Disorders of
Temperature Regulation
Bryan E. Bledsoe, FACEP
Midlothian, TX
Temperature Regulation
Hypothermia
 Hyperthermia

Heat Cramps
 Heat Tetany
 Heat Exhaustion
 Heat Syncope
 Heat Stroke


Fever
Temperature Regulation

Humans are
warm-blooded
mammals who
maintain a
constant body
temperature
(euthermia).
Temperature Regulation

Temperature
regulation is
controlled by
the
hypothalamus
in the base of
the brain.
Temperature Regulation
 The
hypothalamus functions as a
thermostat for the body.
 Temperature receptors
(thermoreceptors) are located in
the skin, certain mucous
membranes, and in the deeper
tissues of the body.
Temperature Regulation
When an increase in body temperature
is detected, the hypothalamus shuts off
body mechanisms that generate heat
(for example, shivering).
 When a decrease in body temperature
is detected, the hypothalamus shuts off
body mechanisms designed to cool the
body (for example, sweating).

Temperature Regulation

Body Temperature = Thermogenesis–Heat Loss
Temperature Regulation
 Basal
 The
Metabolic Rate:
metabolism that occurs when the
body is completely at rest.
Temperature Regulation
 Metabolic
 The
Rate:
body continuously adjusts the
metabolic rate in order to maintain a
constant CORE temperature.
Temperature Regulation
Normal body
temperature is
approximately 37º
C (98.6º F).
 However, what is
normal for an
individual may
vary somewhat.

Hypothermia
 Definition
of Hypothermia:
CLASSIC DEFINITION: A state of low
body temperature, specifically a low CORE
temperature (< 35º C or < 95º F).
 ALTERNATIVE DEFINITION: It is best
defined as the unintentional decrease of
around 2º C (3.6º F) from the “normal”
CORE temperature

Hypothermia

What is the
CORE
temperature?

The deep internal
temperature of
normothermic
humans.
Hypothermia

How is the CORE
temperature
measured?


There is little variance in
CORE temperature
because of perfusion.
Esophageal and
tympanic temperatures
are essentially the same
as the temperature of the
pulmonary artery.
Hypothermia

In steady-state
conditions, the
rectal temperature
is a good index of
CORE
temperature.
Hypothermia

Oral temperature
is an excellent
index of CORE
temperature,
provided the
mouth is kept
closed.
Hypothermia


The type of
temperature
measurement
utilized is less
important than using
the same device
and measurement
site to detect trends.
Thermometer must
be able to read low
temperatures.
Hypothermia

Heat loss results
from:
Conduction
 Convection
 Radiation
 Evaporation
 Respiration

Heat = Molecular Motion
Hypothermia

Conduction:


Heat loss occurs due
to direct contact of
the body with a
cooler object.
Heat flows from
higher temperature
matter to lower
temperature matter.
Hypothermia

Convection:


Heat loss occurs due
to air currents
passing over the
body.
Heat must first be
conducted to the air
before convection
can occur.
Hypothermia

Radiation:
Heat loss results
from infrared
rays.
 All objects not at
absolute zero will
radiate heat to the
atmosphere.

Radiation
Radiation
Hypothermia

Evaporation:


Heat loss occurs as
water evaporates
from the skin.
Heat loss occurs as
water evaporates
from the lungs during
respiration.
Hypothermia
 Respiration:
 Respiration
combines the heat loss
mechanisms of convection, radiation,
and evaporation.
 Expired air is normally 98.6 degrees
F. and 100% humidified.
Heat-conserving Mechanisms



Vasoconstriction of
blood vessels in the
skin.
Stimulated through
activation of the
sympathetic nervous
system.
Causes pale, cool
skin.
Heat-conserving Mechanisms



Piloerection is more
commonly called
“goose bumps” or
“goose flesh.”
Evolutionary remnant.
Caused by sympathetic
stimulation of arrector
pili muscles.
Heat-conserving Mechanisms

Increased heat
production:
Shivering
 Activation of futile
cycles (chemical
thermogenesis)
 Increased
thyroxine release

Hypothermia

When the core
temperature of
the body drops
below
95º F, an
individual is
considered to be
hypothermic.
Hypothermia
 Clinically,
hypothermia results from:
 Inadequate
heat generation by the
body (thermogenesis).
 Excessive cold stress.
 A combination of both.
Hypothermia



Normal Range:
 96-100º F
Mild Hypothermia:
 90-95º F
Severe Hypothermia
 < 90º F
Hypothermia
 Predisposing
Factors to
Hypothermia:
 Patient
Age
 Patient Health
 Medications
 Prolonged or Intense Exposure
 Co-existing Weather Conditions
Hypothermia
 Patient
Age:
 Pediatric
and geriatric patients cannot
tolerate cold environments and have
less capacity for heat generation.
 Older patients often become
hypothermic in environments that
seem only mildly cool to others.
Hypothermia
 Patient
Health:
 Hypothyroidism
(suppresses
metabolic rate)
 Malnutrition, hypoglycemia,
Parkinson’s disease, fatigue, and
other medical conditions can interfere
with the body’s ability to combat cold
exposure.
Hypothermia
 Medications:
 Some
drugs interfere with the body’s
heat-generating mechanisms.
 These include: narcotics, alcohol,
antihistamines, antipsychotics,
antidepressants, and many others.
Hypothermia
 Prolonged
 The
or Intense Exposure:
length and severity of cold
exposure have a direct effect on
morbidity and mortality.
 The Wind Chill Index (WCI) must be
taken into consideration.
Hypothermia

Coexisting
Weather
Conditions:



High humidity,
brisk winds,
accompanying rain can
all magnify the effect of
cold exposure on the
body by accelerating
heat loss from the skin.
Hypothermia
 Degrees
 Mild–
of Hypothermia:
Core temperature > 90 degrees
F (32 degrees C)
 Severe– Core temperature < 90
degrees F (32 degrees C)
Signs and Symptoms
 MILD
Hypothermia:
 Lethargy
 Shivering
 Lack
of Coordination
 Pale, cold, dry skin
 Early rise in blood pressure, heart,
and respiratory rates.
Signs and Symptoms
 SEVERE
 No
Hypothermia:
shivering
 Heart rhythm problems
 Cardiac arrest
 Loss of voluntary muscle control
 Low blood pressure
 Undetectable pulse and respirations
Prevention
 Preventive
 Warm
Measures:
dress
 Plenty of rest
 Adequate diet
 Limit Exposure
Treatment
 Treatment
for Hypothermia:
1. Remove wet garments
2. Protect against further heat loss
and wind chill.
3. Maintain patient in horizontal
position.
Treatment
 Treatment
for Hypothermia:
4. Avoid rough handling.
5. Monitor the core temperature.
6. Monitor the cardiac rhythm.
Treatment
 ECG
changes seen in hypothermia:
Prolongation of first the PR interval, then
the QRS, then the QTc interval.
 J waves (also called Osborne waves) can
occur at any temperature < 32.3º C (90º F).
 Most frequently seen in Leads II and V6.
 The size of the J waves increase with
temperature depression.

“J” or Osborne Waves
“J” or Osborne Waves
“J” or Osborne Waves
Rewarming
 Methods
 Active
of Rewarming:
External Rewarming
 Active Internal Rewarming
Rewarming

Active Rewarming of MILD
Hypothermia:
Active external methods:
 Warm blankets
 Heat packs
 Warm water immersion (with caution)
 Active internal methods:
 Warmed IV fluids

Rewarming

Active Rewarming of SEVERE
Hypothermia:
Active external methods:
 Warm blankets
 Heat packs
 Warm water immersion (with caution)
 Active internal methods:
 Warmed IV fluids
 Warmed, humidified oxygen

Rewarming
Rewarming of the SEVERE
hypothermia patient is best carried out
in the Emergency Department using a
pre-defined protocol, unless travel time
exceeds 15 minutes.
 Most patients who die during active
rewarming die from ventricular
fibrillation.

Rewarming

Application of external heat in the
prehospital setting is usually not
effective and not recommended
because:
More heat transferrence is required than
generally possible in the prehospital
setting.
 Application of external heat may cause
“rewarming shock.”

Rewarming
 Rewarming
Shock:
Occurs due to peripheral reflex
vasodilation.
 Causes the return of cooled blood and
metabolic acids from the extremities.
 May cause a paradoxical afterdrop in the
core temperature further worsening
hypothermia.

Rewarming
 Rewarming
 Can
Shock:
be prevented in the prehospital
setting by using warmed IV fluids
during active rewarming.
Rewarming


Portable IV fluid heaters
are available in the
United States and
Canada.
Devices fit in-line and
are powered by DC
power sources.
Rewarming

The device is
single-use and
remains with the
patient in the
hospital (both the
ED and on the
floor).
Rewarming

The HOT IV is
powered from a
Physio-Control
battery or from a
DC converter
plugged in to an
AC outlet.
Issues in Hypothermia
 Benefits
of IV Fluid Warming:
 Maintains
euthermia
 Increases patient comfort
 Prevents shivering
Issues in Hypothermia
 Benefits
of IV Fluid Warming:
 Prevents
cold-induced dysrhythmias
 Decreases hemorrhage in abdominal
trauma patients
 Decreases the incidence of infectious
complications in abdominal trauma
patients
Issues in Hypothermia
 Benefits
 Allows
of IV Fluid Warming:
active internal rewarming to
begin in the prehospital setting.
 Less labor-intensive, freeing
emergency personnel to manage
other, more pressing care needs.
Cardiac Arrest
 Other
Clinical Concerns:
 Resuscitation
of cardiac arrest due to
hypothermia is only successful when
the patient is being re-warmed.
 The hypothermic cardiac arrest
patient is not DEAD until he is WARM
and DEAD!
Survival from Hypothermia
48.2º F (9º C)
- Lowest reported
survivor from therapeutic exposure.
 59.2º F (15.2º C) – Lowest reported
infant survival from accidental exposure.
 60.8º F (16º C) – Lowest reported adult
survival from accidental exposure.

Survival from Hypothermia
64.4º F (18º C) – Asystole.
 66.2º F (19º C) – Flat EEG.
 71.6º F (22º C) – Maximum risk for
ventricular fibrillation.
 77º F (25º C) – Cerebral blood flow
decreased by 66%.
 78.8º F (26º C) – No reflexes or
response to painful stimuli.

Issues in Hypothermia
 Other
Clinical Concerns:
 Hypothermia
is common, even in
persons with minor trauma.
 Hypothermia can worsen infectious
complications of abdominal trauma.
 Hypothermic trauma patients suffer
increased blood loss compared to
their normothermic cohorts.
Issues in Hypothermia

Considerations in Emergency Care:
“Most traditional methods of
maintaining trauma patient
temperature during prehospital
transport appear to be
inadequate.”
From: Watts DD, Roche M, et al. The utility of traditional
prehospital interventions in maintaining thermostasis.
Prehosp Emerg Care 1999;3(2)115-122
Issues in Hypothermia

Considerations in Emergency Care:
“Based upon our findings, accidental
hypothermia poses a relevant problem in
the prehospital treatment of trauma
patients. It is not limited to a special
season of the year.”
From: Helm M, Lampl L, Hauke J, Bock KH. Accidental
hypothermia in trauma patients. Is it relevant to preclinical
emergency treatment? Anaesthesist 1995;44(2):101-107
Issues in Hypothermia

Considerations in Emergency Care:
“Thus, hypothermia is common in
patients undergoing a laparotomy for
trauma. Hypothermic patients with
similar injury severity have greater
blood loss.”
From: Bernabei AF, Levision MA, Bender JS. The effects of
hypothermia and injury severity on blood loss during trauma
laparotomy. J Trauma 1992;33(6):835-839
Hyperthermia
 Heat
cramps
 Heat tetany
 Heat exhaustion
 Heat syncope
 Heat stroke
Hyperthermia
Abnormal
elevation in body
temperature.
 Not a normal
physiological
response (such
as fever).

Hyperthermia
Caused by
environmental
temperature
increase.
 Increased
humidity.
 Still air.

Hyperthermia



Heat waves not
uncommon.
More devastating
where heat waves
are uncommon.
600 heat-related
deaths in 1995
Chicago heat wave.
Heat Cramps





Brief, painful muscle
contractions.
Frequent complication
of heat exhaustion.
Salt depletion and other
electrolyte problems
commonly associated.
Self-limited.
Symptomatic treatment.
Heat Tetany



Carpopedal spasms
that occur in hot
environments.
Secondary to
hyperventilation
from body’s attempt
to cool.
Resolves when
hyperventilation
slows.
Heat Exhaustion


Results from
cardiovascular strain
as body attempts to
maintain normal
temperature.
Usually develops
and continues over
several days.
Heat Exhaustion



Most common
between body
temperature of
102.9° (39.4° C) and
104° (40° C).
Finding is unreliable.
Diagnosis should be
made on physical
assessment.
Heat Exhaustion
Firefighters at
increased risk of
developing heat
exhaustion.
 Rehab sector
essential for
major fires in
warm weather.

Heat Exhaustion

Symptoms:








Dizziness
Headache
Fatigue
Irritability
Anxiety
Chills
Nausea/vomiting
Heat cramps
Heat Exhaustion

Signs:
Tachycardia
 Hyperventilation
 Hypotension
 Syncope

Heat Exhaustion
 Treatment:
 Remove
patient from warm
environment.
 Remove bulky clothing.
 Fluids (IV or PO).
 Antiemetics
 Removal from duty.
Heat Syncope
Form of postural hypotension.
 Results from massive vasodilation.
 Dehydration usually a contributing
factor.
 Most common in persons not
acclimatized to the heat.
 Usually occurs during the early stages
of heat exposure.

Heat Syncope

Treatment:
Symptomatic
 Cool
 Fluids
 Rule out other
causes of
syncope.

Heat Stroke
Heat stroke is a
life-threatening
emergency!
 Heat stroke is a
total failure of
temperature
regulation.

Heat Stroke
Core temperature
>104.9° (40.5° C).
 Loss of sweating
(anhidrosis).
 Altered mental
status.

Heat Stroke


Anhidrosis may or
may not be present.
Just because a
patient is sweating
does not mean they
are not suffering
heat stroke.
Heat Stroke

Treatment must
include:
CPR if required.
 Fluid and
electrolyte
replacement.
 Immediate
cooling.

Heat Stroke




Goal of cooling is to get body temperature
down to 104° (40° C).
Preferred method is immersion in cold water
or ice-water bath.
Evaporative cooling (moistened sheets) and
ice packs) can be used but less effective.
Essential to remove from bath as soon as
target temperature reached to avoid
overcooling and activation of reflex
mechanisms.
Fever
Fever



Fever is not an abnormal increase in body
temperature.
It is a resetting of the body’s set-point above
normal.
Causes:



Abnormalities within the brain (tumors,
hemorrhage compress hypothalamus)
Dehydration
Toxic substances within the body (pyrogens).
Fever
 Definitions:
 Any
oral temp ≥ 98.9° (37.2° C) in
the early morning.
 Any oral temp ≥ 100° (37.8° C) at
any time.
Fever
 How
hot is high?
 Human
upper limit of fever is 105.8107.6°F (41–42°C).
 Almost never exceeds 42° C unless
there’s a failure in thermoregulation.
Fever
 How
hot is high?
 104°
(40° C) may be the upper limit of
fever in infants <12 weeks old.
 Remember that young infants can
have infections with normal or
lowered body temps.
Fever

Can high fever can
cause damage in
and of itself?


Seizures and
complications.
Brain damage
because of the
infection causing the
fever (meningitis or
encephalitis).
Fever


No human studies
published.
Animal studies
suggest that a body
temp of ≥ 107.5°
(42° C) in humans
may trigger enough
adverse effects on a
cellular level to
cause death.
Fever

Animal studies:


Temperature >105°
may cause
respiratory alkalosis
and occasional
electrolyte
imbalances
Temperature >105.8°
may cause cellular
swelling and damage
in the brain, kidneys
and liver
Fever
 When
set-point in hypothalamus
changes, it usually takes several
hours to reach new set-point.
 Signs and symptoms common
during this phase (blood
temperature lower than
hypothalamic set-point).
Fever
Fever is generally uncomfortable.
 Signs and Symptoms:

Chills
 Flushing of the skin
 Teeth chattering
 Feels cold
 Shivering
 Skin cold to touch (phase-dependent)

Fever
 It
is important to remember that
fever is a normal response to many
diseases.
 Although uncomfortable, it is rarely
harmful.
Febrile Seizures
 Incidence
of 2-5% in US.
 6 months – 3 years (median 18-22
months).
 Boys more often than girls.
 Often occurs with the first fever of
an illness.
Febrile Seizures
 Characteristics:
 85%
of all febrile seizures last for <15
minutes and don’t recur within 24
hours.
 50% have temp between 39°-40°C.
 25% have temp > 40°C.
Febrile Seizures:

Characteristics:
1/3 will have recurrence of febrile seizures.
 The younger the age at 1st febrile seizure,
the higher the incidence of recurrence.
 El-Radhi, 1998


Presenting temp <39° for 1st febrile seizure
have 2.5x risk for recurrence within the same
illness and 3x risk for recurrence with other
illnesses
Febrile Seizures


Simple febrile
seizures are
generalized tonicclonic with brief
post-ictal period.
Complex or atypical
febrile seizures can
be focal, atonic, or
prolonged
Febrile Seizures
 Multiple
studies
have revealed
several genetic
loci that code
for susceptibility
to febrile
seizures.
Febrile Seizures
 Fever
+ Seizure ≠ “Febrile Seizure”
 Meningitis/Sepsis
 Seizure
disorder
 Medication/Poison-induced
 Febrile
Seizure is NOT an EMS
diagnosis!
Febrile Seizure
 Myths:
 Rate
of temperature rise does not
appear to be a cause of febrile
seizures.
 No studies have demonstrated that
febrile seizures without complicating
hypoxia cause brain damage.
Febrile Seizures
 Myths:
 Febrile
 Risk



 If
seizures cause epilepsy.
factors for afebrile seizure:
Complex 1st Febrile Seizure.
Abnormal neuro state before 1st Febrile
Seizure.
Afebrile seizure history in parents or siblings
>2 risk factors, 10% chance of
developing “epilepsy”
Febrile Seizures
 Myths:
 Treating
the fever will prevent the
seizure.
 Antipyretics
are not protective.
 Rectal/oral diazepam at time of fever is
protective.
 Daily oral phenobarbital is protective but
has undesirable side effects.
Febrile Seizures

There is no
evidence that
bringing the fever
down by any
means will stop or
prevent a febrile
seizure.
Febrile Seizures
 Bottom
line:
 They’re
more scary than dangerous.
 Most resolve without anticonvulsant
treatment.
 Antipyretic treatment does not
prevent or treat febrile seizures.
 Not all seizures with fever are febrile
seizures.
Fever

Fever treatment:

Treatment of
choice is
antipyretics
(acetaminophen,
ibuproprofen).
Fever
There is no evidence to support one
antipyretic over another when
considering effectiveness
 No delivery route (po/pr) has been
proven more effective than another, but
there has been recent evidence to
suggest that higher doses may be
needed when given rectally.

Fever
 Acetaminophen
10-15 mg/kg po/pr
q4h.
 Ibuprofen 10mg/kg po q6-8h.
 No demonstrated benefit to
alternating the two meds but there
is a significant chance of dosing
error and possible overdose.
Fever
 Other
cooling methods:
 Never
use ice, cold water or alcohol.
 Use tepid water or cool compresses
over head and pulse points.
 Avoid inducing chills.
Fever
 Should
we treat fever?
 Animal
studies suggest that the fever
mechanism is a positive adaptive
response
 Triggers
host immune responses
 May stabilize cell membranes
Fever
 Should
we treat fever?
 Increased
metabolic stress and
oxygen demand:
 Patients
with poor cardiac reserve
 Patients with poor pulmonary reserve
 Lowers
the “seizure threshold”
Fever
 Reasons
 Patient
to treat fever:
comfort
 Parent comfort
Fever

Should EMS
providers treat
fever?
Fever

Should EMS providers treat fever?


Pros:
 Providing an additional service to our
customers.
 Comfort measure.
Cons:
 Treat and release?
 Documentation of fever.
 Dosing of meds.
 Reinforcement of fears.
Fever
Cultural
considerations.
 Relates to ancient
beliefs of “hot”
and “cold”
illnesses.

Fever

Summary:
Fever is not the clearly defined concept
many believe it to be.
 Both the lay public and the medical
community need more education about
fever.
 “Fever Phobia” is unfounded.
 Fever treatment by EMS personnel is
controversial.

Temperature Regulation

For more detailed
information on
temperature
regulation and
hypothermia, see
the March 2003
issue of JEMS
magazine.