Hypothermia

No previously healthy person should die of hypothermia after they have been rescued and treatment has been started."

Cameron C. Bangs, M.D. The Mountaineers 1986

Objectives

• Describe the regulation of temperature by the hypothalamus

• Discuss effects of cold exposure.

• Discuss hypothermia causes, signs and symptoms and prevention

• Discuss management and specific re-warming methods in the field

Hypothermia - definition

– A state of low body temperature, specifically a low CORE temperature (< 35º C) and confirmed with a low reading thermometer.

– Temperatures below 30º C indicate severe hypothermia

– MEDICAL EMERGENCY; life threatening condition.

Hypothermia – review of anatomy and physiology

• Humans are warm-blooded mammals who maintain a constant body temperature

Hypothermia – review of anatomy and physiology

• Temperature regulation is controlled by the hypothalamus in the base of the brain

Hypothermia – review of anatomy and physiology

Hypothermia – heat loss

Hypothermia – effects of cold exposure

• Muscular

– Muscle and tendon tears– Shivering

• Cardiovascular

– Angina on decreased exertion– in BP - risk of stroke, MI or

heart failure– Osborn or J wave on ECG

• Respiratory

– Asthma– Rhinorrhoea on return to warm

room

Hypothermia – effects of cold exposure cont’

• Peripheral nervous system

– Loss of manual dexterity– Loss of sensitivity

• Central nervous system

– Co-ordination impaired– Visual acuity reduced– Alertness reduced– Reflexes slowed– Increased mistakes– Visual and auditory input

misinterpreted

• Other

– Increased risk of diving ills

Hypothermia - prevention

• Eat properly and often

• Warm liquids and water

• Wear clothing properly (layers worn loosely)

• Keep active

• Stay dry

• Warm living quarters and limit exposure

• Get plenty of rest

• Buddy watch/observation

• If in water

Hypothermia – prevention

Floor’s too cold

I think I’ll sleep here!

Hypothermia - predisposing factors

• Previous cold weather injury

• Inadequate nutrition

• Alcohol, nicotine use

• Dehydration

• Overactivity (sweating)

• Underactivity

• Long exposure to the cold

• Sick or injured

• Ethnic/geographic origin

• Age

• Poor physical condition

• Little experience/training in cold weather

• Poor clothing and equipment

Hypothermia – presentation and diagnosis

• Consider hypothermia based on history and a temperature taken with a low reading thermometer

• The body’s normal physiological response to a cold challenge

– Blood is shunted from the periphery to the core

– Mild shivering: if exercise is not adequate for heat production

– A normal level of consciousness

– Fine motor function may be impaired

– Increased urination causing a loss of fluid

Hypothermia – signs and symptoms

Core Temp ‘C Signs and Symptoms

37.6 ‘Normal’ rectal temperature.

37 ‘Normal’ oral temperature.

36 Increased metabolic rate to attempt to balance heat loss. Respiratory and pulse rate increase.

35 Shivering maximum at this temperature. Hyper-reflexia, dysarthria, delayed cerebration.

34 Patients usually responsive and with normal blood pressure, lower limit compatible with continued exercise.

33 – 31 Retrograde amnesia, consciousness clouded, blood pressure difficult to obtain, pupils dilated, most shivering ceases.

30 – 28 Progressive loss of consciousness, increased muscular rigidity, slow pulse and respiration, cardiac arrhythmia develops, ventricular fibrillation may develop if heart irritated.

27 Voluntary motion lost along with papillary light reflex deep tendon and skin reflexes. Appears dead.

26 Victims seldom conscious.

25 Ventricular fibrillation may appear spontaneously.

24 – 21 Pulmonary oedema develops: 100% mortality in shipwreck victims in World War II.

20 Heart standstill.

18 Lowest adult accidental hypothermic patient with recovery.

17 Iso-electric EEG.

15.2 Lowest infant accidental hypothermic patient with recovery.

9 Lowest artificially cooled hypothermic patient with recovery.

4 Monkeys revived successfully.

1 – 7 Rats and hamsters revived successfully.

Hypothermia – signs and symptoms cont’

• Initial Symptoms

– Shivering

– Dizzy, drowsy

– Withdrawn behavior

– Irritability

– Confusion

– Slowed, slurred speech

– Altered vision

– Stumbling

• Severe Stages

- Stops shivering

- Desire to lie down and sleep

- Heartbeat and breathing is faint or undetectable

- paradoxical undressing – 20-50% suffer this

- Unconsciousness followed by DEATH

Hypothermia – signs and symptoms cont’

Mountaineer found on Everest showing signs of paradoxical undressing

Hypothermia - aspects of rescue

• Rarely availability are tympanic thermometers and rectal temperature difficult therefore diagnosis will usually be clinical.

• Casualties in water must be rescued horizontally or head down if possible

• Shelter is of paramount importance

• Wet clothes NOT removed until sheltered in warm, safe environment

• Initially insulate with blankets and additional clothes. Keep covered and insulated even when in the warmth to prevent further heat loss

• Physical exercise is contraindicated where the core temperature is < 35’C

• Handle casualties gently when managing airway to avoid V - Fib

Hypothermia – complications

• Death can occur as a consequence of

– Concomitant illness/injury

– Continued heat loss

– The “after – drop” in temperature (controversial)

– Relative hypovolaemia due to vasodilation

– Circulatory overload by too rapid re-warming – excessive fluid shifts into intravascular space

– Ventricular fibrillation - most patients who die during active re-warming die from ventricular fibrillation

Hypothermia - management

Safety – self, scene, casualty

Assess and treat

C - Catastrophic haemorrhage

A - Airway with C – spine control

B - Breathing

C - Circulation

D - Disability (CNS)

E - Environment and extremities

Hypothermia – management cont’

• Re-warming should be methodical and at rate of 0.5’C per hour

• Recommended re-warming methods:

– Prevent further cold exposure

– Airway warming devices – Res-Q-Air/Little Dragon

– Generalised surface re-warming with Bair Hugger

– remove wet clothing

– Re-warm in dry clothing, blankets or sleeping bag

– Heat packs placed in groin and axilla

Hypothermia – management cont’

• Recommended re-warming methods:

– warm, sweet liquids if conscious or warm IV fluids

– minimize handling of the unconscious victim with a low heartbeat so as to not induce cardiac arrest

– Blood glucose checked

– Urgent contact with Topside Support

– Do not rub skin, use alcohol or use radiant heaters

Hypothermia – red flags

– Minimize handling of the unconscious victim with a low heartbeat so as to not induce cardiac arrest

– Avoid adrenaline and other drugs in cardiac arrest until core temperature > 30’C. Between 30’ and 35’C double the interval time between administration of drugs

– If VT/VF occur – defibrillate – if VT/VF persists after three shocks delay further shocks until core temeprature is >30’C

– Do not overheat the patient. In comatose casualties a period of therapeutic hypothermia (32 – 34’C) may be beneficial

– The patient is not dead until he is warm and dead

Hypothermia and cardiac arrest

• Cardiac arrest difficult to diagnose in hypothermia

– Profound reduction in level of consciousness

– Bradypnoea

– Bradycardia

– Hard to palpate pulses

• Giving impression of ‘dead’ patient when they are not

Hypothermia and cardiac arrest

• Indications for initiating CPR:

• No carotid pulse after feeling in correct place for at least one minute

• Cardiac arrest is witnessed; pulse present then disappears

• Reasonable chance arrest occurred within last two hours

• CPR can be started in the knowledge that it will be effective before movement of the patient takes place

• Core temperature must be 30’C or above or it is likely to be unsuccessful

• Maintain CPR during re-warming

Hypothermia – long term effects

• Pancreatitis

• Haemolysis

• Renal failure

• Coagulopathy

Questions

Summary

• Effects of cold exposure can show signs and symptoms that affect

many systems including the heart

• Signs and symptoms range from difficulty with fine motor in the early

stages to deeply unconscious and dead

• Management includes gentle re-warming using both external and

internal methods

• “A hypothermic patient is not dead until he is warm and dead”