Benefits of Nitrox.

[buff]

I see people interested in breathing FIO2 greater than 21%-i.e. NItrox. Some folks have expressed interest in 100% FIO2!!!! I am a R.N. and in the ICU we try to avoid high FIO2 at all costs-avoid retinopathy of prematuraty in the infants, and general O2 toxicity for older folks. How long can you go without damage to your lungs with high FIO2-be it 40% or 100%??

[Tavi]

Hi buff,

The advantages of Nitrox are shorter surface intervals, and longer bottom times.This is especialy helpful in repetetive dives.Also many people don't get that tired feeling after diving.

Yes, Oxygen toxicity is an issue!

Everything you need to know is covered in the Basic Nitrox coarse.The advanced coarse covers mixtures above 40%.

Tavi

[DocVikingo]

Hi buff,

As I read your inquiry, it seems to focus not on the benefits of nitrox, but rather on the matter of pulmonary O2 toxicity. Do I have it right?

Your exact question is, "How long can you go without damage to your lungs with high FIO2-be it 40% or 100%?" This, by the way, would not be answered in any introductory nitrox course of which I am aware.

As an RN, you of course appreciate that the question does not contain sufficient specificity to provide a reliable answer. A reasonably accurate answer would require information on flow rate, percentage of oxygen, age of recipient, atmospheric pressure during administration (e.g., hospital room v hyperbaric chamber), nature of the pulmonary O2 toxicity (e.g., reversible v permanent) & other factors. Even knowing these, there are wide individual differences in susceptibility.

Here are some rough examples of durations: (1) at low flow rates or somewhat reduced concentrations, O2 can be administered virtually around the clock for very long periods of time without evidence of significant lung damage; (2) 100% O2 delivered at high flow rates at normal atmospheric pressure has been documented to cause reversible pulmonary O2 toxicity in as little as 12 hours, although this is not common. It becomes more common at durations exceeding 24 hours; (3) 100% O2 at normal flow rates delivered at 2ATA in a hyperbaric chamber can cause reversible lung damage in as little as 3 hours, although this is not common. It becomes more common at durations exceeding 6 hours.

At the flow rates of standard scuba regulators, customary nitrox blends, i.e., EAN32-EAN36 & recreational bottom times & depths, the risk of O2-related lung damage appears extraordinarily remote, indeed. Even in technical diving where higher concentrations of O2 may be breathed for longer periods of time, exposures would be far less than those known to result in pulmonary O2 toxicity.

I hope this has shed some light on the issue. If not, come back & let's toss it around some more.

DocVikingo

[scubadoc]

Hi 'buff':

Can't add very much to Doc Vikingo's explanation above. I suspect the problem in your mind is getting things squared away between O2 at sea level and O2 under pressure.

Maybe some basics about oxygen toxicity might be helpful. This can be found at our web site at http://www.scuba-doc.com/oxtox.html .

Oxygen toxicity is cumulative and can be measured in units called 'oxygen toxicity units' (OTUs). Not only does it cause pulmonary damage but it can cause seizures under water - uniformly fatal unless a knowledgeable buddy is close by.

The equation for calculating toxicity units is as follows:

OTU=t(PO2 - 0.5 divided by 0.5) to the 0.83 power

t=duration of exposure in minutes, PO2 is the oxygen partial pressure in bars, and 0.5 is the exposure threshold in bars.

For a diver starting fresh, daily exposures in OTUs are totalled and compared to a curve for allowable exposure. Divers whose cumulative exposure falls below the curve normally have few symptoms. Recovery takes place at about 300 OTUs/day. This curve is published in Bove's textbook on page 47. This also has a Repex table of operational oxygen exposure limits:

Repex Operational Exposure Limits are as follows:

1 day exposure=850 OTUs limit

2 day exposure=700 OTUs Limit (Total= 1400)

3 day exposure=620 OTUs Limit (Total=1860)

4 day exposure= 525 OTUs Limit (Total=2100), etc.

NOAA O2 PP and exposure time limits are also in a Table in Bove's text, 'Diving medicine' on page 46.

There is also more information on our web page at http://www.scuba-doc.com/gasesprbs.html#O2toxicity