Heat Stroke Flashcards
what produces most body heat?
muscular activity
which structures in the body control body temperature?
central and peripheral thermoreceptors
what acts as the thermoregulation centre in the brain?
anterior hypothalamus
what is the role of the thermoreceptors?
indicate when temperature is above or below the ideal set point
what does the body do if the temperature is above the set point?
heat dissipation
what does the body do if the temperature is below the set point?
heat conservation and production
what temperature is classed as hyperthermia?
> 39.2 C
what are some of the causes of hyperthermia?
pyrexia
increased heat production due to increased muscular activity
heat stroke
what are the 2 types of heat stroke?
classic heat stroke (reduced heat loss)
exertional heat stroke - overheating due to over-exercise in high temps
what causes heat stroke?
failure of heat dissipation
what may lead to failure of heat dissipation?
upper respiratory obstruction
increased environmental temperature/humidity
poor environmental ventilation
circulatory compromise
obesity
breed disposition
what body temperature carries risk of organ damage/failure?
> 41.6 C
why does a temperature of >41.6 C risk permanent organ damage/failure?
caused by cell death due to large increase in oxygen demand and DIC
what are the major clinical signs of heat stroke?
stress
hyperthermia
tachycardia
hypovolaemia
hyperdynamic pulses
peripheral vasodilation
collapse
hyperaemic mm (bright red) with rapid CRT
when might heat stroke patients appear normothermic?
due to impaired peripheral perfusion - widespread vasodilation
what are the symptoms of advanced stage heat stroke?
hypovolaemia
increased intestinal mucosal permeability and impaired GI perfusion
tachypnoea
secondary respiratory complications
why might a patient in advance stage heat stroke be hypovolaemic?
GI losses
vasodilation - relative hypovolaemia due to systemic compromise
why are patients in heat stroke at higher risk of sepsis?
increase intestinal mucosal permeability and impaired GI perfusion –> endotoxin translocation –> sepsis
how can risk of sepsis due to gut translocation be reduced in the heat stroke patient?
patients with severe GI compromise may require mucosal protectants (omeprazole) and IV antibiotics
which secondary respiratory complications can occur as a result of heat stroke?
aspiration pneumonia
pulmonary oedema
pulmonary haemorrhage (DIC)
what are some of the secondary complications of heat stroke?
impaired renal perfusion
CNS compromise
disseminated intravascular coagulation
why is impaired renal perfusion occur as a secondary complication to heat stroke?
due to peripheral shunt of blood - peripheral vasodilation results in reduced blood pressure
why does CNS compromise occur as a secondary complication of heat stroke?
direct thermal damage
or
secondary effects (hypoglycaemia)
what blood abnormalities may be seen as a result of heat stroke?
hypoglycaemia
hyperbilirubinaemia
electrolyte derangements
thrombosis
what may occur to the muscles as a result of heat stroke?
myopathy
where is most heat lost in cases of increased body temperature?
through the body surface
what is the cardiac effect of increased peripheral circulation?
increased cardiac output to compensate
why do many of the secondary complications of heat stroke occur?
due to decreased perfusion of vital organs
what is the initial patient response to an increase in environmental temperature?
as environmental temperature exceeds body temperature, patient relies on panting to compensate
what is involved in emergency management of heat stroke?
active cooling
oxygen supplementation and monitoring oxygenation
maintain a patent airway - assess for obstruction
IVFT
bloods
monitor for increased ICP
at what body temperature should we start actively cooling a patient?
> 41 C
why should cold water not be used for active cooling?
using water that is too cold will cause peripheral vasoconstriction and impair heat loss further
at what body temperature should we stop actively cooling a patient?
< 39.4 C to prevent hypothermia
how often should we measure a patients temperature during active cooling>
every 5 mins minimum
why is it important to supplement oxygen in heat stroke patients?
will have very elevated RR (fast panting)
how can we monitor oxygenation in heat stroke patients?
SpO2 or arterial blood gas
why is it important to give heat stroke patients IVFT?
isotonic crystalloids to support circulation
to replace deficits (requires continuous re-assessment)
what blood values are valuable to obtain in a heat stroke patient?
PCV
total solids
glucose
electrolytes
coagulation factors
why is it important to look for abnormal coagulation factors in heat stroke patients?
looking for evidence of coagulopathies - clotting disorders caused by hyperthermia
why might patients with heat stroke have increased ICP?
cerebral vasodilation due to peripheral vasodilation
is pyrexia beneficial to the patient?
yes
why is pyrexia beneficial to the patient?
decreases replication of pathogens and increases function of WBCs
should we actively cool patients with pyrexia?
no - beneficial to the body
when is it appropriate to administer antipyretic drugs?
patients with cancer and immune compromise
what is an antipyretic drug?
a drug used to prevent/reduce fever e.g. paracetamol, NSAIDs
what are some of the causes of pyrexia?
inflammatory disease - infectious, immune-mediated
neoplastic disease
other causes - opioids, hepatic encephalopathy
blood transfusion (esp xenotransfusion)
