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DOI: 10.1161/CIRCULATIONAHA.105.166566
2005;112;136-138; originally published online Nov 28, 2005; Circulation
Part 10.4: Hypothermia
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Part 10.4: Hypothermia
U
nintentional hypothermia is a serious and preventable
health problem. Severe hypothermia (body temperature
H1102130°C [86°F]) is associated with marked depression of
critical body functions that may make the victim appear
clinically dead during the initial assessment. But in some
cases hypothermia may exert a protective effect on the brain
and organs in cardiac arrest.
1,2
Intact neurologic recovery may
be possible after hypothermic cardiac arrest, although those
with nonasphyxial arrest have a better prognosis than those
with asphyxial-associated hypothermic arrest.
3–5
With this in
mind, lifesaving procedures should not be withheld on the
basis of clinical presentation.
4
Victims should be transported
as soon as possible to a center where monitored rewarming is
possible.
General Care for All Victims of Hypothermia
When the victim is extremely cold but has maintained a
perfusing rhythm, the rescuer should focus on interventions
that prevent further heat loss and begin to rewarm the victim.
These include the following:
●
Prevent additional evaporative heat loss by removing wet
garments and insulating the victim from further environ-
mental exposures.
●
Do not delay urgent procedures, such as intubation and
insertion of vascular catheters, but perform them gently
while closely monitoring cardiac rhythm. These patients
are prone to develop ventricular fibrillation (VF).
For patients with moderate to severe hypothermia, therapy
is determined by the presence or absence of a perfusing
rhythm. We provide an overview of therapy here and give
more details below. Management of the patient with moderate
to severe hypothermia is as follows:
●
Hypothermia with a perfusing rhythm
–Mild (H1102234°C [H1102293.2°F]): passive rewarming
–Moderate (30°C to 34°C [86°F to 93.2°F]): active exter-
nal rewarming
–Severe (H1102130°C [86°F]): active internal rewarming; con-
sider extracorporeal membrane oxygenation
●
Patients in cardiac arrest will require CPR with some
modifications of conventional BLS and ACLS care and
will require active internal rewarming
–Moderate (30°C to 34°C [86°F to 93.2°F]): start CPR, attempt
defibrillation, establish IV access, give IV medications spaced
at longer intervals, provide active internal rewarming
–Severe (H1102130°C [86°F]): start CPR, attempt defibrillation
once, withhold medications until temperature H1102230°C
(86°F), provide active internal rewarming
–Patients with a core temperature of H1102234°C (H1102293.2°F)
may be passively rewarmed with warmed blankets and a
warm environment. This form of rewarming will not be
adequate for a patient with cardiopulmonary arrest or
severe hypothermia.
6
–For patients with moderate hypothermia (30°C to 34°C
[86°F to 93.2°F]) and a perfusing rhythm and no preced-
ing cardiac arrest, active external warming (with heating
blankets, forced air, and warmed infusion) should be
considered (Class IIb). Active external rewarming uses
heating methods or devices (radiant heat, forced hot air,
warmed IV fluids, warm water packs) but no invasive
devices. Use of these methods requires careful monitoring
for hemodynamic changes and tissue injury from external
heating devices. Some researchers believe that active
external rewarming contributes to “afterdrop” (continued
drop in core temperature when cold blood from the
periphery is mobilized). But recent studies have indicated
that forced air rewarming (one study used warmed IV
fluids and forced air rewarming) is effective in some
patients, even those with severe hypothermia.
7,8
–For patients with a core body temperature H1102130°C (86°F)
and cardiac arrest, active internal rewarming techniques
(invasive) are needed. With or without return of sponta-
neous circulation, these patients may benefit from pro-
longed CPR and internal warming (peritoneal lavage,
esophageal rewarming tubes, cardiopulmonary bypass,
extracorporeal circulation, etc).
Modifications of BLS for Hypothermia
If the hypothermic victim has not yet developed cardiac
arrest, focus attention on warming the patient with available
methods. Handle the victim gently for all procedures; phys-
ical manipulations have been reported to precipitate VF.
4,9
If the hypothermic victim is in cardiac arrest, the general
approach to BLS management should still target airway,
breathing, and circulation but with some modifications in
approach. When the victim is hypothermic, pulse and respi-
ratory rates may be slow or difficult to detect. For these
reasons the BLS healthcare provider should assess breathing
and later assess the pulse for a period of 30 to 45 seconds to
confirm respiratory arrest, pulseless cardiac arrest, or brady-
cardia that is profound enough to require CPR.
10
If the victim
is not breathing, start rescue breathing immediately. If pos-
sible, administer warmed (42°C to 46°C [108°F to 115°F])
humidified oxygen during bag-mask ventilation. If the victim
is pulseless with no detectable signs of circulation, start chest
compressions immediately. If there is any doubt about
whether a pulse is present, begin compressions.
The temperature at which defibrillation should first be
attempted in the severely hypothermic patient and the number
(Circulation. 2005;112:IV-136-IV-138.)
? 2005 American Heart Association.
This special supplement to Circulation is freely available at
http://www.circulationaha.org
DOI: 10.1161/CIRCULATIONAHA.105.166566
IV-136
of defibrillation attempts that should be made have not been
established. But if ventricular tachycardia (VT) or VF is
present, defibrillation should be attempted. Automated exter-
nal defibrillators (AEDs) may be used for these patients. If
VF is detected, it should be treated with 1 shock then
immediately followed by resumption of CPR, as outlined
elsewhere in these guidelines for VF/VT (see Part 5: “Elec-
trical Therapies: Automated External Defibrillators, Defibril-
lation, Cardioversion, and Pacing”). If the patient does not
respond to 1 shock, further defibrillation attempts should be
deferred, and the rescuer should focus on continuing CPR and
rewarming the patient to a range of 30°C to 32°C (86°F to
89.6°F) before repeating the defibrillation attempt. If core
temperature is H1102130°C (86°F), successful conversion to nor-
mal sinus rhythm may not be possible until rewarming is
accomplished.
11
To prevent further core heat loss, remove wet garments and
protect the victim from further environmental exposure.
Insofar as possible this should be done while providing initial
BLS therapies. Beyond these critical initial steps, the treat-
ment of severe hypothermia (temperature H1102130°C [86°F]) in
the field remains controversial. Many providers do not have
the time or equipment to assess core body temperature or to
institute aggressive rewarming techniques, although these
methods should be initiated when available.
4,9,12,13
Modifications to ACLS for Hypothermia
For unresponsive patients or those in arrest, endotracheal
intubation is appropriate. Intubation serves 2 purposes in the
management of hypothermia: it enables provision of effective
ventilation with warm, humidified oxygen, and it can isolate
the airway to reduce the likelihood of aspiration.
ACLS management of cardiac arrest due to hypothermia
focuses on more aggressive active core rewarming techniques
as the primary therapeutic modality. The hypothermic heart
may be unresponsive to cardiovascular drugs, pacemaker
stimulation, and defibrillation.
9
In addition, drug metabolism
is reduced. There is concern that in the severely hypothermic
victim, cardioactive medications can accumulate to toxic
levels in the peripheral circulation if given repeatedly. For
these reasons IV drugs are often withheld if the victim’s core
body temperature is H1102130°C (86°F). If the core body temper-
ature isH1102230°C, IV medications may be administered but with
increased intervals between doses.
As noted previously, a defibrillation attempt is appropriate
if VF/VT is present. If the patient fails to respond to the initial
defibrillation attempt or initial drug therapy, defer subsequent
defibrillation attempts or additional boluses of medication
until the core temperature rises above 30°C (86°F).
9
Sinus
bradycardia may be physiologic in severe hypothermia (ie,
appropriate to maintain sufficient oxygen delivery when
hypothermia is present), and cardiac pacing is usually not
indicated.
In-hospital treatment of severely hypothermic (core tem-
perature H1102130°C [86°F]) victims in cardiac arrest should be
directed at rapid core rewarming. Techniques for in-hospital
controlled rewarming include administration of warmed,
humidified oxygen (42°C to 46°C [108°F to 115°F]), warmed
IV fluids (normal saline) at 43°C (109°F), peritoneal lavage
with warmed fluids, pleural lavage with warm saline through
chest tubes, extracorporeal blood warming with partial by-
pass,
4,9,12,14,15
and cardiopulmonary bypass.
16
During rewarming, patients who have been hypothermic
for H1102245 to 60 minutes are likely to require volume adminis-
tration because the vascular space expands with vasodilation.
Routine administration of steroids, barbiturates, and antibiot-
ics has not been documented to increase survival rates or
decrease postresuscitation damage.
17,18
If drowning preceded hypothermia, successful resuscita-
tion is unlikely. Because severe hypothermia is frequently
preceded by other disorders (eg, drug overdose, alcohol use,
or trauma), the clinician must look for and treat these
underlying conditions while simultaneously treating the
hypothermia.
Withholding and Cessation of
Resuscitative Efforts
In the field resuscitation may be withheld if the victim has
obvious lethal injuries or if the body is frozen so that nose and
mouth are blocked by ice and chest compression is
impossible.
19
Some clinicians believe that patients who appear dead after
prolonged exposure to cold temperatures should not be
considered dead until they are warmed to near normal core
temperature.
10,11
Hypothermia may exert a protective effect
on the brain and organs if the hypothermia develops rapidly
in victims of cardiac arrest. When a victim of hypothermia is
discovered, however, it may be impossible to distinguish
primary from secondary hypothermia. When it is clinically
impossible to know whether the arrest or the hypothermia
occurred first, rescuers should try to stabilize the patient with
CPR. Basic maneuvers to limit heat loss and begin rewarming
should be started. Once the patient is in the hospital, physi-
cians should use their clinical judgment to decide when
resuscitative efforts should cease in a victim of hypothermic
arrest.
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IV-138 Circulation December 13, 2005