The Dangers of Dehydration
Why you should wet your whistle before and after you dive.
by Samuel Shelanski, M.D.
Through the Skin
Through the Lungs | Through Urination | Through Other Diuretics
Through Blood Loss | Through the Gut
It seems
odd in a way: Divers can be floating in millions of gallons of water, yet
find themselves as parched as desert sands. Unfortunately, this predicament
can have serious consequences for divers. There are several ways in which
diving and the under water environment contribute to dehydration. It is
important to understand these factors and how to prevent or remedy them,
since dehydration is thought to increase the risk for DCS.
When a
person is dehydrated, there is a reduced volume of blood in the body. Less
volume means less blood flow to the tissues. This in turn affects the body's
ability to wash out waste, such as nitrogen. The result is that a diver
surfaces without having off-gassed as efficiently as he would have if he had
been well hydrated. The increased nitrogen remaining in the body translates
into a higher risk of DCS.
Blood flow to certain tissues is further compromised during dehydration by
the body's own means of compensating for a low blood volume. To guarantee an
adequate supply of blood to vital organs like the brain and kidneys, the body
signals blood vessels supplying other parts, like skin and muscles, to clamp down,
restricting flow even more.
In addition to the increased risk of DCS, dehydration can adversely affect
divers in other ways. Since there is a reduced volume of blood circulating
through the body, the heart has to work harder and pump faster in order to
meet the body's demand. This leads to decreased endurance and increased
fatigue, which diminishes diving performance. Clearly, it's important to be
aware of those factors that can lead to dehydration. (top)
Dehydration results when fluid intake is not
sufficient to replace the amount of fluid that is lost. Anything that reduces
fluid intake or increases fluid loss, increases the likelihood that a person
will become dehydrated. There are only five ways that the body loses fluid:
through the skin, the lungs, urination, blood loss or the gut. All of these
can lead to dehydration in divers. (top)
For many
of us, a dive trip conjures up visions of tropical locales. Much, if not most
diving occurs in warm places. As a result, fluid loss through the skin, as
sweat, often plays a large role in dehydration. Heavy perspiration can lead
to rapid fluid loss in a warm climate and can cause a person to become
dehydrated quickly if those fluids are not replenished. (top)
The lungs
can also be a significant source of fluid loss for the diver. The air on
airplanes, in air-conditioned rooms and even in our tanks is extremely dry.
Each breath of dry air that we take is humidified by the lungs, and that
moisture is lost when we exhale. Over the course of a long flight, a night in
a hotel or a multi-tank day, fluid loss through the lungs can be substantial.
(top)
Another
way that diving causes the body to lose fluid is summed up in the old saying:
"There are two types of divers: those who pee in their wetsuit, and
those who lie about it!"
Whether or not it is discussed in polite company, darn near all of us have
had the urge to go while diving, often soon after we've entered the water,
even if we've just voided. This is an explainable physiological phenomenon,
known as immersion diuresis.
When we are above water, the greatest force upon our bodies is gravity. When
we are sitting or standing, the force of gravity causes blood to collect or
pool in the legs. When we enter the water, the most significant force acting
upon the body is the atmospheric pressure of the water, which serves to force
the pooled blood out of the legs and into the body's general circulation.
Another response of the body upon entering the water is to clamp down the
blood vessels to the skin in order to minimize heat loss. This also serves to
push more blood to the center of the body.
Your body perceives this increased blood flow as a volume overload, and
signals the kidneys to make more urine to correct it. The result is that all
too familiar urge.
It is important to mention that the increase in circulating blood does not
offset the effects of dehydration. There is still less blood flowing through
your body than there would be if you were well hydrated. (top)
Drinking
alcohol or caffeinated beverages and some medications can lead to increased
fluid loss as well. If you can't forgo that morning cup of coffee or beer
with dinner, consume both caffeine and alcohol in moderation when diving. All
medications should be cleared with a physician prior to a dive trip, even
over-the-counter medicines. In particular, some menstrual preparations
contain diuretics - drugs that make you urinate - and should be strictly
avoided while diving. (top)
Menstruation
is of particular importance, since some women can become slightly dehydrated
during their menses. This is thought to be caused by a fluid shift from the
blood vessels into the surrounding tissue rather than to actual blood loss. There
has been much speculation and research into whether women are at increased
risk of DCS if they dive during while menstruating, but to date the results
are inconclusive (see Dive Medicine, RSD, June '95) (top)
Finally,
it's worth mentioning traveler's diarrhea as a potentially huge source of
fluid loss. Many of the top dive locations are in less developed parts of the
world, and more than a few divers have been affected by this annoying
ailment. While uncomfortable and unpleasant, diarrhea's greatest danger to
divers is that it can result in massive dehydration in a very short period of
time.
Even with the large fluid loss that can occur with diarrhea, dehydration can
be avoided by drinking enough fluids to offset fluid loss. Unfortunately,
divers often do not have access to an adequate supply of liquids. How many of
us have ever been able to get enough to drink on an airplane? Likewise, a
single juice or soda between dives is usually not nearly enough liquid to
replenish what our bodies need. Yet this is often what is available,
particularly on day boats. What can a diver do? (top)
Several
regulator manufacturers have designed models that trap some of the exhaled
moisture and prevent the dry mouth that accompanies diving. While some of
these are very effective, this is more a matter of comfort than of preventing
any significant fluid loss. It's important to note that these regulators are
not suitable for cold-water diving, as the increased moisture predisposes
these regulators to freeze-up.
The real key to preventing dehydration is to stay ahead of the game. Drink a
minimum of two liters of water or juice each day; more if it's very hot or if
you're diving multiple tanks. The drinks should be spaced out over the course
of the day rather than consumed in a short period of time. Again, avoid
caffeinated beverages. And bring a water bottle along on the boat. This will
ensure that you have sufficient fluid to drink between dives. (top)
Questions for Dr. Shelanski should
be addressed to RSD,
Dive Medicine, 6600 Abercorn St.,
Suite 208, Savannah, GA 31405; e-mail RSDmgzn@aol.com.
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