Hypothermia

 

Definition

Defined by core temperature, rectal, oesophageal

Below 35`C

Some US sources say below 34`C

 

 

Causes of accidental hypothermia

Illness - CVA, MI, hypothyroidism, diabetic coma, trauma, falls in the elderly - immobilisation

 

Psychiatric - Overdose, psychiatric illness

 

Alcohol - Vasodilation, hypoglycaemia will inhibit shivering

 

Environmental - Cold environments, immersion in water, getting wet, social conditions

 

At a temperature of 27`C the metabolic rate is 2.5 times lower than at 37`C.

 

Is preventable, uncommon in Siberia

 

Other factors

Subcutaneous fat

Acclimatisation to cold

 

Iatrogenic causes

Surgery, up to 50% of cases - may effect organ function and outcome, immunity, coagulation, cardiac function

A and E

Corridors

Reduced mobility

Drugs, eg. chlorpromazine, sedatives

Washing

 

 

Assessment

Degree of hypothermia, mild (35 - 32`C), moderate (32 - 28), severe (<28)

Duration of hypothermia

 

Rapid onset

Over less than 12 hours

 

Insidious onset

Over more than 12 hours

Results in cold-induced diuresis and increased loss of blood volume

Also carries a poorer prognosis

 

 

Clinical features

 

Reduced enzymic activity

 

Normal physiological functions reduce, heart, brain, muscle, cellular biochemistry slows and becomes disordered

 

Cool people, 36 - 35`C

Cold pale skin, poor muscle coronation, shivering, piloerection, tachycardia, hyperpnoea

 

Mild hypothermia, 35 32`C

Below 35`C mental function significantly declines

Increasing confusion and decreasing levels of consciousness

 

Progressive decreased motor function - central and peripheral reasons

 

Hypothalamus mediated attempted sympathetic compensation

Shivering is maximal at about 35 - 32`C and the person feels intensely cold

Peripheral vasoconstriction ----- diuresis

Tachycardia and increased BP

Tachypnoea

Hyperglycaemia

 

Cold diuresis

 

As hypothermia develops the hypothalamus is no longer able to induce sympathetic stimulation of peripheral vessels so they dilate. This will cause the hypothermic person to feel warm.

 

Moderate hypothermia 32 - 28

Loss of sympathetic compensations - No shivering, vasodilation, bradycardia, hypotension, dilated pupils,

 

Reduced renal function - ATN may occur secondary to a hypovolaemic renal hypoperfusion and reduced cardiac output

 

Muscle rigidity, risk of convulsions, ECG changes, coagulopathies

 

Progressive reducing level of consciousness

 

Cold oedema

 

SA and SV node depression - ventricular ectopics (PVCs), possible AF

Increasing risk of cardiac arrythmias, risk of cardiac arrest

 

Hypothermia of 32`C or less is frequently lethal, probably most commonly form VF

 

Severe / profound hypothermia, less than 28`C

Coma pulse and respirations not detectable - may mimic death

Acidosis

26 - 27`C Spontaneous arrythmias, fibrillation risk, cyanosis, barely detectable vital signs

24`C Cessation of respiration

20`C Heart spontaneous stops

Management

 

Rewarming

Passive using the bodies own metabolic activity, the patient is insulated to prevent further heat loss then their own metabolism warms them up

 

Active using sources of external heat

 

Active external

Huddling

Warm baths 40 50`C

Warm air

 

Active internal

Inhalation of warmed air, less than 40`C

Warmed IV fluids

Gastric or peritoneal lavage

Rewarm the trunk first, not the peripheries

 

Always remember rapid rewarming may cause metabolic and cardiac instability

 

Decision making

Rapid onset of hypothermia use rapid warming, slow onset or prolonged hypothermia rewarm slowly

 

Water immersion hypothermia

 

Normally use passive rewarming in mild to moderate cases of less than 12 hours duration

 

Use passive rewarming if the core temperature is above 32`C in the elderly or above 30`C in younger people

 

If the body temperature does not start to rise or the patient is persistently hypotensive go on to active rewarming.

 

Below 30 - 32`C active, but gentle, rewarming is necessary as the patients metabolic rate will be too low to generate heat for active rewarming

 

 

Treatment of mild to moderate hypothermia

Warm environment

Prevent further heat loss

Dry

Layers

Reduce heat loss form head

Space blanket

Warm food and drink

Not hot - vasodilate the stomach and global vasodilation --- after drop

Do not wash, only manage incontinence

Carbohydrates

Treat gently and avoid sudden or vigorous movements risk of cardiac arrythmias

 

IV fluids may be necessary to maintain the circulating volume as vasodilation induced by the warming occurs. (This will be more of a problem in cases of longer duration.)

 

Avoid drugs as they may have a toxic effect

 

Rewarm gradually while correcting metabolic abnormalities and correcting cardiac arrythmias

 

Care of pressure areas

 

 

 

Observations

 

Monitor BP, P, R

 

Electrocardiograph rhythm

 

Monitor blood glucose, as shivering stops below about 31`C and cells become resistant to insulin, hyperglycaemia develops, insulin may be given but beware of a rebound hypoglycaemia

 

Monitor serum potassium, hypothermia may effect the sodium potassium pump and hyperkalaemia may occur during hypothermia or rewarming. Hyperkalaemia is a poor prognostic indicator

 

Fluid balance chart - monitor renal output for the possibility of acute renal failure secondary to hypoperfusion

 

Urine testing - moderate hypothermia urine may be alkaline, in more severe cases it will reflect an systemic acidosis

 

Observe for frostbite

 

 

Treatment of severe hypothermia

After cases of rapid cooling, eg. when people have fallen into cold water warm up rapidly or they may continue cooling and suffer cardiac arrest.

 

Gradual cooling, eg. older person who has collapsed or after prolonged exposure or immersion risk of complications so warm up gradually

 

No faster than 1`C per hour, probably 0.5`C per hour. If faster death may result as the cold heart cannot increase output to match increased oxygen demand

 

Give oxygen to improve oxygenation of hypoperfused areas and to reduce irritability of tissues

 

Core temperature every 15 minutes

 

CPR may be needed during rewarming

 

No one is dead until warm and dead

 

 

Complications

 

Early complications of rewarming

A hypothermic heart has a lower threshold to ventricular fibrillation, so avoid reducing venous return, rescue flat.

 

Patients will be hypovolaemic and hypotensive due to vasodilation

 

During rewarming there is vasodilation, this increases the cardiac output demand which may lead to VF and possible early rewarming death

 

As the peripheries are reperfused, venous return of cold blood is increased, this may cause core temperature to continue to drop. If a lot of cold blood returns to the heart death may occur.

 

After drop

A lowering of temperature after the core has been warmed, caused by the return of cold blood from the peripheries

Warming of peripheries - peripheral vasodilation - cold blood returns to the heart - death

Therefore do not rewarm the peripheries before the core

 

Later complications of rewarming

Post rewarming death

May occur in the elderly with diseases which contributed to the exposure

 

Excess fluid will be trapped in the tissues, cold oedema - return of this fluid to the blood can lead to fluid overload

 

Toxins from the periphery are released into the systemic circulation

 

Renal failure, bronchopneumonia, pancreatitis, rhabdomyolysis, hepatic damage

 

 

Health promotion

 

Pre-discharge advice

Social services

Benefits

Clothing

Keeping dry

Use night caps

Prevent in hospitals

 

 

Induced hypothermia

 

Cold brain metabolises more slowly

 

Heat shock proteins released when tissue is heated, similar ones may be released when the brain is cold to protect the brain from damage

 

Could be a normal protective mechanism in babies. Mild cooling seems to be OK say down to 33

 

May be used during cardiac and neurosurgery

 

 

 

 

 

Health and the weather

 

 

 

Warmer weather more pollen and fungal spores hay fever, asthma

 

Hot weather more thromboembolic disease sweat blood more concentrated

 

UK increase in mortality and morbidity every winter 20 30% increase in mortality compared to summer

 

Worse when the temp is low, delayed effect:

 

Heart attack - incidence increased after 3 days

Stroke - after 5 days

Respiratory infections - after 12 days

 

 

 

Pathophysiology

 

Cold increases BP, fibrinogen levels also increase.

 

Cold peripheral shut down blood leaves skin so less blood is required - fluid is removed from the blood, (we pass more urine when cold) more fluid in tissue spaces blood more concentrated clotting more likely - more thromboembolic disease.

 

Respiratory infections cold and shivering increases the likelihood of developing respiratory infections, however there is no evidence cold actually reduces immune function.

 

Crowding in poorly ventilated spaces may lead to flu epidemics

 

Falls on slippery surfaces lead to broken bones eg. hip fractures in the elderly

 

 

Epidemiology

 

In the UK the amount of hypothermia (2% of hospital admissions in winter) is probably because we dress the same in the cold as in more temperate weather. In colder countries people tend to account for the cold more so do not become so cold. The increase in mortality in colder countries is actually less than in the UK.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Hypothermia

core temperature, rectal, oesophageal, below 35`C

 

 

Causes of accidental hypothermia

Illness

 

Psychiatric

 

Alcohol

 

Environmental

 

At a temperature of 27`C the metabolic rate is 2.5 times lower than at 37`C.

 

Other factors

Subcutaneous fat Acclimatisation to cold

 

Iatrogenic causes

 

Assessment

Degree of hypothermia, mild (35 - 32`C), moderate (32 - 28), severe (<28)

Duration of hypothermia

 

Rapid onset

Over less than 12 hours

 

Insidious onset

Over more than 12 hours

Results in cold-induced diuresis

 

 

 

Clinical features

 

Cool people, 36 - 35`C

Cold pale skin, poor muscle coronation, shivering, piloerection, tachycardia, hyperpnoea

 

Mild hypothermia, 35 32`C

Below 35`C mental function significantly declines

Increasing confusion and decreasing levels of consciousness

Progressive decreased motor function - central and peripheral reasons

 

Hypothalamus mediated attempted sympathetic compensation

Shivering is maximal at about 35 - 32`C and the person feels intensely cold

Peripheral vasoconstriction ----- diuresis

Tachycardia and increased BP

Tachypnoea

Hyperglycaemia

 

As hypothermia develops the hypothalamus is no longer able to induce sympathetic stimulation of peripheral vessels so they dilate. This will cause the hypothermic person to feel warm.

 

Moderate hypothermia 32 - 28

Loss of sympathetic compensations - No shivering, vasodilation, bradycardia, hypotension, dilated pupils,

 

Reduced renal function

 

Muscle rigidity, risk of convulsions, ECG changes, coagulopathies

 

Progressive reducing level of consciousness

 

Cold oedema

 

SA and SV node depression - ventricular ectopics (PVCs), possible AF

Increasing risk of cardiac arrythmias, risk of cardiac arrest

 

Hypothermia of 32`C or less is frequently lethal, probably most commonly form VF

 

Severe / profound hypothermia, less than 28`C

Coma pulse and respirations not detectable - may mimic death

Acidosis

26 - 27`C Spontaneous arrythmias, fibrillation risk, cyanosis, barely detectable vital signs

24`C Cessation of respiration

20`C Heart spontaneous stops

 

Management

 

Rewarming

Passive

 

Active

 

Active external

Huddling

Warm baths 40 50`C

Warm air

 

Active internal

Inhalation of warmed air, less than 40`C

Warmed IV fluids

Gastric or peritoneal lavage

Rewarm the trunk first, not the peripheries

 

Always remember rapid rewarming may cause metabolic and cardiac instability

 

 

Treatment of mild to moderate hypothermia

Warm environment

Prevent further heat loss

Dry

Layers

Reduce heat loss form head

Space blanket

Warm food and drink

Not hot - vasodilate the stomach and global vasodilation --- after drop

Do not wash, only manage incontinence

Carbohydrates

Treat gently and avoid sudden or vigorous movements risk of cardiac arrythmias

 

IV fluids

 

Avoid drugs as they may have a toxic effect

 

Rewarm gradually while correcting metabolic abnormalities and correcting cardiac arrythmias

 

 

 

Observations

 

Monitor BP, P, R

 

ECG

 

Blood glucose, as shivering stops below about 31`C and cells become resistant to insulin, hyperglycaemia develops, insulin may be given but beware of a rebound hypoglycaemia

 

Monitor serum potassium

 

Fluid balance chart

 

Urine testing

 

Observe for frostbite

 

 

Treatment of severe hypothermia

After cases of rapid cooling, eg. when people have fallen into cold water warm up rapidly or they may continue cooling and suffer cardiac arrest.

 

Gradual cooling - warm up gradually

 

No faster than 1`C per hour, probably 0.5`C per hour. If faster death may result as the cold heart cannot increase output to match increased oxygen demand

 

Give oxygen

 

CPR may be needed during rewarming

 

No one is dead until warm and dead

 

 

Complications

 

Early complications of rewarming

Ventricular fibrillation - rescue flat.

 

Hypovolaemic and hypotensive due to vasodilation

 

During rewarming there is vasodilation, this increases the cardiac output demand which may lead to VF and possible early rewarming death

 

As the peripheries are reperfused, venous return of cold blood is increased, this may cause core temperature to continue to drop. If a lot of cold blood returns to the heart death may occur.

 

After drop

A lowering of temperature after the core has been warmed, caused by the return of cold blood from the peripheries

Warming of peripheries - peripheral vasodilation - cold blood returns to the heart - death

Therefore do not rewarm the peripheries before the core

 

Later complications of rewarming

Post rewarming death

 

Cold oedema - return of this fluid to the blood can lead to fluid overload

 

Toxins from the periphery are released into the systemic circulation

 

Renal failure, bronchopneumonia, pancreatitis, rhabdomyolysis, hepatic damage

 

 

Health promotion

 

Pre-discharge advice

Social services

Benefits

Clothing

Keeping dry

Use night caps

Prevent in hospitals