DISORDERS CAUSED BY HEAT

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DISORDERS CAUSED BY HEAT

• Dr Majid Golabadi
• Occupational Medicine specialist

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medical disorders coused by excessive exposure
to hot environments

• heat stroke,
• heat exhaustion,
• heat cramps,
• heat syncope,
• skin disorders

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The transfer of heat between skin and environment

• Convection
• Conduction
• Radiation
• Evaporation

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acclimatization

• The scheduled and regulated exposure to heated
  environments of increasing intensity and duration
  allows the body to adjust to heat
• Beginning to sweat at lower body temperatures,
  Increasing the quantity of sweat produced,
  Reducing the salt content of sweat,
• Increasing the plasma volume, cardiac output,
  and stroke volume while the heart rate decreases.

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Heat Stroke

• Life-threatening medical emergency
• Thermal regulatory failure
• Cerebral dysfunction with altered mental status
• Core (rectal) temperature approaches 4l.lC
  (106F)
• Hyperventilation, respiratory alkalosis and
  compensatory metabolic acidosis
• Abnormal bleeding, renal failure, or arrhythmias

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Heat Cramps Heat Exhaustion Heatstroke
Pathophysiology Salt deficiency Volume/electrolyte depletion Thermoregulatory failure
Symptoms Painful muscle cramps/ spasm Weakness Nausea Vomiting Weakness Headache Syncope Nausea Vomiting Intense thirst (water depletion) Fatigue Muscle cramps (salt depletion) Malaise Irritability Confusion Prodromal heat exhaustion Collapse Severe/sustained physical exertion (exertional heat stroke) Psychotic behavior
Objective findings Euthermia Core temperature lt 38C (100.4F) Profuse sweating Orthostatic vital signs Tachycardia Hyperventilation Tetany Core temperature gt40C(104F) Altered mental statusbizarre behavior Hot dry skin (classic heat stroke) Moist skin (exertional heat stroke) Coma Hypotension/shock Seizure Tachycardia Cyanosis Rales
Laboratory Elevated creatine phospho-kinase (CPK), creatinuria Oliguria Hyperuricemia CPK elevation Dissemination intravascular coagulation Respiratory alkalosis Hypokalemia Thrombocytopenia Myoglobinuria Hypoglycemia Transaminase elevation
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threshold limit values for exposure to heat in
occupational settings

• wet-bulb globe temperature (WBGT)
• Heat-index guidelines

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In occupations in which workers are exposed to
excessive heat

• Medical evaluation to identify at risk
  individuals for heat disorders
• Training early signs and symptoms of heat
  disorders
• Advising of the importance of proper nutrition
  and fluid intake.
• Providing cool drinking water or
  electrolyte-carbohydrate solutions and shaded
  rest areas for workers

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management

• Monitoring for hypovolemic and cardiogenic shock,
  
• Maintaining a patent airway, providing oxygen
• Correcting fluid and electrolyte imbalances,
• Supporting vital processes.
• If hypovolemic shock is suspected, 500-1000 mL of
  5 dextrose in 1 or 0.5 normal saline solution
  may be given intravenously without overloading
  the circulation.
• Fluid output should be monitored
• Monitored for complications, including renal
  failure (caused by dehydration and
  rhabdomyolysis), hepatic failure, or cardiac
  failure, respiratory distress, hypotension,
  electrolyte imbalance (hypokalemia), and
  coagulopathy.

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prognosis

• Elevated creatine phosphokinase (CPK)
• Elevated liver enzymes,
• Metabolic acidosis
• are predictors of multiorgan dysfunction

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• Because hypersensitivity to heat continues in
  some patients for prolonged periods following
  heat stroke, they should be advised to avoid
  reexposure to heat for at least 4 weeks.

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Heat Exhaustion

• Etiology
• prolonged exposure to heat and insufficient salt
  and water intake can cause heat exhaustion,
  dehydration, and sodium depletion
• Symptoms and signs
• weakness, nausea, fatigue, headache, confusion,
  a core (rectal) temperature exceeding 38C
  (100.4F), increased pulse rate, and moist skin,
  Hyperventilation and respiratory alkalosis

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Heat Exhaustion

• Treatment
• Placing the patient in a cool and shaded
  environment and providing hydration (1-2 L over
  2-4 hours) and salt replenishmentorally if the
  patient is able to swallow. Physiologic saline or
  isotonic glucose solution should be administered
  intravenously in more severe cases.
• At least 24 hours' rest is recommended.

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Heat Cramps

• Etiology
• Result from dilutional hyponatremia caused by
  replacement of sweat losses with water alone
• Symptoms and signs
• Slow and painful muscle contractions and severe
  muscle spasms that last from 1-3 minutes and
  involve the muscles employed in strenuous work.
  The temperature may be normal or slightly
  increased

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Heat Cramps

• Treatment
• The patient should be moved to a cool environment
  and given a balanced salt solution or an oral
  saline solution. Salt tablets are not
  recommended.
• Rest for 1-3 days with continued salt
  supplementation in the diet may be necessary
  before returning to work.

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Heat Syncope

• Etiology
• In heat syncope, sudden unconsciousness results
  from volume depletion and cutaneous
  vasodilatation with consequent systemic and
  cerebral hypotension. Episodes occur commonly
  following strenuous work for at least 2 hours.
• Symptoms and signs
• The skin is cool and moist and the pulse weak.
  Systolic blood pressure is usually under 100 mmHg

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Heat Syncope

• Treatment
• Recumbency, cooling, and rehydration. Preexisting
  medical conditions should be monitored and
  treated if necessary

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Skin Disorders Caused by Heat

• Miliaria (heat rash) is caused by sweat retention
  resulting from obstruction of the sweat gland
  duct.
• Erythema abigne ("from fire") is characterized by
  the appearance of hyperkeratotic nodules
  following direct contact with heat that is
  insufficient to cause a burn.
• Intertrigo results from excessive sweating and
  often is seen in obese individuals. Skin in the
  body folds (e.g., the groin and axillas) is
  erythematous and macerated
• Heat urticaria (cholinergic urticaria) can be
  localized or generalized and is characterized by
  the presence of wheals with surrounding erythema
  ("hives").

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