Transcript Cold Injuries: An Update on Hypothermia and Frostbite

Cold Injuries: An Update on
Hypothermia and Frostbite
John Dobson and Nici Singletary
Cold Injuries
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Refresher. Please MODIFY its contents to
meet your patrol’s needs. A large-group
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HYPOTHERMIA
Definitions
Shell = skin, subcutaneous tissues and
extremities; temperature of the shell
varies according to environment
Core = brain, heart, deep
vessels and organs; are
maintained at a steady
temperature
Definitions
Continued:
Core Body Temperature
Measured by rectal, esophageal, or
tympanic thermometer
Oral temperatures read 1 degree less
than rectal
Definitions
Continued:
Hypothermia -- a cooling of the core
o
o
body temperature to less than 35 C (95 F):
o
o
Mild: 32.2-35 C (90–95 F)
o
o
Moderate: 26.6-32.2 C (82-90 F)
o
o
Severe: less than 26.6 C (80 F)
Epidemiology
 Between ’79 – ’98: 13,970 deaths in US
 49% of the decedents were 65 or older
 Urban settings still account for the
majority of cases
Classifications
Acute – duration less than an hour
Sudden rapid cooling – as in an injured
alpine climber; without lowered O2 content
in air, cooling causes decreased O2
consumption, slowed metabolism, and
decreased organ ischemia
Classifications
Subacute – duration 1 - 24 hours
Blood sugar reserves are used; fairly
abrupt onset of cooling then follows,
i.e., uninjured alpinist stranded in the
mountains.
Classifications
Chronic – duration greater than 24 hours
Seen in urban winter environment;
often with pre-existing illness, i.e.,
psychiatric disorder, or drug/alcohol
use
Onset slow
Mortality
 Mortality
rates are less than
10% for hypothermia alone!
 Mortality rates are 75-90% for
hypothermia accompanied by
an underlying illness!
Thermoregulation
 A balance of heat production
(thermogenesis) and heat
dissipation (thermolysis)
 Hypothalamus (endocrine gland) controls
heat conservation and dissipation via the
autonomic nervous system and the
endocrine system
Thermoregulation Continued:
 Thermogenesis depends on glycogen (sugar)
reserves and O2 for metabolism; so heat
production is decreased in exhausted,
hypoxic, traumatized persons
 Heat conservation occurs
by vasoconstriction, which
eventually produces
behavior changes
Pathophysiology
 Multiple systems are affected
 Cold is protectant of tissues,
especially the brain
body can be very cold, have circulatory
arrest, and still can have an excellent
chance for survival
 Basal Metabolic Rate (BMR) decreases
o
o
to 50% of normal level at 30 C (86 F)
Respiratory
Changes
 Increased quantity/viscosity of lung secretions
 Decreased thoracic cage elasticity and
pulmonary compliance (lung stiffness)
 Decreased respiratory rate, with respiratory
o
o
arrest occurring at < 24 C (75 F)
CNS Effects
 Mild -- 34
o
o
C (93 F) – agitation, shivering
o
o
 Moderate -- 30 to 34 C (86-93 F) – confused but
verbalizing, shivering stops
o
o
 Severe -- < 30 C (86 F) -- pupils dilated,
hyporeflexia
o
o
-- < 28 C (82 F) -- hypertonic coma
(pseudo rigor mortis)
Cardiac Effects
 Primary hypothermia death due
to a failure of myocardial conduction,
which eventually causes asystole
 Increased heart rate occurs with
o
o
mild hypothermia 32.2-35 C (90-95 F)
o
o
 Progressive slowing of heart rate below 30 C (86 F)
o
 At < 28C (82 F), blood pressure falls, ventricular
fibrillation occurs, then asystole
Hypothermia
Risk Factors
 Elderly
 Homeless
 Mentally ill or incapacitated
 Outdoor work (exposure)
 Trauma (traumatic brain injury, cord
transection)
 Cardiovascular disease
Hypothermia Risk Factors
Excessive alcohol
 Hypothyroidism
 Infections (sepsis)
 Exhaustion, heavy exertion

Hypothermia Risk Factors
 Burns
 Poor nutrition
 Inadequate clothing
 Inadequate housing or heating
 Drugs: sedatives, narcotics
General
Management
 Prevent further heat loss
 Monitor core temperature & pulse
 Re-warm patients with core temperature of
o
o
< 34 C (93 F) [passive or active external]
 Careful transportation to hospital
Passive Rewarming
 For patients with mild
hypothermia who are
capable of generating
body heat, i.e., previously
healthy individuals
Blankets
Warm room
Active External
Rewarming
 Person to person heat transfer – “body to body"
 Warm water immersion -- hot tub
 Radiant heat -- heat lamp, electric blanket
 Warm packs -- hot water bottles
 Forced hot air – electric heater with fan
Which Rewarming
Technique?
34°C to 36°C:
Passive rewarming -- remove wet clothing;
apply blankets
Active external rewarming (i.e. radiant heat)
Which Rewarming
Technique?
30°C to 34°C:
Passive rewarming (completely dry off),
apply blankets
Active external rewarming
• hot water bottles to trunk areas
• electric heater with fan
Warm IV solution by EMS personnel
AHA Assessment and
Rx Recommendations:
 Assess breathing frequently, and for 30–45 sec
each time you check; perform rescue breathing
with humidified O2 via bag-valve-mask, if
indicated
 Assess pulse frequently, and again for 30–45
seconds each time you check; if no pulse and
no signs of circulation, begin CPR plus AED for
Ventricular Fibrillation – max of 3 shocks
AHA Recommendations
Continued:
 Obtain rectal body temperature in field
(but don’t delay transport)
 Prevent further heat loss
 Treat gently
 Transport promptly
 Start warm IV with normal saline (EMS)
Hypothermia
Summary
Hypothermia -- a cooling of
the core body temperature to
o
o
less than 35 C (95 F)
 Multiple systems are affected
 Cold is initially protectant of
tissues, especially the brain
 Primary hypothermia death due an eventual
failure of myocardial conduction - asystole
Hypothermia
Summary
 Prevent further heat loss
 Monitor core temperature & pulse
 Re-warm patients with core temperature of
o
o
< 34 C (93 F) [passive or active external]
 Carefully transport to hospital
Remember
A patient is not dead until they are
“warm dead!”
Snowy Mountains and Fog In Valley
Frostbite
Frostbite
 Actual freezing of a body part;
occurs when the temperature
of the body part falls below the freezing
o
o
point of body tissue (about minus 4 C or 25 F)
 Irreversible tissue damage depends on the
extent and duration of freezing at the tissue
level
Frostnip
 Cold-induced area of superficial
blood-vessel constriction
 Mild tingling or pain followed by numbness
 Gray or yellowish patch of exposed skin
 After warming, affected part is tender, pink,
warm, and may be shiny or slightly swollen
 Complete recovery in 1-2 weeks
Frostbite
Post-Rewarming
Classification
 Difficult to predict the severity of
injury when frostbite is first seen
 Severity established only after
re-warming has occurred
 3-4 days usually needed to know
if superficial or deep
Superficial
 Only the skin has been frozen
 Large blisters filled with clear or yellow
fluid develop in about 12 hours
 Erythema with rewarming; persistent
increased skin sensitivity
Deep
Complete anesthesia (lack of sensation)
Hemorrhagic (blood-filled) blisters
Edema proximal to frostbite in 5-7 days
Deep -- Progressive
 Completely
through dermis
 Subcutaneous tissue, muscle, bone
 Causes eventual mummification
Predisposing Factors
 Low external temperatures
 Wind (convective loss)
 Humidity (conductive loss)
 Skin wetness
 Poor hydration
 Hypoxia
Frostbite Risk Factors
 Nicotine
 Prior
frostbite
 Alcohol
 Psychiatric/mental incapacity
 Motor vehicle failure or trauma
Epidemiology
 Increased numbers of homeless;
growing participation in outdoor sports
Chamonix, France -
~ 80 cases/year seen
75% are superficial frostbite
Foot (big toe) in 57%
Hands (rarely thumb) in 46%
Face in 17%, especially nose, ears
Pathophysiology
 Process similar to that for
thermal burns, with direct
cellular damage or death
 Phase I: Cooling and freeze effects
 Phase II: Thawing & progressive necrosis
 Phase III: Late, permanent effects
Phase I – Pre-Freeze
Cooling
o
o
At tissue temperatures 3-10 C (37 to 50 F)
Initial peripheral blood vessel constriction
Tissue hypoxia
Phase I – Freezing Effects
 At tissue temperatures of
o
o
-15 to -6 C (5 to 21 F)
 Ice crystal formation
directly damages the
cell membrane
 Cellular death depends
on rapidity of cooling, intracellular ice
formation and mechanical destruction of cells
Phase II: Thawing
 Momentary constriction of arterioles and
venules, then resumption of capillary flow
produces a reactional “flush” of blood
 Rapid rewarming restores
circulation to most blood
vessels in 5 –10 minutes
Phase II: Thawing and Necrosis
 Progressive hypoxia occurs with deep frostbite
Increased blood viscosity
slows small blood vessel flow
Vasoconstriction adds to
increased blood viscosity
 Result: total interruption of
microcirculation in 20 minutes
to a few hours after rewarming
Phase III: Permanent Damage
 Begins 48 hrs after rewarming
 Progressive vascular necrosis
is associated with:
Marked edema
Blisters proximal to injury
Dry gangrene necrosis with
demarcation at 22 - 45 days
 Damage is irreversible
Emergency Care
 Immediate, rapid rewarming:
o
o
immerse in 40 to 42 C (104 to108 F) water-bath,
15-30 minutes, with active motion of joints
 AVOID REFREEZING
 Maintain hydration
 Appropriate wound care:
apply a dry, sterile, soft dressing
 Elevate frostbitten parts
Prognosis
 3-4 days needed to know
if deep or superficial
 Amputations traditionally
delayed until dry necrosis occurs
 30 + days for appearance of cut line of
demarcation for amputation
(“Frostbite in January, amputation in July”)
Consequences
 Amputation
 Sensitivity problems (pain, cold sensitivity)
 Finger joint pain, stiffness and flexion
contractures
 Late: osteoporosis and early arthritis from
cartilage injuries
Beck
Weathers
Mount Everest
1996