why VENTID symptoms happened. Even if a dive's maximum pp02 is <= 1.2 and ultimately symptoms that occur are not often related to nitrox, any symptom or sign would need to be examined since oxtox is potentially fatal, whereas mnost other reasons are not.

To date, no recreational oxtox has yet been reported, and anecdotal VENTID reports could be attributed to other issues: equalization, sea sickness, fatigue etc.

 

[mars2u]

Hi Doppler,

Thanks for the response and I appreciate your input, but let me give you my interpretation albeit with little personal experience. I'm not necessarily referring to a tonic phase of oxygen toxcicity although I see your point there.

Hypothetical situation: You're diving and start to notice one or more of the following:

1) vision becomes distorted (some claim tunnel vision)- could be an obvious sign

2) ears start ringing -could be due to decompression
3) Nausea -could be seasickness
4) Twitchiness (especially facial)- this is probably an obvious sign
5) Irritabilitiy -could be due to fatigue or other factors
6) Dizziness -could be due to fatigue or other factors

Some have claimed these after surfacing also...I've heard of the twitchiness example specifically.

Although the chief sign is convulsions, and I see your point there...but what if you recognize one or more of the above and make a controlled ascent?
In my opinion, you have taken a O2 hit if you feel that it's not another possible scenario or you are in denial..IMHO
Am I not correct in this analysis?
This is where my surface interval point for the next dive comes in play. When do you dive again? When the symptoms go away after 24hrs.?

Oxtox "ceilings" are different for everyone IMHO

Also, and more importantly there are those (not me personally) that are on various medications (levothyroxines for one) but dive under these meds.(this is a seperate topic and my opinion/understanding is that diving is unwise and the risk increases in oxtox regardless of their PPO level per the tables). This should be a major concern for them and I think they need to be especially careful.

Just my .02

 

[Doppler]

mars2u once bubbled...
Hi Doppler,

SNIPPED

Hypothetical situation: You're diving and start to notice one or more of the following:

1) vision becomes distorted (some claim tunnel vision)- could be an obvious sign

2) ears start ringing -could be due to decompression
3) Nausea -could be seasickness
4) Twitchiness (especially facial)- this is probably an obvious sign
5) Irritabilitiy -could be due to fatigue or other factors
6) Dizziness -could be due to fatigue or other factors

SNIPPED

In my opinion, you have taken a O2 hit if you feel that it's not another possible scenario or you are in denial..IMHO
Am I not correct in this analysis?
SNIPPED

Also, and more importantly there are those (not me personally) that are on various medications (levothyroxines for one) but dive under these meds.(this is a seperate topic and my opinion/understanding is that diving is unwise and the risk increases in oxtox regardless of their PPO level per the tables). This should be a major concern for them and I think they need to be especially careful.

Just my .02

I know that the CONVENTID stuff is taught and needs to be but think it's a poor indication of the onset of CNS oxygen toxicity (By poor read unreliable and variable -- in short, unscientific.) I have never toxed either wet or dry so cannot speak from experience but there is ample documentation to indicate that the transition from facial twitching, for example, to a full-blown Tonic-Clonic type episode can be instantanious or may never take place... I have a buddy who is a cave explorer who can discuss this at some length but he is not on this board. Perhaps someone else can speak from experience.

I would also suggest that anyone -- in a recreational setting and working in exposures within NOAA guidelines -- who surfaces from a dive complaining of VENTID symptoms or who displays obvious signs, should stay out of the water until they have thoroughly investigated the possible causes and exhausted the possibility that they have some predisposing factor -- either via prescription drug use, recreational drug use of physical make-up -- to CNS toxicity. The greater likelihood is "ordinary" vertigo, bad temper, seasickness, et al.

To talk to the point you make about people who surface making such complaints. I do not believe it is correct to say they have "taken a hit," and are in denial. To take a hit means to have experienced a full-blown CNS episode... there are no half measures. However, as stated, they have experienced something unusual and should investigate -- see above. I think using the term: "I have taken..." or "She took a CNS hit on that last dive," confuses the main issues and is probably not the most accurate accessment of the situation. Better perhaps to say: "Wow, they felt really wierd on that dive. Let's reanalysis that mix, recalculate the MOD and look again at the partial pressure of oxygen they experienced on their dive."

As already mentioned by Saturation, the risks associated with diving Nitrox seem to have been managed very well in the recreational diving community. But there still seems to be some misundertanding of the risk factors... perhaps can be attributed to sloppy instruction materials and we should see about getting them changed .

You also mentioned OxTox "ceilings" being different from person to person. This may be true and it may be that OxTox tolerances will vary form day-to-day for any one person, but this whole issue is managed in a reponsible way by the NOAA guidelines and while still an important issue to keep in mind, is not really relevant in a recreational setting.

Run your CNS clock at less than 80%, watch your daily exposures, ANALYSE your mix, check and recheck calculations and mark the MOD on your tank. Plan your dive and dive your plan, and you have successfully managed the risks of the CNS toxicity.

The best advice I can give you is: "Go dive Nitrox." Spread the word... air belongs in the tires of your mountain bike!

DD

 

[mars2u]

I know that the CONVENTID stuff is taught and needs to be but think it's a poor indication of the onset of CNS oxygen toxicity (By poor read unreliable and variable -- in short, unscientific.)

Now that's disturbing being a newbie. Thanks for your input. I know from what you've written to me that you're knowledgeable in this.
I appreciate your candidness.

Thanks again.

 

[rmediver2002]

Have you ever taken an O2 hit, or seen someone else take one on a working dive? Also what's the lowest ppO2 that you have heard anybody tox from?

I have never had a hit myself, nor do I know anyone that took one during a dive. I have seen several occur during the decompresion phase on sur "d" dives (inside a chamber) the symptoms were in all cases twitching.

We did have a patient go into convulsions during a recompression treatment table but I was not on that chamber crew.

The lowest level is 2.21, there are some second hand accounts posted from time to time in fathom about combat divers getting hits. The partial pressure for transit depth is:

15 FSW = 1.45 pp O2
excursion depth 50 fsw = 2.51 pp O2
and lock out from a sub would be 60 FSW = 2.81

The big factors are that the diver can remain at transit depth for over an hour.

Excursion depth is a one time limited exposure (less than :05)

and lock out depth is very short duration at the begining of an exposure...

Pulmonary toxicity is another issue

Not going to see this one unless your sitting in on a treatment table 7, takes about 72 hours and feels like burning on inspiration...

I have never toxed either wet or dry so cannot speak from experience but there is ample documentation to indicate that the transition from facial twitching, for example, to a full-blown Tonic-Clonic type episode can be instantanious or may never take place...

The first symptom to present can be convulsions, the other symptoms are not as dangerous in comparison but they are not indicators of a more serious symptom coming... Any can appear without warning

I know that the CONVENTID stuff is taught and needs to be but think it's a poor indication of the onset of CNS oxygen toxicity (By poor read unreliable and variable -- in short, unscientific.)

I would ask that this statement / opinion be explained more in depth, as for my opinion it (VENTID-TC) is a good tool for students to use in remembering some of the signs and symptoms of O2 Tox.


Jeff Lane

 

[Doppler]

Jeff: Here, perhaps, is a more complete explaination of what I meant when I wrote "I know that the CONVENTID stuff is taught and needs to be but think it's a poor indication of the onset of CNS oxygen toxicity (By poor read unreliable and variable -- in short, unscientific.)"

While I agree with your statement that it may be a good tool to get students to remember the signs and symptoms -- and did not say otherwise -- it is still potentially misleading and open to abuse... as is any "medical" assessment in the hands of laypersons. More to the point, I have heard instructors and their students refer to the signs and symptoms covered by CONVENTID as a panacea that will give them all the information they need to AVOID taking a CNS hit. As in "If you feel this way, it's early on-set of CNS toxicity." That maybe but the connotation is that limits can be pushed until one experiences said symptoms and then you can back off a bit.

What I want to get across -- and what I will continue to promote to students and to nitrox instructor candidates -- is that CNS toxicity can happen without warning -- even as an Off-Oxygen Effect -- and the symptoms outlined in the VENTID nemonic are so easily misinterpreted to render them useless as a way to manage CNS risk. Don't exceed NOAA guidelines and you'll be operating within an area of risk found acceptable by the majority of recreational divers.

Incidently, I have experienced early stage pulmonary toxicity but not as part of a chamber ride...

Take care

DD

 

[rmediver2002]

Yes I am in agreement with your statement as well...

One addition I would recommend is having students calculate both MOD and duration of exposure...

But either way, you can lead a horse to water....


I have had people come to check out NITROX and get upset that I will not allow them to use a pre-calculated chart to figure MOD...


When did you experience pulmonary O2? What was you profile like?

Jeff Lane

 

[Doppler]

rmediver2002 once bubbled...


SNIPPED


When did you experience pulmonary O2? What was you profile like?

Jeff Lane

multiple days, deep mix, lots of decompression and running the CNS clock very high (damn Buhlmann profiles ). We were out of country and actually had calculated and watched our OTU's very closely -- as well as usual precautions -- for this reason. Experienced irritation and what felt like decreased vital volume on day five... while doing what I felt at the time was mild hiking around the jungle looking for big snakes... Took the next day off, and things returned to "normal." Of course, most of the rest of the party suggested it was Old Age and had nothing to do with diving! May have been true. Extraordinary circumstances though and quite unique in my experience, to the point where I think we could almost throw away the need to teach recreational divers about pulmonary toxicity units and tracking OTUs and concentrate more on understanding the real villian... CNS. Save whole body 'til they enroll in a tech class.

Take care mate.

P.S. Nice picture of the steps at Manatee. Love that cave... worth the drive to Cheifland...

DD

 

[TheDarknessLord]

Hi,
I'm a PADI EANx diver and IANTD Nitrox Cave Diver, and I suggest to never reach 100% CNS per day, remember that for each dive you have to add the % CNS to the total per day... If you are a PADI EANx diver, and you reach 100% of CNS wait until the day after before dive again! If yuo want to learn more in deep Nitrox, you must take an IANTD course, or another tech course, PADI is to soft in this world, but they are good enough to recreational diving.
EANx is the best mix for recreational and for DECO stops ever so far!!!

 

[Saturation]

Doppler once bubbled...


I know that the CONVENTID stuff is taught and needs to be but think it's a poor indication of the onset of CNS oxygen toxicity (By poor read unreliable and variable -- in short, unscientific.) I have never toxed either wet or dry so cannot speak from experience but there is ample documentation to indicate that the transition from facial twitching, for example, to a full-blown Tonic-Clonic type episode can be instantanious or may never take place... I have a buddy who is a cave explorer who can discuss this at some length but he is not on this board. Perhaps someone else can speak from experience.

I agree fully and its not something one would like to experience. Elsewhere on scubaboard is a detailed thread were others discuss NOAA clock issues and the value of VENTID. Search for it using "NOAA clock" as keyword.