Exertional Heat Stroke Flashcards
What is hyperpyrexia
Temperature set point is elevated in the absence of impaired thermoregulation
Describe the sequence of events when the hypothalamus detects an increase in temperature
Voluntary - remove clothes, drink, change environments
Parasympathetic activation - sweat
Sympathetic activation - vasodilate and reduce basal metabolic rate
At what temperature can vasodilation no longer compensate for hyperthermia
38
Dehydration leads to a x osmotic x volaemic state. Why?
Hyperosmotic and hypovolaemic
Sweat is hypotonic
dehydration leads to a hyperosmotic state which causes….
An increased temperature threshold for sweating and vasodilation (body doesn’t want to lose more hypotonic sweat)
Dehydration leads to a hypovolaemic state which in terms of temperature regulation does what
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
What is heat stress
The bodies initial reaction to heat can cause cramps and syncope
Define heat exhaustion and compare it to heat stroke
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
How would someone with heat exhaustion present
Cramps, weakness, nausea, syncope
Sweating but may feel cool
Tachycardic but weak pulse
How would someone with heat stroke present
Throbbing headache, mental state changes, N&V
Hot and dry skin
Tachycardic and strong pulse
How is someone with heat related illness managed
Ice packs, ice bath, remove all clothes, cold IV fluids, fans
What happens to splanchnic blood flow in hyperthermia and what is the result
Reduced blood flow = cellular hypoxia = ROS production = mucosal injury = permeable = endotoxin release
What is the result of endotoxin release (following reduced splanchnic blood flow)
Pyrogens - increase hypothalmic temperature set point
Cytokines - trigger systemic inflammatory response leading to organ damage
Describe the effects of hyperthermia on the brain
Cerebral oedema
Central pontine myelinolsis (due to hypernatraemic state)
Haemorrhage (due to coagulopathy)
What happens to the kidneys as a result of hyperthermia
Pre renal AKI and rhabdomyolysis
What happens haematologically following hyperthermia
DIC
What would an ECG of a hyperthermic patient show
Long QT (due to reduced Ca, K, Mg) ST changes (ischaemia) Tachyarrhythmias
Why do you get cardiac arrest in hyperthermia
Systemic inflammatory response gives shock picture Heat is cytotoxic = myocardium death Deranged metabolites (metabolic acidosis from lactate but respiratory alkalosis from blowing off heat)
Which drugs can lead to hyperthermia
Sympathomimetics, anticholinergics, Bblockers, CCB, amphetamines
Define classic vs exertional heat stroke
Classic: due to environmental temperatures - often occurs in elderly
Exertional: due to strenuous exercise often in hot/humid environment
Heat related illness differentials:
Infection, ACS, hypoglycaemia, drugs, serotonin syndrome
What is the primary prehospital goal for heat stroke
Rapidly cool to 39 degrees c
What is malignant hyperthermia
Disorder of skeletal muscle calcium homeostasis leading to muscle contractures and hyper metabolic crisis
What causes malignant hyperthermia
Genetically susceptible individual
Halogenated anaesthetics or depolarising muscle relaxants
How is malignant hyperthermia managed
Stop agent, O2, correct electrolytes and acidosis, active cooling, Dantrolene
