Cold Water Shock

As part of the packrafting culture of safety promotion we have been taking a deep dive into exploring some of the leading causes of fatalities on the water. The aim with these articles is to try to build risk literacy around the water in order to help ensure that the 2021/22 season is free from fatalities in the packrafting community.

In the previous article we identified the 1:10:1 pathway coined by Dr Gordon Giesbrecht which breaks down into:

1 Minute of Cold water Shock response.

10 mintues of meaningful movements.

1 hour before we succumb to the effects of hypothermia.

At any point during this 1:10:1 pathway, drowning may occur and as such this was the focus of the first article. Our focus on this article is the less well understood autonomic conflict caused by cold water shock.

The reason I wanted to cover autonomic conflict is that it is not commonly understood and is under-represented in drowning statistics despite the evidence that suggest it might be responsible for up to 60% of drownings that occur in and around cold water. Alex Hutchinson made some interesting observations around the effects of cold water on water fatalities and the over representation of “flush drownings” recently in his Outside magazine article. However, the work of Dr Mike Tipton MBE (Professor of Human & Applied Physiology at the Extreme Environments at Portsmouth University) provides us with further insight into cold water shock, for which he was awarded his MBE (check out his talk on WEMcast if you’re interested to learn more).

So what do we know about cold water shock. Well the cold water shock is a response of the sympathetic nervous system that is triggered when our cutaneous cold receptors under our skin detect a rapid change in temperature. We’ve all experienced this at some stage I’m sure. It’s the thing that triggers that gasping when you get into super cold water. The good news is that it doesn’t tend to last that long hence Dr Giestbrecht’s 1 minute description (although the mean length of this response is actually 71 seconds…. which isn’t quite as pithy as 1:10:1!). During this time hyperventilation sees respiratory output soar between 600% and 1000%.

So why does this matter to us? There’s a few reasons. Firstly uncontrollable gasping can be fatal in and of itself. As mentioned in the previous article, the lethal does of freshwater into the lungs is around 3 litres (less than 2 litres for salt water). A single gasp can mean aspirating between 1.9-3.3 litres of water so a single gasp can be lethal and lead us down the drowning pathway. Empirical evidence shows that adults will inhale over 110 litres of air in a minute during cold water shock. This hyperventilation in of itself can be problematic as the quality of our breathing is effected which can make us lose consciousness. This loss of consciousness can (quite obviously) cause swim failure and stops us from protecting our airways by keeping our heads up and we aspirate water. The other reason it matters as it can inform our decisions whilst packrafting to mitigate these risks. Ever wonder why raft guides and instructors talk about the Rapid Safe or Safe Float position? (Feet on the surface of the water facing down stream, arms out to the side sculling for steering).

Well part of the reason is to prevent a potentially shitty situation getting worse. Your feet are up so they can’t get entrapped on the bottom on the water and you can push off objects like rocks if you look like you’re going to bash into them. But also it keeps you safe because it is mostly likely that during this initial 1 minute (or 71 seconds) that you’ll be experiencing this uncontrollable breathing. Having your feet first means waves are breaking more over your feet and body than blindly breaking over your head and compromising your airway. It’s also why people like the Royal National Lifeguard Institute launched it’s “fight your instincts not the water” campaign whereby recommendations were made to float rather than swim when you initially fall in the water so you can get your breathing under control.

We can also take steps to lessen the effects of cold water shock. There has been suggestions that repeated exposure can acclimatise you to cold water shock although there is no evidence at this stage to back this up. One certainty however is through reducing the strength of the response by exposing fewer cutaneous receptors. Wearing a wetsuit can help to an extent but wearing a drysuit will increase your chances of survival massively. Commonly a dry suit is thought to be a more comfortable way to paddle and perhaps it’s safer because it helps prevent hypothermia, however it’s contribution towards the reduction in deaths caused by cold water shock is massive. According to American Whitewater death caused by hypothermia is lower than 2% although “flush drownings” which is a generic catch-all term is the leading cause of death (19% of all fatalities on rivers in the last 20 years in the US). It is possible that cold water shock makes up a significant % of these flush drownings, especially given the correlation between cold water and flush drownings identified by Hutchinson. Here in NZ it has been long understood that the cold leads to more fatalities than “flush drowning”. So I’ll say it again for those people at the back, wear a drysuit when packrafting. The kokatat swift entry is an incredible dry suit for packrafting (hence it’s the only dry suit we sell) as it’s lighter than a wetsuit, simple and cheaper than most drysuits on the market. Get in touch if you’d like to buy one, we can do lay-by options to make it more affordable.

So we’ve established one reason that cold water shock can dangerous. Nothing really that ground breaking there i’m sure. However, a less well understood cause of death is autonomic conflict. As mentioned ealier, the sympathetic nervous system triggers the cold water shock response, however we have another autonomic response that is triggered by cold water known as the mammalian dive reflex. You may be aware of this too. It’s stronger in younger people and gets less strong as we age. This dive reflex is a product of our parasympathetic nervous system that is triggered by the ophthalmic division of trigeminal nerves on our face. This response slows our heart rate (as low as 33 beats per minute), reducing the strength of our heart beats, selectively vasoconstricts blood vessels and aids breath holding. Basically it does the polar opposite of our other autonomic response (the sympathetic nervous system) is driving us to do, hence autonomic conflict.

What has been found by Dr Mike Tipton, is that when the cutaneous receptors are triggered on their own in cold water shock, around 1% of people studied will present arrhythmia (irregular heart beat indicative of heart problems being experienced). When subjects were submerged with their face in the water too, 82% of them displayed arrhythmia. That’s a huge increase and no surprise that some of these arrhythmias can be fatal tachycardias, ventricular fibrillations and lead to myocardial infarctions (heart attacks). To further complicate matters these myocardial infarctions can also cause agonal gasping which leads to water aspiration. Because of the pathway this autonomic pathway takes us down, upon post mortem only the heart attack will be detected and not the cause of the heart attack. Given that we now know 82% of people will experience arrhythmia, it doesn’t seem unlikely that many of our “flush drownings” are actually autonomic conflict fatalities. Especially when we can see there is a significant correlation between cold water and flush drownings.

Sobering huh. So how do we prevent this? Well one smart ass on my course suggested ensuring we only we ever submerge our heads not our body’s so only one autonomic response is triggered…. but as dumb as this seems he’s kinda right. I’m not suggesting we just fall in with our faces and some how levitate our bodies, but again, if we wear a dry suit, only our parasympathetic nervous system is stimulated.

I should point out at this stage that whilst my bank manager would dearly love for you all the buy shiny new drysuits through Packrafting Queenstown, it is entirely possible to repair dry suits and replace gaskets. In keeping with out sustainability drive we would strongly urge you to make your gear last another season by repairing it rather than replacing it. Especially if you have a kokatat suit as they have a reasonable lifetime guarantee so there’s no excuse!

So one last point before we leave cold water shock (and move into hypothermia next yippeee!!). How cold is cold water? Many of you reading this might think, “ah that’s alright I don’t really paddle in the winter” or “my local river’s not really cold enough to trigger this stuff”, but the truth is cold water is actually far warmer that we commonly think. Officially it’s 15 degrees Celsius (or about 59 degrees fahrenheit for you Americans). That’s not that cold at all (says the south islander who works on water that was frozen only hours earlier!) . NIWA have some cool data on river temperatures in NZ that averages out between 12-16 degrees. But realistically you can expect to start to go down this Cold water shock/hypothermia pathway in water as warm as 22 degrees eventually. But more on that in the next article.