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Environmental Heat Illness

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Chicago 1995 Heat wave. July 12 July 20. Daily temps 34o-40oC (93o-104oF) Peak Heat Index on Day 2. 48.3oC (119oF) (94oF, 70% humidity) ... – PowerPoint PPT presentation

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Title: Environmental Heat Illness


1
Environmental Heat Illness
  • Michael P. Poirier, MD, FAAP, FACEP
  • Division of Emergency Medicine
  • Childrens Hospital of The Kings Daughters
  • Norfolk, Virginia

2
Outline of Lecture
  • Review of thermoregulation
  • Brief review of the spectrum of minor heat
    illness from heat cramps to heat exhaustion
  • In-depth review of classic and exertional heat
    stroke

3
Chicago 1995
  • Chicago 1995 Heat waveJuly 12 July 20Daily
    temps 34o-40oC (93o-104oF)Peak Heat Index on
    Day 248.3oC (119oF) (94oF, 70 humidity)gt 600
    excess deaths gt3300 E.D. visits

4
New York Times-- Sports Desk --August 2, 2001
  • Heat Kills a Pro Football Player
  • N.F.L. Orders a Training Review

5
Coach to be arraigned in high school player heat
death.
6
Heat Illness Risk
7
Heat Production
  • Basal rate 75 kcal/hr
  • Sitting in sun 150 kcal/hr
  • Moderate work 300 kcal/hr
  • Strenuous activity 600 - 900 kcal/hr

8
Mechanisms of Heat Transfer
  • Conduction
  • direct contact
  • thermal conductivity of water is 32 times that of
    air
  • Convection
  • vasodilatation of peripheral vessels
  • Radiation
  • only effective if ambient temp lt body temp
  • Evaporation
  • most effentient, less effective when RH gt 75

9
Heat Transfer
10
Hyperthermia vs. Fever
  • Hyperthermia occurs when thermoregulatory
    mechanisms are overwhelmed by excessive metabolic
    production of heat, excessive environmental heat
    or impaired heat dissipation.
  • Fever occurs when the hypothalamic set point is
    increased by the action of circulating pyrogenic
    cytokines.

11
Thermoregulation with Heat Stress
Metabolic Heat Load (Exercise)
Environmental Heat Load
Body heat
Core temperature
Sweating
Cutaneous vasodilatation
Heat loss by evaporation
Heat loss by radiation from skin surface
12
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13
Spectrum of Heat Illness
  • Heat Rash/Heat edema/Heat cramps/Heat syncope
  • Heat exhaustion
  • Heat stroke
  • classic
  • exertional
  • accidental

14
Accidental
15
Spectrum of Heat Illness
  • Heat Rash (Prickly heat, miliaria rubra)
  • Acute inflammatory skin eruption
  • Caused by blockage of sweat glands
  • Papulovesicular erythematous rash, pruritic
  • Mainly in skin folds
  • Treatment Cool baths, loose clothes, cool
    environment, avoid talcum powder

16
Heat Rash
17
Heat Edema
  • Swelling of hands and feet occurs mainly in
    nonacclimatized people.
  • Heat stress causes cutaneous vasodilatation and
    pooling of increased interstitial fluid in
    dependent extremities.
  • Self limited, without systemic involvement.
    Resolves in a few days
  • Treatment reassurance, elevation of
    extremities, compression stockings. Avoid
    diuretics - could exacerbate volume depletion

18
Heat Cramps
  • First described in 1923 in English coal miners,
    miners cramps
  • Originally believed related to excess water
    intake
  • Prospective studies have demonstrated no Na
    concentration or plasma volume differences in
    ultramarathon runners with or without heat cramps
  • Newly postulated mechanism of altered spinal
    neural reflex activity

19
Heat Syncope
  • Cause temporary ineffective circulating volume
    due to
  • dependent blood pooling
  • peripheral vasodilatation
  • Treatment resolves quickly with assumption of
    horizontal position hydration
  • Prevention avoidance of protracted standing
  • use of frequent muscle flexion and postural
    changes acclimatization

20
Heat Exhaustion -- Diagnosis --
  • Malaise, nausea, headache, sluggishness
  • A result of dehydration-induced heat retention
    that is insufficiently severe to cause heat
    stroke
  • Mental status normal, temp normal or slightly
    elevated
  • Might not be a continuum to heat stroke.

21
Heat Exhaustion -- Treatment
  • Rest, move to cool environment
  • Assess temperature
  • Assess hydration
  • Most cases are managed with oral hydration
    without Emergency Department visit

22
Heat Stroke
  • Thermoregulatory failure
  • Medical emergency
  • Classic, exert ional and accidental
  • History of heat stress, rectal temp gt 40oC, CNS
    dysfunction

23
Chicago 1995 Heat wave
  • Damatte, et al Annals of Internal Medicine, Aug
    1998
  • (1995 Chicago Heat Wave gt 600 deaths)
  • Observational study of 58 critical care patients
    in 12 hospitals exertional heat stroke patients
    excluded
  • 60 mechanical ventilation
  • In-hospital mortality of 21
  • Additional mortality of 28 after 1 year
  • Severe functional impairment at discharge 33
  • gt 50 had moderate-severe renal insufficiency
  • 45 had evidence of D.I.C.
  • Only 1/58 patients cooled to lt 39.0 oC within 30
    minutes
  • CT scanning a delay

24
Heat Stroke-- Diagnostic Criteria --
  • Signs
  • Temperature gt 40oC
  • Profound CNS signs (coma, delirium, seizure)
  • Hot, dry skin
  • Must assume heat stroke with CNS dysfunction
    during periods of high environmental
    temperatures.

25
Classic Heat Stroke
Exertional Heat Stroke
Age Health status Activity Drug
use Sweating Lactic acidosis Rhabdomyolysis Acu
te renal failure Hypocalcemia DIC CPK Hypoglycemia
Mechanism
Elderly Chronic illness Sedentary Anticholinergics
, diuretics, Antipsychotics, antihypertensives
Antidepressants Usually absent Usually absent
poor prognosis if present Unusual lt 5 of
patients Uncommon Mild Mildly elevated Uncommon Po
or dissipation of environmental heat
Men (15- 45yrs) Healthy Strenuous
exercise Usually no meds Often
present Common Frequently severe 25-30 of
patients Common Marked Markedly
elevated Common Excessive endogenous heat
production
From Knochel et al Disorders of heat
regulation. In Kleeman et al. Clinical
disorders of fluid and electrolyte metabolism,
New York, 1987, McGraw-Hill
26
Pathophysiology of Heat Stroke-- Systemic
Considerations --
Skin temp
Skin blood flow
Compensatory splanchnic vasoconstriction
Venous pooling
Decreased venous return
Compensatory tachycardia
Further venous pooling
Hypotension
Cutaneous vasoconstriction
Heat storage
27
Heat Stroke Cardiovascular Effects
  • Tachycardia and hypotension
  • Cardiovacuslar drift- increased HR, reduced
    stroke volume
  • Hypo-dynamic variety - myocardial depression
    and/or volume depletion
  • Hyper-dynamic - severe peripheral vasodilatation

28
Heat Stroke Renal Effects
  • Rhabdomyolysis alone may produce elevated
    creatinine
  • Urine dipstick has false negatives check the CPK
  • Myoglobin converted to nephrotoxic metabolites
  • Urate crystals

29
Heat Stroke Hematologic Effects
  • Results from direct thermal injury of vascular
    endothelium
  • vascular permeability
  • expression of adhesion molecules (ICAM-1,
    vWF, E-selectin, L-selectin)
  • coagulation / DIC
  • protein C,S
  • antithrombin III
  • fibrinolysis
  • Strong correlation between DIC and subsequent
    ARDS and mortality

30
Heat Stroke Neurologic Effects
  • Disorientation, seizures, coma
  • Hyperthermia reduces cerebral blood flow thought
    to be due to hyperventilation-induces cerebral
    vasoconstriction.
  • Increase brain metabolism
  • Depletion of brain glycogen

31
Hemorrhagic Shock and Encephalopathy syndrome
(HSES)
  • Unique form of heat stroke in infants lt 1 year
    old
  • Shock, encephalopathy, coagulopathy, diarrhea,
    renal and hepatic dysfunction associated with
    hyperpyrexia
  • Neurologic sequelae may be severe
  • Treatment Rapid cooling, volume replacement,
    supportive care

32
Heat Stroke - Multisystem Sequelae
Ambient temp
Prolonged sweating
Anticholinergic meds
Seizures
Exercise
K
Vasodilatation
Fluid losses
Muscular hyperactivity
Muscle perfusion
Shock
Sweating ceases
Rhabdo myolysis
Acidosis
Further core temp
Myoglo- binuria
K
DIC
Acute renal failure
CNS damage
Myocardial injury
Arrhythmias
33
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34
Differences in Children
  • Greater surface area to body mass
  • Slower rate of acclimatization
  • Higher production of metabolic heat per kg of
    body weight
  • Blunted thirst response
  • Decreased ability to dissipate heat
  • Lesser sweating capacity

35
Treatment of Heat Stroke
  • Four phases
  • Remove from environment that caused the problem
  • Assess and stabilize airway, breathing,
    circulation
  • Cool as rapidly as possible
  • Supportive therapy to minimize derangements
    produced by heat injury

36
Heat Stroke Treatment
  • Underlying principle Prognosis related to speed
    of cooling to lt 39oC
  • Cooling modalities Cold water immersion vs.
    evaporative, internal vs. external
  • Fluid requirements may be modest, depending on
    classic vs. exertional
  • Alpha adrenergic drugs to be avoided
  • Consider mannitol and/or urinary alkalization
  • Shivering preferentially treated with
    benzodiazepine
  • Seizures are catastrophic complication

37
Heat StrokeControversy on Cooling
  • Cold water immersion criticized on theoretical
    concerns of vasoconstriction and shivering
  • Immersion induced peripheral vasoconstriction has
    not been demonstrated
  • Shivering is not a big deal
  • Thermoregulatory response to heat is 90
    dependent on core temp, 10 on skin temp

38
Heat Stroke Cooling strategies
  • Completely undress
  • Tepid water spray
  • Large fans for convective air currents
  • Ice packs to neck, axilla and groin
  • Standard temperature IV fluids
  • Treat shivering with benzodiazepines
  • Goal 39 oC within 45 minutes

39
Treatment - ABCs
  • Intubate if unable to protect airway
  • Remove restrictive clothing
  • IV access
  • Cardiac monitor/NG/Foley
  • Constant core temp monitoring using esophageal or
    rectal probe

40
Heat Stroke ED Treatment
  • ABCs
  • Cooling to lt 39 oC
  • evaporative cooling is preferred
  • mortality is directly related to duration of
    hyperthermia
  • Avoid overzealous fluid administration
  • Alpha-adrenergic hemodynamic support to be
    avoided until normo-thermia achieved
  • Mannitol and urinary alkalinization

41
Treatment Core Cooling
  • Adjuncts to external cooling.
  • Cold humidified oxygen
  • Cold intravenous fluids
  • Peritoneal, gastric, thoracic and rectal lavage
  • Cardiopulmonary bypass
  • Stop cooling when core temp 39.C Continue to
    monitor/identify rebound

42
These dont work
  • Antipyretics
  • Interrupt the change in hypothalamus set point
    caused by pyrogens
  • Do not work on a healthy hypothalamus that has
    been overloaded as in heatstroke
  • May be harmful by worsening hepatic,
    hematological and renal complications
  • Dantrolene no proven efficacy

43
Heat Illness Conclusion
  • Heat Stroke treatment- ABCs
  • Cooling
  • Supportive care and treatment of multi-organ
    system dysfunction
  • Prognosis directly dependent upon speed of
    cooling
  • Goal to reduce temperature to lt 39oC within 30
    minutes
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