A recent scholarly analysis of cold-water immersion, appearing in the Journal of Applied Physiology, investigates the mechanisms of cold-water fatalities. Conducted by Italian scientists Laura Leuci and Luca Carenzo, it compiles peer-reviewed physiological findings to offer survival guidance for individuals and rescue teams.
In May, under clear skies, newlyweds Jeru Bague and Mariz Bello capsized from their paddleboard on Browning Lake near Squamish, British Columbia, tragically drowning.
Falling into cold water is more complicated than it seems. It’s not just about hypothermia, which usually doesn’t kick in for half an hour or so. In fact, a substantial proportion of cold-water deaths occur either long before hypothermia hits or shortly after the swimmer is rescued.
Cold-Water Dangers
Over half of open-water drowning cases happen within three meters of safety, with two-thirds involving proficient swimmers. A recent review outlines the often-overlooked dangers of cold-water immersion and strategies to enhance survival chances.
Scientists divide these dangers into four distinct stages that progress chronologically. The first stage occurs when you’re suddenly immersed in cold water, below 15 degrees Celsius or 59 degrees Fahrenheit. You’ll take a big, involuntary gasp of air, which can kickstart the drowning process if you’re underwater.
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After the big gasp, you’ll typically start hyperventilating for one to three minutes. This can also be a problem, as you may find it difficult to time your rapid breaths between waves, raising your risk of inhaling water.
The key countermeasure here is what the Royal National Lifeboat Institution calls “Float to Live,” which advises you to float on your back with your face out of the water until the hyperventilation subsides. Modern lifejackets are designed to push you toward the appropriate position automatically.
Even if you do float, there’s another key risk during this initial stage. The cold shock triggers your sympathetic nervous system, which tells your heart to beat in a rapid and ultra-regular rhythm, increasing by 15 to 30 beats per minute within a few seconds.
This can lead to “autonomic conflict,” which creates electrical instability in the heart that may lead to dangerous arrhythmias, though likely only if there’s a pre-existing heart condition. The more you expose yourself to cold water, the weaker your cold shock response gets, with protective effects lasting for months.
Survival Tactics
If you survive the initial shock, then the cold itself will start kicking in over the following 30 minutes, acting from the outside in. As your limbs, muscles, and extremities get colder, they’ll gradually lose function. Your fingers, for example, get markedly clumsier when skin temperature drops below 15 C (59 F).
To minimize the risk of swimming failure, you have to make a choice that is important for your survival: Should you swim towards safety or stay put? In 12 C (54 F) water, people can typically make it about 1,250 meters (4,100 feet) in a swimsuit or 800 meters (2,625 feet) in clothes before hitting failure.
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Ideally, you should swim on your back, only kicking your legs, while keeping your arms close to your body to minimize heat loss. If safety is farther away than that, then you need to focus on staying warm. Instead of swimming, assume the Heat Escape Lessening Position (HELP): knees to chest, arms close to the body.
Eventually, typically sometime after the first half-hour, your core temperature may drop below 35 C (95 F). Now you’re hypothermic, which means your decision-making and consciousness will be clouded. Somewhere below about 30 C (86 F), you’ll lose consciousness.
Leuci and her colleagues note that there are a surprising number of cases where hypothermia victims have been revived long after their heart stopped. In one example, someone survived three hours with a core temperature that reached 13.7 C (56.7 F).
Sometimes people die just as they’re being rescued, or immediately before or after. This happens frequently enough that it’s clearly not just a matter of bad timing. Something about the rescue process triggers the event, and researchers are still working to understand the exact mechanisms behind this phenomenon, including the potential role of a “parasympathetic surge” triggered by the emotional impact of impending rescue.
The loss of hydrostatic pressure when being pulled out of the water can also cause a potentially calamitous drop in blood pressure, and rescuers are advised to keep victims horizontal during and immediately after getting them out of the water if possible, to minimize this risk and prevent further complications, such as a sudden and dangerous drop in blood pressure, which can be fatal.
