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Dr Mike Gonevski

The very first time I dived in cold water was in the Great Lakes. Tobermory, the diving capital of Canada on Lake Huron to be exact. I felt clumsy and awkward in my rented 7mm wet suit. With single digit water temperature it was a necessity rather than a luxury. Needless to say, none of that lycra-sleek-comic-book- superhero stuff that is the only thing you need to dive in tropical waters, will suffice here. I also had, on good "expert" advice, enough weight on my weight belt to sink a small inflatable boat. For some reason I could not stop thinking that the effect cold water diving had on me must be similar to the effect of a Pan Galactic Gargle Blaster, especially the part of having your brains smashed with a slice of lemon wrapped around a large gold brick. Minus the lemon. Minus the gold. Now, I want to make it perfectly clear that I savour pain, Descartes might have said: "I hurt, therefore I am", but talk about too much of a good thing, all at the same time.

It took me a few dive trips before I warmed up (pun intended) to the concept of cold water diving. Not diving however was never an option.

Back to present day and the oh-so-familiar UK waters. Little choice, if any, in fact only one - cold water diving. Unless global warming really shifts the tropics a few degrees up North this will remain the case for the foreseeable future.

Does it make you wonder what happens to your body while diving in cold water, besides being cold? There are certain physiological changes that happen to each and every one of us the moment you enter the water. The heart rate increases immediately with about 20 beats per minute, which in itself leads to an increase in the cardiac output and the amount of blood circulating the body. This is almost simultaneously followed by peripheral vasoconstriction which drains the blood from the periphery and rushes it to the core. These normal physiological changes as a result of immersion in cold water lead to significant stress on the heart by drastically increasing the amount of blood that the heart transports and also a rapid increase in blood pressure. I hope it now starts to make sense why cardiovascular health is so important for divers.

The cardiovascular system is not the only one that responds to the cold in a dramatic way. The initial gasp on entering cold water can be followed by uncontrollable increase in rate of respiration; in other words, your breathing becomes very rapid, three, four, even more times the normal. This response continues for one to two minutes. And if the water conditions are rough or if there is submersion of the head this can lead to water inhalation and drowning as a result. The increased rate of respiration leads to a decrease in the amount of CO2 circulating in the blood. That low CO2 level dilates the vessels in the brain, decreases the amount of blood that reaches it with an end result of confusion and decreased consciousness.

Over time a profound decrease in muscle strength and performance sets in. This can progress to the point of inability to perform simple tasks and self-rescue. Fear and panic set in and from there to another grim statistic is just a short step.

This however doesn't have to be the case. If there is a sudden exposure to cold water with some thermal protection the immediate disabling effects may be reduced. Now, I'm merely stating the obvious here, the colder the environment and the longer the exposure, the thicker the protection needs to be. In a diver with thermal protection the same processes take place although the outcome is slightly more favourable. Peripheral vasoconstriction temporarily prevents heat loss. This is followed by vasodilation, which allows the blood to flow to the cold extremities. If vigorous exercise is undertaken or if shivering develops there is an increase in metabolic heat production. Exercise always increases the rate of body heat loss. Water is particularly effective at removing body heat, with a conduction capacity 25 times that of air. Then it becomes a matter of simple thermodynamics, the higher the difference between the body and surrounding water, the higher the rate of heat transfer. If heat loss from the body is greater than heat production, body temperature falls and hypothermia develops. In other words, a diver will lose body heat much faster in water than in air at the same temperature, which eventually leads to hypothermia, a drop in body temperature to below 35 C.

The signs of progressive hypothermia are predictable and can be loosely tied to different core temperatures. All divers who have dived in cold water have at some point experienced the early features of hypothermia shivering and pallor of skin, especially in peripheral areas such as fingers, toes and ear lobes, numbness, increased heart rate, urge to urinate and slight incoordination in hand movement. Common sense declares that they should leave the water at this early stage or at least try to minimize the time spent underwater. Although depending on the type of diving it may not be always possible.

If however the exposure to cold continues and body temperature falls by another 2 C, (33 C-35 C) loss of coordination and uncontrollable shivering may impair the ability to swim as well as the performance of finely coordinated movements. Working with equipment and instruments may become almost impossible. There is also slowing of shivering, weakness, apathy, drowsiness, confusion and slurred speech.

Further drop in body temperature with another 2-3 C (32 C-35 C) the diver may become weak, apathetic, confused and helpless.

A body temperature of less than 30 C results in unconsciousness and drowning is a real possibility at this stage. If the body temperature continues to drop death occurs even if drowning is prevented.

Management of a Diver with Hypothermia

Suspecting and recognising that there is hypothermia is the first step in management. There are various degrees of hypothermia, with mild hypothermia presenting little risk to the diver and a severe one - the possibility of death. The mildly hypothermic diver will be awake, shivering but still able to converse intelligently. Moderately hypothermic diver will be confused, apathetic, uncooperative, may have difficulty with his speech. The severely hypothermic diver may appear unconscious, with a slow heart rate and respiration or may even appear dead to the untrained observer. It is extremely important to remember that these divers have to be rewarmed extremely carefully, as they easily become worse, even placed in cardiac arrest by careless attempts at rewarming. This is an actual emergency and improper handling can actually create a fatal outcome. The cold heart is very sensitive and divers who are alive when found can easily develop cardiac arrest if handled roughly during the initial evaluation and transportation due to severe cardiac arrhythmia. The rescuer must transport and rewarm the victim without precipitating cardiac arrest.

Rewarming is of extreme importance, of course, but should not be attempted unless it can be done properly. However, it sometimes is necessary to rewarm a hypothermia victim in an area far from medical care. The first attempts should be concentrated on preventing further heat loss by removing wet clothes and covering in layers. Remember to provide layers between the victim and the ground or deck and to cover the head, which is a major source of heat loss. The fully alert and cooperative diver may be given warm liquids to drink; this will deliver negligible amounts of heat but will correct any dehydration. I'm afraid that I cannot recommend coffee, tea and alcohol as they will increase dehydration and heat loss further. Oral fluids can include any of the sports drinks rich in electrolytes. If the diver is awake, do not exercise him as this will bring cold blood from the periphery to the core. All things in order, the mildly to moderately hypothermic diver will return to a normal state very soon.

Immersion in a hot bath is considered to be risky, unless limited to the trunk only, with the extremities left out.

The severely hypothermic victim can be unconscious or appear dead. But do not assume that they are dead when they are cold unless they are warm and dead. Look carefully for signs of life by carefully checking for breathing, any movement or pulse in the groin or the carotids in the neck area. If breathing is present and the heart is beating, then CPR is not needed. If the breathing rate is less than six per minute consider administering 100% Oxygen via a nasal mask. In fact, administering Oxygen is always a good idea. If there are no signs of life, start CPR and make arrangements for transport to the nearest medical facility. Rewarming of the severely hypothermic victim cannot be accomplished in the field. It is important to continue CPR until emergency assistance arrives, as there have been cases of successful resuscitation after prolonged CPR as paradoxically, hypothermia can have a cardio protective effect.


The prevention of hypothermia in divers requires training, good judgement and experience. The diver must understand the external insulation of body heat and must be able to control heat loss. Most of the diving on this planet is usually in waters considerably colder than what is considered normal body temperature of 37 C. Recreational divers sometimes encounter very cold conditions in ice diving or winter diving in deep quarries and lakes. All ocean divers dive in water that is below body temperature. Wet suits provide some protection but they also become compressed with depth and thus lose much of their insulation properties. The thick undergarments worn under a dry suit are also effective but also compresses and lose some of its insulation value and if they get wet, they lose practically all of their insulating value.

The diver must be also prepared for heat preserving actions to be taken once in the water. These include remaining still and assuming the H.E.L.P. position (heat escape lessening position). This position is assumed by drawing the knees up to the chest and holding them with crossed arms. The position is unstable and not easy to achieve without practice, as one tends to fall over forward and backward so regular practice is prudent. Another surprisingly effective way to conserve heat is the huddle position with other divers, where everyone wraps around one another and pulls into a tight circle, remaining as still as possible.

To reduce heat loss, it is best not to swim anymore than a short distance, as although swimming generates some metabolic heat, this is more than offset by heat loss into the water during movement. Divers should abort dives once they start feeling cold, and should ensure adequate time on the surface in a protected and warm environment, before returning to dive. Hours are needed to regain the core body temperature. Sweating is a good sign that hypothermia is no longer a problem.

I still dive in cold waters. Somehow I managed to warm to them. Although that first feeling of having a couple of Pan Galactic Gargle Blasters never quite left me. I've just grown used to the side effects.

Happy diving!

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