Freelance Traveller

by Robert O'Connor

Disorders of Temperature Regulation

Overview

Internal temperature is tightly controlled in humans and other warm-blooded animals by a series of feedback loops.

Sensors : warm and cold receptors in the skin, blood vessels and gut (sparsely distributed in the last two).

Control centre : the anterior hypothalamus at the base of the brain in humans.

Effectors : nerves to sweat glands, muscle and the higher centres of the brain.(Sweating, shivering and moving around are good ways to modulate temperature).

Normal core temperature is 37 +/- 0.5 °C (98.6 +/- 0.9 °F). The 'core' is defined as the metabolically active organs (heart, lungs, liver, kidneys, brain and the blood). This may be increased by up to four degrees C with maximal exercise (e.g,. marathon runners).

Measuring Metabolic rate

A specific activity scale, the Physical Activity Ratio (PAR), is a way of expressing the energy cost of an activity in terms of basal metabolic rate.

At extremes of temperature, or in situations where the normal compensatory mechanisms can't work, serious injury can occur.

Hypothermia

An abnormally low core temperature.

Mild hypothermia is most commonly encountered during general anaesthesia. Patients are unconscious and paralysed. Body cavities are open permitting evaporation. Theatres are often cooled to keep the surgical team comfortable.

Controlled hypothermia is used in cardiac and neurosurgery to permit longer operating times. Core temperature averages 20°C (68°F) on cardio-pulmonary bypass.

Uncontrolled hypothermia is usually secondary to exposure, with complicating factors of extremes of age or other medical predispositions, e.g., hypothyroidism (underactive thyroid).

Metabolic rate decreases by 6% for every degree fall in core temperature (compound interest effect).

It is therefore difficult to distinguish between someone who is very cold and a corpse. Resuscitation continues until core temperature is normalised, at which time brain death can be confirmed or excluded.

The big problem with moderate to severe hypothermia is that heart muscle becomes very irritable at low temperature. Death occurs because of ventricular fibrillation (VF) - a rapid, dis-coordinated movement of the heart muscle which is ineffective at pumping blood. VF can be triggered by rough handling (a bumpy ambulance ride or a sudden jolt is sufficient). Standard treatment for VF is DC electric countershock, which attempts to 'reset' the heart muscle. It is usually ineffective until core temperature exceeds 30&deglC, however. CPR is performed until cardio-pulmonary bypass is initiated, or the victim warms up enough.

Frostbite or frostnip may arise in extremities whose temperature drops below freezing. At somewhat warmer temperatures immersion in cold water can lead to similar injuries from localised shunting of blood away from the cold part (e.g., trench foot).

Management

Mild : gentle external rewarming e.g., heated blankets

Moderate : ABC - control airway, ensure breathing, give warmed IV fluids, consider internal rewarming (fluid-filled gastric tubes, etc.)

Severe : ABC - as above, internal rewarming advantageous. Cardio-pulmonary bypass optimal until gravisonic modulator available.

 

Hyperthermia

Core temperature greater than 38°C (100.4°F)

Heat production exceeds heat transfer rate. Evaporation (sweat) and convection are the most effective mechanisms under usual circumstances. Extremes of age or exercise, and some medical conditions are significant predisposing factors to the development of hyperthermia.

Metabolic rate increases by 6% for each °C increase in core temperature. Cardiac output increases by 3L/min/°C (normal resting adult value 70mL/kg/min) increase in temperature as heat transfer to the skin is attempted. Patients look very flushed and have a rapid, high volume pulse.

The highest reliably recorded core temperature was 44.4°C (112°F) in a woman who suffered an adverse reaction to a general anaesthetic (malignant hyperthermia).

Active organs literally cook themselves.

Brain: confusion leading to coma and seizures

Heart: haemorrhage or muscle death (infarction)

Muscle: dissolves : rhabdomyolysis

Liver: fails : internal haemorrhaging

Kidneys: will fail because of muscle proteins in blood

Blood: activation of clotting factors leads to random clotting with an overall 'thinning' of the blood: disseminated intravascular coagulation (DIC).

 

Treatment

Evaporative cooling (allow fluid to evaporate off skin).

Conductive cooling (second line, e.g. cold packs/ice baths)

IV hydration (aggressive)

ABC if unconscious or fitting (+anticonvulsants)

(Antidotes for provocative drugs, if available)

 

**Game rules

To Avoid hypothermia/hyperthermia

Average, End.

Check every hour.

To treat hypothermia/hyperthermia

(damage level), Medical/First Aid, Edu, uncertain

Burns

Radiant energy will cause surface damage. Tissue survival is unlikely beyond 45°C (113°F).

Burn severity depends on the percentage of body surface area (BSA) involved, the depth of involved tissue, and the regions involved.

The "Rule of 9's" is used to calculate the percentage BSA

• Head and neck 9%
• Anterior trunk 2 X 9 = 18%
• Posterior trunk 2 X 9 = 18%
• Upper limbs 9 each
• Lower limbs 18 each
• Genitalia/perineum 1

There are modifications of this rule for infants.

Superficial (first degree [1°])

Skin (the epidermis or superficial layer) becomes reddish (erythema) and very sensitive. Resolution in two weeks without scarring is anticipated. (e.g., sunburn).

 

Deep dermis (second degree [2°])

The dermis, or living layer of the skin, is partially involved. Blistering of the skin is evident on inspection. Pain is common and often intense. Resolution over months is common, with scarring usually a complication associated with infection. (e.g., flash injuries).

 

Full thickness (third degree [3°])

The skin feels leathery. There is no sensation as the nerves have been destroyed. Healing is by scarring and may take months with or without treatment. Plastic surgery is usually required. (e.g., from burning clothing or house fire).

Burns of the face and neck are potentially life threatening. The intense inflammatory response which occurs in response to thermal injury leads to gross swelling (oedema) which can cause airway obstruction.

Inhalation of hot gases can injure the lungs and airway. People that cough up blood stained or sooty material require close attention.

Circumferential burns of limbs or trunk are dangerous in that scarring (eschar) which develops over the days after the burn usually contracts, embarrassing circulation or breathing.

Management

Burns induce an intense inflammatory reaction as the body attempts to repair itself. Metabolic rate can increase to more than eight times its resting value (equivalent to calisthenics or cross-country skiing!). Pain when present is intense.

Immediate Action

• Remove patient and rescuer from dangerous situation, if possible.
• Cool burned areas with water
• Give pain relief.
• Determine areas involved as per trauma rules. Use rule of 9's above to estimate %BSA.

ABC as per Trauma Management may be indicated:

1. Airway - may need to create a surgical airway in those with severe face and neck burns. (Major+ damage, unconscious, failed catastrophe check)
2. Breathing - High flow oxygen is mandatory. Ventilation is sometimes required, especially with airway burns. (Major+ face or neck damage)
3. Circulation - Aggressive fluid resuscitation is required for burns greater then 15-20% BSA (up to 10L on day of burn IV). Burned surfaces rapidly lose fluid. Fluid requirements are greatly increased anyway because of metabolic rate. Regimens vary from centre to centre. Large amounts of salt-containing fluid IV is the first line treatment.

Definitive Treatment

Severe (>20% BSA), circumferential limb, hand, face and neck burns are best managed in specialised units. Critically ill patients can be stabilised in ICU and transferred.

Generally, the inflammatory response begins to settle after 3 to 4 days. Hydration requirements decrease (day 1,2 and 3 post burn roughly half that of initial day -> back to normal).

Infection is the major problem at this stage. Aggressive antibiotic treatment combined with surgery to remove dead tissue is often required.

Treatment task, progress and aftercare as per Trauma rules.

Electric Currents

Key variables : amount of current, duration, tissues traversed by current arc.

Microshock occurs when there is a small current leak which travels along a direct path to the heart eg. pacing wires or through IV lines. VF can result.

Tetany refers to current induced muscle spasm. Alternating current is much better than direct current at inducing this (automatic over 20-30
cycles per second. Domestic mains usually 50 - 60 Hz).

Burns occur at entry and exit points of current arc. Currents can also be induced in carried metal objects (tools, keys, cigarette lighters, coins, etc.) leading to distant burns.

Limb loss can arise from sustained muscle contraction (can shear muscle from bone, or cause fractures), congealing of blood and solid tissues or calcining of bone (turns to ash).

Rules

Laser weapons produce point burns. They can ignite clothing. Rigid armours are usually ceramic or metallic and will not burn, they will just have holes punched in them!

Plasma weapons act like a combination of fire and lightning. Damage dice can be divided up at the referee's discretion.

Microshock : catastrophe check when IV lines in place. VF on Spectacular Failure.

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