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