Together with other RNLI small craft inspectors, I attended the Southeast Group Sea Check Seminar on sea safety during a January weekend. The various lectures and discussion groups included those on life rafts, fire fighting appliances, the latest radio regulations and equipment for distress calling and rescue coordination, etc., as well as an entertaining session firing off flares, rockets and smoke bombs. The most thought provoking lecture, however, was that on drowning and hypothermia. The following article includes virtually the whole of the information we had the chance to absorb. It represents the most up to date knowledge on these subjects presently known.

There has been considerable research carried out by the Institute of Naval Medicine for the Royal Navy and in other centres in the UK and worldwide into the effects, on humans, of immersion in cold water.

Cold water is defined as having a temperature of less than 15° Celsius. The Titanic disaster is one of the best known examples of a mass immersion incident. The ship struck an iceberg at 2340 and started to sink necessitating the order to abandon ship. 712 people went into lifeboats (there was room for 1178) and nearly 1500 people went into the water (water temperature was approximately 0°C. and the weather was fine and clear). By the time the SS Carpathia arrived on the scene, one hour and fifty minutes later, all those in the water had died, whereas most of those in the lifeboats were OK. It was believed, up until the 1970's that these people had died because they drowned but we now know that the great majority, probably all, died due to the effects of cold - hypothermia, because most of them did have some sort of lifebelt or lifejacket but wore inadequate clothing.

From a military perspective, during World War 2 the RN lost 45,000 men at sea. Two thirds of these (30,000) were as a result of drowning or hypothermia. A proportion of those casualties who were pulled from the sea collapsed and died at, or just after, the point of rescue.

The UK is surrounded by cold water. Sea temperatures follow land temperatures with a lag of about two months so that the coldest water temperature is in March (4 - 7° C) and the warmest in September.

However, sea temperature rarely rises above 15°C. Statistics from 1983 show that between 400 and 1000 people die each year in UK waters. This represents the fourth greatest cause of accidental death in adults and the third greatest in children. The greatest numbers of deaths occur in young males (between the ages of 15-35) because these people are most likely to be involved in aquatic sports or horseplay (often with the effects of alcohol intoxication). There is also an increase in the number of deaths during the Easter and early Spring Bank Holidays because when the sun is shining warmly people wrongly assume that the water is warm too.

The most alarming point about these statistics is that two thirds die within a mere 3 metres of safety and 60% of them were considered to be 'good' swimmers. Since even poor to average swimmers might be expected to swim 3 metres to safety, and given the fact that it takes at least 30 minutes for a body to become truly hypothermic i.e. to have a core temperature less than 35°C, there are obviously mechanisms causing death by drowning within a short space of time.

STAGES OF IMMERSION

There are four stages in the immersion process, each associated with its own risks:

1. INITIAL IMMERSION STAGE - first 2-3 minutes - risk of drowning very high. 2. SHORT TERM IMMERSION - next 3-15 minutes - risk of drowning still high. 3. LONG TERM IMMERSION - from 30 minutes and longer - onset of hypothermia. 4. POST IMMERSION STAGE - on and after rescue - risk of post-rescue collapse.

INITIAL IMMERSION STAGE The initial immersion stage, also known as COLD SHOCK starts the moment you enter the water and lasts for 2-3 minutes. As well as the psychological effects of jumping into cold water (we tend not to enjoy the process!) there are a number of dramatic unavoidable physiological effects:

i. THE GASP REFLEX - an immediate sharp intake of air. If the water is anything other than flat calm there is an obvious risk of sucking in a quantity of water causing panic, coughing, choking and drowning.

ii. UNCONTROLLABLE BREATHING (HYPERVENTILATION) - The gasp reflex is immediately followed by hyperventilation (up to 50 - 60 breaths per minute) which flushes Carbon Dioxide out of the blood stream and leads to muscle spasms and cramps. Once again the risk of drowning is high.

iii. INCREASED HEARTRATE - Cardiac output increases on entering cold water. A normal resting pulse is, on average, 70 - 80 beats per minute. This may rise on immersion to 150 -180 beats per minute. This may cause heart failure (Myocardial Infarction, etc.) particularly in those with a history of heart trouble.

iv. PERIPHERAL VASOCONSTRICTION - The body tries to conserve heat by closing down the superficial circulation in the skin and extremities (shutting down the radiators). This peripheral vasoconstriction coupled with the increased heart output causes...

v. INCREASED BLOOD PRESSURE - An increase in the pump rate and peripheral resistance pushes the blood pressure up. There is an increased risk of suffering from a stroke.

vi. DECREASED BREATH HOLD TIME - Cold water reduces your ability to hold your breath by up to 70% (i.e. to a maximum of 7 - 20 seconds). This may cause problems to those trying to escape from submerged helicopters, boats, etc.

The correct use of a life jacket and splash screen will enable the victim to concentrate on maintaining his airway clear of the water and allow him to rest and recover during this stage.

SHORT TERM IMMERSION STAGE The storm of activity that the body undergoes in the initial stage begins to abate after about three minutes but even after this the risk of drowning is still quite high because of the effects of local cooling which all combine to bring about Swimming Failure:

i. EXHAUSTION - The effects of local cooling means that the arms and legs are cold and the muscles stiffen, making swimming more difficult and tiring. A person's automatic desire to keep their face up out of the cold water causes the legs to sink down and makes the swim position vertical, with increased drag, this is much more inefficient and leads to the rapid onset of exhaustion.

ii. REDUCED GRIP STRENGTH - As the hands become colder they lose grip strength and dexterity. Any safety drills that need to be carried out should be done before they become impossible to complete.

iii. SWIMMING/ BREATHING ASYNCHRONY

The wet, and dry suits provide a measure of protection from these responses.

LONG TERM IMMERSION STAGE Heat loss in water is 26 times greater than in air so, once immersed, the body begins to lose heat to the surrounding water leading to the onset of hypothermia. The wearing of a survival suit which traps a layer of air between the body and the water can increase the chances of survival.

The rate at which the body cools depends on the water temperature and the length of time immersed but it generally takes at least 30 minutes for true hypothermia to set in (i.e. to reach a core body temperature of 35°C and below).

These are the signs and symptoms of increasing hypothermia:

37-35°C Increasing shivering as the body tries to generate heat by muscular activity. Shivering becomes violent and uncontrollable at about 35°C. Increasing mental confusion, disorientation, amnesia and loss of will to survive - A switch Off Phenomenon - At 35°C a casualty loses the ability to maintain his airway unless correctly wearing a life jacket and splash screen.

33°C Shivering ceases and is replaced by persistent muscle rigidity (including disorders of heart rhythm - arrhythmias). Below 33°C the casualty becomes stuporous.

30°C Profound hypothermia. Casualty becomes unconscious and may appear dead.

28°C Ventricular Fibrillation likely to occur spontaneously - treat casualty gently.

26 -24°C Death is likely to occur.

POST IMMERSION STAGE If you haven't drowned during the first two stages or succumbed to hypothermia in the third stage you may be forgiven for believing your problems are at an end when the rescue team arrives - unfortunately this is not the case.

Death on or after rescue may still occur due to:

i. Drowning Complications (Primary & Secondary).

ii. Post Immersion Collapse.

iii. Re-warming Collapse.

DROWNING COMPLICATIONS (PRIMARY) - Include Hypoxaemia, Acidosis, Electrolyte Imbalance, Atelectasis, Pulmonary Oedema, Pneumonia, Brain Damage.

DROWNING COMPLICATIONS (SECONDARY) - Secondary drowning, although unusual can occur up to 72 hours after rescue. Symptoms include difficulty in breathing, coughing up frothy pink sputum, shallow rapid pulse rate and collapse, chest x-rays show massive oedema and consolidation. Treatment requires intensive care, mechanical ventilation, 100% oxygen therapy, etc. The condition has a very high mortality rate. If this condition is suspected the casualty should be taken to hospital without delay. If there is any possibility that the casualty has inhaled the slightest quantity of water he should be advised of the symptoms of Secondary Drowning and told to seek immediate medical care if they should develop.

POST IMMERSION COLLAPSE - Casualties who are immersed benefit from hydrostatic squeeze by the surrounding water. This hydrostatic pressure helps to maintain the circulation by forcing the blood into the central core of the body where the vital organs are. If the casualty is recovered from the water in a vertical position gravity and the loss of hydrostatic squeeze causes the blood to pool in the legs which may lead to circulatory collapse and death. Casualties should always be recovered in a horizontal position whenever possible. (several deaths are said to have occurred among the Fastnet casualties after rescue due to their being lifted from the sea into the helicopter in a vertical position.) Different types of sling are now being introduced for helicopter rescue.

REWARMING COLLAPSE - If a hypothermic casualty is allowed to re-warm too quickly or unsupervised the peripheral circulation may open up too quickly which can also lead to circulatory collapse. Casualties must always be closely monitored/supervised in the recovery period.

TREATMENT OF THE IMMERSION CASUALTY

Treatment of the immersion casualty depends on four basic principles:

i. Restoration of adequate ventilation and heart action.

ii. Prevention of further heat loss - insulation.

iii. Re-warming - either passive or active.

iv. Correction of acidibase balance (advanced medical care).

RESTORATION OF ADEQUATE VENTILATION & HEART ACTION - As in all First Aid the principal is

A-B-C (Airway, Breathing, Circulation). Before commencing Cardio-Pulmonary Resuscitation (CPR) the fist assessment to be made is whether the casualty is unconscious because he has drowned or because he is hypothermic. The following questions should be answered: What was the attitude of the body in the water (was the airway in the water)? What was the sea state like? Was he wearing a life jacket and splash screen? What protective clothing was worn? How long in the water? What is the water temperature?

If the diagnosis is hypothermia then CPR should not be commenced unless you are confident it can be maintained effectively until the casualty is re-warmed. Starting and stopping CPR kills those who would have survived without CPR. Never pronounce a casualty dead until he or she has been re-warmed.

If the diagnosis is drowning (without hypothermia) then CPR may be commenced - remember that most casualties vomit during the recovery phase so ensure that the airway is protected either by placing them on their side or by the use of a cuffed endotracheal tube.

INSULATION - The casualty should be wrapped in blankets and insulated at the earliest possible opportunity to prevent further heat loss. Do not remove the casualty's clothing until he is in shelter and re-warming has commenced.

REWARMING - If the casualty is shivering and conscious he can be actively re-warmed by putting him in a warm bath (40-41°C or elbow hot). The whole body, except for the head, should be immersed and the water should be constantly stirred and maintained at the correct temperature. The casualty should be undressed after he has been placed in the bath. The casualty should remain in the bath until he feels comfortably warm but should be removed before he starts to sweat. If a bath is not available a shower can be used under close supervision and as long as the casualty is sitting down (on the floor) with the knees drawn up. Beware of the dangers of re-warming collapse. Hot, sweet drinks may be given if the casualty is conscious and able to accept them. Alcohol should never be given because it dilates the peripheral circulation and lowers blood sugar.

If the casualty has stopped shivering and has a lowered level of consciousness then they should be re-warmed passively and slowly. They should be wrapped in blankets and kept in a warm environment where their own metabolism will re-warm them at the rate of half to one degree per hour.

Always closely monitor the core temperature during re-warming (passive or active) and never leave the casualty unattended.

CORRECTION OF ACIDOSIS - Acidosis is most likely to occur during the re-warming phase but will usually correct itself over time and with care.

GOLDEN RULES

So remember - falling into water is dangerous. The only people who need not fear water are those born to be hanged! i. Wear the right kit (immersion suit, lifejacket, splash screen etc.), use lifelines when necessary try to enter the water slowly if at all possible. ii. Do not swim for the first minute or two until breathing and heart rate have settled down, concentrate on breathing and keeping your airway clear of the water. iii Horizontal lift to recover casualty from the water. iv. ABC - differentiate between hypothermic and drowning casualties v. Avoid manhandling hypothermic casualties. vi. Insulate to prevent further heat loss. vii. Re-warm - actively or passively as appropriate. viii. Observe, monitor and hospitalise casualties as soon as possible