Hyperthermia & hypothermia

Question 1

What is hypothermia?

Answer 1

core body temperature <35°C

Question 2

What are the risk factors for hypothermia?

Answer 2

General anaesthetic use, older age, very young age, immobility, substance misuse, hypothyroidism, stroke, homelessness, parkinson’s disease

Question 3

What are the different ways hypothermia can be classified?

Answer 3

May be mild (32-35°C), moderate (28-32°C) or severe (<28°C)
1. Mild ⇒ tachycardia, tachypnoea, vasoconstriction and shivering
2. Moderate ⇒ cardiac arrhythmias, hypotension, respiratory depression, reduced consciousness and may cease to shiver
3. Severe ⇒ markedly reduced consciousness/coma, apnoea, arrhythmia, fixed and dilated pupils

Question 4

What is hyperthermia?

Answer 4

core body temperature >40°C

Question 5

What is meant by “heat stroke”?

Answer 5

life-threatening condition that presents with hyperthermia and CNS dysfunction

Question 6

What are the risk factors for hyperthermia?

Answer 6

older age, impaired cognition, medicines, lack of acclimatisation to hot environments, dehydration, environmental factor

Question 7

What are the different ways hyperthermia can be classified?

Answer 7

Classic heat stroke (passive exposure to environmental heat), exertional heat stroke (due to strenuous physical exercise), heat exhaustion (no CNS dysfunction)

Question 8

What is meant by “malignant hyperthermia”?

Answer 8

• Following exposure to potent anaesthetics (suxamethonium) in susceptible individuals.
• The most common cause is an autosomal dominant mutation in the RYR1 receptor, which increases calcium levels in the sarcoplasmic reticulum and increases metabolic rate
• Dramatic increase in metabolism, critical temperature elevation and rhabdomyolysis (occurs when damaged muscle tissue releases its proteins and electrolytes into the blood. These substances can damage the heart and kidneys and cause permanent disability or even death.) with potential hyperkalaemia.
• FHx, muscle rigidity, tachycardia, decreased urine output, muscle cramps.
• IV Dantrolene.

Question 9

What signs of hypothermia can be found on physical examination?

Answer 9

• Shivering
• cognitive impairment (stage 2)
• frostbite
• tachypnoea + tachycardia + hypertension (mild)
• respiratory depression + bradycardia + hypotension (moderate)
• coma + apnoea (severe)

Question 10

What signs of hyperthermia can be found on physical examination?

Answer 10

• CNS dysfunction (altered level of consciousness, agitation, lethargy, seizures, irritability)
• anhidrosis (hot, dry skin)
• intense thirst
• weakness
• anxiety
• dizziness
• N&V
• syncope

Question 11

What investigations are used to daignose/ monitor hypothermia?

Answer 11

• Core Temperature Measurement (Hypothermia)
• 12 Lead ECG (Hypothermia) → J wave/Osborn wave, Broad (prolonged) QRS complexes
  J Wave = Hypothermia

Question 12

What investigation is used to diagnose/ monitor hyperthermia?

Answer 12

Rectal Temperature (Hyperthermia)→ most accurate measurement of core hyperthermia

Question 13

How is hypothermia managed?

Answer 13

1. Mild Hypothermia → passive external rewarming (remove wet clothing, cover with blankets, warm room)
2. Moderate Hypothermia → active external rewarming (warm blankets, radiant head, forced warm air
3. Severe Hypothermia → IV administration of warmed crystalloid
4. Complications (Hypothermia) → cardiac arrhythmias, hypoglycaemia, hyperkalaemia, rhabdomyolysis, GI disorders

Question 14

How is hyperthermia managed?

Answer 14

1. Heat Stroke → stabilisation (ABC, remove clothing), rapid active cooling (whole body iced water immersion)
2. Heat Exhaustion → oral isotonic fluids + active cooling
3. Complications (Hyperthermia) → ARDS, shock, AKI, DIC, CVD