Exertional Heat Stroke Flashcards

1
Q

What is hyperpyrexia

A

Temperature set point is elevated in the absence of impaired thermoregulation

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2
Q

Describe the sequence of events when the hypothalamus detects an increase in temperature

A

Voluntary - remove clothes, drink, change environments
Parasympathetic activation - sweat
Sympathetic activation - vasodilate and reduce basal metabolic rate

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3
Q

At what temperature can vasodilation no longer compensate for hyperthermia

A

38

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4
Q

Dehydration leads to a x osmotic x volaemic state. Why?

A

Hyperosmotic and hypovolaemic

Sweat is hypotonic

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5
Q

dehydration leads to a hyperosmotic state which causes….

A

An increased temperature threshold for sweating and vasodilation (body doesn’t want to lose more hypotonic sweat)

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6
Q

Dehydration leads to a hypovolaemic state which in terms of temperature regulation does what

A

Less blood volume so less available at skin surface to disipate heat
Combined with vasodilation this leads to a reduced BP detected by baroreceptors
As a result there is peripheral vasoconstriction and reduced sweating

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7
Q

What is heat stress

A

The bodies initial reaction to heat can cause cramps and syncope

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8
Q

Define heat exhaustion and compare it to heat stroke

A

Heat exhaustion - temp <40. Can still thermoregulate. Dehydration induced heat retention. Imbalance of water and electrolytes
Heat stroke - temp >40 + mental state changes. Can’t thermoregulate. There is a systemic inflammatory response leading to organ damage

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9
Q

How would someone with heat exhaustion present

A

Cramps, weakness, nausea, syncope
Sweating but may feel cool
Tachycardic but weak pulse

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10
Q

How would someone with heat stroke present

A

Throbbing headache, mental state changes, N&V
Hot and dry skin
Tachycardic and strong pulse

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11
Q

How is someone with heat related illness managed

A

Ice packs, ice bath, remove all clothes, cold IV fluids, fans

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12
Q

What happens to splanchnic blood flow in hyperthermia and what is the result

A

Reduced blood flow = cellular hypoxia = ROS production = mucosal injury = permeable = endotoxin release

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13
Q

What is the result of endotoxin release (following reduced splanchnic blood flow)

A

Pyrogens - increase hypothalmic temperature set point

Cytokines - trigger systemic inflammatory response leading to organ damage

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14
Q

Describe the effects of hyperthermia on the brain

A

Cerebral oedema
Central pontine myelinolsis (due to hypernatraemic state)
Haemorrhage (due to coagulopathy)

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15
Q

What happens to the kidneys as a result of hyperthermia

A

Pre renal AKI and rhabdomyolysis

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16
Q

What happens haematologically following hyperthermia

A

DIC

17
Q

What would an ECG of a hyperthermic patient show

A
Long QT (due to reduced Ca, K, Mg)
ST changes (ischaemia)
Tachyarrhythmias
18
Q

Why do you get cardiac arrest in hyperthermia

A
Systemic inflammatory response gives shock picture
Heat is cytotoxic = myocardium death
Deranged metabolites (metabolic acidosis from lactate but respiratory alkalosis from blowing off heat)
19
Q

Which drugs can lead to hyperthermia

A

Sympathomimetics, anticholinergics, Bblockers, CCB, amphetamines

20
Q

Define classic vs exertional heat stroke

A

Classic: due to environmental temperatures - often occurs in elderly
Exertional: due to strenuous exercise often in hot/humid environment

21
Q

Heat related illness differentials:

A

Infection, ACS, hypoglycaemia, drugs, serotonin syndrome

22
Q

What is the primary prehospital goal for heat stroke

A

Rapidly cool to 39 degrees c

23
Q

What is malignant hyperthermia

A

Disorder of skeletal muscle calcium homeostasis leading to muscle contractures and hyper metabolic crisis

24
Q

What causes malignant hyperthermia

A

Genetically susceptible individual

Halogenated anaesthetics or depolarising muscle relaxants

25
Q

How is malignant hyperthermia managed

A

Stop agent, O2, correct electrolytes and acidosis, active cooling, Dantrolene