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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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 body temperature to less than 35 o C (95 o F):
Mild: 32.2-35 o C (90–95 o F)
Moderate: 26.6-32.2
o C (82-90 o F)
Severe: less than 26.6
o C (80 o 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 use – duration greater than 24 hours Seen in urban winter environment; often with pre-existing illness, i.e., psychiatric disorder, or drug/alcohol 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 to 50% of normal level at 30 o C (86 o F)
Respiratory Changes
Increased quantity/viscosity of lung secretions
Decreased thoracic cage elasticity and pulmonary compliance (lung stiffness)
Decreased respiratory rate, with respiratory arrest occurring at < 24 o C (75 o F)
CNS Effects
Mild -- 34 o C (93 o F) – agitation, shivering
Moderate -- 30 to 34 o C (86-93 o F) – confused but verbalizing, shivering stops
Severe -- < 30 o C (86 o F) -- pupils dilated, hyporeflexia -- < 28 o C (82 o 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 mild hypothermia 32.2-35 o C (90-95 o F) Progressive slowing of heart rate below 30 o C (86 o F) At < 28C (82 o 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 < 34 o C (93 o 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
the core body temperature to less than 35 o -- a cooling of C (95 o 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 < 34 o C (93 o 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 point of body tissue (about minus 4 o C or 25 o 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 At tissue temperatures 3-10 o C (37 to 50 o F) Initial peripheral blood vessel constriction Tissue hypoxia
Phase I – Freezing Effects
At tissue temperatures of -15 to -6 o C (5 to 21 o 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: immerse in 40 to 42 o C (104 to108 o 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