Thursday, May 22, 2008

To swim or not to swim to safety in cold water

In Canada, 2007 people died from cold water immersion between the years 1991 and 2000.

Last summer researchers published a study which addressed the question of what the best approach should be for those who find themselves immersed in cold water after a boating accident. The Ducharme and Lounsbury (2007) article, from which the opening statement above was taken, reviews the available literature in order to verify or improve the advice offered to those of us who head out on water that is often cold.

A National Research Council press release summarizes some of the important points taken from the research article:
  1. Stay calm. Unless you're wearing an immersion suit, you'll experience cold shock when you go into cold water due to rapid cooling of the skin. You won't be able to control your breathing, and you won't get far if you try to swim at this point. Your breathing will return to normal in two to three minutes.
  2. Make a plan. While you're waiting for the cold shock to subside, consider your situation and decide whether to swim or stay.
  3. If you decide to swim, look for the shore and decide if you can make it. Most people who participated in the researchers' studies could swim between 800 and 1500 metres in cold water, or for 45 minutes, before the muscles in their arms and legs cooled to the point that they could no longer swim.
  4. If you decide to stay, try to get out of the water as much as possible. Complete any tasks that require the use of your hands, such as tying knots or turning on flares, as soon as possible. As your hands cool, they lose dexterity.
  5. Stick to your decision-don't change your mind midway. After over 30 minutes in cold water, you may become hypothermic, and you won't make the best decisions.
I briefly experienced the cold shock described in point number one a few weeks ago after dumping in the Garden River. It was an interesting sensation for sure and I'm glad that I experienced it five feet from shore in four feet of water rather than 500 feet from shore in deep water. Regarding the cold shock response and the difficulty in breathing that ensues, Ducharme and Lounsbury point out that "people must remain almost vertical during the initial phase of immersion in an effort to avoid drowning." So, if you dump, don't panic and immediately swim for shore. Take a few moments to get your wits and your breath, then make a decision on how to save yourself. I wonder how many drowning deaths in cold water are related to that single factor.

Another interesting point from the research article, hypothermia does not set in as quickly as commonly believed. A swimmer in cold water may have 45 minutes before cooling of the muscles leads to incapacitation, not hypothermia. The authors also address swimming technique. Legs-only swimming is slow and uses a large amount of energy. Using the arms increases the rate of heat loss, but the pace of swimming is greatly increased and the authors conclude that "if one decides to swim for it in a cold water temperature (below 15 °C), the chosen pace should be as fast as possible."

The researchers also point out that due to the greater heat loss in the water, it is always best to get as much of the body out of the water as possible, even if your lower body remains in the water (such as lying on an overturned canoe). Another factor is clothing, and even though the clothes will slow down a swimmer, they will also slow the heat loss and are therefore valuable.

I would like to add one more point. If you find yourself immersed in water cold enough to result in experiencing a "cold shock response," you better have a pfd on or quite probably none of the above will matter!

Ducharme, M.B., and Lounsbury, S. 2007. Self-rescue swimming in cold water: the latest advice. Appl. Physiol. Nutr. Metab. 32(4): 799–807

For more on cold water immersion, check out the web site of University of Manitoba professor Dr. Geisbrecht. Watch the videos, they are worth the time.