Heat IllnessHeat Illness

LA Wilson MD, FACEPLA Wilson MD, FACEP

Heat Illness- TopicsHeat Illness- Topics

EpidemiologyEpidemiology Pathophysiology: heat transfer, response Pathophysiology: heat transfer, response

to heat stress, path to heat illnesses.to heat stress, path to heat illnesses. Clinical features of heat illnessClinical features of heat illness Treatment and PreventionTreatment and Prevention

Heat IllnessHeat Illness

Most common cause of environmentally Most common cause of environmentally related death in the U.S. during the past related death in the U.S. during the past decadedecade

More than floods, tornadoes, lightning, More than floods, tornadoes, lightning, hurricane, cold, or winter related fatalitieshurricane, cold, or winter related fatalities

Heat IllnessHeat Illness

Annual heat related deaths 1 per million Annual heat related deaths 1 per million in ages 5-44 yearsin ages 5-44 years

5 per million for the population over 85 5 per million for the population over 85 years of ageyears of age

400 heat related deaths per year in the 400 heat related deaths per year in the US over the past 10 yearsUS over the past 10 years

Risk Factors for Heat Risk Factors for Heat IllnessIllness

Hot, humid environmental conditionsHot, humid environmental conditions

DehydrationDehydration

Use of heavy equipment or clothingUse of heavy equipment or clothing

(football or hockey uniform)(football or hockey uniform)

High-intensity exerciseHigh-intensity exercise

Short-term illness or feverShort-term illness or fever

Eating disordersEating disorders

ObesityObesity

Risk Factors for Heat IllnessRisk Factors for Heat Illness

DeconditioningDeconditioning

Certain medications (e.g., diuretics)Certain medications (e.g., diuretics)

Chronic or long-term diseases (e.g., diabetes)Chronic or long-term diseases (e.g., diabetes)

Alcohol consumptionAlcohol consumption

Other substance abuse (heroin, cocaine, Other substance abuse (heroin, cocaine, Ecstasy)Ecstasy)

Recent move to hot, humid environmentRecent move to hot, humid environment

Elderly and very youngElderly and very young AcclimatizationAcclimatization

Medication and Heat Medication and Heat IllnessIllness

Medications that interfere with heat loss:Medications that interfere with heat loss: Antipsychotics, tranquilizers, Antipsychotics, tranquilizers,

anticholinergics, antiparkinsonian agents, anticholinergics, antiparkinsonian agents, cardiovascular meds (beta blockers, calcium cardiovascular meds (beta blockers, calcium channel blockers, vasodilators, diuretics), channel blockers, vasodilators, diuretics), sleep aids, stimulantssleep aids, stimulants

Thermoregulation

Metabolic Heat Environmental Heat

Body Temperature

++

Heat TransferHeat Transfer

RadiationRadiation Conduction; ConvectionConduction; Convection EvaporationEvaporation

RadiationRadiation

Main heat loss at low temperatureMain heat loss at low temperature In hot weather causes heat gainIn hot weather causes heat gain 100-250 ckal/hr heat burden from sun 100-250 ckal/hr heat burden from sun

light possiblelight possible

ConductionConduction

Kinetic energy of warm surface (skin) Kinetic energy of warm surface (skin) transferred to less kinetically active transferred to less kinetically active molecules of a cool surface (solid molecules of a cool surface (solid objects, water or air)objects, water or air)

Conduction normally accounts for less Conduction normally accounts for less than 3% of the bodies heat lossthan 3% of the bodies heat loss

In still air, the air next to the skin will In still air, the air next to the skin will rapidly warm to the skin temperature- rapidly warm to the skin temperature- insulator zoneinsulator zone

ConvectionConvection

Allowing for air movement, and thus Allowing for air movement, and thus replacing the warm air with cooler air will replacing the warm air with cooler air will result in a more rapid conductive heat lossresult in a more rapid conductive heat loss

Conduction coupled with convection may Conduction coupled with convection may account for 15% of heat lossaccount for 15% of heat loss

Heat loss by conduction in water is 32 Heat loss by conduction in water is 32 times more efficient than in air at the times more efficient than in air at the same temperaturesame temperature

EvaporationEvaporation

Primary heat loss in high temperaturesPrimary heat loss in high temperatures Basal levels: 600 ml of water loss Basal levels: 600 ml of water loss

through respiration and sweating dailythrough respiration and sweating daily 25% of heat loss in cooler temperatures25% of heat loss in cooler temperatures 100% at higher temperatures100% at higher temperatures High humidity impairs heat loss by High humidity impairs heat loss by

evaporationevaporation

EvaporationEvaporation

Dependent on adequate hydrationDependent on adequate hydration 1% dehydration impairs heat dissipation and the 1% dehydration impairs heat dissipation and the

physiological responsesphysiological responses Each 1% body weight loss to dehydration Each 1% body weight loss to dehydration

results in a core temperature increase of 0.1-0.3 results in a core temperature increase of 0.1-0.3 degrees C (0.18-0.54 deg F)degrees C (0.18-0.54 deg F)

Well acclimatized and trained athletes will Well acclimatized and trained athletes will hypohydrate and produce sweat at a more rapid hypohydrate and produce sweat at a more rapid rate than can be absorbed through the GI tract.rate than can be absorbed through the GI tract.

Physiological Response Physiological Response to Heat Stressto Heat Stress

Temperature regulation fails as Temperature regulation fails as temperature deviates from the normaltemperature deviates from the normal 35 C (95 F) >core temperature > 40 C (104 F)35 C (95 F) >core temperature > 40 C (104 F)

May sustain with body temperature as May sustain with body temperature as high as 42 C (107.6 F) for short times high as 42 C (107.6 F) for short times without ill effectswithout ill effects

Highest core temperature of heat stroke Highest core temperature of heat stroke survivor was 46.5 C (115.7 F)survivor was 46.5 C (115.7 F)

Physiological Heat Physiological Heat ResponseResponse

Vasodilatation (mainly in skin)Vasodilatation (mainly in skin) Increased sweatingIncreased sweating Decreased heat productionDecreased heat production Behavioral heat controlBehavioral heat control

VasodilatationVasodilatation

Skin blood flow increase from 0.2L/min to Skin blood flow increase from 0.2L/min to max of 8L/minmax of 8L/min

Cardiac out put increase of 3L/min/1 Cardiac out put increase of 3L/min/1 degree C elevationdegree C elevation

Sweat and Heat Sweat and Heat productionproduction

Cholinergic and catecholamine Cholinergic and catecholamine stimulation by elevated temperature stimulation by elevated temperature increase sweatingincrease sweating

Anterior hypothalamus signals the Anterior hypothalamus signals the posterior hypothalamus to decrease body posterior hypothalamus to decrease body heat production primarily by inhibiting heat production primarily by inhibiting shiveringshivering

Behavioral ResponsesBehavioral Responses

Dressing appropriatelyDressing appropriately Finding cooler environmentsFinding cooler environments

AcclimatizationAcclimatization

Maximized at 7-10 daysMaximized at 7-10 days Primarily improved sweating, enhanced Primarily improved sweating, enhanced

skin blood flow, improved cardiovascular skin blood flow, improved cardiovascular function and reset the thermoregulatory function and reset the thermoregulatory set pointset point

Heat InjuryHeat Injury

Three processesThree processes Increased heat productionIncreased heat production Increased external heat gainIncreased external heat gain Decreased heat lossDecreased heat loss

Non-exertional (classic) Non-exertional (classic) heat injuryheat injury

Periods of high environmental heat stressPeriods of high environmental heat stress Slow rise in heat burden allow volume Slow rise in heat burden allow volume

and electrolyte abnormalities to developand electrolyte abnormalities to develop Elderly and the young at riskElderly and the young at risk Those with psychological, physiological, Those with psychological, physiological,

pharmacological impairment at riskpharmacological impairment at risk

Confinement Confinement HyperpyrexiaHyperpyrexia

July 2000- June 2001:July 2000- June 2001: 1960 nonfatal and 78 fatal heat injuries to 1960 nonfatal and 78 fatal heat injuries to

children left in closed vehicles on hot children left in closed vehicles on hot daysdays

Many of the deaths related to Many of the deaths related to confinement in cars or trucksconfinement in cars or trucks

Exertional Heat injuryExertional Heat injury

Physically fit participating in athletic eventsPhysically fit participating in athletic events Jobs performed in high heat stress Jobs performed in high heat stress

conditions such as military or fire fightersconditions such as military or fire fighters Basal heat production is 60 kcal/hr per Basal heat production is 60 kcal/hr per

square meter (100 kcal/hr for average 70 square meter (100 kcal/hr for average 70 kg man).kg man).

With exertion the rate can increase by a With exertion the rate can increase by a factor of 20.factor of 20.

Heat Related IllnessesHeat Related Illnesses

Heat EdemaHeat Edema Prickly HeatPrickly Heat Heat CrampsHeat Cramps Heat TetanyHeat Tetany Heat SyncopeHeat Syncope Heat ExhaustionHeat Exhaustion Heat StrokeHeat Stroke

Heat CrampsHeat Cramps

Involuntary spasmodic muscle contractions, Involuntary spasmodic muscle contractions, commonly of the calves, but other muscles commonly of the calves, but other muscles possible.possible.

Occurs most commonly several hours after Occurs most commonly several hours after vigorous physical activity but may occur with or vigorous physical activity but may occur with or without exercise.without exercise.

Related to relative deficit in fluids, sodium and Related to relative deficit in fluids, sodium and potassiumpotassium

Treatment is fluid and electrolyte replacementTreatment is fluid and electrolyte replacement Two salt tabs (650 mg each) in a quart of water Two salt tabs (650 mg each) in a quart of water

delivers 0.1% saline solution.delivers 0.1% saline solution.

Heat TetanyHeat Tetany

Carpal Pedal spasm resulting from Carpal Pedal spasm resulting from hyperventilation- common result from hyperventilation- common result from short exposures to extreme heat stressshort exposures to extreme heat stress

Heat SyncopeHeat Syncope

Orthostatic hypotension due to Orthostatic hypotension due to vasodilatation, decreased motor tone and vasodilatation, decreased motor tone and perhaps fluid loss.perhaps fluid loss.

Common in non-acclimatized persons in Common in non-acclimatized persons in heat stress environmentsheat stress environments

Heat ExhaustionHeat Exhaustion

Nonspecific symptoms resulting from Nonspecific symptoms resulting from volume depletion and sometimes salt volume depletion and sometimes salt depletiondepletion

Weakness, Malaise, Nausea, vomiting, Weakness, Malaise, Nausea, vomiting, headache and myalgiasheadache and myalgias

Hypotension, tachycardia, tachypnea, Hypotension, tachycardia, tachypnea, diaphoresis and syncopediaphoresis and syncope

Temp range from normal to 40 C (104 F)Temp range from normal to 40 C (104 F)

Heat ExhaustionHeat Exhaustion

Treatment:Treatment: Fluid resuscitation, electrolyte replacementFluid resuscitation, electrolyte replacement Careful hydration when co-morbidities exist Careful hydration when co-morbidities exist

such as CHFsuch as CHF

Heat Exhaustion vs. Heat Heat Exhaustion vs. Heat StrokeStroke

Classical differentiation includes:Classical differentiation includes: AnhidrosisAnhidrosis CNS changes CNS changes Core temp > 40 C (104 F)Core temp > 40 C (104 F)

Heat Exhaustion vs. Heat Heat Exhaustion vs. Heat StrokeStroke

Exertional heat stroke victims may Exertional heat stroke victims may perspireperspire

Defining CNS changes is subjectiveDefining CNS changes is subjective There is no temperature threshold for There is no temperature threshold for

heat strokeheat stroke

Heat StrokeHeat Stroke

End organ damage- hepatic enzyme End organ damage- hepatic enzyme elevation may be used to define heat elevation may be used to define heat strokestroke

Hepatic enzyme elevation may be Hepatic enzyme elevation may be delayeddelayed

Heat StrokeHeat Stroke

Hyperpyrexia and CNS dysfunction Hyperpyrexia and CNS dysfunction should have heat stroke in the should have heat stroke in the differential.differential.

Heat Stroke Dif DX:Heat Stroke Dif DX:

Drug toxicityDrug toxicity Drug or Alcohol withdrawal syndromesDrug or Alcohol withdrawal syndromes Serotonin SyndromeSerotonin Syndrome Neuroleptic Malignant SyndromeNeuroleptic Malignant Syndrome

Heat Stroke Dif DXHeat Stroke Dif DX

Infections- Sepsis, other systemic infections, Infections- Sepsis, other systemic infections, MeningitisMeningitis

Endocrinopathies (DKA, Thyroid Storm)Endocrinopathies (DKA, Thyroid Storm) Neurologic: Status epilepticus, brain Neurologic: Status epilepticus, brain

hemorrhagehemorrhage

Heat Stroke and the CNSHeat Stroke and the CNS

Cerebellum susceptible: Ataxia may be Cerebellum susceptible: Ataxia may be seen earlyseen early

Virtually any neurological signs are Virtually any neurological signs are possible: + Babinski, posturing, possible: + Babinski, posturing, hemiplegia, seizure, comahemiplegia, seizure, coma

Cerebral edema is commonCerebral edema is common Lower temperature for longer do more Lower temperature for longer do more

poorly than higher temperature for short poorly than higher temperature for short periodsperiods

Heat Stroke DiagnosisHeat Stroke Diagnosis

Diagnosis of exclusionDiagnosis of exclusion Evaluate all the possible causes, and Evaluate all the possible causes, and

treat as appropriatetreat as appropriate

ResuscitationResuscitation

ABCD, EABCD, E Fluid resuscitation is paramountFluid resuscitation is paramount Assess for end organ damage: CBC, Assess for end organ damage: CBC,

CMP, UA, myoglobin, CMP, UA, myoglobin, CoolingCooling

CoolingCooling

EvaporativeEvaporative ImmersionImmersion Ice packing- hypothermia blanketIce packing- hypothermia blanket Cold gastric lavageCold gastric lavage Cold peritoneal lavageCold peritoneal lavage

Morbidity and MortalityMorbidity and Mortality

End organ damageEnd organ damage Muscular: rhabdomyolysis, shiveringMuscular: rhabdomyolysis, shivering Neurological: delirium, seizures, coma: Neurological: delirium, seizures, coma:

cerebral edema and deathcerebral edema and death Cardiac: heart failureCardiac: heart failure Pulmonary: edema, ARDSPulmonary: edema, ARDS Renal: oliguria: ARFRenal: oliguria: ARF GI: diarrhea; hepatic failure, GI hemorrhageGI: diarrhea; hepatic failure, GI hemorrhage

Morbidity and MortalityMorbidity and Mortality

End organ damageEnd organ damage Metabolic: hypokalemia, hypernatremia; Metabolic: hypokalemia, hypernatremia;

Hyperuricemia, hyperkalemia, Hyperuricemia, hyperkalemia, hypocalcemia; lactic acidosis highly hypocalcemia; lactic acidosis highly correlated with morbidity and mortalitycorrelated with morbidity and mortality

Hematologic: thrombocytopenia, DICHematologic: thrombocytopenia, DIC

PreventionPrevention

Avoid strenuous out door activity during Avoid strenuous out door activity during heat stress periodsheat stress periods

Light colored, loose clothingLight colored, loose clothing Increase carbohydrate and decrease Increase carbohydrate and decrease

protein protein HYDRATE, HYDRATE, HYDRATEHYDRATE, HYDRATE, HYDRATE Avoid AlcoholAvoid Alcohol

PreventionPrevention

Do not take salt tabletsDo not take salt tablets Avoid direct sun exposureAvoid direct sun exposure Use the shadeUse the shade

Public PreventionPublic Prevention

Pay attention to environmental conditionsPay attention to environmental conditions Air conditioning and heat breaksAir conditioning and heat breaks Emphasize hydrationEmphasize hydration Social services to the home bound and Social services to the home bound and

chronically illchronically ill AcclimatizationAcclimatization Educate parents, coaches, teachersEducate parents, coaches, teachers

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