Sea Safe Seminar
April 29, 2010
Hypothermia and Immersion in Cold Water
Practical lessons for the sailor
Justin Byrne, MD
Assistant Professor of Medicine, Tufts University School of Medicine
Non-immersion Hypothermia - A common problem and not just for frostbiters.
When might this occur? On an overnight race (Beringer, MHOR, Bermuda Races, overnight cruises etc.) and even on long day races/cruises particularly when weather shifts from sunny & warm to cloudy and cold or wet (that never happens in New England though.) Common scenarios are several hours of warm, sunny sailing followed by a prolonged seat on the rail (or helm) in wet shorts, t-shirt and flip flops after the sun goes away. Made much worse by that pesky sunburn, maybe a bit of sweating from grinding earlier, any rain/fog, any alcohol.
Why is it a problem? Not so much for the risk of severe hypothermia (unconsciousness, cardiac arrhythmia, shock.) but for the symptoms of mild to moderate hypothermia resulting in an impaired sailor. See some of the symptoms listed below and see if you agree this can be a dangerous situation. These are also important signs to be on the lookout for in your crew.
Increased muscle tone, uncontrollable shivering, impaired judgment, altered mood, loss of fine motor control (especially in hands) and loss of balance, loss of sensation, altered speech, depressed level of consciousness.
The biggest risk of mild to moderate hypothermia in a sailor out of the water is traumatic injury and accidental drowning. Ultimately, the captain in responsible to make sure their crew is capable of safely maneuvering on the deck of a working sailboat.
How to avoid it? Be aware that even in July and August there can be sudden changes in temperature, wind and precipitation on the ocean that can quickly result in significant loss of body heat. All crew should have appropriate clothing for cold/wet conditions if they are going to be at sea for more than a few hours even in warm weather. Most of you know what "appropriate clothing" means but just as a reminder - Wool and fleece will continue to insulate even if wet but do not work well to block the wind, cotton looses all its ability to insulate when wet, there are countless types of wind/waterproof shells for sailors which will do nothing for the person in wet shorts sitting on the rail in 20 kts breeze when the sun goes down, and a wool or fleece hat can do more to retain body heat than even the most expensive Musto or Atlantis vest. Layers, layers, layers.
How to treat it? Early detection is key. No one wants to be seen as a complainer or weaker than the rest of the crew. Once hypothermia starts people may lose their common sense to go below to warm up. Be vigilant to signs in your crew. Insist that people bring appropriate gear or provide it yourself. Mild to moderate hypothermia can usually be corrected by going below, changing into dry clothes, drinking fluids and eating some carbs helps a lot. No one should be on deck if they are shivering. Someone should periodically check on the person who went below to make sure they are all right.
Immersion in Cold Water - This is the scary one.
What is considered "Cold Water"? The definition of cold water is variable (see box below). The temperature of thermally neutral water, in which heat loss balances heat production for a nude subject at rest (i.e., not shivering), is approximately 33°to 35° C (91.4°to 95° F). Hypothermia eventually results from immersion in water below this temperature. For practical purposes, significant risk of immersion hypothermia usually begins in water colder than 25° C (77° F).
The average sea temperatures for Boston Harbor for 2009 are listed below.
Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Temp 40 36 41 49 58 63 67 68 63 56 51 42
The Official Canadian Temperature Conversion Chart
The effect of sudden cold-water immersion on the human is poorly understood both by the general public and by medical and rescue personnel. Many individuals believe that an individual who falls in ice water will die of hypothermia within minutes, even if dressed in winter clothing. Most adults could survive for an hour or more if they take appropriate action. The improper assumption of impending death only serves to induce panic, poor decisions, and exhaustion from thrashing about, causing problems for both the primary victims and those who are trying to rescue them.
The body's response to cold water immersion (head above water):
Phase 1: Cold Shock Response (Initial Immersion, 0 to 2 Minutes)
Rapid skin cooling initiates an immediate gasp response, the inability to breath-hold, and hyperventilation. The gasp response may cause drowning if the head is submersed during the initial entry into cold water. Subsequent inability to breath-hold may further potentiate drowning in high seas. Finally, subsequent hyperventilation normally diminishes within seconds to minutes but could be increased and exaggerated indefinitely as a result of emotional stress and panic. Uncontrolled hyperventilation can cause numbness, muscle weakness, or even fainting, leading to drowning. Any of these respiratory responses can lead to aspiration of water into the lungs, panic, and subsequent drowning.
Phase 2: Cold Incapacitation (Short-Term Immersion, 5 to 15 Minutes)
For those surviving the cold-shock response, significant cooling of peripheral tissues continues, especially in the extremities, with most of the effect occurring over the first 15 minutes of immersion. This cooling has a direct and deleterious effect on neuromuscular activity. This effect is especially significant in the hands leading to finger stiffness, poor coordination of gross and fine motor activity, and loss of power. The loss of motor control makes it difficult, if not impossible, to execute survival procedures, such as grasping a rescue line or hoist. Thus, the ultimate cause of death is drowning, either through a failure to initiate or maintain survival performance (i.e., keeping afloat, swimming, grasping onto a life raft) or excessive inhalation of water under turbulent conditions. If cold-water immersion does occur, however, it is best to quickly determine and execute a plan of action: (1) try to enter the water without submersing the head; (2) escape (e.g., pull oneself out of the water, inflate and board a life raft); (3) minimize exposure (e.g., get as much of one's body as possible out of the water and onto a floating object); (4) ensure flotation if one must remain in the water (e.g., don or inflate a PFD); and (5) call for assistance (e.g., activate signaling devices). It may be difficult to execute these actions while the cold-shock responses predominate. However, once the respiratory effects are under control, immediate action should be taken. If self-rescue is not possible, actions to minimize heat loss should be initiated by remaining as still as possible, by keeping as much of the body on top of a floating object as possible, by adopting the heat-escape lessening position (HELP) (where arms are pressed against the chest, and legs are pressed together), or by huddling with other survivors. Drawstrings should be tightened in clothing to decrease the flow of cold water within clothing layers.
Phase 3: Onset of Hypothermia (Long-Term Immersion, Longer Than 30 Minutes)
Most cold-water deaths likely result from drowning during the first two phases of cold-water immersion, as discussed earlier. In general, true hypothermia usually becomes a significant contributor to death only if immersion lasts longer than 30 to 60 minutes.
Phase 4: After-Rescue Collapse
Hypothermia victims who survive prolonged exposure to cold water can experience symptoms ranging from fainting to cardiac arrest during rescue attempts. The reasons for this include sudden vigorous movements further dropping body temperature, the hydrostatic effects on blood pressure from being suddenly lifted out of the water and reperfusion of blood through cold extremities bringing cold blood back to the heart.
Time Available if You Fall into Ice Cold Water: 1-10-1 Principle[*]
* Times are subject to individual variability and factors such as water temperature and amount of the body immersed.
Factors affecting how quickly your body will loose heat in water:
Clothing, flotation (how much of your body is in the water, particularly your head), body movement, sea state, and body morphology (children and taller, thinner people loose heat faster). Surprisingly, alcohol has a minimal effect on heat loss in cold water immersion. Although, when highly intoxicated persons enter cold water (usually by falling in), hypothermia is seldom a problem because they usually drown quickly.
Decision to Swim for Shore or Wait for Rescue:
In cold-water immersion, physical activity increases heat loss through increased blood flow to the periphery. This is especially pertinent when immersed victims engage in excessive movement in the water. In general, if any other people know you are in the water you should limit movement of any kind other than to maintain your head above water. If you are completely alone and in shivering cold water most people can swim up to about 1,000 yards to safety if they do so within the first 30 minutes of going into the water. After 30 minutes the ability to swim successfully is greatly reduced.
Treatment of hypothermia due to cold water immersion:
If practical, conscious victims should not be allowed to assist in their own rescue. Exertion, even after escape from the water, results in a continued drop in core body temperature as blood is now required to pump through the cooled muscles of the arms and legs. Also, if practical, victims should be removed from the water as horizontal as possible (The result of sudden removal of a hypothermic patient from the water is similar to sudden deflation of antishock trousers on a patient in hypovolemic shock: abrupt loss of blood pressure) and, if possible, to get the victim lying down as quickly as possible on board (feet elevated).
For the unconscious victim routine CPR protocols should be followed. Cold immersion victims in cardiac arrest can often be revived after very long resuscitation efforts. Hypothermic patients with any detectable pulse or respiration do not require the chest compressions of CPR, even though severely depressed pulse and respiratory rate may be present. Hypothermia victims will often have depressed levels of consciousness and the inability to feel pain. They should be assessed for injuries and movement limited until they can be assessed by EMS.
Do: Remove wet clothing and insulate the victim against further heat loss. Cover the head and protect from the wind. Seek immediate medical attention (EMS, Coast Guard etc.) Warm-body to cold-body heating is usually inefficient for the conscious victim and can cause the victim to consciously stop shivering which is much more efficient. (But can be an option for the unconscious, non-shivering hypothermia victim.) Awake and alert victims can be given warm fluids and high carb foods, but only if they are completely alert and have normal speech. If heating pads are available, place only on central areas (groin, arm pits, neck) and avoid direct contact of heat source with skin.
Do Not: Rub or massage arms or legs, apply heat to arms or legs, try to feed a person who is confused, has difficulty moving or slurred speech. Never give alcohol to a person with hypothermia.