Thursday, 18 August 2011

Dehydration and Diving


The Dangers of Diver Dehydration
Ironic but true. Scuba diving can get a scuba diver dehydrated if there is an inadequate quantity of water in his body. That can cause major problems as water is crucial for the smooth functioning of a dozen biophysical systems and biochemical processes. At the cell level, chemical reactions in the cell require water. At the tissue level, water keeps the tissues flexible and plump. Water is also needed for blood production and circulation through the cardiovascular system.
A scuba diver can lose fluids through sweat or urination. Yes, divers do sweat even underwater. But breathing causes the most loss of water for divers. Have you ever observed what happens when you breathe near a piece of glass? The glass becomes foggy. This shows that when you breathe normally, you are expelling high amounts of moisture into the air. Since the scuba tanks contain air that is drier than surface air, you tend to breathe out more moisture underwater. Moisture tends to flow from wet to dry areas just as heat gets transferred from warmer to cooler bodies.

It is not difficult to achieve the proper level of hydration before and while scuba diving. Before setting off, just drink lots water or a sports drink which does not contain too much sugar. In warmer weather and for longer dives, you will need to drink more fluids. Drink slowly, so your body gets enough time to absorb the fluids without the kidneys getting overwhelmed. But remember to avoid caffeinated drinks like coffee and colas or any alcoholic beverages for many hours before the dive. Photo by/ Ahmed F.Gad  - Copyright © 2010
Dehydration means your body does not have as much water and fluids as it should. Dehydration can be caused by losing too much fluid, not drinking enough water or fluids, or both. Vomiting and diarrhea are common causes. Pressurized airplane cabins, scuba air, alcoholic and other diuretic drinks, diuretic medications and certain medical conditions such as diabetes can cause dehydration.

Children divers are more susceptible to dehydration than adults because of their smaller body weights and higher turnover of water and electrolytes. The elderly and those with illnesses are also at higher risk.

Dehydration is classified as mild, moderate, or severe based on how much of the body's fluid is lost or not replenished. When severe, dehydration is a life-threatening emergency. It is a known hazard to divers by increasing the risk for decompression illness.

Some of the smptoms of dehydration include:

    * Dry or sticky mouth
    * Low or no urine output; concentrated urine appears dark yellow
    * Not producing tears
    * Sunken eyes
    * Lethargic or comatose (with severe dehydration)
 
A physical examination may also show signs of:
    * Low blood pressure
    * Blood pressure that drops when you go from lying down to standing
    * Rapid heart rate
    * Poor skin turgor -- the skin may lack its normal elasticity and sag back into position slowly when pinched up into a fold by the doctor; normally, skin springs right back into position
    * Delayed capillary refill
    * Shock

Diuretics add to the dehydration that occurs with exercise from  sweating, insensible and respiratory water loss; the diver also has to take into consideration some additional concerns for fluid loss and replacement.
 
 1. Scuba tanks have extremely dry air inside. As this air is taken into the lungs and saturated--nearly twice the normal amount of water is lost from the body. 
 2. Negative pressure breathing causes divers to lose about 350 cc/hour from their circulating blood volume, a phenomenon called immersion diuresis and seen also in snorkelers and swimmers. 
3. Cold inhibits anti diuretic hormone, causes peripheral vasoconstriction, driving fluid back into the core and stimulating diuresis resulting in losses of plasma volume. 
4. The hypercarbia (high blood carbon dioxide) associated with diving decreases anti diuretic hormone, promoting fluid loss from the plasma volume. 
5. Diuretics such as alcohol, coffee, tea also contribute to fluid losses, contributing to predive dehydration. 
6. In addition to the above, the state of chronic hypovolemia (low fluid vloume) and hypokalemia (low serum potassium) caused by oral diuretics is dangerous to divers by increasing their susceptibility to decompression illness and cardiac arrhythmias, respectively.

Dehydration affects the rate of nitrogen release. This makes ascents take longer and the diver’s oxygen may run out. In this situation, a diver faces an unpleasant choice. Compared to decompression sickness, dehydration causes lesser harm. Yet, the consequences like lowered blood flow, which makes the heart pump faster are still unpleasant enough and you must make all efforts to avoid this. If dehydrated, the diver will fatigue more rapidly, spoil his enjoyment and have to surface quicker.

It is not difficult to achieve the proper level of hydration before and while scuba diving. Before setting off, just drink lots water or a sports drink which does not contain too much sugar. In warmer weather and for longer dives, you will need to drink more fluids. Drink slowly, so your body gets enough time to absorb the fluids without the kidneys getting overwhelmed. But remember to avoid caffeinated drinks like coffee and colas or any alcoholic beverages for many hours before the dive. 

Inadequate fluid in the blood vessels of the neck and head cause headaches, so look out for headaches – they are the first indication that you may be facing dehydration. Before the dive, examine your urine to ensure that it’s clear and light colored. Once you have surfaced, re-hydrate slowly.

So, use common sense and go for safe dive!

Useful Links:
http://www.divecrew.co.uk/dive-news/2009/09/dehydration-and-diving-not-a-good-mix 
http://scuba.about.com/b/2011/04/05/dehydration-and-diving.htm
http://scuba-doc.com/dehyd.htm
http://www.scubadivingsolutions.com/dehydration.html
http://scubadoc.blogspot.com/
http://womensdivewatch.org/dehydration-and-diving.htm

Further reading: "Diving Medicine", Bove and Davis, Philadelphia, WB Saunders, 1990, ed 2.





 

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