Environmental medicine

19 Environmental medicine



Chapter Contents


Heat 697

Cold 698

Drowning and near-drowning 699

Ionizing radiation 700

Electric shock 701

Bioterrorism/biowarfare 701


Heat


Body core temperature (TCore) is maintained at 37°C by the thermoregulator centre in the hypothalamus.



• Heat acclimatization. This occurs over several weeks. The sweat volume increases and the sweat salt content falls. Increased evaporation of sweat results in a reduced TCore.

• Heat cramps. Painful muscle cramps, usually in the legs, occur in fit people during exercise in hot weather. They respond to combined salt and water replacement, and in the acute stage to stretching and muscle massage. TCore remains normal.

• Heat illness (heat exhaustion). At any environmental temperature (especially with TEnv of > 25°C), and with a high humidity, exercise in clothes that inhibit sweating can cause an elevation in TCore in less than 15 mins. Heat illness with a TCore > 37°C causes weakness, cramps and syncope, and may progress to heat injury.


Management


Reduce (TEnv) and cool the patient with sponging and fans. Give O2 by mask.


Oral rehydration with both salt and water (25 g of salt per 5 L of water/day) is given initially, followed by normal daily fluids. In severe heat illness, IV 0.9% saline is given. Monitoring of serum sodium with correction of secondary potassium loss is required.



Heat injury (heat stroke)


Heat injury (heat stroke) is an acute life-threatening condition when TCore rises above 41°C. Headache, nausea, vomiting and weakness, progressing to confusion, coma and death occur. The skin feels intensely hot to the touch, usually with absence of sweating.


Heat injury develops in unacclimatized people in hot, humid windless climates, often without exercise. Drugs and alcohol, e.g. antimuscarinics, diuretics and phenothiazines, contribute.



Prevention



• Acclimatization, fluids and appropriate clothing.


Management


Management is as above. Intensive care may be necessary for severe cases. Intravascular volume can remain normal and the use of IV fluids must be monitored with a CVP line.


Prompt treatment is essential, as complications of hypovolaemia, intravascular coagulation, cerebral oedema, rhabdomyolysis, and renal and hepatic failure can occur rapidly.



Cold


Hypothermia is defined as a core temperature of less than 32°C and is often lethal when TCore falls below 30°C.



Hypothermia



• Hypothermia can occur when TEnv is below 8°C with inadequate heating and clothing. Drugs, e.g. hypnotics, alcohol, hypothyroidism or intercurrent illness also contribute. The elderly have diminished ability to sense cold and also have little insulating fat. Neonates and infants become hypothermic rapidly because of a relatively large surface area in proportion to subcutaneous fat.

• Hypothermia often occurs in climbers, skiers and polar travellers, and in wartime. Wet, cold conditions with wind chill, physical exhaustion, injuries and inadequate clothing are contributory.

• Serious hypothermia can develop following immersion for more than 1 hour in water temperatures of 15–20°C. In water temperatures below 12°C limbs rapidly become numb and weak. Recovery takes place gradually, often taking several hours.


Clinical features


Mild hypothermia (TCore < 32°C) causes shivering and initially intense discomfort. As the TCore falls below 32°C, severe hypothermia causes impaired judgement — including lack of awareness of cold. Drowsiness and coma, followed by death, occur.



Diagnosis


Someone who feels icy to the touch — abdomen, groin, axillae — is probably hypothermic. If the patent is clammy, uncooperative or sleepy, TCore is almost certainly ≤ 32°C.


Pulse rate and systemic BP can fall. Cardiac output and cerebral blood flow are greatly affected by change in posture in hypothermia, and can fall further if the upright position is maintained or the thorax is restrained by a harness. Respiration becomes shallow and slow. Muscle stiffness develops; tendon reflexes become sluggish and/or lost.


In coma, pupillary and other brainstem reflexes are lost; pupils are fixed and may be dilated in severe hypothermia.


Reduction in the temperature of haemoglobin causes a falsely high arterial PO2 and oxygen saturation. Using a pulse oximeter, the level of arterial oxygen saturation (SaO2) will, however, be correct.


Bradycardia with ‘J’ waves (rounded waves above the isoelectric line at the junction of the QRS complex and ST segment (Fig. 19.1)) is pathognomonic of hypothermia. Prolongation of PR and QT intervals and of the QRS complex also occurs. Ventricular dysrhythmia (tachycardia/fibrillation) or asystole is the usual cause of death.


image

Fig. 19.1 ECG showing J waves.

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  4. Water, electrolyte and acid-base balance

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Apr 2, 2017 | Posted by in GENERAL SURGERY | Comments Off on Environmental medicine

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