Dehydration - is it really *that* bad?

[Mr Carcharodon]

With a very severe exposure to nitrogen (more than a thousand minutes past NDL), and severe dehydration, there can be a significant effect e.g.: Fahlman A, Dromsky DM. Aviat Space Environ Med. 2006 Feb;77(2):102-6. That said given the type nitrogen exposures recreational divers experience it is unlikely there is a significant effect or if there is it would take a testing over tens of thousands of dives to show it.

Dehydration usually gets trotted out to “explain” DCS cases usually without evidence of any kind. There is not a dive table or computer algorithm any place that uses dehydration as a parameter because there is no known relationship. Dive tables and computers use depth, time and FN2 because those are the factors that drive nitrogen load. Drinking a glass of water might give you a marginal edge and the only downside is that doing so may distract you from the primary factors that drive nitrogen exposure. There was a recent thread on skin bends where the poster focused on dehydration being the cause while ignoring that that case occurred after a long series of repetitive dives all done right to the edge of no decompression limits. Pay attention to depth, time and mix, and how close you are to the limits, those are the primary factors.

 

[tajkd]

With a very severe exposure to nitrogen (more than a thousand minutes past NDL), and severe dehydration, there can be a significant effect e.g.: Fahlman A, Dromsky DM. Aviat Space Environ Med. 2006 Feb;77(2):102-6. That said given the type nitrogen exposures recreational divers experience it is unlikely there is a significant effect or if there is it would take a testing over tens of thousands of dives to show it.

Dehydration usually gets trotted out to “explain” DCS cases usually without evidence of any kind. There is not a dive table or computer algorithm any place that uses dehydration as a parameter because there is no known relationship. Dive tables and computers use depth, time and FN2 because those are the factors that drive nitrogen load. Drinking a glass of water might give you a marginal edge and the only downside is that doing so may distract you from the primary factors that drive nitrogen exposure. There was a recent thread on skin bends where the poster focused on dehydration being the cause while ignoring that that case occurred after a long series of repetitive dives all done right to the edge of no decompression limits. Pay attention to depth, time and mix, and how close you are to the limits, those are the primary factors.

I have to agree strongly with Mr Carcharodon. There is basically one study in pigs where they withheld food/water, gave them laxatives, and forced them to die from rapid recompression. 1/3 of the control group had DCS from the study and 2/3 of the laxative group. There is no empirical evidence relating dehydration with dcs and, as stated, the cause gets brought up to explain the unexplained. That said, if you notice signs of dehydration, you should get fluids (water) into you simply to maintain the best health you can while performing such a challenging task as scuba.

 

[danvolker]

With a very severe exposure to nitrogen (more than a thousand minutes past NDL), and severe dehydration, there can be a significant effect e.g.: Fahlman A, Dromsky DM. Aviat Space Environ Med. 2006 Feb;77(2):102-6. That said given the type nitrogen exposures recreational divers experience it is unlikely there is a significant effect or if there is it would take a testing over tens of thousands of dives to show it.

Dehydration usually gets trotted out to “explain” DCS cases usually without evidence of any kind. There is not a dive table or computer algorithm any place that uses dehydration as a parameter because there is no known relationship. Dive tables and computers use depth, time and FN2 because those are the factors that drive nitrogen load. Drinking a glass of water might give you a marginal edge and the only downside is that doing so may distract you from the primary factors that drive nitrogen exposure. There was a recent thread on skin bends where the poster focused on dehydration being the cause while ignoring that that case occurred after a long series of repetitive dives all done right to the edge of no decompression limits. Pay attention to depth, time and mix, and how close you are to the limits, those are the primary factors.

I would have to agree with you that only very sketchy direct evidence has been linked in the studies passed around--at least that I have seen...
One area I think the researchers "should look" at, would be a correlation between cramping muscles and constriction of blood vessels..... and the relationship between this and bubble formation where constrictions begin to cause bubble formation/growth/aggregation. While anecdotal, I would expect that many divers that allow them selves to get quite dehydrated, and who then cramp up, would be far more likely to experience some form of DCS.
This is a long way from research that points to DCS from dehydration....I think there are some common sense precautions we need to make, among them, we don't purposely do things that are likely to cause cramping and restricted bloodflow after a big dive, or multiple dives.

I was in a Doppler study once, where it was shown very conclusively that holding a heavy object throughout an aggressive dive profile, will actually cause a large increase in bubbling in the muscles effected by holding the heavy object....whether a very heavy speargun or very heavy camera and strobe combo. This ties in pretty well, from a common sense perspective....call it an observation the researchers could use to structure some future work.

 

[vladimir]

Among the many issues with coke or pepsi...

* massive spiking of insulin with each bottle or can.....leads to insulin resistance in many people, which can easily lead to diabetes...recently insulin resistance has been linked to Alzheimer's ( as a form of brain starvation from no longer being able to use sugar, due to insulin resistance..interestingly, the brain can also run on ketones, and this has led to using the MCT of Extra virgin Coconut oil as an alternative food source for the brain, and some spectacular reversals of mental function in many Alzheimer's patients...)
* I agree the diuretic issue of Coke is not a big deal compared to the sugar issue....but plain water is just as free on diveboats as coke, and MUCH better for you.
* Also, there is a strong liklihood that sodas will act like bromides in lowering thyroid output....helping to make a heavy coke drinker more prone to being hypothyroid....We have a huge population of people taking synthetic thyroid drugs, due to so much prevalence of hypothyroidism...this is incredibly foolish as a medical response. If you know that in most/many that the thyroid is being shut down by "foods" like soda, breads, clorine, etc, and that most of these people are Iodine depleted--thus their Thyroid is underactive....WHY NOT RESTORE proper Iodine levels and let the body restore proper thyroid involvement....Instead of making lifelong addicts to synthetic thyroid that can not possibly keep you as healthy as a properly functioning thyroid gland--why not make a big stink about how coke and pepsi contribute so much to thyroid problems......
ps. on this.... Lugols Solution has as much iodine in one dropper as about 60 bottles of the useless Kelp cr*p that health food stores sell to people hoping to boost their iodine..... You do NOT want to buy Iodized Sodium Cloride, as it is a very unhealthy salt in this synthetic form.....Sea Salts easily available even at Publix are much better for you, but not a significant source of Iodine.

Perhaps all true, but none of it is relevant to the question of proper hydration. Heavily sugared drinks are—from a nutritional perspective—probably one of the worst foods you can ingest. We agree on that. I don't advocate drinking them and I don't drink them. Nevertheless, you can adequately hydrate yourself before a dive with Coke.

 

[rhwestfall]

from a purely speculative position - anything that reduces the "stressors" should be beneficial.....

 

[Wayne at DiveSeekers]

I guess we can go round and round on this, but here is another published study.

[h=1]Dehydration effects on the risk of severe decompression sickness in a swine model.[/h]Fahlman A, Dromsky DM.
[h=3]Source[/h]Naval Medical Research Center, Diving Medicine, 503 Robert Grant Ave., Silver Spring, MD 20910-7500, USA.

[h=3]Abstract[/h][h=4]BACKGROUND:[/h]Several physiological factors have been suspected of affecting the risk of decompression sickness (DCS), but few have been thoroughly studied during controlled conditions. Dehydration is a potential factor that could increase the risk of DCS. It has been suggested that hydration may enhance inert gas removal or increase surface tension of the blood.
[h=4]HYPOTHESIS:[/h]Dehydration increases DCS risk.
[h=4]METHODS:[/h]Littermate pairs of male Yorkshire swine (n=57, mean +/- 1 SD 20.6 +/- 1.7 kg) were randomized into two groups. The hydrated group received no medication and was allowed ad lib access to water during a simulated saturation dive. The dehydrated group received intravenous 2 mg x kg(-1) Lasix (a diuretic medication) without access to water throughout the dive. Animals were then compressed on air to 110 ft of seawater (fsw, 4.33 ATA) for 22 h and brought directly to the surface at a rate of 30 fsw x min(-1) (0.91 ATA x min(-1)). Outcomes of death and non-fatal central nervous system (CNS) or cardiopulmonary DCS were recorded.
[h=4]RESULTS:[/h]In the hydrated group (n=31): DCS=10, cardiopulmonary DCS=9, CNS DCS=2, Death=4. In the dehydrated group (n=26): DCS=19, cardiopulmonary DCS=19, CNS DCS=6, Death=9. Dehydration significantly increased the overall risk of severe DCS and death. Specifically, it increased the risk of cardiopulmonary DCS, and showed a trend toward increased CNS DCS. In addition, dehydrated subjects manifested cardiopulmonary DCS sooner and showed a trend toward more rapid death (p < 0.1).

[h=4]CONCLUSION:
[/h]Hydration status at the time of decompression significantly influences the incidence and time to onset of DCS in this model.

PMID:16491576 [PubMed - indexed for MEDLINE]

A discussion whether or not to or not to should really not be on the table. Why even potentially take an added risk? Just HYDRATE!

 

[danvolker]

Perhaps all true, but none of it is relevant to the question of proper hydration. Heavily sugared drinks are&#8212;from a nutritional perspective&#8212;probably one of the worst foods you can ingest. We agree on that. I don't advocate drinking them and I don't drink them. Nevertheless, you can adequately hydrate yourself before a dive with Coke.

I don't think we can agree on the coke being able to "adequately hydrate you" though.
First, you are in the area of extra-cellular hydration only, so you will not be helping your muscles much at all--you will do little to prevent cramping that you COULD DO if you were getting intra-cellular hydration which also included the right balance of potassium to sodium.
Second, you may actually cause some cramping with the high sugar concentration of the soda, particularly if your body spikes insulin in response to the coke, and then your muscles are running profoundly low on available energy for the upcoming dive(s). Some people will tolerate the huge sugar spike better than others ( in other words, some will get a big insulin spike, some will only get a small insulin spike.)
I do not believe divers should drink sodas as the primary beverage for diving--but this IS what is standard now. Why should we tell them they are fine smoking cigarettes if they like them, or eating a cup of sugar whenever they feel like having sweets....why should they hear that coke or pepsi is OK? How does this help anyone, other than make a nutritionally dysfunctional person feel better about their desires for sugar ?

The message from you to divers, and particularly from TS&M because she is so well known and her opinions so highly respected, should be that coke or pepsi ( sodas) are NOT acceptable for Hydration , whether for diving or for any other sports related activity.

I realize I do not have the right to suggest what either of you should say.....

 

[Mr Carcharodon]

Animals were then compressed on air to 110 ft of seawater (fsw, 4.33 ATA) for 22 h and brought directly to the surface at a rate of 30 fsw x min(-1) (0.91 ATA x min(-1)).

Wayne,

When was the last time you went 1300 minutes past your NDL and did not do any deco? How relevant is that study for recreational or tech divers? Do you know any tech divers that do deco dives and omit thousands of minutes of decompression?

There is a potential risk you will be hit in the head by a meteorite. Are you wearing a helmet to mitigate that risk now? If not are you being reckless?

 

[TSandM]

Dehydration is posited as a contributing factor to DCS, but there is very little data to prove that it is an independent variable. Dehydration in divers occurs for multiple reasons, including hot climates and wind, seasickness and poor oral intake, and volume centralization and immersion diuresis. Over the course of a diving day, assuming you are NOT seasick, you will experience some volume depletion, but you will not reach severe (clinical) levels of dehydration if you continue some oral intake.

Most of the volume losses divers experience are in the form of water. Water is the primary component of both sweat and urine, and is pretty much the sole component of respiratory fluid loss. Sweat contains a small amount of salt and potassium, but is VERY hypotonic, so the losses, unless you are running marathons in Singapore in the summertime, are small. The kidneys are EXTREMELY good at conserving salt and reasonably good at conserving potassium as well. So the bottom line is that, unless you are one of Dan's high performance athletes, you can really ignore electrolyte losses under almost all moderate conditions. They may become relevant in extremely hot places, and will become relevant if you are vomiting or having diarrhea.

There are many reasons to avoid sugared soft drinks, the biggest among them being the empty calories. But it is better to drink soft drinks than to drink nothing. Water is preferable, but where bottled water is unavailable and other water is questionable, at least canned soft drinks are almost certain not to harbor pathogens.

Regarding fluid losses . . . the body is about 70% water in an adult. This water is divided into three compartments: Intravascular (blood volume), interstitial (between the cells) and intracellular. The intracellular component is by far and away the largest, but you do not ever lose volume directly from this compartment. Real-time volume losses are primarily from the intravascular volume -- that's the compartment from which the kidneys take fluid to make urine, which is the largest volume loss. Intravascular volume runs about 5 to 6 liters in an average adult, and 10% dehydration is considered mild, which is about what divers without illness will reach. So you're looking at 5 or 600 ccs of fluid to replete -- that's two to three cups of water or other beverage during a diving day. I suspect most of us drink more than that!

 

[bleeb]

1) Roughly how much body fluid does one lose in say a 60 min dive - and how much extra water is required to compensate an hours worth of diving?

In terms of what you loose breathing, it's not about time. I think it's actually more about how much gas you're breathing, since you're rehydrating it from approximately zero water content to 100% RH @ body temperature. If I did the math correctly, that's about 100 mL of water for 80 cu. ft. of gas, or just a little under half a cup. Not an excessively huge amount, but your system will probably notice it if you're already a bit dehydrated. (Note that I'm only talking about the human body in a general physical sense, and not trying to quantify the specific effects on nitrogen uptake and offgassing.)