Textbook of Maritime Medicine

10.8.1   Acclimatization

Henrik L. Hansen

The conditions caused by heat, may, as described in the section below, be serious and life-threatening. There are well-documented cases of fatal incidents on board merchant ships also in recent years. They have occurred in excessive hot engine rooms but also among seamen who were working on open deck under excessive temperatures and without access to shade. Young and previously healthy seamen may be hit by heat cramps, heat collapse and even fatal heat strokes. Chronic diseases and other pre-existing conditions may although worsen the prognosis.

If the ship sails from a warm to a hot climate, the crew will have good time for acclimatisation. The body needs approximately about five days to adapt to a different climate, but some individuals may need up to a couple of weeks. It is therefore a special risk factor if crew members are flown from a temperate climate into a very hot area and start to work right away.

The aim of the acclimatisation is to be able to sweat more than normally, to reduce the loss of salt when sweating and to be able to redistribute the body heat and in this manner reduce the body temperature. These measures will reduce the risk of excessive body temperatures.

The seaman going to a hot area should try to start the acclimatization several days before the arrival to the area. This may be achieved by actually being exposed to increasingly higher temperatures. The same effect can be achieved by physical training. One should also get used to a high fluid intake. An intake of 3 to 5 litres per 24 hours is needed when working under high temperatures. Thirst is in a hot climate not a reliable sign that a person needs fluids. Extra salt intake is recommended. This may be achieved from salty foodstuffs like chips and sausages and by directly adding salt to the food. Seamen at special risk should be especially careful. Seamen with cardiovascular disease, chronic lung disease, and overweight and on certain medications (diuretics, antihypertensive and certain medicines used for treatment of neurological and psychiatric diseases) should be extra careful.

When in the hot climate, it is of importance to drink water all day through, also in the early mornings and late afternoons and evenings. During the hottest period of the day, sweating may far exceed the stomachs capacity to absorb fluids and dehydration will take place if no precautions have been taken. Intake of fruits may be important as it is an important supplement of other salts not present in ordinary salt. Drinks with high sugar content, like some “sport drinks”, should be avoided.

When working in hot climates, light, loose-fitting clothing will allow perspiration to evaporate and cool the body. Wide-brimmed hats in light colors keep the sun from warming the head and neck. Detailed planning of the work on board is essential. Long periods of work in the engine room should be avoided. Those in charge of the planning of the work should ensure many breaks with access to fluids and cooler surroundings. If work on open deck is needed, for example during prolonged mooring operations, there should be arranged access to shade and fluids.

Alcohol is seldom available on ships today, but if available, it should be avoided when working in hot climates. Also caffeinated drinks and heavy meals should be avoided. All crew members should be instructed in looking after each others and be aware of the first signs of serious conditions due to heat exposure like heavy sweating, paleness, muscle cramps, tiredness, weakness, dizziness, headache  and nausea or vomiting

10 .8.2     Conditions caused by Heat

Aksel Schreiner 

Heat regulation

The heat in the human body comes from the metabolism of nutrients and physical activity. The body can receive heat from external sources (sun, stoves etc) and it can lose heat to the environment (cold weather, immersion in water, sweating etc). A thermostat in the brain keeps the temperature of our inner body – the core temperature- nearly constant. The main regulatory mechanism is to increase the blood flow to the skin. If this appears to be insufficient, the production of sweat will increase. The sweat requires heat to evaporate and this heat is taken from the skin. The sweat contains water and salts that are then lost from the body, and the body may become depleted. To prevent depletion it is necessary to increase the intake of water and salt. If the intake of salt and water is insufficient, the kidneys will reduce the excretion of salt and water. The excretion of water in the gut will also be reduced, something which may lead to obstipation.  If these regulatory mechanisms are insufficient, blood will be re-directed from the skin to the brain and to other vital organs. The sweating will then subside and the temperature will rise. This is the mechanism behind the heat collapse and the heat stroke.

Heat cramps (Miners’ cramps)

The stokers who worked in the steamers of the past were well acquainted with heat cramps. This condition arises mainly in individuals with good physical condition when they are exposed to sudden and strong physical strain and sweat a lot (For example during a football match ashore)

The temperature of the air may be normal. The cramps may occur in all muscles of the body, but particularly in the legs. The condition is harmless if the patient is brought to a cool place and is given salt containing drinks.

Heat collapse

Heat collapse is the most common of the conditions induced by heat. It develops on the ground of loss of water and salt combined with an overload on the heat regulatory mechanism, most often following physical activity.

The first symptoms are malaise, vertigo, headache and anorexia sometimes followed by loss of consciousness. The skin is greyish pale, cold and damp. The pupils are dilated, the blood pressure often reduced. The body temperature is usually normal, but may be slightly less than normal.

A person with heat collapse should be moved to a cool place. He should be positioned with his upper body elevated and be given salt containing beverages.

Heat stroke

Heat stroke is the most serious of the conditions caused by heat, and may be fatal. It is most often seen in individuals suffering from chronic diseases. In the maritime industry heat stroke has been observed in persons with alcohol and drug problems. The condition may occur when the air temperature is high, especially when the relative humidity in the air is also high. Direct sun exposure is not a prerequisite. Most cases occur indoors.

The cause of heat stroke is a complete breakdown of the heat regulatory system. Early recognition is important. The cardinal signs are severe hyperthermia (T > 41 C), cessation of sweating and mental disturbances. The patient may complain of headache, malaise and vertigo. He gives an impression of fever and exhaustion and may faint. Body temperature in excess of 42 C signals great danger. The condition requires rapid and intensive action. Loss of time must be avoided. Medical evacuation is indicated when possible.

Treatment

•        undress the victim and move him to a cool place with circulation of fresh and  
         cold air. Fans are useful. Oxygen may help
•        insert a large gauge intravenous catheter
•        in case of convulsions, administer 5 mg of diazepam intramuscularly
•        start infusion of physiological saline solution or Ringer’s solution (a bolus of 2 litres 
         over the first hour and an additional one litre per
         hour for the next 3 hours) Be aware of possible lung oedema (fluid in the lungs)
•        monitor blood pressure
•        seek telemedical advice
•        as soon as possible flush the patient with large amounts of cold water from any
         source, or submerge the patient in ice cold water.    
         Measure the body temperature every 10 minutes. When the temperature has fallen
         below 39.5 degrees C, the patient may leave the 
         water.
•        continue rinsing with a sponge and cold water, or place rubber gloves filled with
         ice cubes in the arm pits and groins
•        the patient should remain in a cold place until all symptoms have subsided

Fever

Fever represents an elevation of the body temperature that is caused by the thermostat in the brain being set to a value higher than normal. Metabolic products from – or induced by –bacteria, viruses, fungi or parasites may cause the thermostat to change its setting. Also substances from damaged tissue and some poisons may have this effect. When under such circumstances the temperature rises, the body  “misunderstands” and the individual will feel cold and shiver despite that the temperature goes up. The other way round he will sweat and feel warm when the temperature falls.

The fever may in some instances contribute to the defence against infections, but not always. Long lasting fever in excess of 39.5 degrees C may be harmful to the brain. During strong physical activity, and during the first few weeks of a stay in a hot climate, the body temperature will be somewhat higher than normal. The normal body temperature varies between 36.0 to 37.5 degrees C. It is on its lowest late at night and in the morning, highest in the evening.

Literature

Stephen L. Gaffin, Daniel S. Moran. Clinical Management of Heat-Related Illnesses. In: Paul S. Auerbach ed.Wilderness Medicine. Philadelphia., Mosby 2007 : 268-283

10.8.3     Hypothermia 

Leif Aanderud 

Accidental hypothermia is a major cause in deaths misclassified as drownings. In waters with temperatures less than 25 ^oC, the body will loose heat, if not protected by insulating clothing.

The heat loss is increased by a factor of  25 by immersion compared to air. The loss is greatest from arms and legs which account for 30% of the body weight, but 50% of the body surface. A subcutaneous fat depot is valuable in this situation, since fatty tissue has only 50% of the conductance of muscle tissue.  90% of the body heat is lost through the skin (1). Shivering will increase heat production, but ceases at appr. 33 ^oC. It depletes the body’s glycogen stores.  Perhaps not known to many:: muscle strength is decreased by 50% after 3 hours immersion in water with 23 ^oC (2).

Estimated survival time in breaking waves at 6.1^oC with light clothing will be in the range of 1,3 – 4 hours (3).

Stages of hypothermia

Mild: 35-34oC:              Shivering, ataxia and loss of fine motor control

Moderate: 34-30^oC:     Reduced consciousness, apathy, low pulse rate, slow respiration, low blood pressure

Deep <30 ^oC:                 Loss of conscience, pulse and respiration may be difficult to register, muscle rigidity, pupils dilated

                                           (not an indication of brain stem demage), danger of heart fibrillation .

Rescue

Hoist and handle the patient in supine position, avoid standing and trying to walk around. This will reduce the risk of orthostatic hypotension. 20 % of the deaths occur after rescue. The unconscious patient should be handled with great care to avoid sudden movements which can provoke heart fibrillation.

After rescue

• Risk for orthostatic hypotension
• Hypovolaemia due to immersion diuresis
• Risk for ventricular fibrillation at temperatures < 30 ^oC

Clinical examination

• Consciousness?
• Respiration rate
• Pulse rate
• Rectal temperature measurement with digital thermometer
• Pupil size and reaction

First aid

If no pulse and respiration: give 30 chest compressions (rate appr. 100/min.) and two  mouth to mouth inflations (or mask and bag ventilations, preferably with oxygen) and continue this treatment until stopped (doctor’s order).

Stop further heat loss (warm room, dry clothing)

Start re-warming if evacuation to hospital is not possible

Re-warming methods

The aim is to warm the vital organs (primarily the heart) first without heating the major muscle masses in the extremities.

Method                                                                           Heating rate

Spontaneous re-warming in sleeping bag                                      0.6 deg. C/hour

Breathing heated air 43-45 deg.C                                                     1.2 deg. C/hour

Air heating of the trunk                                                                          5.8 deg. C/hour

Hot bath 41-42 deg.C                                                                             2.4 deg.C/hour

Rewarming of distal parts of arms and hands,                              6.1 deg. C/hour                  

calves and feet in water 42 deg.C                   

Intravenous infusion of Ringer acetate or 0,9% NaCl solution heated to 42 ^oC is also recommended if feasible.

A hot bath may be recommended to waken persons who are able to cooperate, but exerts a considerable strain on the heart in elderly persons. Warming of the distal part of the extremities (up to the elbows and knees) in warm water is very efficient due to the abundance of peripheral arterio-venous shunts. The returning warm venous blood is therefore transported centrally without losing heat to the muscles. The hypothermic patient should not be allowed to stand in a warm shower unattended, nor be left alone walking about. He should b placed comfortably supine until warm. Warm, sugar-containing fluids should be given by mouth to the conscious patient to correct the low blood sugar levels caused by shivering. Prolonged periods in water cause increased urinary fluid loss, and these patients need extra supply of fluids, per os or i.v.

During re-warming, the core temperature may initially drop another few degrees due to circulation to the great muscles.

Frostbite

Frostbites occur in low temperatures combined with wind, humidity and physical passivity. Tissue damage will result when its temperature has reached the freezing point and the local circulation comes to a halt. Loss of bullae and tissue may be the final results.

Fig.10.8.1: Superficial frostbite

Superficial frostbites affect the superficial layers of the skin, with soft and normal subcutaneous tissue.  The affected area is white like wax and painful, with lost sensitivity to touch and needle prick. Rewarming with 37 ^oC heat is sufficient.

Fig. 10.8.2: Deep frostbite

Deep frostbites affect all layers of the skin, the affected area is hard like frozen chicken. Blisters and wounds may develop.

Re-warming is preferably with water heated to 42 ^oC in the course of 10 minutes. This is a painful procedure, and swelling will occur. Wounds and blister are treated as in burns.

References

1. Murray P HJ. Hypothermia. In: Hall JB, Schmidt GA, Wood LDH, editors. Principles of critical care. New York: McGraw-Hill, 1998: 1645-55.
2. Bergh U, Ekblom B. Influence of muscle temperature on maximal muscle strengthe and power output in human skeletal muscles. Acta Physiol Scand 1979; 107:33-7.
3. Steinman AM, Kubilis PS. Survival at sea: the effects of protective clothing and survivor location on core and skin temperatures. Washington, DC: US Coast Guard; 1986. Report No: CG-D-26-86.
4. Hayward JS, Eckerson JD, Kenna D. Thermal and cardiovascular changes during three methods of resuscitation from mild hyopthermia. Resuscitation  1984; 11:21-33.
5. Vanggaard L, Aviat Space Environ Med 1999;70:1081-8).

Last Updated on Thursday, 29 July 2010 09:53