Decompression Myths: Part 4

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.