Cold Injuries: An Update on Hypothermia and Frostbite John Dobson and Nici Singletary.
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Transcript of Cold Injuries: An Update on Hypothermia and Frostbite John Dobson and Nici Singletary.
Cold Injuries: An Cold Injuries: An Update on Update on Hypothermia and Hypothermia and FrostbiteFrostbite
Cold Injuries: An Cold Injuries: An Update on Update on Hypothermia and Hypothermia and FrostbiteFrostbite
John Dobson and Nici Singletary
Cold InjuriesCold Injuries
This PowerPoint was developed to be used as an instructor- aid for the 2002 OEC Fall Refresher. Please MODIFY its contents to meet your patrol’s needs. A large-group mini-presentation is a good teaching style for this exercise. Your review should not take more than 30 minutes – maximum! Instructor notes are included at the bottom of many slides.
HYPOTHERMIA HYPOTHERMIA
Definitions 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:Definitions Continued:
Core Body Temperature Measured by rectal, esophageal, or
tympanic thermometer Oral temperatures read 1 degree less
than rectal
Definitions Continued:Definitions Continued:
Hypothermia -- a cooling of the core body temperature to less than 35oC (95oF):
Mild: 32.2-35oC (90–95oF)Moderate: 26.6-32.2oC (82-90oF)Severe: less than 26.6oC (80oF)
Epidemiology Epidemiology
Between ’79 – ’98: 13,970 deaths in US49% of the decedents were 65 or olderUrban settings still account for the
majority of cases
ClassificationsClassifications
Acute – duration less than an hourSudden 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 Classifications
Subacute – duration 1 - 24 hoursBlood sugar reserves are used; fairly abrupt onset of cooling then follows, i.e., uninjured alpinist stranded in the mountains.
ClassificationsClassifications
Chronic – duration greater than 24 hoursSeen in urban winter environment; often with pre-existing illness, i.e., psychiatric disorder, or drug/alcohol useOnset slow
MortalityMortality
Mortality rates are less than
10% for hypothermia alone!Mortality rates are 75-90% for
hypothermia accompanied by an underlying illness!
ThermoregulationThermoregulation
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: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 Pathophysiology
Multiple systems are affectedCold 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 30oC (86oF)
Respiratory Changes Respiratory Changes
Increased quantity/viscosity of lung secretionsDecreased thoracic cage elasticity and
pulmonary compliance (lung stiffness)Decreased respiratory rate, with respiratory
arrest occurring at < 24oC (75oF)
CNS EffectsCNS Effects
Mild -- 34oC (93oF) – agitation, shiveringModerate -- 30 to 34oC (86-93oF) – confused but
verbalizing, shivering stopsSevere -- < 30oC (86oF) -- pupils dilated,
hyporeflexia -- < 28oC (82oF) -- hypertonic coma
(pseudo rigor mortis)
Cardiac EffectsCardiac Effects
Primary hypothermia death due to a failure of myocardial conduction, which eventually causes asystole Increased heart rate occurs with
mild hypothermia 32.2-35oC (90-95oF) Progressive slowing of heart rate below 30oC (86oF) At < 28C (82oF), blood pressure falls, ventricular fibrillation occurs, then asystole
Hypothermia Risk FactorsHypothermia Risk Factors
ElderlyHomelessMentally ill or incapacitatedOutdoor work (exposure)Trauma (traumatic brain injury, cord
transection)Cardiovascular disease
Hypothermia Risk FactorsHypothermia Risk Factors
Excessive alcohol Hypothyroidism Infections (sepsis) Exhaustion, heavy exertion
Hypothermia Risk FactorsHypothermia Risk Factors
BurnsPoor nutritionInadequate clothingInadequate housing or heatingDrugs: sedatives, narcotics
General ManagementGeneral Management
Prevent further heat lossMonitor core temperature & pulseRe-warm patients with core temperature of
< 34oC (93oF) [passive or active external]Careful transportation to hospital
Passive RewarmingPassive Rewarming
For patients with mild hypothermia who are capable of generating body heat, i.e., previously healthy individuals
Blankets
Warm room
Active External RewarmingActive External Rewarming
Person to person heat transfer – “body to body"
Warm water immersion -- hot tubRadiant heat -- heat lamp, electric blanketWarm packs -- hot water bottlesForced hot air – electric heater with fan
Which Rewarming Technique? Which Rewarming Technique?
34°C to 36°C: Passive rewarming -- remove wet clothing;
apply blanketsActive external rewarming (i.e. radiant heat)
Which Rewarming Technique?Which Rewarming Technique?
30°C to 34°C: Passive rewarming (completely dry off), apply blanketsActive external rewarming
• hot water bottles to trunk areas• electric heater with fan
Warm IV solution by EMS personnel
AHA Assessment and Rx Recommendations: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:
AHA Recommendations
Continued:
Obtain rectal body temperature in field
(but don’t delay transport)Prevent further heat loss Treat gentlyTransport promptlyStart warm IV with normal saline (EMS)
Hypothermia SummaryHypothermia SummaryHypothermia -- a cooling of
the core body temperature to less than 35oC (95oF)
Multiple systems are affectedCold is initially protectant of
tissues, especially the brainPrimary hypothermia death due an eventual failure of myocardial conduction - asystole
Hypothermia SummaryHypothermia Summary
Prevent further heat lossMonitor core temperature & pulseRe-warm patients with core temperature of
< 34oC (93oF) [passive or active external]Carefully transport to hospital
RememberRemember
A patient is not dead until they are “warm dead!”
Snowy Mountains and Fog In ValleySnowy Mountains and Fog In Valley
FrostbiteFrostbite
FrostbiteFrostbite
Actual freezing of a body part;
occurs when the temperature of the body part falls below the freezing
point of body tissue (about minus 4oC or 25oF)Irreversible tissue damage depends on the
extent and duration of freezing at the tissue level
FrostnipFrostnip
Cold-induced area of superficial
blood-vessel constrictionMild tingling or pain followed by numbnessGray or yellowish patch of exposed skinAfter warming, affected part is tender, pink,
warm, and may be shiny or slightly swollen Complete recovery in 1-2 weeks
Frostbite Post-Rewarming Classification
Frostbite Post-Rewarming ClassificationDifficult to predict the severity of
injury when frostbite is first seenSeverity established only after
re-warming has occurred3-4 days usually needed to know
if superficial or deep
SuperficialSuperficialOnly the skin has been frozenLarge blisters filled with clear or yellow
fluid develop in about 12 hoursErythema with rewarming; persistent
increased skin sensitivity
DeepDeepComplete anesthesia (lack of sensation)Hemorrhagic (blood-filled) blistersEdema proximal to frostbite in 5-7 days
Deep -- ProgressiveDeep -- ProgressiveCompletely through dermisSubcutaneous tissue, muscle, boneCauses eventual mummification
Predisposing FactorsPredisposing Factors
Low external temperaturesWind (convective loss)Humidity (conductive loss)Skin wetnessPoor hydrationHypoxia
Frostbite Risk FactorsFrostbite Risk Factors
NicotinePrior frostbite AlcoholPsychiatric/mental incapacityMotor vehicle failure or trauma
EpidemiologyEpidemiology
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
PathophysiologyPathophysiology
Process similar to that for
thermal burns, with direct
cellular damage or deathPhase I: Cooling and freeze effectsPhase II: Thawing & progressive necrosisPhase III: Late, permanent effects
Phase I – Pre-FreezePhase I – Pre-Freeze
CoolingAt tissue temperatures 3-10oC (37 to 50oF)
Initial peripheral blood vessel constriction
Tissue hypoxia
Phase I – Freezing EffectsPhase I – Freezing EffectsAt tissue temperatures of -15 to -6oC (5 to 21oF) 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 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 NecrosisPhase II: Thawing and NecrosisProgressive 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 DamagePhase III: Permanent Damage
Begins 48 hrs after rewarmingProgressive vascular necrosis
is associated with:Marked edemaBlisters proximal to injuryDry gangrene necrosis with demarcation at 22 - 45 days
Damage is irreversible
Emergency CareEmergency Care
Immediate, rapid rewarming: immerse in 40 to 42oC (104 to108oF) water-bath, 15-30 minutes, with active motion of joints
AVOID REFREEZINGMaintain hydrationAppropriate wound care:
apply a dry, sterile, soft dressingElevate frostbitten parts
PrognosisPrognosis
3-4 days needed to know
if deep or superficialAmputations traditionally
delayed until dry necrosis occurs30 + days for appearance of cut line of
demarcation for amputation (“Frostbite in January, amputation in July”)
ConsequencesConsequences
AmputationSensitivity problems (pain, cold sensitivity)Finger joint pain, stiffness and flexion
contracturesLate: osteoporosis and early arthritis from
cartilage injuries
Beck
Weathers
Mount Everest 1996
Beck
Weathers
Mount Everest 1996