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Hypothermia
By
Paul Rega MD, FACEP
Key Celsius/Fahrenheit
Conversions
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19°C
20°C
25°C
28°C
30°C
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=
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66°F
68°F
77°F
82°F
86°F
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32°C
33°C
34°C
35°C
43°C
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90°F
91°F
93°F
95°F
109°F
Diagnosis of Hypothermia
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Requires
• 1) High index of suspicion
• 2) Low-reading thermometer (down to
25°C)
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At least 10cm into rectum
Check for fecal cache
• Impaction will give a falsely elevated reading
Definition
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Core temperature <35º C (95º F)
Mild: 32.1º C-35º C
Moderate: 28º C-32º C
Severe: <28º C
Classification
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Accidental
• Primary: Patients with normal intact
thermoregulatory system
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Usually exposed to extreme cold
• Secondary: Patients with impaired
thermoregulatory system
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Intentional
Frequency
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700 die annually from accidental
primary hypothermia
Majority
• Urban setting due to environmental
exposure
• Aggravated by homelessness, illicit drug
use, alcoholism, mental illness
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Minority
• Outdoor setting: hunters, swimmers,
hikers, etc.
Mortality
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Mild (32-35° C): No significant
morbidity/mortality
Moderate (29° C-32° C): 21%
mortality
Severe (<28° C): Even higher
mortality rate
Hypothermia and Trauma
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38,520 trauma patients (2000-2002)
• 16 yo and greater
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1,921 (5%) hypothermic on
admission
Hypothermia independently tripled
chances of death
Isolated head injury: hypothermia
associated with >twice risk of death
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CCM 33:1296-1301
At risk populations
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Very young/elderly
• May present with symptoms not
clinically obvious (e.g. altered mental
status)
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Those with decreased muscle mass
Trauma, burns, and other stressors
worsen body’s response to cold.
Normal Physiology
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Body regulates core temp through
mechanisms of heat loss and heat
gain
Hypothalamus controls
thermoregulation
Rest: 40-60kcal heat/m² produced
Shivering: Heat production increases
2-5 times
Hindered by endocrine derangements
Heat Loss
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Conduction (Transfer of heat from body to environment)
• Water has 25-35 times heat conduction ability of air
Convection
• Heat transfer from movement of liquid or gases over a victim
• e.g. Wind chill
Conduction + convection: 15% heat loss
• Cold water immersion increases conductive heat loss up to 25
times
Radiation (Heat transfer by electromagnetic waves through
space)
• 55-65% of heat loss
Evaporation (sweat, exhaled breath)
• Heat loss from conversion of water to a gas
• Respiration + evaporation: Remainder of heat loss
Heat Gain
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Peripheral vasoconstriction
Increased metabolic rate
Shivering
Behavior
• Warm clothes
• Removal from cold environment
Hypothermic Predisposing Factors
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Impede circulation
• Dehydration, DM, Peripheral vascular
disease, tight clothes, tobacco
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Increase heat loss
• Burns, skin diseases, environment,
alcohol/drugs, infancy,
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Decrease heat production
• Endocrine failure, hypoadrenalism,
hypoglycemia, hypopituitarism,
hypothyroidism, infancy, old age,
malnutrition
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Impair thermoregulation
• DM, Parkinson’s, spinal cord injuries, stroke
Answer
Answer
CNS in Hypothermia
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All organ systems affected
<33°C: Abnormal brain activity
19°-20°C: EEG consistent with brain death
Cardiovascular Response in
Hypothermia
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Osborne J waves
T-wave inversion
Prolonged PR, QRS, and QT intervals
Bradycardia, slow a fib, v fib, asystole
• Bradycardia: Decreased depolarization of
pacemaker cells
 Refractory to atropine since not vagally
mediated
• Atrial/ventricular arrhythmias
• 25°C: Asystole/ventricular fibrillation
Increased risk of thrombosis and embolism
• Due to decreased intravascular volume and
increased blood viscosity
Osborne or J wave was first described in 1938. It is
best seen in leads aVL, aVF, and the lateral chest leads.
Its presence is suggestive of, but no pathognomonic for,
hypothermia. May appear at temperatures below 32°C.
Bradycardia appears in 50% of patients with
temperatures below 28°C.
The presence of acute atrial fibrillation often precedes
ventricular fibrillation.
These rhythms may be refractory to
electricity and drugs in severe
hypothermia
Pulmonary Response in
Hypothermia
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Rate initially increases then decreases below
32ºC.
Tidal volume decreases
Cough/gag reflexes fail
Risk of aspiration grows
Decreased O2 delivery to tissues
Higher O2 and CO2 levels and a lower pH than a
patient’s actual values because analyzers warm
blood to 37 °C
Interpret uncorrected ABGs (i.e. at the patient’s
core temp)
Aspiration pneumonia and pulmonary edema:
common
Renal Response
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Loss of ability to concentrate urine
Cold diuresis initially result of increased
blood flow to kidneys with peripheral
vasoconstriction
Volume depletion can result in decreased
renal blood flow.
Decreased renal blood flow (depressed by
50% at 27°-30°C) and increased tissue
breakdown products
• Acute tubular necrosis
• Renal failure
Mild Hypothermia (32°-35° C)
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Lethargy
Increased metabolic activity
Superficial vessels constrict
Confusion
• Altered judgment, amnesia, dysarthria: <34 °C
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Shivering
• Greatest between 34 °-35 °C
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Loss of fine motor coordination
Ataxia & apathy at 33 °C
Respiratory rate may be higher
Pulse/blood pressure intact
• May be increase in CO, Heart rate, and B/P
Moderate Hypothermia
(28°-32° C)
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Delirium
Stupor
Shivering dissipates
Metabolic activity slows
Drop in O2 and CO2 production
Slowed reflexes
Drop in CO, heart rate, B/P
Arrhythmias may begin at 30 °C
• Atrial fibrillation
• Ventricular hyperactivity
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Pupils dilate and minimally react to light (may
mimic death)
Severe Hypothermia
(<28° C)
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Very cold skin
Unresponsive
Coma
Difficulty breathing to apnea
Shock
Arrhythmias
• Markedly susceptible to v. fib.
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Rigidity
Pupils fixed
General Care
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Remove wet clothes
Insulate victim from environment
Don’t delay urgent procedures (e.g.
intubation, IVs)
Remember: Because of rigidity of
jaw and chest wall, it may be next to
impossible to intubate orotracheally
as well as to ventilate a patient.
Caution
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Perform procedures gently
Monitor cardiac rhythm
• May go into V. fib.
Rewarming Techniques
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Passive external
Active external
Active internal (core)
Passive External Rewarming
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Usually adequate for mild hypothermia
Place in warm environment
Remove wet clothing
Cover with blankets
Rewarming rate: 0.5°C-1°C/hour
Active External Rewarming
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Added for moderate-severe hypothermia
Hot water bottles to groin/axillae (43°C)
Radiant heaters
Heating pads, circulating hot water
mattresses
Forced air rewarming
• Rewarming rate: 2.4°C/hour
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Warm IV solutions
Rate: 1°C-2.5°C/hour
Complications of External
Rewarming
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Core Temp afterdrop: Cold blood
returning from periphery further cools
body core
Rewarming acidosis: Cold blood returning
from periphery brings lactic acid with it.
Rewarming shock: Relative hypovolemia
occurs secondary to peripheral
vasodilatation
Note: Complications minimized using
combo of external rewarming with active
core rewarming.
Active Core Rewarming
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Core temp <30°C
Best especially if core temp is <30ºC or
cardiac instability is present
Techniques
• Warmed (42°C-45°C) humidified O2
• Warmed (42°C-44°C) IV fluids (D5NS
preferred): 150-200cc/hr
• Gastric, colonic, bladder, peritoneal lavage
(40°C-45°C) with warm saline potassium-free
solutions
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Rewarming rate: 1°C-3°C/hour
Active Core Rewarming
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Closed thoracic cavity lavage
• Chest tube anteriorly, chest tube posteriorly
• 14 cases (8-72 yrs of age): Thoracic cavity
lavage
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Mean core temp: 24.5°C
most without B/P or pulse
Predominant rhythm: V. fib.
7: Thoracotomy; 7: thoracostomy
Median rewarming rate: 2.95°C/hour
Median time to sinus rhythm: 120 min.
Median length of hospital stay: 2 weeks
4 died
Survivors: 8 neurologically intact; 2 with residual
impairments
Active Core Rewarming
(Extracorporeal)
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Hemodialysis, AV rewarming, VV rewarming
Cardiopulmonary bypass (CPB)
• Provides central rewarming and circulatory support
• 32 patients (mean age: 25.2 years)
• Mean time from discovery to CPB: 141 min.
• 15 long-term survivors
 All in cardiopulmonary arrest at hospital
 All intubated and receiving CPR prior to hospital
 Mean core temp rose from21.8°C to 35.6°C within
97.9 min after rewarming (other CPB reports:
8°C-10°C/hour)
 Follow-up: no or minimal cerebral impairment
• Keys to success:
 Hypothermia: deep
 No prior hypoxic brain damage prior to
hypothermia
 Young
 Great medical infrastructure in Switzerland
 Hypothermia maintained prior to CPB
Key Points
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Method of rewarming dependent on
core temp and patient stability
Active rewarming recommended with
life-threatening dysrhythmias
All hypothermic patients must be
examined for any trauma or
underlying medical condition
Pre-hospital Care
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Avoid needless sudden movements
• Especially with cold-water immersion
Supine to avoid postural hypotension
O2
Monitors
CPR and intubation should not be withheld if needed
Trauma immobilization as needed
Intense vasoconstriction at <30 °C may make IV meds
ineffective
Lidocaine/atropine: ineffective
Prophylactic (<30 °C) and therapeutic bretylium
• Treat life-threatening arrhythmias only; the remainder will
self-correct with re-warming
• Attempt defibrillation up to 3 times and no re-attempts
until core temp reaches 30ºC
• Magnesium sulfate: Helpful in spontaneous resolution of v
fib
Reduce further heat loss
Begin re-warming
• Heat packs in axillae, groin, belly
Intubate as needed; pre-oxygenate first
Resuscitate cold and dead to warm and dead (at least by 3033ºC)
ER Care
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Baseline studies
• CBC, lytes, BUN. Cr, BS, ABGs, PT/PTT
• Tox screen where appropriate
• EKG
• CXR
Labs in Hypothermia
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Coagulation mechanism can fail
• Failure of enzymatic reactions of the clotting cascade
Coag studies typically performed at 37 °C and so results
may be deceptively normal
DIC may develop
Hyperglycemia in acute hypothermia
Hypoglycemia in chronic or secondary hypothermia
K+: Levels of 10mmol/L associated with low likelihood of
recovery
Classic EKG changes of hyperkalemia may be absent or
diminished
Hct may be deceptively high
• Hypothermic patients are volume contracted because of cold
diuresis
• Increase 2% for each 1 °C drop in core temp
Differential Diagnosis
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Alcohol/other intoxicants
Endocrine problems
Hyper/hypoglycemia
Hypoxemia
Narcotics
Uremia
Trauma
Infection
Psychiatric
CNS: SAH, space-occupying lesions
Positive Benefit of Hypothermia
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May exert a protective effect on brain
and organs in cardiac arrest.
Hypothermia with Perfusing
Rhythm
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Mild (> 34°C or 93.2°F): Passive
rewarming
• Warmed blankets
• Warm environment
Hypothermia with Perfusing
Rhythm
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Moderate (30° C-34° C or 86° F –
93.2° F): Active external rewarming
• Heating blankets
• Forced hot air
• Warmed infusions
• Warmed water packs
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Carefully monitor for hemodynamic
changes
Hypothermia with Perfusing
Rhythm
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Severe (<30°C or 86 °F): Active
internal rewarming
• Peritoneal lavage
• Esophageal rewarming tubes
• CP bypass
• Extracorporeal circulation
Cardiac Arrest at 30 °-34 °C
(Moderate Hypothermia)
Overview
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CPR
Defib once
IV
Intubate
IV medications
Active Internal
Rewarming
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Cardiac Arrest at < 30 °
(Severe Hypothermia)
Overview
CPR
Defib once
IV
Intubate
IV medications when at core temp
>34 °C
Active Internal Rewarming
BLS Modifications
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Check breathing and pulse for 30-45
sec. to confirm arrest state.
• If doubt, commence CPR anyway
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Warmed humidified O2 if possible
(42°-46° C)
1 defib attempt and defer further
attempts until patient warmed to 30°32° C
ALS Modifications
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Intubation
• Delivers warmed O2 better
• Prevents aspiration
Focus on active core rewarming: warmed humidified O2 (42-46
°C), warmed IV fluids (43 °C, warm peritoneal lavage fluids,
pleural lavage extracorporeal blood warming)
Hypothermic heart unresponsive to drugs, pacemakers, and
defib
Drug metabolism reduced
Cardioactive drugs can accumulate to toxic levels in peripheral
circulation
IV drugs often withheld at temps <30 ° C
IV meds given at >30 °C but at increased intervals
May not need to pace bradycardic rhythm since it may be
physiologic due to hypothermia
If after rewarming and return of pulse, the B/P is low push
fluids to compensate for vasodilation
References
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Li J. Hypothermia.
www.emedicine.com/emerg/topic279.htm
Accessed 11/18/05
Ulrich AS, Rathlev NK. Hypothermia and
localized Cold Injuries. Emerg Med Clin N Am
2004; 22:281-298.
Phillips TG. Hypothermia.
www.emedicine.com/med/topic1144.htm.
Wang HE, Callaway CW, et al. Admission
Hypothermia and Outcome after Major Trauma.
Crit Care Med 33(6):1296-1301
Hypothermia.
www.vnh.org/GMO/ClinicalSection/19Hypothermi
a.html. Accessed 12/11/05
References
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Plaisier BR. Thoracic Lavage in Accidental
Hypothermia with Cardiac Arrest – Report of a
Case and Review of the Literature. Resuscitation
2005; 66:99-104.
Walpoth BH, Walpoth-Aslan BN, et al. Outcome
of Survivors of Accidental Hypothermia with
Circulatory Arrest Treated with Extracorporeal
Blood Warming. NEJM 1997; 337:1500-1505.
Rice R. Hypothermia – Potentially Deadly All Year
Around. JAAPA 2005; 18:47-52.
2005 American Heart Association Guidelines for
Cardiopulmonary Resuscitation and Emergency
Cardiovascular Care, Part 2: Hypothermia.
Circulation 2005; 112(suppl IV):IV-136-139.