Thermo- regulation

© 2015 WMA

Thermoregulation

Thermo- regulation

© 2015 WMA

Thermoregulation 1

Structure: • Temperature sensors • Endocrine system • Muscles • Skin

Function:

•Maintain body core at 37°C

Problem: •Too little heat •Too much heat

Thermo- regulation

© 2015 WMA

Normal Body Compensation

Heat Response:

• Vasodilation

• Sweat

Cold Response:

• Shivering

• Vasoconstriction

• Cold diuresis

“You can watch these mechanisms work, but they are

not under your direct control.”

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Thermo- regulation

© 2015 WMA

Compensation Factors

Voluntary Efforts:

• Clothing and shelter

• Eating and drinking

Fitness and morphology:

• Larger muscle mass generates more heat.

• Long and thin people lose heat more quickly.

• Fit people generate heat more easily.

• Acclimatized people dissipate heat more easily.

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Thermo- regulation

© 2015 WMA

Impaired Compensation

• Immobilized by injury, unable to generate heat

• Multiple trauma, volume shock

• Illness that impairs circulation, metabolism, sweat production, or temperature sense

• Drugs that inhibit temperature regulation: cocaine, methamphetamine, diuretics, behavioral medications, pseudoephedrine.

• Extremes of age

• Sunburn

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Thermo- regulation

© 2015 WMA

Transfer of Heat Energy

Conduction: by direct contact

Convection: by wind or moving water

Radiation: by long-wave energy

Evaporation: by water absorbing energy as it evaporates from skin Respiration:

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Thermo- regulation

© 2015 WMA

Mild Hypothermia

Mechanism:

• Heat loss exceeds heat production

• Onset can be acute (sudden) or sub-acute

Signs and Symptoms:

• Altered mental status (mild to moderate mental status changes)

• Significant shivering

• Shell/core effect (peripheral vasoconstriction)

• Core temp 35-32°C

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Thermo- regulation

© 2015 WMA

Mild Hypothermia

Acute:

• Rapid onset, minutes to hours (cold water)

• Usually not dehydrated or calorie depleted

• Spontaneous rewarming is usually possible

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Low Risk High Risk

Thermo- regulation

© 2015 WMA

Mild Hypothermia 8

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Low Risk ? High Risk

Sub-Acute:

• Slow onset, hours to days

• Dehydrated and calorie depleted

• Will not rewarm spontaneously

Thermo- regulation

© 2015 WMA

Mild Hypothermia

Treatment:

• FOOD / CALORIES!

• Warm, sweet fluids

• Trap heat with proper clothing/shelter

• Insulate from ground and weather

• Remove wet clothing to reduce evaporation

• Consider adding hot water bottles, etc.

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Exercise only after improvement in mental status is noted.

Thermo- regulation

© 2015 WMA

Rewarming Methods

Gordon G. Giesbrecht, PhD

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Thermo- regulation

© 2015 WMA

Calories and Fluid 11

Sugar

Carbs / Proteins

Fat

Tinder

Sticks

Logs

Thermo- regulation

© 2015 WMA

• Don’t be lazy; correct cold response! • Stay hydrated and well fed.

• Keep insulation dry and clean. • Dress for the conditions.

• Protect the patient!

Hypothermia Prevention

Early recognition = easy cure

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Thermo- regulation

© 2015 WMA

Signs and Symptoms:

• Significantly altered mental status (V, P, or U)

• No shivering

• Core temperature < 32°C

• VS may be undetectable

• Cardiac irritability

• Dehydration, metabolic derangement

Severe Hypothermia 13

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Low Risk High Risk

Thermo- regulation

© 2015 WMA

Severe Hypothermia

Evacuation:

• Package with added heat source to minimize continued heat loss

• Urgent but gentle evacuation to hospital maintained in horizontal position

• PPV with heated and humidified O2, 6/min

• Warmed IV if available

• No chest compressions if it will delay transport

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Thermo- regulation

© 2015 WMA

Severe Hypothermia

No Chance of Survival:

• Obvious lethal injury

• The chest is frozen

• The core temperature is below 10°C

• Submerged underwater more than one hour

• Airway packed with snow in prolonged avalanche burial

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Wilderness Perspective

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Thermo- regulation

© 2015 WMA

A hypo-wrap can be used to help prevent hypothermia.

Hypothermia Package

“Adding heat to the package in the form of hot water

bottles or a forced air warming device will be useful if it

does not delay evacuation.”

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Thermo- regulation

© 2015 WMA

Heat Related Illness

Heat Exhaustion

Heat Stroke

Exertional Hyponatremia

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Thermo- regulation

© 2015 WMA

Heat Exhaustion

Mechanism:

• Fatigue from exertion or intolerance to heat

• May include volume depletion if fluid has not been available

Signs and Symptoms:

• Awake, normal mental status, subdued

• Near normal core temperature

• Might be sweating; might have normal vital sign pattern normal or early compensated volume shock depending on fluid status

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Thermo- regulation

© 2015 WMA

Heat Exhaustion 21

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Low Risk High Risk

Treatment:

• Reduce exercise and heat exposure

• IV or PO fluids and food or electrolytes if s/sx of volume depletion.

• Evacuate if not improving

Thermo- regulation

© 2015 WMA

Heat Stroke

Mechanism:

• High heat challenge, environmental and/or metabolic

• Inadequate cooling

Signs and Symptoms:

• Significant mental status changes, seizures

• Hot, dry or sweating. Temp > 40.5°C

• Potential vital sign pattern for volume shock

• Skin may be red, or pale with shell/core

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Thermo- regulation

© 2015 WMA

Heat Stroke 23

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Low Risk High Risk

Emergency Treatment:

• Immediate and aggressive cooling!

Thermo- regulation

© 2015 WMA

Cooling Method

1. Ice water

immersion 2°C

2. Cold water

immersion

3. Half the body

submersed at

1.3° C

4. Cold water

immersion 14° C

5. Water, gauze

sheet and fan

6. Fan with water

6 5

4

3 2

1

Ra

te o

f Te

mp

era

ture

Ch

an

ge

83min

17min

9.5min

Cooling Rates from 42oC to 39oC

Hand cooling device and ice to major arteries were even slower

Data from Casa DJ, et al.Current Sports

Medicine Reports 2005.4:309-317

30min

Thermo- regulation

© 2015 WMA

Heat Stroke

Continued Care (post recovery):

• IV or PO hydration for normal urine output

• Food as tolerated

• Protect from heat challenge

• Evacuate to hospital, emergent if abnormal mental status or abnormal urine output

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Thermo- regulation

© 2015 WMA

Hyponatremia

Mechanisms:

• Excessive fluid intake (overhydration)

• Possibly some loss of electrolytes through sweat

Signs and Symptoms:

• Altered mental status (slow mentation, tremors, seizures)

• Nausea, headache, weakness

• Near normal urine output

• Core temperature normal

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Thermo- regulation

© 2015 WMA

Hyponatremia 26

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Low Risk ? High Risk

Treatment:

• Rest

• Fluid restriction unless there is evidence of volume depletion

• Evacuate if not improving

Thermo- regulation

© 2015 WMA

Heat Related Illness Wilderness Perspective

High Risk Problem:

• VS do not return to normal

• Persistent altered mental status

• Decreased urine output

• Urine color becomes red or brown

• You cannot prevent exposure to heat

• The patient is getting worse

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Thermo- regulation

© 2015 WMA

Drink in response to thirst.

Replace fluid and electrolytes.

Beware if not acclimatized!

Beware of impaired compensation due to medications, illness and injury.

Prevention of Heat Illness 28