Accidental hypothermia
Author(s): Philip Miller MD,
CCFP(EM)
Date Created: July 2012
Global Health Emergency Medicine Teaching Modules by GHEM is licensed under
a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License.
Learning Objectives
 Understand the physiology of hypothermia
 Recognize predisposing factors
 Have an approach to the management of
accidental hypothermia
 Understand the treatment of cardiac arrest
scenarios
Hypothermia
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Epidemiology and Definitions
Pathophysiology
Clinical features
General approach
Advanced cardiac life support
Rewarming
Key Concepts
 Hypothermia simplified:
 Take precautions to prevent ventricular
fibrillation (VF)
 Optimize conditions for return of
spontaneous circulation (ROSC) in cardiac
arrest scenarios
 Identification and treatment of precipitants
 Use of appropriate rewarming techniques
Case
 2 year old, with Grandma who lost track of him by
a lake
 Found 2 hrs later, face down in the lake
 No pulse, not breathing
 Brought to Emergency Room
 Rectal temperature 19°C
 Asystole
 How do you manage this patient?
 Should you intubate him?
 How long should you continue resuscitative efforts?
What is hypothermia?
 Definition: core temperature less than 35ºC
Epidemiology
 Actual incidence is not known and underreported
 Survival has been reported as low as 32%
from avalanche victims and 70% in patients
with alcohol or other drug intoxication
Pathophysiological progression
 32-37ºC: vasoconstriction, shivering, and
nonshivering thermogenesis (increase in
basal metabolic rate)
 24-32ºC: decreased basal metabolic rate,
less shivering
 <24º: autonomic and endocrinological
mechanisms for heat generation fail
Approach to accidental hypothermia
Goal: optimize heart for ROSC
Approach to accidental hypothermia
Cardiac arrest (usually
VF or asystole)
Signs of life
CPR
Defibrillate if indicated
Rewarming techniques
Post-warming care
Identify and treat
underlying precipitants
Hypothermia myths
 Hypothermia ‘only occurs in winter’
 Hypothermia ‘only occurs in northern
latitudes, and high altitude’
 Although less common, hypothermia does
occur in summer months, and in warm
climates
Accidental hypothermia - etiology
Wilderness setting
Cold exposure
Submersion
Immersion
Urban setting
Trauma
Homicide or suicide
Alcohol and drugs of abuse
Sepsis/ infection
DKA
Mountain Accidents
Hypoglycemia
Psychiatric illness
Metabolic – thyroid, Addison’s
Epidemiology of predisposing
factors
Predisposing factors
(%)
Predisposing factors
in those who died (%)
Major medical illness
44
16
Injury/ trauma
19
19.5
Infection
18
37.3
Submersion
9
27.8
Overdose
6
8
Frostbite
8
22.6
Danzl, Ann Emerg Med 1987
Mortality
Core Temperature
Mortality (%)
< 32°C
23
> 32°C
7
Overall
17
Danzl, Ann Emerg Med 1987
Factors that affect thermoregulation:
 Decreased heat production
 Increased heat loss
 Impaired thermoregulation
Decreased heat production
 Endocrinologic failure – hypopituitarism,
hypoadrenalism, hypothyroidism
 Malnutrition and decreased subcutaneous fat
 Neonates: less subcutaneous tissue,
ineffective shivering mechanisms, lack
behavioural defense mechanisms
 Elderly: decreased ability to sense cold,
decreased adaptive behavioural mechanisms
Increased heat loss
 Exposure during resuscitation
 Cold saline infusions
 Loss of skin barrier (eg burns, skin
conditions)
 Ethanol
Impaired thermoregulation
 Centrally mediated lesions (subdural
hematoma, malignancies, CVAs)
 Medications (antidepressants,
antipsychotics, anxiolytics)
Normal physiological response
 Shivering can double heat production and
increase basal metabolic rate by 2-5x
 However, increased heat production can
only last a few hours because of fatigue
and glycogen depletion
How is heat lost?
 Radiation – transfer by electromagnetic waves
 Conduction – transfer by direct physical
contact
 Convection – heat loss to air and water vapour
molecules circulating around the body
 Evaporation – conversion of liquid to gas (eg
sweat on body)
 Respiration
Hemodynamic changes
 Progressive bradycardia (usually refractory
to atropine)
 Progressive decreased mean arterial
pressure
 Decreased cardiac index
ECG changes
 Osborn (J) wave – may
appear at any temperature
under 32ºC
 Increasing PR interval
 Increasing QRS interval
 Long QT interval
 Artifact from shivering may
obscure ECG
Graham 2001
http://en.wikipedia.org/wiki/Osborn_wave
Dysrhythmias
 Cardiac rhythm disturbances can be from
many factors
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Acid base disturbances
Hypoxia
Sensitization of conduction system
Decreased refractory period
Dysrhythmias
 Atrial fibrillation
 Ventricular fibrillation
 Can be related to physical jostling, autonomic
dysfunction, hypoxia, acid-base disturbances
 Decreased threshold for ventricular
dysrhythmias
 Asystole can happen spontaneously below
25ºC
Mechanical trauma causing VF?
 Anecdotal reports in humans but limited
evidence
 A 2007 study on induced hypothermia in
pigs:
 Once below 25°C, 5/10 pigs developed VF
 Below 25°C, 2/10 pigs developed VF after
mechanical trauma (dropping backboard from
6 and 12 inches)
Grueskin 2007
Dysrhythmias
Graham 2001
Mean core
temp (C)
% of ECGs
% died
Normal sinus
rhythm
34.3
41
31
Sinus
tachycardia
33.0
7
8
Sinus
bradycardia
32.3
12
4
Atrial
fibrillation
31.0
25
35
Junctional
bradycardia
30.5
5
12
Renal effects
 Cold diuresis:
 Kidneys excrete dilute urine
 Cold water immersion may increase urine
output by 3.5 times
Danzl 2010
Coagulation effects
 Impaired enzymatic activity of clotting
cascade (from cold)
 Increased fibrinolytic activity
 Platelet sequestration
 Also hypercoagulability and intravascular
clotting
Danzl 2010
Laboratory features
 Arterial blood gas can give a falsely
elevated pO2 and pCO2 and falsely lower
pH
 Falsely elevated hematocrit as a result of
decreased plasma volume
Danzl 2010
Lab features
 Lab tests are done at 37ºC, so there may
be a clinically evident coagulopathy, but
normal coagulation studies
 Can see leukopenia and thrombocytopenia
 Lactate levels may be very high but not
necessarily correlated with mortality
Danzl 2010
Hypothermia
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
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
Epidemiology and Definitions
Pathophysiology
Clinical features
General approach
Advanced cardiac life support
Rewarming
What are some clinical features of
hypothermia?
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Confusion
Dizziness
Dyspnea
Uncoordination
Apathetic
Paradoxical undressing
Decreased level of consciousness
Danzl 2010
Hypothermia Swiss Staging System
 Stage 1 - Conscious, shivering
 Usually 32-35°C
 Stage 2 - Impaired consciousness, not
shivering
 28-32°C
 Stage 3 - Unconscious, not shivering, vital
signs present
 24-28°C
 Stage 4 - No vital signs
 < 24°C
Brown 2012
General Principles of Management
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Prevent further cooling
Accurate temperature measurement
ABCs
Advanced cardiac life support
Rewarming techniques
Identify and treat precipitants
Prehospital initial management
 Remove all wet clothing
 Rewarm patient with blankets and possibly
reflective foil wrapping
 Accurate core temperature measurement may
be difficult in the field
 Be careful moving patients – cold heart is
prone to VF
 Insulate patient from further heat loss
When to withhold (not start)
resuscitation
 Obvious lethal injuries
 Frozen head and mouth and blocked with
ice
 Frozen and CPR not possible
Danzl 2010
ABCs
 Intubation
 Theoretical risk of inducing VT - but this is not
seen in prospective observational studies
 May be very difficult if pt is extremely cold/rigid
 Pulse check for 30-60s (pulse and respirations
can be difficult to detect in the hypothermic
patient)
 If possible, give warmed humidified O2 during bagmask-valve
 CPR/ defibrillation
Advanced cardiac life support
 ‘The temperature at which defibrillation
should occur, and the number of attempts
has not been established’
Vanden Hoek 2010
Advanced cardiac life support
(ACLS)
 ACLS medications may not work in the
hypothermic heart
 Drug metabolism is theoretically decreased
and may build up to toxic levels
Vanden Hoek 2010
Advanced cardiac life support
 Oral medications won’t work effectively
because of decreased GI motility
 Intramuscular medications won’t work
effectively because of peripheral
vasoconstriction
Danzl 2010
Medications
 Most dysrhythmias convert with rewarming
 Defibrillation attempts are usually
ineffective below 28-30ºC
Danzl 2010
Dysrhythmias
 Bradycardias – usually physiologic
 Pacing not needed unless hemodynamic
compromise persists after rewarming
 Atrial fibrillation usually converts with
warming
 Ventricular fibrillation
 Lidocaine and procainamide don’t work very
well in hypothermia
 Evidence is limited for medications in VF
Vanden Hoek 2010
Soar 2010
Current recommendations
 For patients < 30°C, it is reasonable to
shock if in VT/VF
 Further shocks are ‘reasonable’ along with
warming strategies
 Current benefit of medications in humans
under 30°C not known, although animal
studies suggest a benefit
Vanden Hoek 2010
Comparing different guidelines
 American Heart Association Guidelines
 The value of more than 1 shock if < 30°C is
not known
 May be reasonable to perform further
defibrillation attempts
 European Resuscitation Council Guidelines
 Consider 3 defibrillation attempts if < 30°C
 If not successful, consider withholding further
until temp > 30°C
Brown 2012
Overview of accidental hypothermia
Cardiac arrest (usually
VF or asystole)
Signs of life
Rewarming techniques
CPR
Defibrillate if indicated
Rewarming techniques
Goal: optimize heart for return of spontaneous
circulation and normal sinus rhythm
Post-warming care
Identify and treat
underlying precipitants
IV fluids
 Patients are usually hypovolemic and
should receive warmed saline solution,
heated to 40ºC
 Can microwave IV bags – 2 mins on high
power for 1L
 There is significant loss of heat through IV
tubing
 Ringer’s lactate is inefficiently metabolized
by the liver
Danzl 2010
Measuring temperature
 Continuous core temperature is important (rectal
temperature can lag behind core temperature
changes, and difficult if ongoing CPR)
 Tympanic temperature equilibrates most rapidly
with core temperature, but is less accurate, and
has more variability
 Esophageal probe is ideal, but rarely available
in the prehospital setting or low resource setting
Core temperature afterdrop
 Further drop in patient’s core temperature
after removal from cold
 Caused by countercooling of blood, and
rewarming of extremities
Danzl 2010
Rewarming definitions
 Passive external rewarming
 Letting the patients warm themselves
Conscious, shivering
Remove wet clothing
Apply dry blankets
 Active external rewarming
 Applying heat to the patient externally
Impaired consciousness,
unconscious, or no vital signs
Brown 2012
Forced air
heating systems
or warm blankets
Warm air device – ‘Bair Hugger’
Rewarming definitions
 Active internal rewarming
 Minimally invasive
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Warmed O2
Warmed IV fluids
Bladder lavage
Gastric/ Bowel lavage
Impaired
consciousness or
unconscious
Unclear when to start
 Invasive – local resource-dependent
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Brown 2012
ECMO
CPB
Thoracic lavage*
Dialysis
Peritoneal lavage
No vital signs
The cardiac arrest patient in low
resource settings
No pulse
CPR and ACLS
ECMO available?
Cardiopulmonary bypass available?
Thoracic
lavage?
Peritoneal lavage?
Dialysis?
Resource poor settings
 Decisions about duration of resuscitation,
intubation, thoracic lavage, and other
invasive modalities for rewarming should
be tailored to the availability of resources,
and local practice
Airway and rewarming management
in resource-limited settings
 On one hand, patients who arrive in cardiac
arrest have poor outcomes, and intubation
in certain cases may be an unjustified use
of resources (in resource-limited settings)
 On the other hand, hypothermia is an
instance where good neurological
outcomes have been documented, and
aggressive treatment may be warranted
Minimally invasive internal
rewarming techniques
 Airway rewarming - does very little to
increase core temperature (about
1.5°C/hr)
 Gastric/bowel/ bladder lavage also does
very little to increase core temperature
because of large surface area to warm
 Warmed IV solutions do nothing to warm
patient, but should be used to prevent
further heat loss from cold IVs
Vanden Hoek 2010
Brown 2012
Cardiopulmonary bypass
 Is the most rapid and efficient method
 Provides simultaneous rewarming and
circulatory support
 Rewarming rates as high as 1–2°C every
3–5 min have been reported
 Not as useful in patients with trauma or
known coagulopathy as anticoagulation is
needed
Vanden Hoek 2010
Walpoth 1997
Brodman 2011
Brown 2012
Thoracic lavage
 Rates of 3-6°C/ hr have been reported
 In patient in cardiac arrest, can put 2 chest
tubes bilaterally (i.e. 4 in total)
 If putting chest tubes in a patient with a
pulse, can put 2 chest tubes to right chest
(i.e. 2 in total)
 Right-sided chest tubes because if pt has a
pulse, there is a possibility to induce VF with
left sided chest tubes
Plasier 2005
Thoracic lavage method
 2 large bore chest tubes to each
hemithorax
 1 directed anteriorly – Warm fluid flows in
 1 directed posteriorly – Allows fluid to drain out
 Drainage by gravity into chest tube
drainage reservoir
 Previous thoracic surgery/ infections and
adhesions may make the procedure
impossible
Plasier 2005
http://www.ebmedicine.net/topics.php?paction=showTopicSeg&topic_id=179&seg_id=3771 (accessed Mar 4th, 2013)
Thoracic lavage method
 Heat saline bags via microwave or level 1
infuser (tap water use has been reported)
 Monitor input and output to avoid
intrathoracic hypertension
 On completion, remove anterior chest tube
and then remove posterior chest tube after
complete drainage
Plasier 2005
How to connect the tubing??
One option: can use the adapter on NG tubes to
connect the chest tube to the saline tubing
Connect anterior chest tube to warmed saline
Connect posterior chest tube to regular chest tube setup
http://emcrit.org/podcasts/severe-accidental-hypothermia/ (accessed Mar 4 2013)
Dialysis/ peritoneal lavage
 Dialysis – can insert a hemodialysis
catheter, and dialysis machine will warm
blood
 Peritoneal lavage – can call General
Surgery for insertion
Rewarming rates
Brown 2012
Technique
Rewarming rates
Cardiopulmonary
bypass
9-18°C / Hr
Thoracic lavage
3-6°C/Hr
Peritoneal lavage
2-3°C/ Hr
Warmed IV solutions
0°C / Hr
Shivering
1.5°C / Hr
Blankets
2°C / Hr
Warmed O2
1.5°C/ Hr
Ongoing management
 If intubated:
 Nasogastric tube
 Indwelling foley catheter and continous urine
output measurement
 Continuous cardiac monitoring
 Try to avoid central venous catheters – can
increase risk of dysrhythmias
Bloodwork
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Complete blood count and differential
Electrolytes
Creatinine
Glucose
Serum calcium, magnesium, amylase, lipase
Coagulation studies
Toxicology screen, thyroid studies
Blood cultures
Remember the common causes...
 Associated illness with accidental
hypothermia:
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Trauma – iatrogenic or wilderness related
Psychiatric – mental illness, suicide attempt
Drug related – alcohol and others
Infectious – many causes
Metabolic: hypoglycemia, hypothyroidism,
adrenal insufficiency
Failure to rewarm
 May be reasonable to attempt
methylprednisolone or hydrocortisone,
because cold exposure can induce adrenal
unresponsiveness
 Empiric thyroxine should be reserved for
suspected myxedema coma
Danzl 2010
Empiric antibiotics?
 Rewarming rates seem to be related to
underlying etiology
 Patients with underlying infections (HIV,
sepsis, pneumonia) tend to rewarm at
much slower rates than those with
underlying hypoglycemia, intoxication, or
immersion
 It may be appropriate to administer empiric
antibiotics in certain situations
Delaney 2006
When to stop warming
 “When they’re warm and dead”
 Exact core temperature of when to stop is
not known – no evidence
 If you have achieved temp of 30-32°C and
they remain in asystole, it is reasonable to
stop*
Vanden Hoek 2010
Brown 2012
Case resolution
 2 year old with core temperature 19°C
 Intubated, warm fluids, warm O2, warm air
device
 Ambient temperature of room increased
 Received warm fluid peritoneal lavage
 CPR ongoing for 6 hrs
 Temperature reached 34°C with persistent
asystole
 Patient pronounced dead
Quiz Question 1
 Name 6 types of active invasive internal
rewarming?
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Cardiopulmonary bypass
ECMO
Dialysis
Thoracic lavage
Peritoneal lavage
Bowel/ bladder irrigation
Quiz Question 2
 Name 5 factors associated with accidental
hypothermia?
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Sepsis/ infection/ HIV/ TB
Metabolic causes (hypoglycemia, DKA)
Psychiatric illness
Homicide or suicide
Alcohol and drug related causes
Trauma/ submersion/ immersion/ avalanche
Quiz Question 3
 Which of the following is false?
 A) It is possible to induce VF iatrogenically
 B) medical mercury thermometers are accurate at all
temperature ranges
 C) Most dysrhythmias will resolve with rewarming
 D) Warmed O2 and warmed IV solutions are
ineffective methods of rewarming
 E) Thoracic lavage is an effective rewarming
technique in the pulseless patient
Summary






Prevent further cooling
Accurate temperature measurement
ABCs
Advanced cardiac life support
Rewarming techniques
Identify and treat precipitants
Accidental hypothermia - etiology
Wilderness setting
Cold exposure
submersion
Urban hypothermia
Trauma
Homicide or suicide
Alcohol and drugs of abuse
immersion
Sepsis/ infection
DKA
avalanche
Hypoglycemia
Psychiatric illness
Metabolic – thyroid, Addison’s
Overview of accidental hypothermia
Cardiac arrest (usually
VF or asystole)
Signs of life
Rewarming techniques
CPR
Defibrillate if indicated
Rewarming techniques
Goal: optimize heart for return of spontaneous
circulation and normal sinus rhythm
Post-warming care
Identify and treat
underlying precipitants
General References
 Journal Articles:
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Vanden Hoek TL et al. Cardiac Arrest in Special Situations : 2010 American
Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency
Cardiovascular Care. Circulation 2010, 122:S829-S861.
Brown D et al. Accidental Hypothermia. N Engl J Med 2012; 367;20:1930-1938.
Danzl DF et al. Multicenter hypothermia survey. Ann Emerg Med September
1987;16:1042-l055)
Grueskin J et al. A Pilot Study of Mechanical Stimulation and Cardiac
Dysrhythmias in a Porcine Model of Induced Hypothermia. Wilderness and
Environmental Medicine 2007, 18:133-137.
Graham C et al. The electrocardiogram in hypothermia. Wilderness and
Environmental Medicine 2001, 12:232-235.
Walpoth BH et al. Outcome of survivors of accidental deep hypothermia and
circulatory arrest treated with extracorporeal blood warming. N Engl J Med
1997;337:1500-5.
General References
 Journal Articles cont.
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Brodmann MM et al. The Bernese Hypothermia Algorithm: A consensus paper on in-hospital
decision-making and treatment of patients in hypothermic cardiac arrest at an alpine level 1 trauma
centre Injury, Int. J. Care Injured 2011;42: 539–543.
Delaney KA et al. Rewarming Rates in Urban Patients with Hypothermia: Prediction of Underlying
Infection. Academic Emergency Medicine 2006; 13:913–921.
Vretenar VF et al. Cardiopulmonary bypass resuscitation for accidental hypothermia. Ann Thorac
Surg 1994;58:895-898.
Plaisier BR. Thoracic lavage in accidental hypothermia with cardiac arrest — report of a case and
review of the literature. Resuscitation 2005; 66: 99–104.
Soar J et al. European Resuscitation Council Guidelines for Resuscitation 2010 Section 8. Cardiac
arrest in special circumstances: Electrolyte abnormalities, poisoning, drowning, accidental
hypothermia, hyperthermia, asthma, anaphylaxis, cardiac surgery, trauma, pregnancy, electrocution.
Resuscitation 81 (2010) 1400–1433.
 Chapters in Textbooks:

Danzl DF. (2010). Accidental Hypothermia. Marx JA, Hockberger RS, Walls RM (eds). Rosen's
Emergency Medicine: Concepts and Clinical Practice. (pp 1868-1881). Philadelphia, PA.
 Web Links:

Severe Accidental Hypothermia [http://emcrit.org/podcasts/severe-accidentalhypothermia/]. Accessed July 3, 2012.