Post on 22-Dec-2015
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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
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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