heat related illness richard dionne md emergency medicine – university of ottawa march 2013
TRANSCRIPT
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Heat Related Illness
Richard Dionne MDEmergency Medicine – University of Ottawa
March 2013
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Heat Related Illness
• Goals & Objectives
• Discuss the thermoregulation differences between hyperthermic entities and fever
• Discuss the differences between Heat Exhaustion and Heat Stroke and their target organ injuries
• Identify the differential diagnosis and the proper investigation in the ER
• Discuss the acute management in the ER
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Basics
• Severe illness secondary to overwhelming heat stress
• Dehydration – electrolytes – thermoregulation dysfunction – MOF
• Increase temperature – increase O2 consumption and metabolism
• Failure of Oxydative Phosphorylation and certain enzymes > 42 °C
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Classification1- Hyperthermic Diseases
A - Minor Cramps / Edema / Syncope / Prickly Heat
B - Major Heat Exhaustion Heat Stroke
2- Hyperthermic EntitiesA - Malignant HyperthermiaB - Neuroleptic Malignant Syndrome
3- Febrile Illnesses
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Hyperthermia« Auto-Regulation »
Peripherical & Central Thermistors
Central Thermostat(Anterior Hypothalamus)
Modulation Response
Peripherical Adaptation Mechanism
(vasodilation & sweating)
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Hyperthermia vs Fever
Hyperthermia…• Thermoregulatory mecanism are surpassed …
• Peripherical mechanism dont suffice,
• The Hypothalamic « set point » is normal …
Fever…• Cytokins reaches Anterior Hypothalamus
• Resets the Thermostat... new « set point »
• Peripherical mechanism are intact...
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Heat Exhaustion
• Core T < 40° C
• Fluid & electrolyte depletion
• Thermoregulation is maintained
• CNS function is preserved
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Heat Stroke
• Core T > 40.5 C• Loss of thermoregulation, severe CNS
dysfunction & MOF
• Triad: Hyperthemia / CNS / Anhydrose
• Classic• Exertional
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Heat Stroke
• Classic Heat Stroke (non-exertional)
– Compromised thermoregulation – (cannot remove from source)
– Days– Severe dehydration – Warm & dry skin
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Heat Stroke
• Exertional Heat Stroke
– Younger / athletic with combined environmental & exertional heat stress
– Internal heat production overwhelms dissipating mechanisms…
– Sweating may be present at beginning
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Heat Cramps
• Secondary to excessive sweating and sodium loss– Cramps in heavily exercised muscles– Primarily in lower extremities– During or after exercise
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Prickly Heat
• Blockage of sweat glands leading to a maculopapular rash over clothed area …
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Heat Edema
• Swelling of dependent areas of body (usually lower limbs)– Resolves with acclimatization & rest
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Etiology
• Pre-existing conditions:
– Age extremes – Dehydration– Cardiovascular disease– Obesity– Hyperthyroidism– Febrile Illness– Skin disease that interferes with sweating (psoriasis /
eczema)
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Etiology
• Pharmacologic:
– Sympathomimetics– LSD / PCP– MAO inhibitors– Anticholinergics– Antihistamines– B-blockers– Diuretics– Drug & alcohol withdrawal
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Etiology
• Physical / Environmental:
– Prolonged exertion– Lack of mobility– Lack of air conditioning– Excessive humidity– Lack of acclimatization
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Heat Exhaustion « labs »
Possibly normal Hematocrit / natremia Hypoglycemia ? BUN / Creatinine Concentrated urine
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Imaging
• ECG: cardiac risks• CT-scan Head: r/o CNS primary• Chest X-ray: ARDS?
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Differential DiagnosisSepsisMeningitisMalariaThyroid stormStatus EpilepticusCerebral HemorrhageMalignant HyperthermiaNeuroleptic malignant syndromeTetanusToxicology ASA / PCP / stimulants / Anticholinergic
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Heat Stroke
ClassicalExertionnal
predisposing factorshealthy
olderyounger
sedentaryexercise
anhidrosisdiaphoresis
heat wavesporadic
mild CPKrhabdomyolysis
mild coagulopathyDIC
mild acidosismarked lactic acidosis
oliguriaacute renal failure
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Treatment
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Heat Exhaustion« Treatment »
Rest / Shade / Cooling methods Rehydration …
PO … 0,1% NaCl solution IV … 0,9% NS ( modest to avoid overhydration) Peds 20 cc/Kg
Shivering & seizures: Benzos
Danger : Sodium levels
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Cooling measures
• Evaporative• Very effective• Spray with fine mist• Airflow with fans• Prevent shivering
• Conductive• Ice pack groin / axilla & neck• Immersion not practical ad risk if seizures
“Stop cooling at 39°C to risk hypothermia!”
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« Mecca Body Cooling Unit »
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Not this way ?
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Heat Stroke« Complications »
Rhabdomyolysis & Renal Failure Hypoglycemia / Na / K / Ca
Severe Hepatocellular damage AST/ALT can be in the 1000 ’s < 24h
Coagulopathy / DIC / hemorrhage
Refractory Hypotension
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Bad Prognosis
Coagulopathy Lactic Acidosis (classical) T° > 42.2°C & prolonged hyperthermia Prolonged coma > 4 hrs Hypotension Acute Renal Failure Hyperkalemia AST > 1000 U/L
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Hyperthermia
Hepatic Clotting Fibrinolysis Endothelial Megakaryocyte damage factors damage damage
Depletion DIC Thrombolysis Thrombocytopenia clotting factors
Hemorrhage
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Hypotension
CVP & CVP & CVP & Cardiac Output Cardiac Output Cardiac Output
Hypovolemic Hypodynamic Hyperdynamic
Fluids Fluids & Pressors Cooling & fluids NS 250-500 cc then slowly (rarely) modest 300 cc/h NScorrect BP > 90/60 or CVP N
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Prevention
1- Rely not on thirst2- Drink on schedule3- Favor sports drinks4- Monitor weight5- Watch urine6- No caffeine or alcohol7- Key on meals8- Stay cool when you can
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Summary
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Malignant Hyperthermia
Autosomal Dominant conditionSevere muscular hypermetabolism produced by excessive
release of calcium from sarcoplasmic reticulum in response to anesthetic agents …
Treatment Dantrolene : 1-2 mg/Kg IV q 6h (max 10mg/Kg/24h)
calcium release from sarcoplasmic reticulum
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Neuroleptic Malignant Syndrome
Dopamine receptor blocade at Corpus Striatum
Muscular Spasticity & Dystonia
Heat Production
Target Organs (rhabdomyolysis, etc)
Treatment : DantroleneBromocriptine (Dopamine Agonist)
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Points to remember ...
In doubt treat as « Heat Stroke »
ASA & Acetaminophen = no place
Dantrolene & Steroids = no place
Keep away from :
Levophed (alpha-adrenergics) vasoconstriction & no benefit to cardiac output
Atropine (anticholinergics) inhibition of sweating
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Remember
« Heat stroke victims should be cooled as rapidly as possible. The more rapid the cooling, the lower the mortality. »
« It does not take long to either boil an egg or to cook neurons. »
D Hamilton
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Heat Related IllnessKey Concepts
• Antipyretics are ineffective and should not be used
• Diaphoresis is common in exertional heat stroke• Rapid (convective) cooling should be initiated
rapidly• Heatstroke can cause right-sided cardiac dilation
and elevated CVP, resembling Pulmonary Edema, but requires crystalloid resuscitation
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Questions ?