Health Matters
Nitrox use: the pros and cons for working divers
The majority of dive centres and safari boats offer oxygen enriched air (EAN) in a bid to make scuba safer and
reduce the incidence of decompression sickness (DCS) among diving tourists. But what about dive guides and
instructors, is it the best gas for them? In the first of her series of columns on medical issues, world-renowned
diving doctor Dr Anke Fabian explores the question.
N
itrox reduces the nitrogen saturation when diving according to the dive time, temperature, individual daily condition and breathing
air tables remarkably, however, at the same time it increases the frequency (oxygen uptake) during the dive. Recommendations for
percentage of oxygen uptake and ppO
2
(partial pressure of oxygen) the MOD (maximum operating depth) in nitrox and the bottom- or
with increasing depths. Some dive guides and instructors prefer to decompression mixes in technical diving are given below the critical
stick to compressed air over nitrox. The reasons given are mostly ppO
2
at 1. or 1.6 in consideration of the additional risk factors.
connected to the fear of oxygen toxicity. But is this a real cause for A 100 per cent mix of oxygen is the only life-sustaining medical
concern? treatment, which is scientifically proven to be beneficial as a first
treatment in case of a dive accident, irrespective of the gas mix used
Let’s first compare the advantage of a reduced nitrogen uptake
by the diver.
with the risks caused by a higher oxygen level. There are two forms
of oxygen toxicity with two different target organs: lungs (chronic Other disadvantages of using nitrox include explosive risks (dealing
oxygen toxicity) and the brain (acute oxygen toxicity). with 100 per cent pure oxygen at the filling station) and the need to
have special equipment (depending on the oxygen percentage in
Also known in medical fields as the Lorraine Smith Effect, pulmonary
the gas mix). Each tank needs to be analyzed for O
oxygen toxicity is a direct time/dose relationship on the lungs caused
2
content in the
presence of the proposed user or by the user himself – this takes time,
by a direct effect of O
2
when the ppO
2
is continously exceeding 0.6
as there is usually only one analyzer available at any one time. Another
bar for a long period. It leads to a thickening of the lung membranes,
possible mistake could be the selection of an inappropriate mixture
swelling, collapse of the alveolus (small sacks for gas exchange) and
for the depth of the particular dive.
lung oedema (liquid in the lungs). This then causes an insufficient
gas exchange and a lack of oxygen. Medically speaking, this concerns Advantages for nitrox users in relation to the nitrogen saturation in all
mostly patients in intensive care units. In diving – especially with body compartments (slow and fast tissues) are either a longer no-stop
air oxygen enriched air (nitrox) – the time is comparably shorter time on the basis of equivalent air depth, or a safer decompression
depending on the depth. Still, it takes a minimum of ten to 15 if one sticks to the air tables. The advantages of diving with nitrox
hours exposure time at ppO
2
of 1.7 bar to force the first, even non- on an air-table are obvious in all cases where reducing the risk of
permanent, damage of the lungs. Dive guides may want calculate the decompression sickness risk in areas such as a PFO (patent foramen
dive profile and necessary decompression times for such a dive! ovale) which leads to shunting microbubbles within a small hole in
the heart; those with history of decompression sickness; or divers with
The second form of acute oxygen toxicity targets the brain in the form
a high body mass index.
of generalised cramps and fits, which are very similar to an epileptic
fit, often referred to by medical professionals as the Paul Bert Effect. It
mostly leads to unconsciousness and drowning, as there is almost no Recommended use of nitrox
way to survive it under water. The acute oxygen intoxication depends So when thinking about the benefits and risks, while keeping the
mostly on the actual ppO depth limits for recreational diving in the Red Sea in mind (0 m), one
2
(critical ppO2 is 1.7), but is also related to
2
www.cdws.travel
Issue 1 June 2009
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48