The Crippling Effects Of Cold Water Immersion

On a sunny spring day, or during the early days of winter, the sparkling water beckons. Surrounded by natural beauty and excitement, it's easy to forget the ever-present danger of cold water, and that it can kill within minutes, if not seconds, if you fall in. We spoke with two experts to understand the science behind what happens to a person in the critical minutes after being plunged into cold water, and the best strategies for survival.

0:00–3:00 Minutes: Cold Shock

At the moment of cold water immersion, the initial and greatest threat is cold shock. According to a study published in the journal "Experimental Physiology," cold shock accounts for the majority of immersion deaths in the United Kingdom. When you first plunge into cold water, your heart rate, breath rate, and breath volume spike dramatically. This cardiorespiratory response is driven by the cutaneous cold receptor that sits just beneath the surface of the skin. The instinct to gasp is uncontrollable, and deadly.

"The lethal dose for drowning in saltwater is about 1.5 liters [just over one-third gallon]," says Professor Mike Tipton, MBE, FTPS, a professor of Human and Applied Physiology at the University of Portsmouth (U.K.). "The gasp I get when I got into cold water is between 2 to 3 liters. I've already crossed the lethal dose for drowning if I happen to be under the water or have waves breaking over my airway."

If you manage to hold your breath, it sets off a potentially fatal cascade of physiological responses. As cold shock sends your heart rate through the roof, water on your face triggers the diving response — something all mammals have — which works to slow down the heart and prolong breath-hold. "The heart is being accelerated by the cold shock response and slowed by the diving response. Where that competition occurs, that's where you see arrhythmias. We've called it 'cold shock autonomic conflict,'" says Tipton.

While predisposing factors, like certain heart diseases, increase the chances of a fatal arrhythmia, cold shock autonomic conflict affects most people, including the young and healthy. "If I told you to go underwater and hold your breath for as long as you can, within 10 seconds of breaking, roughly 82% would show some form of arrhythmia or dysrhythmia," says Tipton. Cold shock only lasts for the first few minutes of immersion and there are a few vital things you can do to improve your chances of survival.

"Your No. 1 objective on immersion, in those first couple of minutes, is to keep the airway clear of the water," says Tipton. "Hold on to something. If you can't do that, then float."

Hopefully, you'll be wearing a life jacket that will help keep your head above the surface. If for some reason you're not, floating becomes imperative. "If you fight that instinct and stay still, you'll float," Tipton says. The body is less dense than water, and clothing traps air, making you more buoyant. "Don't swim immediately, float first, do as little as possible to stay afloat, rest, and recover."

If it's an option, enter the water slowly. "Cold shock is dependent on the speed and size of the surface area of the skin," says Tipton. As for reducing the chance of a heart attack, "Avoid coincident face immersion and long breath-holds, as they're really potent drivers for arrhythmias."

10:00–40:00 Minutes: Swim Failure

"You've survived the cold shock response. Now it's the superficial nerves and muscles that are cooling, particularly in the arms," says Tipton. This cooling will gradually lead to neuromuscular dysfunction and physical incapacitation. "At around about 81 F local temperature, neuromuscular function fails," Tipton says. "It first shows itself in reductions in grip strength and speed of movement on the fingers, and then progresses to limb movement and coordination." As you swim, your body will go from a horizontal position to increasingly upright with a greater sinking force and drag.

The time it takes for this to happen largely depends on water temperature. It takes "about 40 minutes in 68 F, 20 minutes in 54 F, and 10 minutes in 41 F," explains Tipton. This cooling will also drastically reduce your ability to perform vital tasks like release a flare or open a bailer in a life raft. "You'll lose manual dexterity, you lose strength, you lose the ability to grip," he says. "Be aware, stay still, and after the cold shock, you've got about 10 to 20 minutes to do all the things you need to do to get into long-term survival mode."

It's better to stay still because exercise causes you to cool more quickly. However, if you need to take action, "do leg-only exercise," says Tipton. "An enormous amount of heat is lost through the arms when you start exercising" because you're stirring cold water around your torso. When you don't exercise your arms, they help insulate your torso.

If it's not possible to self-rescue, Chief Warrant Officer Daniel Butierries, search and rescue mission controller for U.S. Coast Guard Sector Virginia, suggests huddling together in a group or going into the H.E.L.P. position: "If you're by yourself you can get into a fetal position, with your knees to your chest, to preserve what warmth you have left in your body.

30:00+ Minutes: Hypothermia

So far your core temperature has remained normal. "Humans don't become hypothermic in less than 30 minutes," Tipton says. In cold water immersion, you don't generally die directly of hypothermia. "With hypothermia, you lose consciousness," he explains. "Then you get swim failure and drown if you don't have a life jacket on or can't keep your airway clear of water."

Signs & Symptoms Of Hypothermia

According to Butierries, a whole host of factors determine how long you will survive after 30 minutes. "There's body composition, water temperature, air temperature, water turbulence, sea state. If it's rough weather, you'll succumb to hypothermia quicker. On a relatively calm day you may be able to hold on longer."

Circum-Rescue Collapse

In an ideal world, rescue would mean the end of a harrowing event. But for the cold-water victim, the battle isn't over. Tipton says that sometimes the condition of the victim continues to worsen after rescue, that "this person who has been OK, collapses."

"Circum-rescue collapse" can occur just before, during, or just after rescue. "We think it partly has to do with autonomic conflict — you just relax, and with that comes a collapse in arterial pressure." The withdrawal of the will to survive can have catastrophic consequences, made worse by a rescuer saying things like, "It's OK, you can relax, we've got you." Tipton suggests rescuers say, "We're here to help. Keep fighting for your survival."

It's also important to be careful how you pull someone from the water. "If you start lifting people up and holding them vertically, there's a collapse of arterial pressure," says Tipton. "This is the consequence of losing the hydrostatic pressure that was squeezing blood back to the heart." If their blood pressure collapses, there's a chance "they'll either faint and fall back into the water and drown, or they'll have a heart problem."

Tipton suggests positioning them out horizontally, though he says this isn't always possible if their airway is under threat. In which case, he suggests, "Get him out anyway you can. You're better off dealing with a faint than you are with a drowning."

Once you've got them aboard, "keep the person immobilized, lying horizontally, and try to keep them warm," says Butierries. "Put a life jacket under their head so they're comfortable. If you have blankets or articles of clothing, keep them wrapped up." You should already have called the Coast Guard, so they can send a helicopter or boat to get them to a higher level of care as soon as possible.

While we all hope to never find ourselves in this situation, just understanding the body's response to cold water can help you survive.

"If you know that you're going to have a cold shock response, but that it's going to go away in about a minute or a minute and a half, you have a completely different mindset," says Tipton.