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Myth – Hydration is the most important factor in avoiding DCS

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By Mark Powell

The maintenance of a good state of hydration is generally considered to be very important for overall health and dehydration can have significant implications on health and exercise performance. Dehydration has long been considered by many divers to be one of the most significant, or even THE MOST significant, factor in DCS risk other than following correct dive profiles.

The idea that hydration is the most important factor in avoiding DCS has been repeated so often that it is taken as an undisputed fact. Many diving manuals repeat this misconception and there are countless articles online which make the same point.

As we have already seen in this series, just because something is repeated over and over again, does not mean it is a fact and widely believed rules are sometimes found to be based on no evidence at all.

Historically there has been very little research on this point, as it was taken to be self-evidently true by many, although rejected by others. There were only a very small number of studies investigating the topic although in recent years this gap has been slowly been addressed as researchers have tried to prove or disprove the idea.

If we look at the scientific evidence for the impact of hydration on DCS risk we can find one paper from 2007 which showed that diving causes dehydration [1]. Another showed that prehydration resulted in a reduction in bubbling post dive [2] and a third showed a reduction in DCS risk [3] although there were some queries about this study. None of these were conclusive and the reduction in bubbling and DCS risk was not huge. This seemed to imply that the benefits of hydration have been overstated at best and does not have anywhere near the impact that was believed. This is especially true when compared to the impact of other forms of preconditioning such as vibration or sauna or when compared with other factors such as temperature which provided a much bigger change in DCS risk.

However, some more recent papers seem to show that hydration does indeed have an impact on DCS risk although less than many other factors such as temperature and exercise [4].

At the same time that the benefits of hydration were being questioned, the risks of over overhydration were starting to be considered.

In particular, excessive overhydration (hyperhydration) can increase the risk of immersion pulmonary edema. However, in some circles this has been misinterpreted as meaning that a normal level of hydration is bad as it increases the risk of this condition.

MYTH – Hydration increases the risk of IPO/IPE

Immersion pulmonary odema/edema (IPO/IPE) occurs when fluid leaks into the alveoli in the lungs. This results in sudden shortness of breath, cough and sometimes blood-tinged, frothy sputum.

IPO was once considered rare, but is now more widely recognized. While the actual numbers of cases are unknown, it is most likely underdiagnosed. This might be because:

  • It is difficult to detect in fatalities.
  • It can be mistaken for drowning.
  • Mild cases of IPE can resolve spontaneously.

Factors contributing to IPO may include:

  • Hydrostatic pressure gradient
  • Cold-induced vasoconstriction
  • Exertion
  • Hydrostatic gradient between mouth and alveoli
  • Inspiratory resistance caused by the regulator
  • Increased gas density at depth
  • Excessive pre-dive hydration
  • Hypertension

Many of these factors may be present in adventurous or technical diving. Divers Alert Network (DAN) recommends that you abort the dive as quickly and safely as possible if you experience:

  • Sudden shortness of breath.
  • Persistent cough.

Upon surfacing breathe 100 percent oxygen and postpone further diving until you can consult a physician.

Although mild cases of IPO can resolve without further treatment once a diver has exited the water, respiratory distress while diving can be extremely dangerous. IPO becomes an even greater concern when you face an extended decompression obligation. Here you must balance the risks of:

  • IPE symptoms worsening if you remain under water.
  • Suffering DCS if you shorten or skip decompression stops.

You will notice that in the description above, one of the factors contributing to IPO is listed as “Excessive pre-dive hydration”. As mentioned earlier this has, in some circles, been misinterpreted as meaning that hydration is bad as it increases the risk of IPO.

When considering hydration levels, it is important to remember that there are three relative states. Which in layman’s terms we describe as dehydration, proper hydration and excessive overhydration. I have avoided the more scientific terms hypohydration, euhydration and hyperhydration in order to make this explanation more accessible to the non-scientist.

As proof that this myth exists, I have included below an extract from a genuine email I received from one of my students;

“I genuinely believed (I don’t know where I got this from) that if you drink anything before a dive, you’re putting yourself at risk of getting IPO. I didn’t realise the shear amount you actually had to drink to increase that risk. So on occasion I’ve had a tea between dives and then jumped in for a second dive and in the back of my mind be thinking ‘I hope I don’t start coughing uncontrollably now and give myself IPO because of that tea’”

One of the most commonly referenced articles on IPO, and an article that the student above had definitely read, contains the following quote [6] “I am particularly concerned that many divers overhydrate with fluids before a dive, in the belief that it will protect them against decompression illness. The evidence that it protects is not convincing. In contrast there is unequivocal evidence that excessive hydration increases the risk of IPO in both divers and swimmers. Overhydration has an additive effect on the increase in alveolar capillary pressure resulting from immersion. So I strongly advise divers not to overhydrate before diving.”

As you can see this does not state that an extra cup of tea will cause IPO but you can see how a myth could grow from this. It is easy to take the statement “I strongly advise divers not to overhydrate before diving.” and misremember it as “I strongly advise divers not to hydrate before diving.” This advice does not distinguish or give any advice on where is the line between hydration and overhydration? Is that extra cup of tea enough to tip us over the line into overhydration?

To answer the question about the difference between hydration and excessive hydration it worth looking at the article described as ‘unequivocal evidence’ in [5]. This refers to a study carried out on military swimmers.[6]  An extract of the study is shown below; “Thirty young men on a military fitness training programme were engaged in a swimming time trial over 2.4 km in the open sea. The sea was calm and the measured water temperature 23°. They swam in the supine position wearing only a bathing suit and using fins. Because of the high heat load expected, the swimmers had been instructed to drink large quantities of water before the swim, to avoid becoming dehydrated. They each drank about five litres of water during the two hours preceding the exercise.”

Five litres (8.8 pints) is a huge volume of water to drink in a two-hour period. For someone who was already well hydrated it could easily put them into a position of hyperhydration. Although it might not be a problem for someone who started out in a dehydrated state. The key point is that there is a big difference between proper hydration and excessive overhydration (hyperhydration). A large glass of water, a 1 litr bottle of water or even a large mug of tea is not excessive overhydration.

Conclusion – Myth or not?

Hydration does indeed seem to be a factor in DCS risk and it seems clear that being properly hydrated is a good thing for health in general and also for diving. Hydration is not be the most important factor in reducing DCS risk but anything that reduces DCS risk at all is a positive thing. Excessive overhydration can increase the risk of IPO but excessive overhydration is not the same as being properly hydrated.

Being properly hydrates gives some advantages in reducing DCS risk and likely does not create undue IPO risk. As in so many areas of life there is a balance. Do not dive while you are excessively dehydrated and do not dive while you are excessively overhydrated. Stick to the Goldilocks zone – not underhydrated, not over hydrated but just right.

How to hydrate

The other conclusion we can draw from this discussion is that educators, scientists, researchers, speakers and writers need to be careful about the impression we create. An article or conference presentation may contain perfectly truthful information but that can be misinterpreted and be seen as promoting a very different conclusion to the one intended. This is exactly how myths develop.

Thank you to Neal Pollock who reviewed several early drafts of this article to ensure that my attempts to explain these concepts in non-scientific language did not lose any of the scientific validity. Any errors or misunderstandings are still down to me.

References

[1] Williams ST, Prior FG, Bryson P. Hematocrit change in tropical scuba divers. Wilderness Environ Med. 2007;18(1):48-53.

[2] Gempp E, Blatteau JE, Pontier J-M, Balestra C, Louge P. Preventive effect of pre-dive hydration on bubble formation in divers. Br. J. Sports Med. 2009;43:224–228.

[3] Fahlman A, Dromsky DM. Dehydration effects on the risk of severe decompression sickness in a swine model. Aviat Space Environ. Med. 2006;77:102–106.

[4] Wang Q, Guerrero F, Theron M. Pre-hydration strongly reduces decompression sickness occurrence after a simulated dive in the rat. Diving Hyperb Med. 2020;50(3):288-291.

[5] https://www.bsac.com/news-and-blog/the-hidden-killer-immersion-pulmonary-oedema-ipo/

[6] Weiler-Ravell D, Shupak A, Goldenberg I, Halpern P, Shoshani O, Hirschhorn G, et al. Pulmonary oedema and haemoptysis induced by strenuous swimming. BMJ. 1995;311:361.

From its humble beginning in 1994 to today, the group of training agencies Scuba Diving International (SDI), Technical Diving International (TDI), and Emergency Response Diving International (ERDI) form one of the largest diving certification agencies in the World – International Training. With 24 Regional Offices servicing more than 100 countries, the company today far exceeds the original vision the founders had when they conceived the idea on a napkin, sitting at a kitchen table in the early 1990’s.

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Dive the Egyptian Red Sea this Autumn with Regaldive

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Egyptian Red Sea

October and November are excellent months to visit Egypt, as they offer pleasant water temperatures and comfortable conditions on land. Divers can explore prime dive sites in the northern Red Sea, including the iconic SS Thistlegorm shipwreck and the breathtaking underwater topography at Shark & Yolanda Reef in Ras Mohammed National Park. Additionally, visitors can take advantage of direct flights from the UK to Marsa Alam, which serves as a gateway to bucket list adventures and thrilling shark dives in the Southern Red Sea.

Egyptian Red Sea

The Red Sea offers an unforgettable experience both above and below the water. Every year, thousands of visitors are captivated by this area’s unique blend of spectacular marine life, welcoming climate, and stunning scenery.

A World-Renowned Dive Region 5 Hours Away…

An endless variety of marine life draws divers from across the globe to the warm waters of the Red Sea. For UK divers, this world-renowned destination is just a short flight away. With outstanding water clarity and permanent sunshine, the Red Sea offers the chance to explore its magical underwater world year-round.

Egyptian Red Sea

The sheer abundance of vibrant marine life and corals is what sets the Red Sea apart. Divers and snorkellers can witness an impressive range of invertebrates, including over 200 different types of hard and soft corals, crustaceans, sponges, and hundreds of spectacular fish species.

This incredible variety is further enhanced by the Red Sea’s dramatic underwater landscapes, featuring steep walls, drop-offs, shipwrecks, and deep blue canyons.

Egyptian Red Sea

Which Red Sea Destination to Choose…

Regaldive provides a choice of ten Egyptian Red Sea resorts, along with a range of liveaboard options for those seeking to explore further. Sharm el Sheikh, Hurghada, and Marsa Alam are the gateways to the Red Sea, each offering a unique and distinct charm.

Hurghada presents a glimpse of authentic Egypt, with an excellent selection of dive sites located just a short boat ride away. The smaller resorts of El Gouna and Safaga are ideal for exploring the northern reefs and wrecks while being within easy reach of Hurghada.

The stunning coastline south of Hurghada has become a haven for tranquil, pristine diving. Direct flights into Marsa Alam throughout the winter have made it easier to access the impressive marine parks of the southern Red Sea.

For those seeking ultimate seclusion, the southernmost resort of Hamata offers unparalleled diving within relatively undisturbed reef systems.

The Choice is Yours…

No matter which destination is selected, a Red Sea holiday promises a blend of fantastic diving, beach relaxation, and cultural exploration. With over seven centuries of history, Egypt offers so much more than just diving.

The Red Sea is an ideal starting point for visiting the iconic Pyramids, taking a day trip to Cairo, star gazing with the Bedouins, or visiting the breathtaking city of Luxor on the banks of the Nile. The stunning scenery of the region features the rich seas contrasting with the stark beauty of the desert.

Whether the holiday is spent mostly above or below the waterline, disappointment is unlikely.

Regaldive also offers a variety of resorts and liveaboards in the Red Sea, providing everything a diver could desire. For a blend of experiences, their mini dive safaris combine liveaboard and resort-based diving, while land-based liveaboard trips allow guests to explore Sharm el Sheikh’s diving highlights while staying in beachside cabins.

Find out more about the diving Regaldive have to offer in the Red Sea here.

www.regal-diving.co.uk

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Can reef conservation be both enjoyable and profitable?

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wakatobi

At Wakatobi Dive Resort, guests are always thanked for coming to enjoy this special place, as it is their presence that creates the magic making ongoing reef conservation efforts a reality. “The more you know, the more you notice,” says in-house marine biologist Julia Mellers. “And what better place to learn about reef biodiversity and custodianship than in Wakatobi.”

“My main project for the first year is to establish a way of monitoring the health of Wakatobi’s reef ecosystem,” Julia says. “This will allow us to provide hard scientific proof that Wakatobi’s conservation model measurably benefits reef health. Holding a finger to the pulse of the reef will also assist management decisions, such as identifying priority areas for increased protection.”

Modern methods for reef management

The Wakatobi Reef Health Assessment program utilizes a customized set of modern imaging and data analysis techniques that provide a comprehensive indication of the state of a reef ecosystem. “We use the latest ecological theory, technology, and artificial intelligence to develop a novel package to efficiently and robustly measure reef health,” Julia says. “This will enable us to monitor how Wakatobi’s reefs are faring throughout the protected area without significantly diverting resources from protecting the reefs.”

The process begins in the water, capturing the reef’s sights, sounds, and landscape. Above water, Julia is developing and implementing analysis methods and training machine learning models to extract measures of reef health from captured data. When not on the island, she will research new approaches and ideas for coral reef assessment and help spread the word about Wakatobi’s scientific initiative.

“It’s an absolute privilege to work within a system that benefits both the reefs and the local people,” says Julia. “It also gives us a unique opportunity to assess and document reef health and dynamics within an ecosystem that is actually getting healthier. In stark contrast to declines in coral health recorded elsewhere, our scientific data is already beginning to demonstrate Wakatobi’s astonishing biodiversity – which is evident to anyone who ventures underwater at the resort.”

The program focuses on three indicators of reef health: the diversity of the reef community, which measures the variety and abundance of living organisms colonizing the reef surface; structural complexity, describing the degree to which the reefs incorporate elaborate details; and reef soundscapes, recording the noise a reef’s inhabitants make, including the snapping of shrimp and the feeding sounds of fish. By measuring these elements, it is possible to estimate how much life the habitat supports.

“Luckily, we don’t have to work all that out manually,” Julia says. Artificial intelligence plays a vital role. “I train machine learning models to identify signals of reef functioning that would otherwise be undetectable. For example, a model can be trained to recognize the sounds that characterize a healthy reef. This allows us to monitor the reefs at a scale, and with a thoroughness that would otherwise be inconceivable.”

Julia and the dive team have also started an eDNA survey of the reefs. ”This involves taking seawater samples near the reef at different depths and filtering them to trap environmental DNA (eDNA) that organisms shed into the water,” Julia explains. “The samples are now in a lab, where the DNA is labeled using probes and sequenced to identify which species are around. Using this technique, we should be able to detect hundreds of species from just a single litre of seawater. It’s a very cool process!”

wakatobi

A Wakatobi welcome

Julia says the Wakatobi team has been exceptionally supportive and welcoming. “They are able to maintain a totally laid-back atmosphere while coordinating an exceptionally professional operation.” She adds that Wakatobi feels remote in the best ways, with pristine reefs, peace, and quiet, while also being an extremely comfortable and well-connected place to work.

“Working within a system that works for the reefs because it works for the people is an absolute privilege,” she says. “It also gives us a unique opportunity to unpick reef health and dynamics within an ecosystem that is actually getting healthier. In stark contrast to declines recorded elsewhere, our scientific data is already beginning to demonstrate the astonishing biodiversity evident to anyone who ventures underwater at Wakatobi.”

The Wakatobi team has also proven to be an invaluable source of knowledge about the local ecosystem,” Julia says. “Wakatobi makes the perfect scientific laboratory. Being able to go from library to laptop to reef, all in the space of a hundred meters, is the perfect recipe for generating new ideas and trying them out. It is so exciting to work with open-minded innovators keen to try novel approaches and look at things from different angles.”

“Having such a dynamic team has meant that we’ve made progress quickly,” Julia says. “So far, we have a highly accurate machine learning model that classifies the reef community, a method to analyze the sounds that reef critters make, and a fully automatic way of measuring fish abundance. We are also in a position to add to this repertoire, trialing different techniques to quantify the complex 3D structure that corals make. We have added DNA analysis to the arsenal, which enables us to detect biodiversity invisible to the naked eye.”

From frogs to frogfish

Julia acquired her love of nature and biology from her parents, whom she describes as eco-friendly before the concept became trendy. “Camping, compost heaps, and Attenborough documentaries were features of a nature-centric English childhood. I raised pond-dwelling critters, peered down microscopes, and became transfixed by cephalopods.” Biology was an inevitable choice, she says, and the sea came into her life at a young age. “Having long been a sailor, with a family of sailors, I am at home at sea,” she says. “I took my first sip of compressed air at the bottom of a swimming pool in London and have spent as much time as possible eye-to-eye with octopuses since.”

After completing an undergraduate degree in biology at Oxford University, Julia shifted her Master’s focus to marine biology. It was a move she describes as swapping frogs for frogfish. “I went into marine biology because I see marine biological research as a powerful tool to connect people with the planet,” she says. “Of course, nature should be worth more to us preserved than destroyed – but if you can’t put a price on it, no one pays. Wakatobi has created an economic engine that financially incentivizes reef custodianship. This leads to an ideal scientific setting – demonstrably vibrant reefs linked to genuine socio-economic fairness.“

Julia’s Master’s project was done in collaboration with the Australian Institute of Marine Science and investigated mysterious bare rings of sand that surround reef patches within algal meadows. “We think these ‘reef halos’ form because foraging fish will only venture a short way from the shelter of a coral patch if they are under threat from patrolling sharks,” she says. “Since you can spot these halos from satellite images, they could be a neat way of keeping an eye on shark populations from space… and a possible addition to Wakatobi’s monitoring program”!

As the Reef Health Assessment program progresses, Julia will create new learning and participation opportunities for guests to enhance the depth and enjoyment of their Wakatobi experience. Wakatobi Dive Resort will also continue to provide updates and insights on the important work Julia and the rest of the Wakatobi team are doing to understand and protect some of the world’s most pristine and spectacular coral reefs.

Many thanks go to Wakatobi’s guests, whose continued enjoyment of the marine preserve helps keep ongoing reef protection efforts a reality!

Contact the team at office@wakatobi.com or enquire >here.
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View Wakatobi videos on the YouTube Channel.

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