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Heat Illness

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Heat Illness LA Wilson MD, FACEP – PowerPoint PPT presentation

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Title: Heat Illness


1
Heat Illness
  • LA Wilson MD, FACEP

2
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3
Heat Illness- Topics
  • Epidemiology
  • Pathophysiology heat transfer, response to heat
    stress, path to heat illnesses.
  • Clinical features of heat illness
  • Treatment and Prevention

4
Heat Illness
  • Most common cause of environmentally related
    death in the U.S. during the past decade
  • More than floods, tornadoes, lightning,
    hurricane, cold, or winter related fatalities

5
Heat Illness
  • Annual heat related deaths 1 per million in ages
    5-44 years
  • 5 per million for the population over 85 years of
    age
  • 400 heat related deaths per year in the US over
    the past 10 years

6
Risk Factors for Heat Illness
  • Hot, humid environmental conditions
  • Dehydration
  • Use of heavy equipment or clothing
  • (football or hockey uniform)
  • High-intensity exercise
  • Short-term illness or fever
  • Eating disorders
  • Obesity

7
Risk Factors for Heat Illness
  • Deconditioning
  • Certain medications (e.g., diuretics)
  • Chronic or long-term diseases (e.g., diabetes)
  • Alcohol consumption
  • Other substance abuse (heroin, cocaine, Ecstasy)
  • Recent move to hot, humid environment
  • Elderly and very young
  • Acclimatization

8
Medication and Heat Illness
  • Medications that interfere with heat loss
  • Antipsychotics, tranquilizers, anticholinergics,
    antiparkinsonian agents, cardiovascular meds
    (beta blockers, calcium channel blockers,
    vasodilators, diuretics), sleep aids, stimulants

9
Thermoregulation
  • Metabolic Heat Environmental Heat
  • Body Temperature



10
Heat Transfer
  • Radiation
  • Conduction Convection
  • Evaporation

11
Radiation
  • Main heat loss at low temperature
  • In hot weather causes heat gain
  • 100-250 ckal/hr heat burden from sun light
    possible

12
Conduction
  • Kinetic energy of warm surface (skin) transferred
    to less kinetically active molecules of a cool
    surface (solid objects, water or air)
  • Conduction normally accounts for less than 3 of
    the bodies heat loss
  • In still air, the air next to the skin will
    rapidly warm to the skin temperature- insulator
    zone

13
Convection
  • Allowing for air movement, and thus replacing the
    warm air with cooler air will result in a more
    rapid conductive heat loss
  • Conduction coupled with convection may account
    for 15 of heat loss
  • Heat loss by conduction in water is 32 times more
    efficient than in air at the same temperature

14
Evaporation
  • Primary heat loss in high temperatures
  • Basal levels 600 ml of water loss through
    respiration and sweating daily
  • 25 of heat loss in cooler temperatures
  • 100 at higher temperatures
  • High humidity impairs heat loss by evaporation

15
Evaporation
  • Dependent on adequate hydration
  • 1 dehydration impairs heat dissipation and the
    physiological responses
  • Each 1 body weight loss to dehydration results
    in a core temperature increase of 0.1-0.3 degrees
    C (0.18-0.54 deg F)
  • Well acclimatized and trained athletes will
    hypohydrate and produce sweat at a more rapid
    rate than can be absorbed through the GI tract.

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19
Physiological Response to Heat Stress
  • Temperature regulation fails as temperature
    deviates from the normal
  • 35 C (95 F) gtcore temperature gt 40 C (104 F)
  • May sustain with body temperature as high as 42 C
    (107.6 F) for short times without ill effects
  • Highest core temperature of heat stroke survivor
    was 46.5 C (115.7 F)

20
Physiological Heat Response
  • Vasodilatation (mainly in skin)
  • Increased sweating
  • Decreased heat production
  • Behavioral heat control

21
Vasodilatation
  • Skin blood flow increase from 0.2L/min to max of
    8L/min
  • Cardiac out put increase of 3L/min/1 degree C
    elevation

22
Sweat and Heat production
  • Cholinergic and catecholamine stimulation by
    elevated temperature increase sweating
  • Anterior hypothalamus signals the posterior
    hypothalamus to decrease body heat production
    primarily by inhibiting shivering

23
Behavioral Responses
  • Dressing appropriately
  • Finding cooler environments

24
Acclimatization
  • Maximized at 7-10 days
  • Primarily improved sweating, enhanced skin blood
    flow, improved cardiovascular function and reset
    the thermoregulatory set point

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Heat Injury
  • Three processes
  • Increased heat production
  • Increased external heat gain
  • Decreased heat loss

27
Non-exertional (classic) heat injury
  • Periods of high environmental heat stress
  • Slow rise in heat burden allow volume and
    electrolyte abnormalities to develop
  • Elderly and the young at risk
  • Those with psychological, physiological,
    pharmacological impairment at risk

28
Confinement Hyperpyrexia
  • July 2000- June 2001
  • 1960 nonfatal and 78 fatal heat injuries to
    children left in closed vehicles on hot days
  • Many of the deaths related to confinement in cars
    or trucks

29
Exertional Heat injury
  • Physically fit participating in athletic events
  • Jobs performed in high heat stress conditions
    such as military or fire fighters
  • Basal heat production is 60 kcal/hr per square
    meter (100 kcal/hr for average 70 kg man).
  • With exertion the rate can increase by a factor
    of 20.

30
Heat Related Illnesses
  • Heat Edema
  • Prickly Heat
  • Heat Cramps
  • Heat Tetany
  • Heat Syncope
  • Heat Exhaustion
  • Heat Stroke

31
Heat Cramps
  • Involuntary spasmodic muscle contractions,
    commonly of the calves, but other muscles
    possible.
  • Occurs most commonly several hours after vigorous
    physical activity but may occur with or without
    exercise.
  • Related to relative deficit in fluids, sodium and
    potassium
  • Treatment is fluid and electrolyte replacement
  • Two salt tabs (650 mg each) in a quart of water
    delivers 0.1 saline solution.

32
Heat Tetany
  • Carpal Pedal spasm resulting from
    hyperventilation- common result from short
    exposures to extreme heat stress

33
Heat Syncope
  • Orthostatic hypotension due to vasodilatation,
    decreased motor tone and perhaps fluid loss.
  • Common in non-acclimatized persons in heat stress
    environments

34
Heat Exhaustion
  • Nonspecific symptoms resulting from volume
    depletion and sometimes salt depletion
  • Weakness, Malaise, Nausea, vomiting, headache and
    myalgias
  • Hypotension, tachycardia, tachypnea, diaphoresis
    and syncope
  • Temp range from normal to 40 C (104 F)

35
Heat Exhaustion
  • Treatment
  • Fluid resuscitation, electrolyte replacement
  • Careful hydration when co-morbidities exist such
    as CHF

36
Heat Exhaustion vs. Heat Stroke
  • Classical differentiation includes
  • Anhidrosis
  • CNS changes
  • Core temp gt 40 C (104 F)

37
Heat Exhaustion vs. Heat Stroke
  • Exertional heat stroke victims may perspire
  • Defining CNS changes is subjective
  • There is no temperature threshold for heat stroke

38
Heat Stroke
  • End organ damage- hepatic enzyme elevation may be
    used to define heat stroke
  • Hepatic enzyme elevation may be delayed

39
Heat Stroke
  • Hyperpyrexia and CNS dysfunction should have heat
    stroke in the differential.

40
Heat Stroke Dif DX
  • Drug toxicity
  • Drug or Alcohol withdrawal syndromes
  • Serotonin Syndrome
  • Neuroleptic Malignant Syndrome

41
Heat Stroke Dif DX
  • Infections- Sepsis, other systemic infections,
    Meningitis
  • Endocrinopathies (DKA, Thyroid Storm)
  • Neurologic Status epilepticus, brain hemorrhage

42
Heat Stroke and the CNS
  • Cerebellum susceptible Ataxia may be seen early
  • Virtually any neurological signs are possible
    Babinski, posturing, hemiplegia, seizure, coma
  • Cerebral edema is common
  • Lower temperature for longer do more poorly than
    higher temperature for short periods

43
Heat Stroke Diagnosis
  • Diagnosis of exclusion
  • Evaluate all the possible causes, and treat as
    appropriate

44
Resuscitation
  • ABCD, E
  • Fluid resuscitation is paramount
  • Assess for end organ damage CBC, CMP, UA,
    myoglobin,
  • Cooling

45
Cooling
  • Evaporative
  • Immersion
  • Ice packing- hypothermia blanket
  • Cold gastric lavage
  • Cold peritoneal lavage

46
Morbidity and Mortality
  • End organ damage
  • Muscular rhabdomyolysis, shivering
  • Neurological delirium, seizures, coma cerebral
    edema and death
  • Cardiac heart failure
  • Pulmonary edema, ARDS
  • Renal oliguria ARF
  • GI diarrhea hepatic failure, GI hemorrhage

47
Morbidity and Mortality
  • End organ damage
  • Metabolic hypokalemia, hypernatremia
    Hyperuricemia, hyperkalemia, hypocalcemia lactic
    acidosis highly correlated with morbidity and
    mortality
  • Hematologic thrombocytopenia, DIC

48
Prevention
  • Avoid strenuous out door activity during heat
    stress periods
  • Light colored, loose clothing
  • Increase carbohydrate and decrease protein
  • HYDRATE, HYDRATE, HYDRATE
  • Avoid Alcohol

49
Prevention
  • Do not take salt tablets
  • Avoid direct sun exposure
  • Use the shade

50
Public Prevention
  • Pay attention to environmental conditions
  • Air conditioning and heat breaks
  • Emphasize hydration
  • Social services to the home bound and chronically
    ill
  • Acclimatization
  • Educate parents, coaches, teachers

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