Pulse - March 2023 - 18

THE RVT
Is It Hot in Here or Is It Just Me?
Fever and hyperthermia for the veterinary technician
Mandy Helton BAS, RVTg, VTS(ECC)
I
t's another busy day in the
emergency hospital, and the
next triage presents with a temperature
of 105.6. We all know
the patient has an elevated temperature,
but what is actually
going on? Does the patient have
a fever, or is it hyperthermic?
How do we treat it?
Hyperthermia versus Fever
Hyperthermia and fever have different mechanisms,
and there are different treatments for
each. Hyperthermia is an external, or environmental,
source of an elevated body temperature.
This can happen from exertion such
as seizures or exercise, or it can happen from
spending time in hot environments, such as
being left in a car on a hot summer day. Hyperthermia
often happens acutely, and severe
hyperthermia will often cause shock from vasodilation
and hypovolemia, as these patients
often become dehydrated. These patients will
acquire organ damage such as acute kidney
injury, coagulopathy, and acute liver damage.
Fever is a reset of the body's normal " temperature
set point. " Body temperature is regulated
by the hypothalamus of the brain. Fever
happens when the hypothalamus resets
that set point to a higher temperature, and is
secondary due to infectious or inflammatory
sources. We often see this in cases such as
infection, pneumonia, SIRS, IMHA, ITP
or other immune mediated diseases. Inflammatory
mediators, such as prostaglandins
and cytokines, trigger the hypothalamus
to perform this reset. Fevers are often subacute,
and unless severely high are not likely
to be immediately life threatening. Opioids
and cannabinoids can also cause a fever- like
hyperthermia. Mu and kappa receptor, along
with delta opioid receptor stimulation, may
induce hypothalamus temperature reset
(Blatteis and Romanovski). Some studies
have shown naloxone may be effective in
treating hyperthermia secondary to morphine
administration, and may induce hypothermia
in cats, rabbits and guinea pigs when
18
injected after no opioid administration.
Distinguishing between fever and
hyperthermia
Good triage and history taking are key in distinguishing
between hyperthermia and fever.
Questions to ask on triage may include previous
medical history, recent history of exercise,
seizures, being left in a hot environment,
current medication, possible toxin exposure,
possible exposure to infectious pets, or recent
vomiting or diarrhea. Patients with a recent
history of seizure or exposure to hot environments
will be hyperthermic. These patients
may have accidentally been left in the car or
have been on a hike or outside during a hot
day. Patients who have upper airway disease,
such as collapsing trachea or brachycephalic
airway obstruction syndrome, are more sensitive
to heat injury, even in normal temperatures;
as are patients that are obese. Seizures
cause hyperthermia by heat production from
excessive muscle usage during paddling or
tremoring. Some toxins that cause tremors
may also induce hyperthermia, such as bromethalin
or pyrethrins. Patients with a history
of vomiting, exposure to infectious pets,
infections from bite wounds or abscess, or
history of immune mediated disease may be
febrile. These patients may also be painful,
have coughing, or have a history of decreased
appetite and lethargy. Indoor/ outdoor status
of cats should be assessed in case of abscess
from bite wounds.
Treatment of hyperthermic patients
Hyperthermic patients should receive active
cooling. The goal of treatment for hyperthermic
patients is to bring the body temperature
down to a safe temperature to avoid organ
damage. There is a lot of controversy regarding
active cooling in veterinary patients, however
there is a consensus on quick cooling to
an end goal of 103.0 degrees. Heat in dogs is
lost via panting and through convection and
conduction of the body surface this way. Active
cooling can be achieved by placing patients
on a cool surface, wetting the skin and
fur, and using a fan. IV fluids are also used to
cool the patient, and room temperature fluids
are effective as they are often 30- 40 degrees
cooler than the patient. Temperature should
be monitored every five minutes, and once
the patient reaches 103 degrees active cooling
should be stopped and the patient should be
monitored for further temperature drop.
Controversy over whether ice or ice baths
are effective or cause vasoconstriction is often
debated, however a literature review by
Dr. Baker et al found immersion in ice baths
was not associated with delayed cooling, and
in some studies showed increased cooling.
However, ice baths may be uncomfortable
for the patient and induce shivering. There is
little to no literature on the use of rubbing alcohol
on paw pads. Anecdotally this may increase
cooling by evaporation. There is some
anecdotal thought that this may also cause
vasoconstriction, although neither has not
been proven.
Treatment of febrile patients Febrile patients
should not be actively cooled. Actively
cooling a febrile patient often causes a rebound
fever since the hypothalamus is changing
the " temperature set point. " Additionally,
active cooling of febrile patients may be uncomfortable
(imagine how cold we feel when
we have a fever). Instead, the primary source
of fever should be addressed. Source control
such as wound debridement and antibiotics
for patients that have an infectious source will
often help reduce the fever. IV fluids and antiinflammatory
drugs such as NSAIDs or steroids,
and immunosuppressants for patients
with immune mediated disease, will help with
inflammatory sources of fever.
Conclusion
Fevers and hyperthermia have different etiologies
and treatment plans. As veterinary technicians,
it is important to be able to decipher
between true fever and hyperthermia and the
pathophysiology of each in our hot patients.
This can help ensure the proper treatment for
best outcome. P
References available upon request.
MARCH 2023
PULSE
Pulse - March 2023

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