Oxford University Cave ClubProceedings 10 : "Pozu del Xitu" |
OUCC Proc 10 Contents |
by Skippy (Chris Ankcorn)
The normal body temperature is about 37° C. Accidental hypothermia may be defined as a spontaneous decrease in the core temperature of the body, usually in a cold environment and without any malfunction of the temperature regulation centre of the brain.
At core temperatures of 33-34° C the victim is usually alert, well orientated and co-operative, but as his temperature decreases, drowsiness, difficulty in understanding, slow responses, etc. begin to become apparent.
At this point a victim's blood pressure may be unmeasurable, his pulse very slow or undetectable (not necessarily absent), his breathing very shallow and infrequent. Below about 32° C he will cease shivering and may go very stiff as in rigor mortis. His pupils may be fixed and dilated, and he may appear to all intents and purposes dead.
Note carefully that people have been revived from core temperatures as low as 17° C and so the dictum must be applied that noone is dead until they are warm and dead. Many hypothermic patients have only been diagnosed as such on their way to, or at, the mortuary.
In any situation, early recognition is important. The initial signs are fatigue, weakness, stumbling and general slowing down, and lack of co-ordination. There may also be apathy, confusion or aggression. Shivering may not occur, especially in heavy physical activity. As the victim's temperature drops, judgement and reasoning are impaired. These symptoms are almost always associated with exhaustion in a mountain or caving situation.
There is a decrease in the victim's basal metabolic rate; this may be 50% of normal at 28° C. The heart rate and cardiac output decline. The blood pressure initially rises and the falls gradually. This is because as a consequence of hypothermia, fluid is lost from the blood to the tissues, and so in effect the blood volume is lowered. The body can counteract this by closing down the blood supply (vasoconstriction) to the less vital areas of the body, particularly the skin, which of course also minimises heat loss from the same. The peripheral vasoconstriction may cause a temporary rise in blood pressure, but this mechanism becomes less effective as blood volume is steadily lowered in continuing hypothermia.
The blood supply to the brain drops by 6-7% for every 1° C drop in core temperature, which accounts for the decrease in mental ability.
Initially, the muscles can provide a large amount of heat by shivering when the core temperature is in danger of falling.
As soon as the first symptoms are recognised in a member of the party, it is time to turn round in a cave. First, stop, let the victim have a rest and something to eat, and if he is in wet, inadequate clothing, if possible exchange it for something better from another member of the party. However, it is worth remembering that if one member of the party is affected, there may be others.
Then, if the victim is able, begin to make for the surface. Lighten the victim's load by carrying his ammo box, tackle bag, etc. Do not make the victim travel faster than he wants but try and keep on the move. Exhaustion exacerbates the hypothermia.
If it becomes apparent that the victim is not going to be able to get out under his own steam, or you are worried about his ability to climb a large wet pitch, then lose no time in summoning the Cave Rescue Organisation, as an exhausted hypothermia victim is ripe for a catastrophe on a pitch.
Whilst waiting for aid, try and insulate the victim as much as possible, using whatever is available. The heat loss from an unprotected head is considerable: at 4° C up to half the body's total heat production is lost from the head, so do something about this if you can.
Obviously a space blanket is useful if you have one. The victim should lie down, preferably with his head slightly lower than his feet, and he will lose less heat curled up in a ball. Avoid close contact of anything hot with the skin, as this will cause vasodilation of this area, resulting in a drop in blood pressure and a shunting of cold blood from the extremities to the core.
The provision of heat by the buddy technique - where if a sleeping bag or a space blanket is available, the victim and another person get in it - is not regarded as being very efficient. Moreover, the buddy technique is theoretically unsound because it constitutes a form of partial external warming, but there is no firm evidence on which to judge its efficiency or dangers.
Do not give alcohol, as this makes the problem worse because it is a vasodilator and a central nervous system depressant. This will cause the victim to lose more heat from his skin, and also lower his blood pressure even more. It also lowers the blood sugar and suppresses shivering. If the victim appears to cease respiration, then give mouth to mouth resuscitation at about half the normal rate (about 8 inflations/minute).
The indications for closed cardiac massage, however are in dispute. Although a victim may appear pulseless, this does not necessarily mean he does not have a pulse.
It is known that mechanical stimulation to a cold heart may cause it to fibrillate. Also, cardiac massage often fractures ribs, which may instigate unnecessary complications.
On the other hand, if the victim's heart has stopped, or he is already in ventricular fibrillation, then cardiac massage may help.
On balance therefore, it would seem to be better not to give cardiac massage, especially in a caving situation where it may be very difficult to do or maintain.
The maintenance of adequate blood pressure, and blood supply to the brain is all important. Therefore, when transporting the victim out of the cave it is important to carry him head down whenever possible, so gravity assists the supply of blood to the brain. The victim should naturally be carefully watched in case he vomits and obstructs his own airway.
There are two basic ways to warm a victim up - one by passive rewarming, where the patient is put in a warm bed in a warm room and hopefully does the job himself, or secondly by active rewarming, where the patient is physically warmed up quickly. Hospitals have various sophisticated methods of doing the latter, but the only way available outside of a hospital is to put the victim in a hot bath.
Some rescue organisations do have a portable inhalation rewarming apparatus and this is the only practical out-of-hospital core rewarming technique yet developed.
Mortality rates in accidental hypothermia during rewarming methods range from 30-80%. Different rewarming methods remain a controversial area in hypothermia management. Concern has been raised about the efficacy of actively rewarming the body surface because of the inherent physiological changes which may aggravate the effect of hypothermia on core tissues. There is a well described 'afterdrop' of core temperature after the removal of the subject from his cold environment. This afterdrop may be exaggerated by the peripheral vasodilation which is associated with vigorous external rewarming and causes paradoxical central cooling. This occurs because of shunting of cold stagnant blood from the periphery to the core, thus further chilling the heart and increasing its liability to failure, which is the ultimate cause of death in hypothermia.
However it is generally agreed that for young, healthy adults, subjected to relatively short periods of cold, without having suffered cardiac or respiratory arrest, active rewarming is probably best. For long term hypothermia victims, slow, passive rewarming may be better.
Rapidly rewarm in a bath of hot water at the following temperature:
If no thermometer is available, 41° C is about as hot a bath as you would like to get into. Remember that when the victim is put into the bath, the water immediately cools down and needs warming up again. Only the torso should be immersed to minimise the afterdrop. If the patient suddenly deteriorates after being put in the bath, i.e. starts having a fit or convulsions, take him out of the bath, lay him on the floor and raise his legs to help re-establish an adequate supply to the brain.
After about twenty minutes in the bath, the patient will hopefully have improved, his core temperature will have been raised and sweat may start to appear on his brow. At this time lift him carefully out of the bath with the body horizontal and head lower than the feet, and put him in a warm bed under blankets, still with the head lowered.
There is a serious danger of cardiac arrest if the patient is moved awkwardly, or also the risk of the patient having convulsions caused by lack of blood to the brain if the patient is kept in the head up posture necessary in the bath.
In prolonged hypothermia Th. plasma volume is low that rapid dilation of the peripheral vascular bed can caused an increased return to the heart of cold venous blood, which may further cool the heart and aggravate cardiac failure.
This may be the only choice open to you in a remote situation. Experience with induced hypothermia has shown that even at core temperatures of 27° C the body can still produce enough heat to rewarm spontaneously, so long as adequate insulation is provided. A good sleeping bag in a warm room should be sufficient. The use of hot water bottles, electric blankets, etc. should be avoided.
Pugh reviewed 23 incidents of accidental hypothermia in walkers, campers and climbers in Scotland, Wales and the Lake District. He noted that the casualties in four incidents were unusually thin, skinny individuals with little insulative subcutaneous fat. He also noted that in four other incidents women survived where there male companions died.
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(leading article)