A few years ago I introduced you to the The Predator, aka, cold water immersion. It was a brief introduction and I didn't say much about how he actually kills. I'll try to be more explicit in today's post.
Just to review...
Cold water, as defined here, is water with a temperature of 60 °F or less. Some investigators state that water in the 60-70 °F range also qualifies as cold water. I do not argue this point. I chose 60 °F because whole body exposure to water at this temperature is excruciatingly painful and highly likely to trigger the negative consequences we attribute to immersion. Let's begin. Remember, I'm talking about that ruthless killer Moulton Avery labels as "Predator."
The Predator attacks in four phases. If you capsize in cold water, the initial shock of immersion tricks your respiratory reflexes in ways that can cause you to drown yourself. If this approach fails, the predator then attacks your musculature and deprives you of your ability to self-rescue or swim to safety. At the same time, the predator begins its third phase of attack by slowly sucking the heat from your body until you are rendered unconscious. Finally, if you manage to escape its clutches, the predator may have already sealed your death by putting you at risk for circum-rescue collapse. Those rescued from cold water immersion have died aboard rescue vehicles, in ambulances, and hospital beds hours after their rescue. Cold waters lethal reach extends beyond the water’s edge. It is best to know what you are getting yourself into and to prepare before paddling cold waters on a warm spring or winter day.
Phase 1: Cold Shock and Sudden Disappearance syndrome. If you fall overboard or capsize in waters below 60 °F and are casually dressed, cold water attacks your breathing. It attempts to drown you by triggering your “gasp” reflex. This reflex institutes an uncontrollable urge to suddenly and deeply fill your lungs with air. Unfortunately, if your head is under water when this occurs, your lungs will fill with cold water instead. Once triggered you cannot prevent this chain of events. The reflex is hardwired. Your breathing will lock in full inspiration, further preventing the inspired water from being expelled. The increased fluid in your lungs displaces air, reducing your buoyancy, and causes you to float with gravity towards the sea bottom. This constellation of events is so predictable they have a name; sudden disappearance syndrome.5 In some individuals, the airways also constrict to prevent breathing once surfaced. As if this were not enough, others develop fatal heart arrhythmia, stroke, or develop occluded coronary arteries; i.e., experience a heart attack. All of this occurs within the first minute of exposure.
Phase 2: Swim failure and mental confusion. If you survive the first minute, cold water next targets your abilities to save yourself. Blood flow through your extremities and most organs, with exception of the heart, lungs and brain is reduced. In evolutionary adapted mammals this reflex is beneficial and allows the animal to stay submerged for extended periods. Humans, however, have only a partially developed reflex. Whereas in sea mammals blood flow redistribution occurs in conjunction with a slowed heart rate that tends to keep blood pressure normal and reduce the workload on the heart, humans experience a spike in blood pressure. This can overload the heart causing it to fail, and/or setup an irregular heart rhythm. Skeletal muscle strength and coordination deteriorate rapidly as the muscles and nerves controlling contraction are deprived of oxygen. Re-entering a kayak becomes difficult to impossible. Factor in the fact that fine motor coordination is also effected, you quickly lose the ability to use your radio to call for help. This assumes, of course, that your airway is still open and you are capable of speaking. As stated previously, mental confusion sets in early, depending upon how rapidly the cold water bathing your neck cools the blood supplying your brain. Panic develops as you hyperventilate uncontrollably and errors in judgment follow. “How far is that shore? Can I swim to it? I’ve done it before.” No, no, no! You have never experienced this before. Swimming in cold water has no comparison. In March 1968, 9 elite Marines, trained as water survival instructors, capsized a canoe 100 yards off Quantico’s shoreline. They were wearing sweat suits and had floatation seat cushions, but no PFDs. All 9 drowned. Swimming to shore in cold water is almost always a bad idea. Phase 2 can last between 5 to 15 minutes, but it seems to last forever.
Phase 3: Hypothermia: Even though a person may be shivering uncontrollably, he is not considered hypothermic until body temperature falls below 95 °F. Shivering is a process your body uses to generate heat via muscular exertion. Somewhat surprisingly, most adults remain in the normothermic range for more than 30 minutes following cold water immersion. This is an important fact to know, because knowledge can help you hold your panic at bay. Panic speeds up heat loss by promoting unnecessary movement. Unconscious does not occur until body temperature approaches 92 °F. For the purposes of this article, suffice it to say you will probably have another 1 – 6 hours of consciousness in water between 50 and 60 °F, depending upon your body mass and movements. This time decreases to 30 minutes in 32.5 °F water. Heat loss through exposed skin occurs 25 to 30 times faster in cold water than it does during passage of air at the same temperature over the same surface area. Movement dramatically increases the rate of heat loss. Your best chances for survival, should you be unable to re-enter your kayak, is to assume the HELP position and wait.2
Phase 4: Circum-rescue collapse. Circum-rescue collapse is a general term for the physiological events that occur at the time of rescue or during the re-warming phase. While a victim is in the water, water pressure compresses the extremities and forces blood from the limbs into the vessels of the lungs, heart and brain. At the time of extraction from the water, this pressure is released and blood from vessels of the trunk can refill the extremities. This causes pressure in the vessels supplying the brain to fall. Rescue teams have learned to horizontally extract cold water victims using a stretcher, rather than lifting them vertically from the water, thus reducing the risk of circum-rescue collapse. A similar phenomenon can occur during re-warming. As the victim’s body warms, constricted blood vessels in the extremities open and refill with warm blood that was contained in the trunk. In so doing, cold fluids are flushed from the extremities into the trunk, causing body temperature to plummet. This is called “after-drop.” Circum-rescue collapse carries with it severe, and sometimes fatal, consequences.
Preparing for a cold water paddle. With preparation, you can beat the predator. Dress properly for cold water conditions and always swim test your gear. You should learn the HELP and HUDDLE swim positions in case you find yourself having to remain in cold water for any extended period. Clubs like the Chesapeake Paddlers Association offer classes on cold water immersion.3 Consider taking one and learning more about cold water immersion and proper dress. Wear either a wet suit, or a dry suit with thermal undergarments. Never paddle without a PFD! It is a life saver. Include a diver’s hood in your cold weather gear to keep your neck and head protected. The sensors that trigger the gasp reflex are located in the neck and facial regions. Covering these areas will dramatically reduce your risk. Before every launch, while wearing your PFD, wade into the water and rest there for a few minutes. If you get cold during this brief exposure, you will know you are not dressed for survival. This brief pre-exposure also provides you with an opportunity to test for holes or tears in your dry suit and will let you know if you have inadvertently left a zipper open.
Rescuing a victim after cold water immersion. If you are involved in a cold water rescue, how you treat the victim will vary, depending upon his condition. You can prepare for this by familiarizing yourself with the necessary considerations.4 The first priority always is to get the victim out of the water and onshore as quickly as possible. In the case of mild hypothermia, begin re-warming by replacing his wet clothes with dry clothes and/or blankets. More severe exposure requires additional attention and caution. Remove clothing only if it can be done with a minimum amount of movement. Do not massage the extremities in an attempt to “get the circulation flowing,” and never give a victim alcohol. Both can lead to circulatory collapse and after-drop. Place the victim on his back with his head slightly lowered. Call emergency responders immediately. One final comment: No person is dead until he is warm and dead. I state this to remind you that persons without a pulse and who are not breathing have been successfully resuscitated. Do not stop resuscitation until emergency responders are on the scene. Your job is to keep the predator from claiming his victim. Do not let him win.
5. The Biology of Human Survival. Life and Death in Extreme Environments. By Claude A. Piantadosi, Oxford University press, 2003.