What is dehydration and how does it influence diving safety?
Dehydration occurs when the body loses more fluid than is taken in and this can lead to medical problems that should be avoided.
Generally, these problems (especially in the case of chronic or severe dehydration) can result in headaches, decreased performance, irritability, confusion, fatigue, muscle cramps, reduction of thermoregulation, decreased level of consciousness, the production of kidney stones (long term) and can even lead to shock which is a life threatening condition. It is clear that these problems will negatively influence the medical condition of both divers and non divers and dehydration should therefore be avoided at all times.
But there is another concern: dehydration is a contributing risk factor for Decompression Sickness (DCS). To put it simply, dehydration will reduce the volume of blood plasma and perfusion of tissues (so it thickens the blood and reduces blood flow). The blood is responsible for the transportation of nutrients and for the exchange of gases. If the reduction in blood plasma becomes too great, it could lead to the decreased efficiency of gaseous exchange, thus also affecting the off-gassing of Nitrogen and increasing the risk of developing DCS.
How big is the risk on DCS?
In principle, diving increases the risk of becoming dehydrated. We have seen during some of our DSL projects that many divers are not well hydrated before the dive (and even less after the dive). In normal conditions however proper hydration should not become the main concern of divers, neither should it be ignored.
However, when going on a diving holiday the risk factor rises due to increased frequency of diving and (usually) increased climate. Therefore, appropriate hydration should be a key concern.
Why does the risk factor changes during my diving holiday?
Obviously the risk does not increase just because you are on a holiday, but there are behavioural and environmental factors that contribute to the diver becoming dehydrated much faster and without realising it.
In reality dehydration begins to develop when you enter the airplane that takes you to your preferred dive destination. The air in the cabin is much dryer than the air on earth and our lungs have to work harder to humidify the air, meaning your body is constantly losing fluids whilst on board.
It is recommended to drink 240ml of water each hour of the flight. So, if you would be travelling from the UK to Egypt, you would need to drink 1.2litres of water to maintain a good balance of fluid, while you would need approximately 750ml when flying from Italy to Egypt. These are volumes not many will drink during a flight.
Many travellers also like to drink coffee, coke or a beer during their flight, but these liquids just don't have the same hydrating effect as water. Alcohol and drinks containing caffeine are diuretics, consuming these will result in dehydration as they absorb water from the cells in your body and increase urine production. Consequently, the diver arrives at their destination with mild dehydration.
But this is only the beginning of the holiday. What do divers want to do during their holiday?
Enjoy the sun, enjoy the sea, dive as much as possible and why not have some fun and drinks in the evening.
Let's take a look at why this dehydrates you faster than normal?
Enjoy the sun
The most attractive dive destinations for the regular diver are those "warm water" locations where there are nice, big coral reefs and nicely coloured fish.
In these destinations there is a warm, sunny and sometimes humid climate.
It is clear that in these conditions you sweat and if you sweat you lose fluid, which if not replaced makes you dehydrated.
If you then also get sunburnt you will lose fluids even faster. When you have sunburn, your skin gets red and hot (and sometimes becomes painful) and our body reacts to this by sending fluid to the skin. The sun and wind will evaporate this moisture and even more fluid gets lost in this way.
Actually with these increased outdoor temperatures you also enjoy the wind and since most dives during holidays will be boat dives, you like to feel the wind on your skin which gives you that refreshing feeling. But in reality the wind (wind itself or the wind created by the velocity of the boat) evaporates sweat and moisture, increasing dehydration again.
Sea water - Salt
When coming out of the sea, the (salt) water will dry and leave salt crystals behind on your skin. These can often visually be seen, and have the ability to absorb and hold water molecules. This means it will take the moisture out of your skin, which then will evaporate due to the sun and wind, increasing dehydration further.
There are 3 things particular to diving itself that increase dehydration: Sweating, Immersion Diuresis (increased urine production) and breathing compressed air.
While the dive suit keeps you warm during the dive, it also does not allow you to cool down. So if you already are in a warm climate and are sweating when only wearing a t-shirt, imagine how much you will sweat under the dive suit.
During the dive, the increased ambient pressure and cooler water temperature will cause the blood vessels in the extremities to narrow and blood will be shunted from the extremities to the core of our body (heart, lungs and large internal blood vessels) in an effort to keep you warm. This increased blood volume in our core is seen by our body as a fluid overload. As a reaction the kidneys will produce more urine (which means losing water and salt again). This is also why divers feel the need to urinate during or immediately after the dive and this is referred to as Immersion Diuresis. Although one might think that when urinating a lot you are well hydrated, it actually means you are losing excessive fluids.
Another cause for loss of fluids while diving is the air you breathe. Just as in the airplane the air in the scuba cylinders is dry and you already know you lose more fluid to humidify this dry air. If you then also take into account that due to the colder water temperature, your lungs need to work even more to warm up the air, then you are increasing this moisture loss even more.
You are on holiday and it is not uncommon to have some fun and a few alcoholic drinks when enjoying your free time.
While dinking and diving is never recommended, alcohol also makes you dehydrate faster.
As you know already, alcohol (as well as coffee and other drinks containing caffeine) has a diuretic effect, increasing the urine output. This will make you urinate more frequently making you dehydrate.
Vomiting, because you have been drinking too much or because you suffer from seasickness or for any other reason will heighten the rate of dehydration because you lose large amounts of fluid and electrolytes in a short period of time.
The same negative effect can be seen when you have traveller's diarrhoea, which is an intestinal infection that occurs as a result of unsanitary food handling.
Some medication, especially blood pressure medication has a diuretic effect and as you know this diuretic effect will lead to dehydration.
If you now consider that on a diving holiday, you like to dive daily and even twice a day, then you can understand the increased dehydration and DCS risk.
Obviously the risk does not increase just because you are on a holiday, but there are nine behavioural and environmental factors that contribute to the diver becoming dehydrated much faster and without realising it.
How do you know you are dehydrated?
Check the colour of urine. It should be transparent or light yellow. Darker coloured urine normally means that you are dehydrated (although the colour can also be influenced by certain medication). Little or no urine at all can indicate you are dehydrated but on the other hand a lot of urine does not automatically indicate you are well hydrated.
Symptoms of Mild-Moderate dehydration:
Thirst (drink before you are thirsty as thirst already means you are starting to get dehydrated)
Dry or sticky mouth
Dark coloured urine
Decreased urine output
Symptoms of Severe dehydration:
Extreme thirst and very dry mouth
Dry skin that sags slowly into position when pinched up
Rapid heartbeat, weak pulse
Sunken eyes and/or eyes that do not produce tears
Not passing urine for eight hours
Low blood pressure
Irritability and confusion
Low level of consciousness
Extreme fatigue - Weakness
Most dehydration is mild and can easily be resolved by drinking more water. The use of Oral Rehydration Salts or Isotonic sport drinks in addition to water can also be considered as these will replace salts and electrolytes. However, where more severe symptoms are apparent, immediate medical care is required. It is clear that these problems will negatively influence the medical condition of both divers and non divers and dehydration should therefore be avoided at all times.
How to avoid dehydration?
It is much better to avoid dehydration instead of resolving it. Only by avoiding it, divers will reduce the risk of DCS.
After discussing dehydration and its effects on the body, we can conclude you should rinse yourselves down with fresh water after every dive, keep your dive suit off until right before the dive itself, avoid or moderate alcohol consumption or drinks with caffeine and protect yourselves from too much sun/sunburn.
But the easiest thing to do is to drink plenty of water.
However, you do not want to increase plasma volume too rapidly as this will only increase urine production again and not hydrate the body tissues. Therefore the advice is to drink a glass of water every 15-20 minutes instead of drinking a litre of water just before or after the dive. This will allow the tissues to be hydrated and consequently avoid the decreased gas exchange which can lead to bubble formation and DCS.
How much you actually need to drink depends on many factors, but drinking at least 2 litres extra (in addition to what you normally drink a day) will help you to keep hydrated.
You can also consider eating foods with a high water content, such as fruits and vegetables.
Some companies also sell drinking bags that can be used to drink under water, during the dive.