Exertional Heat Stroke

Question 1

What is hyperpyrexia

Answer 1

Temperature set point is elevated in the absence of impaired thermoregulation

Question 2

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

Answer 2

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

Question 3

At what temperature can vasodilation no longer compensate for hyperthermia

Answer 3

38

Question 4

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

Answer 4

Hyperosmotic and hypovolaemic

Sweat is hypotonic

Question 5

dehydration leads to a hyperosmotic state which causes….

Answer 5

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

Question 6

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

Answer 6

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

Question 7

What is heat stress

Answer 7

The bodies initial reaction to heat can cause cramps and syncope

Question 8

Define heat exhaustion and compare it to heat stroke

Answer 8

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

Question 9

How would someone with heat exhaustion present

Answer 9

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

Question 10

How would someone with heat stroke present

Answer 10

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

Question 11

How is someone with heat related illness managed

Answer 11

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

Question 12

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

Answer 12

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

Question 13

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

Answer 13

Pyrogens - increase hypothalmic temperature set point

Cytokines - trigger systemic inflammatory response leading to organ damage

Question 14

Describe the effects of hyperthermia on the brain

Answer 14

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

Question 15

What happens to the kidneys as a result of hyperthermia

Answer 15

Pre renal AKI and rhabdomyolysis

Question 16

What happens haematologically following hyperthermia

Answer 16

DIC

Question 17

What would an ECG of a hyperthermic patient show

Answer 17

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

Question 18

Why do you get cardiac arrest in hyperthermia

Answer 18

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

Question 19

Which drugs can lead to hyperthermia

Answer 19

Sympathomimetics, anticholinergics, Bblockers, CCB, amphetamines

Question 20

Define classic vs exertional heat stroke

Answer 20

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

Question 21

Heat related illness differentials:

Answer 21

Infection, ACS, hypoglycaemia, drugs, serotonin syndrome

Question 22

What is the primary prehospital goal for heat stroke

Answer 22

Rapidly cool to 39 degrees c

Question 23

What is malignant hyperthermia

Answer 23

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

Question 24

What causes malignant hyperthermia

Answer 24

Genetically susceptible individual

Halogenated anaesthetics or depolarising muscle relaxants

Question 25

How is malignant hyperthermia managed

Answer 25

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