Hypothermia

1
Hypothermia

• Brian Trethowan

2
Hypothermia

• Poikilotherms v homeotherms
• Normal - 36-37.5ºC
• Hypothermia - lt35ºC
• Mild - 35-32ºC, Moderate - 32-28ºC, Severe -
  lt28ºC
• 1 UK winter admissions - esp elderly, 3
• USA - alcoholism, drugs, mental illness,
  immersion
• Mortality ? severity - 21 if 32-28ºC, nearly
  100 if trauma

3
Aetiology

• Severe prolonged hypothermia multiple system
  derangements ? ?tissue oxygen
• Main defence against cold stress - behaviour
• 2nd line - autonomic thermoreguln mounted by post
  hypothalamus - Heat conservation/production
  centre
• 1. peripheral vasoconstriction
• 2. shivering - asynchronous m contraction
• 3. increase in metabolism - thyroid SNS
• 4. horripilation - not very effective

4
Horripilation
5
5 Methods of Heat Loss

• Evaporation
• Convection
• Conduction
• Radiation
• Respiration

6
Heat loss

• Hypothalamus - integrates body temp information
• Cold receptors - skin, deep tissues, sc,
  extrahypothalamic portions, hypothalamus
• 20 of info to be integrated from above
• Each temp-reg response has a threshold T - 36.8
  for vasoconstriction, 36 for nonshivering
  thermogenesis, 35.5 for shiver

7
Causes

• Age - extremes
• Environmental - exposure to cold, immersion, poor
  living conditions
• Drugs - anaesthetic agents, phenothiazines,
  barbiturates, alcohol
• CNS disorders - CVAs, trauma, sc transections,
  brain tumours, wernickes encephalopathy,
  alzheimers, parkinsons, mental illness

8
Causes

• Endocrine dysfunction - hypoglycaemia, DKA,
  hyperosmolar coma, panhypopituatarism,
  hypoadrenalism, hypothyroidism
• Major trauma
• Debility - severe cardiac, renal, hepatic
  impairment, malnutrition, sepsis
• Skin disorders - burns, exfoliative dermatitis

9
Pathogenesis Clinical

• Depresses all organ functions - decreased cardiac
  function, shock, respiratory failure, confusion,
  muscle rigidity, renal failure and death
• SNS stimulation local cutaneous reflexes result
  in vasoconstriction ? shunting of blood to
  central pool

10
Cardiovascular

• Mild hypothermia - SNS stimulation ?
  vasoconstriction, tachycardia ?CO BP
• Further ?T ? cardiac depression ? ?tissue
  perfusion
• CO is halved at 28ºC - ?HR contractility
• Conduction pacemaker ? ? ECG changes
• Progressive bradycardia - prolonged PR,
  QRS(late), QT, non-specific ST changes
• J or Osborn wave - relatively constant lt 33ºC
• AF CHB common below 33ºC
• VF lt 28ºC (earlier if diseased or stimulated)
• Asystole lt 20ºC

11
Osborn
12
Shiver
13
Respiratory

• Mild hypothermia ? ?RR
• Followed by progressive depression of rate, VC
  MV
• Cough reflex abolished - aspiration pneumonia
• Bronchial secretions, atelectasis, pulmonary
  oedema
• lt24ºC - apnoea
• oxyHb dissociation curve ? left ? ?O2 delivery

14
CNS

• Generalised cerebral depression - metab of brain
  ? as core T? - neuroprotective
• ?CO ?blood viscosity ? ?CBF - 7/C
• Confusion ? illogical behaviour- aggresion,
  undressing
• lt28ºC - coma, pupillary dilatation, absence of
  tendon reflexes, rigidity
• lt20ºC - cerebral electrical activity ceases

15
Metabolic

• Shivering - 35-30ºC intense energy release ? ?O2
  consumption BMR
• BMR halved at 28ºC
• Can be limited by fatigue, ?glycogen
• lt30ºC - shivering thermoregulation fail
• 6? in BMR/ºC - O2 follows suit
• Mixed resp/metabolic acidosis is usual -
  hypoventilation ?tissue perfusion
• oxyHb dissociation curve - L ? T, R ? H

16
Renal

• Impairs ADH secretion ? diuresis ?Hct
• Hypovolaemia declared on rewarming
• Electrolyte changes vary
• ?K common - reflects metabolic acidosis, failure
  to excrete H Na-K pumps

17
Haematological

• 35ºC - clotting factor plt function compromised
• Clotting increasingly impaired at lower temp
• Severe cases ? DIC
• Splenic sequestration ? neutropenia
  thrombocytopenia
• Blood viscosity - ?2/ºC

18
Endocrine

• Pancreatitis
• ?insulin secretion peripheral insulin R
• Initial ?cortisol catecholamine as part of
  stress response
• Delayed ?serum thyroxine levels
• lt30ºC - pituitary/pancreatic function cortisol
  secretion blunted
• ?Blood sugar - glycogenolysis insulin R

19
Infection

• Impaired immune response - suppression of
  neutrophil adherence, opsonisation and oxidative
  burst
• Chest infections are particularly common

20
GI

• Hepatic function is depressed - affects most
  enzyme detoxifying processes
• High risk of pancreatitis
• GI motility reduced

21
Management

• Prevent further heat loss
• Commence rewarming with monitoring to prevent Cx
• Mx each case based on aetiology severity as
  well as functional reserve
• Severe hypothermia(esp immersion) can mimic death
  - apnoea, cardiac standstill, coma, unreactive
  pupils, silent ECG/EEG - success possible, 35ºC

22
Management

• Removal from cold environment
• Avoid rough handling - irritable myocardium
• Avoid head up to maintain CPP and CBF
• Aggressive rewarming during resuscitation to at
  least 35ºC

23
Management
24
Cold Weather Injuries

• Freezing
• Frostbite
• Frost nip

• Non Freezing
• Hypothermia
• Chilblains
• Trench/Immersion foot

• Associated Injuries
• Snow Blindness
• Dehydration
• Carbon Monoxide Poisoning

25
Chilblain

• Cause
• Repeated, chronic exposure of bare skin to temps
  32º-60ºF.
• Sign/Symptoms
• Appear as swollen, tender, papules.
• Complaint of burning or prickly sensation.
• Redness.
• Treatment
• Passive warming at room temp.
• No rubbing.
• Protect from trauma and secondary infection.

26
Trench/Immersion Foot

• Cause
• Wet conditions, low temperature.
• Prolonged contact with moisture at temps between
  32º-50ºF
• Signs / Symptoms
• Numbness and pain.
• Swelling, tingling, itching.
• Pale waxy skin.
• Blistering.
• Treatment
• Elevate, wrap in loose dressing.
• Passive re-warming at room temp.
• No massages or rubbing.
• Air dry, no immersion in water.

27
Frostbite

• 1st Degree (Frost Nip)
• Partial freezing
• Stinging

• 3rd Degree
• Blue-gray discoloration
• Bleeding blisters

• 2nd Degree
• Clear Blisters
• Numbness and Burning pain

• 4th Degree
• Blue
• Deeply aching

28
Frostbite

• First Degree or Frost Nip
• Most superficial form of frostbite
• No permanent CWI
• Signs/symptoms
• Redness, mild swelling, pale, and edema
• Treatment
• Warm immediately

29
Frostbite

• True freezing injury of tissues.
• Onset signaled by sudden blanching of the skin of
  nose, ears, cheeks, toes, followed by tingling.
• Frostbite has declared itself when these areas
  are painless.
• Intense coldness followed by numbness.

30
Frostbite

• Second Degree or Superficial

• Entire epidermis.
• Skin redness in fair individuals.
• Grayish discoloration in darker skinned
  individuals.
• Clear blister formation at 24-36 hours followed
  by sheetlike desquamation.
• Persistent cold sensitivity in the area.

31
Frostbite

• Third and Fourth Degree or Deep

• Loss of sensation with pale, yellow, waxy look if
  unthawed.
• Poor capillary refill.
• Tissue loss.
• Hemorrhagic bullae form in 3rd degree injuries at
  12-35 hours unless re-warming is rapid.
• Red discoloring 1-5 days after injury.
• 4th degree characterized by gangrene, necrosis,
  auto-amputation.
• Permanent anatomic and functional loss.

32
Frostbite Treatment

• RAPID re-warming at temps slightly above body
  temperature is the single most effective
  treatment.
• Re-warm until the skin is pliable.
• NO dry heat -- stoves or campfires.
• No re-warming with exercise or rubbing.
• Do not re-warm in the field if there is a risk of
  refreezing.
• Protection from further injury, pad all affected
  areas.
• Loosely wrap with gauze and elevate.
• Remove wet and constrictive clothing.