Diving narcosis and laughing gas

Photo by Derek Keats

I watched a programme the other day about a deep sea mystery. A strangely high number of experienced deep sea divers had been lost on diving trips in a particular bay, and no one seemed to know why. The presenter, being a decent diver himself, went for a dive in the bay and noticed that he could make out the sunlight shining through the water at the other end of an underwater tunnel. His conclusion was that the now deceased divers saw this light and thought they could swim through the tunnel to the other side. What wasn’t obvious to the divers was that this light was deceptively far away and they would have to swim very fast for a long time to make it to the other end of the tunnel before running out of oxygen. But what could cause these supposedly experienced divers to make such a rash, fatal decision?

Nitrogen narcosis can give you tunnel vision, making it harder to read diving instruments. Image by RexxS

Above sea level, nitrogen is a pretty boring gas – it makes up about 80% of the air around us and doesn’t normally do us any harm. However, a problem arises when we breathe it in under high pressure – such as when diving. Several gases, including nitrogen, carbon dioxide, and oxygen are normally dissolved in our bloodstream. When you dive deep underwater, the increase in pressure exerted on your body by the surrounding water causes more of these gases to dissolve into your blood through your lungs when you breathe from the gas tank (because going deep-sea diving without a gas tank would be an even less recommendable thing to do). In fact, for every 10m a diver descends, their blood holds an extra 1.5 litres of dissolved nitrogen.

All that extra nitrogen rushing round in the bloodstream has weird, wonderful, and incompletely understood effects on the brain, collectively known as nitrogen narcosis.

Nitrogen narcosis is experienced by all divers – to varying degrees – and feels essentially like being drunk. Because of this similarity, nitrogen narcosis is often referred to as the ‘Martini effect’. Divers liken every 10m below sea level as the equivalent of having one martini – meaning they feel increasingly intoxicated the deeper they get. Even at comparatively shallow depths (10-30m below the surface), a diver will become less co-ordinated and a bit giddy – 20m lower they’ll start making mistakes and bad decisions and may start laughing for no reason. At 50-70 metres, they may start experiencing hallucinations, sleepiness, terror, poor concentration and confusion, and at 90m they risk losing consciousness or even dying.

So, the worse symptoms of nitrogen narcosis aren’t exactly like getting drunk, because even a huge amount of alcohol doesn’t give people hallucinations (though some alcoholics experience hallucinations when withdrawing from alcohol). Actually, the closest similarity to nitrogen narcosis you can find on dry land is from breathing laughing gas, or nitrous oxide.

A pretty sexist cartoon from ages ago showing some ‘scolding wives’ being prescribed laughing gas. I wonder why they were usually so unhappy with their husbands.

Nitrous oxide has been used by doctors to relax patients since 1794 and it is still used today as a form of pain relief for women during childbirth. It has been in the press a lot recently, dubbed ‘hippie crack’, as it’s often used recreationally (though usually not legally) for its mild hallucinogenic and euphoric ‘feel good’ effects, which have often been likened to nitrogen narcosis. So how does nitrous oxide affect the brain?

Although nitrous oxide is hugely understudied, there are several theories about how it can affect the brain. Because gases like nitrous oxide and nitrogen are really fat-soluble, they may interfere with cell membranes (which are made from fatty molecules) disrupting their normal function. In the case of brain cells, this may alter the way they communicate with one another. In addition, the dissolved gas molecules may directly bind to the receptors on the surface of brain and nerve cells. Nitrous oxide is used as a mild anaesthetic because it has been shown to block NMDA receptors – which normally ‘excite’ the brain – and because it activates potassium channels, which further suppress brain cell excitation. All this means is that brain activity is generally depressed and so users are more prone to making bad decisions or losing concentration.

As I mentioned before, nitrous oxide is also good for pain-relief, as it’s believed to activate opioid centres in the brain. When activated, the opioid system – the same one stimulated by drugs like heroin and morphine – then disinhibits certain adrenergic cells in the spinal cord, which dampen down any feelings of pain.

While there have been reports that nitrogen narcosis also decreases the perception of pain, it’s obviously difficult, and, well, not very practical to test the potential of high pressure deep sea diving on pain relief. Instead, what should be studied more are the effects of nitrous oxide on the nervous system. We’ve used the stuff for more than 200 years and yet the biology behind its uses and its dangers is still not fully understood. What’s more, the fact that people use nitrous oxide recreationally (and probably will continue to do so in spite of its non-legal status in many countries) means we really ought to know what its short and long term effects on the brain are. Unlike the mystery of the missing deep sea divers, the full extent of the ways in which nitrous oxide works remains unsolved.

Post by Natasha Bray

4 thoughts on “Diving narcosis and laughing gas”

  1. Really curious about this topic, some personal reasons:
    1) I’m a scuba instructor, frequently dive deep and deal with (teach about) nitrogen narcosis
    2) Am a chronic pain sufferer (back injury,multiple surgeries) – benefit from scuba (weightlessness) & joke about narcosis & back pain relief while affected
    I do wonder if there are medical benefits/therapies related to these gases & their affects.
    I’m not certain I understand the differences in the compounds (gases), effects & such. The article is vague saying “similar to”, as well as in teaching nitrogen narcosis (nitrogen gas affects under pressure) where we teach there’s no residual & (personal experience/understand) the effect is gone at lower pressure.
    If anyone (author/readers) has recommendations on further readings/studies, related to the similarities, pain therapies, long-term effects (again, understanding with nit-narcosis there’s zero!), I’d appreciate links/ideas/etc.

  2. P.S. Tagging on to my last post – there are some misconceptions & inaccuracies related to scuba in this article, I’d be happy to clarify/explain if anyone’s interested, simple glaring examples:
    1) The increase in nitrogen intake underpressure isn’t sure much about the outside pressure of the water (tho’ related) but due to the fact that you’re breathing (on scuba!) gas that’s pressurized to ambient external pressure. So you’re doubling/tripling/etc the amount of gas in your lungs/system due to the equipment delivering it compressed (more gas in same space/lungful). Otherwise, by authors description you’d have same effect by holding a surface breath & diving deep.
    2) 10m = 1 martini = absolute hogwash. Most people don’t start ‘feeling’ any (even minimal) narcosis until approaching say 90-100′ (30m+), that’s 4x atmospheres of pressure! 3-4x martinis would be WAY more than that min affect. Many/most have to dive deeper, say 120′ or more to get any “drunkenness” feeling. Anecdotal (& diff for everyone, even at diff times) but I’m more of a 130-160′ until I feel *much*. Whereas 5-6+ martinis I’d be *bombed*. 🙂
    3) 90m+ & leading to death… well now you’re venturing into the realm where death is more likely caused by OXYGEN toxicity and not ‘normal’ % of nitrogen being the problem.
    Not to nit-pick, as it’s an interesting article & has increased my interest in exploring nitrogen narcosis vs nitrous oxide affects… but the scuba related descriptions has some flaws & misleading implications.

  3. Re: Missing sea divers – cave/misjudgement
    I’ve re-read several portions of the article, & being lazy here & not completely re-reading….but I think an important point was missed about this story of the divers mis-judging the cave/light source.
    Info missing – the depth!
    Unless this was a very deep cave/area AND we know the gas mixture the divers were using (example: even if “deep enough”, nitrox/enriched-air appropriate for the depth could eliminate the narcosis risk entirely!), where the divers were highly likely to be severely impacted by nitrogen narcosis… no evidence is presence that it had anything to do with the divers. Visibility, size of cave, optical distortions could all be way more likely.

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