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Medicine In Traveller - Regulating Body Temperature

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.
 
PAR Sample Activities
1.0 - 1.4 Reading, writing, eating, standing at rest
1.5 - 1.8 General office work, washing dishes, ironing
1.9 - 2.4 Dusting, cooking
2.5 - 3.3 Walking at 3 - 4 km/h (1.9 - 2.5 mph), vacuum cleaning, making beds, operating machine tools, painting, decorating
3.4 - 4.4 Walking at 4 - 6 km/h (2.5 - 3.7 mph), gardening, window cleaning, mopping floors, sailing, golf, bricklaying, carpentry, motor vehicle repair
4.5 - 5.9 Walking at 6 - 7 km/h (3.7 - 4.4 mph), dancing, slow cycling, swimming, chopping wood or felling trees, labouring, hoeing, road construction
6.0 - 7.9 Walking uphill with load or cross country, climbin stairs, average jogging, cycling, football (soccer), energetic swimming, tennis, downhill skiing
8.0 + Marathon running, biathlon, cross-country skiing

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.
Severity of Hypothermia
Severity Core Temperature, C Core Temperature, F
Mild 32 - 35 89.6 - 95
Moderate 28 - 32 82.4 - 89.6
Severe below 28 below 82.4

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 20C (68F) 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).

Core Temperature Effects
Core Temperature Notable Effects
30C (86F) Unconsciousness
25C (77F) Muscle Rigidity
20C (68F) Brain activity  undetectable

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 38C (100.4F)

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 44.4C (112F) 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.
Modifiers to Hypothermia/Hyperthermia Check
Hypothermia Hyperthermia
Temperature Modifier Temperature Modifier
0C - 10C -1 30C - 40C -2
-20C - 0C -2 40C - 50C -4
-40C - -20C -3 50C - 60C -6
below -40C -4 above 60C -8

Other Factors

Factor Modifier Factor Modifier
Moderate exertion +1 Moderate exertion -1
Heavy exertion +3 Heavy exertion -3
Cold weather clothing +2 Rest/Fluid intake +1
Extreme Cold weather clothing +4 Clothing/Armour Varies with type
Wet or Windy -2 Wet or Windy +2
Immersed -4 Immersed +4
Damage effects on failure
  • 1D of stun damage, plus 1 point of frostbite.
  • When one characteristic reaches zero, further dice are frost damage.
  • When two characteristics reach zero, character is unconscious.
  • Another failure results in VF (Destroyed level damage)
  • 1D of stun damage.
  • When one characteristic reaches zero, character is unconscious.
  • Further damage is from heat.
  • Failure with two characteristics at zero precipitates fits (Destroyed level damage)
To treat hypothermia/hyperthermia
(damage level), Medical/First Aid, Edu, uncertain

Difficulty Levels for Hyperthermia/Hypothermia
treatment tasks

Damage level Difficulty
Superficial Easy
Minor Average
Major Difficult
Destroyed Formidable

 

Modifiers to Uncertainty of Hypothermia/Hyperthermia treatment tasks
Truth level Modifiers to recovery checks
Total Truth +1
Some Truth 0
Some Untruth -1
Total Untruth -2

 

Prior Treatment Modifiers to Hypothermia/Hyperthermia treatment tasks
Hypothermia Hyperthermia
Procedure Modifier Procedure Modifier
Prior Successful ABC tasks (See Trauma (2)), if required +2
Warmed IV fluids +1 Anticonvulsants +2
Blankets +1 Evaporative Cooling +2
    Conductive Cooling +1

Internal Rewarming Or Cooling

Fluid instilled into body cavities +1
Cardiopulmonary Bypass +3
Gravisonic Modulator +4

Burns

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

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

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

Damage Types for Burns
Burn Type Damage Type
Superficial (1) Superficial or Minor
Deep Dermis (2) Major
Full Thickness (3) Destroyed

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.

Plastic Surgery and Skin Grafts
Skin Substitutes Skin Banks (TL7+)
Synthetics (TL7+)
Pseudobiological Substitutes (TL12+)
Dressings Donated (living, dead, other animal (e.g., pig)
Synthetic materials plus growth factors
Epidermal Substitutes Grafts, cultured tissue, pseudobiological materials
Dermal Substitutes
Bilayer substitutes

Treatment task, progress and aftercare as per Trauma rules.

Electric Currents

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

Effects of Electric Current
Current Source Effect
10 - 100 A Earth Leakage Microshock
30 - 400 A Faulty Equipment Tingling (harmless)
1 - 10 mA Pain (withdraw)
10 - 100 mA Tetany (can't let go)
100 mA - 1 A Macroshock (VF)
1 - 1000 A Burns and tissue damage
1000 - 12000 A High-Tension Wires Severe burns, limb loss
above 12000 A Lightning Strike Coma, severe burns, limb loss

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.

Current-Induced Damage
Current Level Damage
1 - 10 mA 1 pt stun per 10 sec in circuit
10 - 100 mA 1 pt per 1 sec in circuit
100 mA - 1 A VF if consciousness check fails, else 2D stun and character is knocked down/back.
1 - 1000 A As above, + 2D burn damage
1000 - 10000 A VF chance, + 4D burn damage
Above 10000 A VF chance, + 6D burn damage, unconsciousness automatic

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

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