Heat Related Illness

Richard Dionne MDEmergency Medicine – University of Ottawa

March 2013

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

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

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

Hyperthermia« Auto-Regulation »

Peripherical & Central Thermistors

Central Thermostat(Anterior Hypothalamus)

Modulation Response

Peripherical Adaptation Mechanism

(vasodilation & sweating)

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...

Heat Exhaustion

• Core T < 40° C

• Fluid & electrolyte depletion

• Thermoregulation is maintained

• CNS function is preserved

Heat Stroke

• Core T > 40.5 C• Loss of thermoregulation, severe CNS

dysfunction & MOF

• Triad: Hyperthemia / CNS / Anhydrose

• Classic• Exertional

Heat Stroke

• Classic Heat Stroke (non-exertional)

– Compromised thermoregulation – (cannot remove from source)

– Days– Severe dehydration – Warm & dry skin

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

Heat Cramps

• Secondary to excessive sweating and sodium loss– Cramps in heavily exercised muscles– Primarily in lower extremities– During or after exercise

Prickly Heat

• Blockage of sweat glands leading to a maculopapular rash over clothed area …

Heat Edema

• Swelling of dependent areas of body (usually lower limbs)– Resolves with acclimatization & rest

Etiology

• Pre-existing conditions:

– Age extremes – Dehydration– Cardiovascular disease– Obesity– Hyperthyroidism– Febrile Illness– Skin disease that interferes with sweating (psoriasis /

eczema)

Etiology

• Pharmacologic:

– Sympathomimetics– LSD / PCP– MAO inhibitors– Anticholinergics– Antihistamines– B-blockers– Diuretics– Drug & alcohol withdrawal

Etiology

• Physical / Environmental:

– Prolonged exertion– Lack of mobility– Lack of air conditioning– Excessive humidity– Lack of acclimatization

Heat Exhaustion « labs »

Possibly normal Hematocrit / natremia Hypoglycemia ? BUN / Creatinine Concentrated urine

Imaging

• ECG: cardiac risks• CT-scan Head: r/o CNS primary• Chest X-ray: ARDS?

Differential DiagnosisSepsisMeningitisMalariaThyroid stormStatus EpilepticusCerebral HemorrhageMalignant HyperthermiaNeuroleptic malignant syndromeTetanusToxicology ASA / PCP / stimulants / Anticholinergic

Heat Stroke

ClassicalExertionnal

predisposing factorshealthy

olderyounger

sedentaryexercise

anhidrosisdiaphoresis

heat wavesporadic

mild CPKrhabdomyolysis

mild coagulopathyDIC

mild acidosismarked lactic acidosis

oliguriaacute renal failure

Treatment

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

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!”

« Mecca Body Cooling Unit »

Not this way ?

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

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

Hyperthermia

Hepatic Clotting Fibrinolysis Endothelial Megakaryocyte damage factors damage damage

Depletion DIC Thrombolysis Thrombocytopenia clotting factors

Hemorrhage

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

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

Summary

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

Neuroleptic Malignant Syndrome

Dopamine receptor blocade at Corpus Striatum

Muscular Spasticity & Dystonia

Heat Production

Target Organs (rhabdomyolysis, etc)

Treatment : DantroleneBromocriptine (Dopamine Agonist)

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

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

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

Questions ?