Hey everyone, it’s Jessica again, and welcome to CritIC.
Normal body temperature is around 36 to 37.5 degrees Celcius (i.e. 96.8 – 99.5 degrees Fahrenheit).
Elevated body temperature can have detrimental effects on the body, so it should be regarded
as an alarm symptom for further investigation.
This video covers hyperthermia, excluding fever, why it’s dangerous and what you should do.
Check out my other video on the causes of hyperthermia.
Now let’s go.
A quick rundown of definitions:
fever is an elevated body temperature due to an increase in hypothalamic setpoint
caused by inflammatory cytokines.
It is a normal physiological response, and, when mild, is considered to be beneficial in recovery.
Hyperthermia is defined as an elevated body temperature that is not due to an increase
in hypothalamic setpoint, i.e. not in response to inflammation.
Hyperthermia should always be regarded as pathological.
In clinical practice, it’s hard to differentiate the two.
And furthermore, new insights in the pathophysiology of hyperthermia related disorders show that
inflammatory cytokines are also involved.
I’ve put some articles in the description if you’re interested to read more on this.
For the purpose of this video, I’ve decided to focus on the classical definitions to keep
things a bit more clear.
The consequences of hyperthermia can be severe.
Hyperthermia causes direct cellular damage, as it affects membrane stability and causes
protein denaturation, especially when temperatures increase over 40 degrees Celsius.
This could result in multiple organ failure.
The brain is particularly susceptible to hyperthermia.
In addition to direct cytotoxic damage to neurons, the integrity of the BBB is disrupted
allowing translocation of systemic toxins to enter the cerebral circulation.
The kidneys are also commonly affected.
First, direct cytotoxic effects cause glomerular and tubular damage.
Second, hyperthermia causes glomerular vasodilation and thus reduces renal perfusion.
And third, direct toxic effects on muscle tissue causes rhabdomyolysis, which causes
renal failure.
Hyperthermia causes vasodilation, and with that low blood pressure and a hyperdynamic
circulation.
As high temperatures continue, troponin levels start to rise.
Whether this is causes by direct cytotoxic effects or by coronary vasodilation
(a type 2 myocardial infarction) is unknown.
Once myocardial damage occurs, cardiac output decreases.
In the gastro intestinal tract, splanchnic blood flow is decreased, causing bowel ischemia.
This, combined with the direct cytotoxic effect of hyperthermia on the intestinal epithelium,
could lead to bacterial translocation and thus gram negative sepsis.
Hepatocellular damage could lead to liver dysfunction.
Hyperthermia causes disseminated intravascular coagulation:
a life-threatening coagulation disorder that is characterized by simultaneous bleeding and clotting.
Labs show low platelets, increased fibrin degradation products such as D-dimer,
prolonged PT and low fibrinogen.
I’ll do a video on this in the future.
So hyperthermia can cause life threatening multi organ failure.
Now what should you do?
First, you need to figure out the cause of the hyperthermia.
We’ll go into this in the next video.
Second, you need to keep your patient on the monitor and run tests on hyperthermia related
complications as discussed earlier:
so you get a complete blood count, a full metabolic panel,
i.e. liver and renal function with electrolytes
(remember that hyperthermia causes a transcellular shift of potassium, leading to hyperkalemia)
CK for rhabdomyolysis, cardiac enzymes,
a full coagulation panel for DIC, inflammatory markers and an arterial blood gas.
Consider a tox screen for the cause.
And lastly, you need to start cooling your patient.
Remember that antipyretics won’t work.
Start cooling with cold packs, cold blankets and iv fluids.
Consider benzodiazepines in shivering and agitation.
Aim for a body temperature below 39 degrees Celsius.
Alright, now that we know what to do and why we need to do this, let’s talk about the
most important causes of hyperthermia in the next video.
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Thanks!