Hypothermia pathophysiology, diagnosis, prehospital care, hospital care, emergency care, hypothermia management

1. HYPOTHERMIA
Munkhtulga G.
2015
“ZEPH”
Young Pathophysiologist student club

2. Definition, classification
• Core body temperature
of less than 35°C (95°F)
and can be clinically
stratified by the
• core temperature into
mild (35°-32°C/95°-89.6°F),
• moderate (32°-30°C/89.
S0-8 6°F),
• and severe ( <30°C/86°F)
subtypes.
• Primary
• healthy person is unable to
compensate for an
excessive exposure to cold
temperatures
• Secondary
• comorbid medical condition
(eg, hypothyroidism,
sepsis, intoxication) disrupts
a patient's normal
thermoregulatory
processes.

3. • Hypothermia occurs as the body loses heat from 1
of 4 major mechanisms: conduction, convection,
evaporation, and radiation.
• Convective (windy environments) and conductive
(cold and wet exposures) mechanisms are
responsible for most cases of accidental
hypothermia.

4. • More common in elderly 65< y/o
• Patients with an initial core body temperature
<23°C (73 .4°) typically do not survive, and the
overall mortality rate of patients with hypothermia
is approximately 40%.

5. Conditions causing hypothermia in children
by physiologic mechanism
Substrate deficiency
Hypoglycemia
Central nervous system conditions that disrupt
hypothalamic and autonomic temperature
regulation
Traumatic brain or spinal cord injury (including
neurosurgical procedures)
Intracranial hemorrhage
Stroke
Brain tumors (eg, craniopharyngioma or
astrocytoma)
Congenital brain malformations (eg, anencephaly
or absence of the corpus callosum)
Familial dysautonomia
Drug overdose with agents that cause central
nervous system depression and vasodilation
Ethanol
Opioids
Clonidine
Benzodiazepines
Barbiturates
Antipsychotic agents (eg, chlorpromazine)
Antidepressants (eg, amitriptyline)
Generalized infection*
Sepsis
Meningitis
Encephalitis

6. Conditions causing hypothermia in
children by physiologic mechanism
• Endocrine or metabolic diseases that
impair energy utilization or basal metabolic
rate
• Adrenal insufficiency
• Hypothyroidism
• Hypoparathyroidism
• Hypopituitarism
• Diabetes mellitus
• Menkes disease (Menkes kinky hair syndrome)
• Organic acidemias
• Aminoacidemias
• Increased insensible losses due to
disruption of skin
• Burns
• Epidermolysis bullosa and other weeping
dermatoses
• Decreased calorie intake with decreased
energy production and loss of insulating
subcutaneous fat
• Malnutrition
• Anorexia nervosa
• Other
• Hyponatremia (eg, water intoxication)
• Episodic spontaneous hypothermia with
hyperhidrosis •
• Child abuse and maltreatment

7. International Commission for Mountain
Emergency Medicine hypothermia scale
Hypothermia (HT)
stage
Clinical assessment
Expected core temperature, C°
(F°)*
HT I Clear consciousness with shivering 35-32 (95-89.6)
HT II Impaired consciousness without shivering 32-28 (89.6-82.4)
HT III Unconsciousness (circulation present) 28-24 (82.4-75.2)
HT IV
Apparent death (circulation absent)
resuscitation possible
<24-13.7 (<75.2-56.7) **
HT V
Death due to irreversible hypothermia
Resuscitation not possible
<13.7-9 (56.7-48.2) **
* Clinical assessment may be used alone to stage hypothermia when core temperature measurement in the
field is not available.
** The core temperature at which irreversible hypothermia with death occurs is not well defined.

8. Pathophysiology
• Body temperature reflects the balance between heat
production and heat loss.
• Heat is generated by cellular metabolism (most prominently
in the heart and liver) and lost by the skin and lungs via the
following processes:
1. Evaporation – Vaporization of water through both insensible
losses and sweat
2. Radiation – Emission of infrared electromagnetic energy
3. Conduction – Direct transfer of heat to an adjacent, cooler
object
4. Convection – Direct transfer of heat to convective air
currents

9. • In response to a cold stress, the hypothalamus
attempts to stimulate heat production through
shivering and increased thyroid, catecholamine,
and adrenal activity.
• Sympathetically mediated vasoconstriction
minimizes heat loss by reducing blood flow to
peripheral tissues, where cooling is greatest

10. MILD
32-35°C (90-95°F)
• Shivering
• Increased metabolism
• Vasoconstriction
• Mild tachycardia
MODERATE
28-32°C (82-90°F)
• Loss of compensatory
shivering
• Decreasing
metabolism
• Decreasing cerebral
blood flow
• Diuresis
• Extravasation of fluids
• Hypovolemia
SEVERE
<28°C (82°F)
• Muscle rigidity
without shivering
• Loss of
thermoregulation
• Vasodilation
• Decreased HR, SV, CO
• Decreased cardiac
conduction
• Increased cardiac
irritability
• Slowed nerve
conduction
• Suspended cerebral
activity

11. Other physiologic effects
• Respiration progressively becomes slow, shallow,
irregular, and then absent.
• Blood volume markedly decreases because of
extravasation due to vascular leak and a profound
"cold diuresis" caused by erroneous signaling to
the kidney about blood volume.
• Cold diuresis is worsened by failure of renal
concentrating function. The hydrostatic effects of
immersion also promote shock after water rescue

12. Other physiologic effects
•Hypothermia increases myocardial irritability. Thus, ventricular
fibrillation (VF) is a frequent problem in severe hypothermia.
•Potential triggers of VF to be avoided during treatment include
rough patient handling, patient exertion, core temperature
afterdrop (further cooling of the body after being removed from
cold exposure),
•administration of room-temperature fluids, direct stimulation of
the myocardium
(eg, subclavian central lines, and rewarming shock).

13. Clinical presentation, History
• usually obvious in patients with significant
exposures.
• Patients may present in wet clothing, be found
outdoors in the cold weather, or be inappropriately
dressed for the environment in which they live.
• In the US, most hypothermic patients are either
intoxicated or suffer from an underlying psychiatric
ill ness or dementia. (drunk people)

14. Clinical presentation
• The history or presentation may be less
obvious for patients with mild hypothermia or
unknown exposures.
• Said patients typically present with nonspecific
neurologic findings, including dizziness, confusion,
slurred speech, or ataxia.

15. PE
• start by assessing and addressing the patient's
airway, breathing, and circulation (ABCs) and vital
signs.
• may present with unstable airways or absent
pulses.
• Carefully measure the patient's core body temperature
by inserting a specialized "low-reading" probe into the
bladder, rectum, or esophagus.
• majority of standard ED thermometers will not record
temperatures below 34.4°C (94°F).

16. MILD
32-35°C (90-95°F)
• Shivering but
conscious
• Cyanosis
• Prolonged capillary
refill
MODERATE
28-32°C (82-90°F)
• Shivering stops,
impaired
consciousness
• Clumsiness
• Confusion or
delirium
• Slurred speech
• Decreasing BP
SEVERE
<28°C (<82°F)
• No shivering,
unconscious, vital
signs may or may not
be present
• Muscle rigidity
• Erythema and edema
• Stupor or coma
• Absent pulses
• Fixed, dilated pupils
• Ventricular
fibrillation
• Asystole

17. • The hypothermic heart is very sensitive to
movement, and rough handling of the patient may
precipitate arrhythmias, including ventricular
fibrillation.
• Take care to avoid jostling the patient during the
physical examination or the performance of
essential procedures.

18. Assessment
• A rectal probe thermometer is practical in most cases.
• In patients with severe hypothermia, particularly those
requiring endotracheal intubation, an esophageal probe
provides a near approximation of cardiac temperature.
• Either device may be inaccurate:
• rectal probe readings may rise following peritoneal
lavage or fall if adjacent to cold feces;
• esophageal probe readings may rise due to warm air
transmitted through the trachea.
• The reliability of tympanic thermometers in the setting of
significant hypothermia has NOT been established

19. Ancillary studies
• Fingerstick glucose
• Electrocardiogram (ECG)
• Basic serum electrolytes, including potassium and calcium
• BUN and creatinine
• Serum hemoglobin, white blood cell, and platelet counts
• Serum lactate
• Fibrinogen level
• Creatine phosphokinase
• Arterial blood gas, uncorrected for temperature
• Chest radiograph (care must be taken to avoid jostling the patient)

20. Arterial blood gas Metabolic acidosis, respiratory alkalosis, or both
Electrolytes No consistent abnormality
Glucose Increased, decreased, or no change
White blood cell and platelets counts Decreased due to splenic sequestration
Hemoglobin, hematocrit Increased due to hemoconcentration
Lipase
May be increased due to hypothermia-induced
pancreatitis
Prothrombin and partial thromboplastin times
Increased in vivo due to inhibition of coagulation
cascade, despite normal reported values
Electrocardiogram
Prolongation of PR, QRS, QT intervals
ST segment elevation
T wave inversions; Osborn J wave
Atrial fibrillation or sinus bradycardia
Chest radiograph
Aspiration pneumonia, vascular congestion,
pulmonary edema

21. • Inhibition of the enzymes of the coagulation
cascade from hypothermia leads to a bleeding
diathesis. Because tests of coagulation (eg,
prothrombin time, partial thromboplastin time) are
always performed at 37ºC, the laboratory will report
deceptively "normal" results despite an obvious in
vivo coagulopathy. Treatment consists of
rewarming; administration of clotting factors is
ineffective.

22. • Oxygenation should be monitored continuously;
however, the response time of pulse oximeters
placed on the finger is slowed by hypothermia.
Probes placed on the ears or forehead appear to be
less influenced by decreased body temperature and
the associated peripheral vasoconstriction.
Assessment of oxygenation is also complicated by
the fact that arterial blood gas analyzers operate at
37ºC, which is (by definition) greater than the body
temperature of a hypothermic patient.

24. How do you diagnose
hypothermia?

25. Hypothermia is diagnosed by
identification of a core body temperature
that is <35ºC (95ºF)
• Children with suspected hypothermia should have
their temperature taken with a low-reading rectal
probe thermometer or, ideally, the core temperature
should be measured using nasopharyngeal,
esophageal, bladder, or central venous catheter
temperature probes
• The clinician should not use standard clinical
thermometers in hypothermic patients because they
do not read below 34ºC (93ºF).
• In addition, the oral, axillary, infrared, and indirect
tympanic membrane sites are unreliable.

26. • Although true tympanic temperatures may closely
reflect core temperatures, indirect infrared tympanic
thermometers, typically available in the emergency
department, are subject to artifact after cold water
exposure and have not been shown to be reliable in
patients with moderate or severe hypothermia.
• When core temperature assessment is not readily
available, assessment of shivering, level of
consciousness, and vital signs provide a means of
estimating the initial stage of hypothermia

27. Initial management

28. • Successful resuscitation of the hypothermic child
requires rapid attention to supportive care (airway,
breathing, circulation), assessment and treatment of
injury or other medical conditions, and rewarming
interventions that vary based upon core body
temperature and the presence or absence of
circulation

29. Stage Rewarming methods* Notes
All
Remove wet clothing
Check ECG, continuously
monitor cardiac rhythm
Provide dry insulation Monitor core temperature
Warm airway humidity Monitor circulation
Warm IV (40-44°C)• Warmed volume support
Mild (32-35°C, 90-95°F)
Active external Watch for afterdrop
Moderate (28-32°C, 82-90°F)
Active external (forced air
preferred)
Watch for afterdrop
Direct heating methods (eg, hot
packs, heating pads) may cause
burns
Severe (<28°C, <82°F) - or if methods above prove ineffective
Circulation intact
Left pleural lavage or forced air
rewarming Δ
As above, plus ensure warming
is effective
Circulation absent Extracorporeal rewarming (ECR)
Left pleural lavage (if ECR is
unavailable)

30. Prehospital rescue and triage
• Suspicion is vital!
• Should consider all children who have altered
mental status or who require critical care.
• Measure core temperature (low reading
thermometer/clinical signs)

31. Prehospital declaration of death
• clinical appearance of death, including rigidity, is
typical of severe hypothermia
• Possible or confirmed severe hypothermia is a
strong contraindication to the declaration of death
in the prehospital setting.
• Successful resuscitation has occurred in patients
with asystole and prolonged avalanche burial (35
minutes or longer) when the airway was patent (not
filled with snow or ice) upon extrication

32. Circumstances that do permit prehospital
declaration of death include:
1. Rescue is impossible or poses undue risk of serious
injury or death to the prehospital providers
2. Injuries are clearly lethal
3. Valid “do not resuscitate” order is in place
Some experts also suggest that the prehospital declaration of
death may be appropriate in a patient after prolonged
avalanche burial (35 minutes or longer) in the combined
presence of an obstructed (snow-packed) airway and
asystole upon extrication

33. Prehospital care and transport
• Patients should be extracted from the cold
environment in a horizontal position, if possible.
• Prehospital providers should avoid patient exertion
and rough handling.

34. Many hypothermic patients arrive at the
hospital colder than they left the scene.
• Rescue, transport, and treatment involve several
risks for iatrogenic cooling. During transport,
rescuers should do all that is possible to prevent
further patient heat loss. Key interventions include:
• Removal of wet clothing
• Gentle insulation of the patient with blankets or
other items (eg, sleeping bag)
• Warming of the transport vehicle
• Provision of warm IV fluids

35. • We prefer to avoid active external rewarming in
transport for children. According to 2 trials
• If active rewarming is to be performed, rescuers
should avoid warming of the extremities and should
provide rapid infusion of warmed normal saline with
appropriate monitoring of cardiac rhythm.

36. Initial hospital care
• Hypothermic children should be maintained in a
horizontal supine position and handled gently with
minimization of movement.
• remove wet clothing and insulate the victim from
further exposure (eg, dry blankets).
• The application of external heat, although almost
automatic in many centers, should be avoided when
circulation is impaired.

37. Initial hospital care - OXYGEN
• Administration of heated, humidified oxygen is an
acceptable therapy for all hypothermic patients.
• The amount of rewarming provided by this
treatment is limited.
• The ideal gas temperature, based on the highest
delivered temperature that will not cause harm, is
45°C (113°F). However, even at 41°C, inspiration of
humidified oxygen prevents further heat loss.

38. Initial hospital care – IV FLUID
• Any intravenous (IV) fluid (eg, normal saline),
administered in volume should be heated to 40° to
44°C (104° to 111°F). Because??
• Avoid delivering fluid that is less than normal body
temperature (37°C (98.6°F)) which can worsen core
hypothermia

39. • Delivery of warmed IV fluids requires the use of
specific technologies, such as trauma-style fluid
warmers with short, large-bore insulated, or
countercurrent tubing.

40. Rewarming techniques
• Passive rewarming
• Active external rewarming
• Active internal rewarming
• Non-invasive (Noninvasive techniques include the
provision of heated, humidified oxygen and warmed
intravenous normal saline)
• Invasive
• Extracorporeal

41. Passive rewarming
• removing cold or wet clothing
• applying dry insulation, such as blankets, in a warm
environment.
• should be accompanied by appropriate active
rewarming techniques when treating children with
hypothermia

42. Active external rewarming
• apply heat externally to the patient. These include
forced air rewarming, radiant heat, and the
application of chemical heat packs or plumbed
water heating pads.

43. • However, they have the potential to promote afterdrop
(further cooling), hypotension (rewarming shock),
ventricular fibrillation, or asystole in patients with
moderate or severe hypothermia.
• These adverse effects arise from mobilization of cold
and acidic blood into the central circulation, especially
if the extremities are warmed early. Thus, when these
methods are used, the trunk should be warmed first.
• should be avoided in patients with severe hypothermia
or absent circulation

44. Invasive active internal rewarming
• heated saline lavage of the left pleural space,
bladder, stomach, and/or peritoneum.
• Invasive techniques are suggested for patients with
severe hypothermia (core temperature <28ºC
(82ºF)), especially with some preserved circulation,
or those with inadequate response to initial
rewarming

45. Extracorporeal active internal rewarming
• Extracorporeal techniques include:
• cardiac bypass and extracorporeal membrane
oxygenation (ECMO).
• These are suggested for children with severe
hypothermia and absent circulation or in patients
for whom other techniques prove ineffective.

46. Supportive care
moderate hypothermia or severe hypothermia
require intensive supportive care of the airway,
breathing, and circulation in addition to rewarming.

47. Airway and breathing
• Warmed, humidified 100 percent oxygen via
nonrebreather mask for all patients
• Bag-valve-mask ventilation in children with
hypoventilation and when preparing for
endotracheal intubation
• Endotracheal intubation in patients with respiratory
failure, uncompensated shock, or cardiac arrest

48. Chest compression
• clinician start cardiopulmonary resuscitation
without delay if there are no signs of life

49. Stage Rewarming methods* Notes
All
Remove wet clothing
Check ECG, continuously
monitor cardiac rhythm
Provide dry insulation Monitor core temperature
Warm airway humidity Monitor circulation
Warm IV (40-44°C)• Warmed volume support
Mild (>34°C, 93°F)
Active external Watch for afterdrop
Moderate (30-34°C, 86-93°F)
Active external (forced air
preferred)
Watch for afterdrop
Direct heating methods (eg, hot
packs, heating pads) may cause
burns
Severe (<30°C, 86°F) - or if methods above prove ineffective
Circulation intact
Left pleural lavage or forced air
rewarming Δ
As above, plus ensure warming
is effective
Circulation absent Extracorporeal rewarming (ECR)
Left pleural lavage (if ECR is
unavailable)

50. Post-resuscitation care
• Pulmonary edema, coagulopathy, and renal failure
are common complications after rewarming that
require continued care. These conditions usually
resolve within a few days.
• Neurologic abnormalities may resolve quickly with
rewarming or persist for weeks to months even in
cases where they eventually resolve.

51. PREDICTION OF
NEUROLOGIC
OUTCOME???
Glasgow Coma Scale, have not proved useful for
hypothermic patients