DISORDERS CAUSED BY HEAT

Dr Majid Golabadi

Occupational Medicine specialist

MEDICAL DISORDERS COUSED BY EXCESSIVE EXPOSURE TO HOT ENVIRONMENTS

heat stroke,

heat exhaustion,

heat cramps,

heat syncope,

skin disorders

THE TRANSFER OF HEAT BETWEEN SKIN AND ENVIRONMENT

Convection

Conduction

Radiation

Evaporation

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.

HEAT STROKE

Life-threatening medical emergency

Thermal regulatory failure

Cerebral dysfunction with altered mental

status

Core (rectal) temperature approaches 4l.l°C

(106°F)

Hyperventilation, respiratory alkalosis and

compensatory metabolic acidosis

Abnormal bleeding, renal failure, or

arrhythmias

Heat CrampsHeat ExhaustionHeatstroke

PathophysiologySalt deficiencyVolume/electrolyte depletionThermoregulatory failure

SymptomsPainful muscle cramps/ spasmWeaknessNauseaVomiting

WeaknessHeadacheSyncopeNauseaVomitingIntense thirst (water depletion)FatigueMuscle cramps (salt depletion)Malaise

Irritability ConfusionProdromal heat exhaustion CollapseSevere/sustained physical exertion (exer tional heat stroke) Psychotic behavior

Objective findingsEuthermia

Core temperature < 38°C (100.4°F)Profuse sweatingOrthostatic vital signsTachycardiaHyperventilationTetany

Core temperature >40°C(104°F)Altered mental status—bizarre behaviorHot dry skin (classic heat stroke)Moist skin (exertional heat stroke)ComaHypotension/shockSeizureTachycardiaCyanosisRales

LaboratoryElevated creatine phospho-kinase (CPK), creatinuria

OliguriaHyperuricemiaCPK elevationDissemination intravascular coagulationRespiratory alkalosisHypokalemiaThrombocytopeniaMyoglobinuriaHypoglycemiaTransaminase elevation

THRESHOLD LIMIT VALUES FOR EXPOSURE TO HEAT IN OCCUPATIONAL SETTINGS

wet-bulb globe temperature (WBGT)

Heat-index guidelines

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

MANAGEMENT Monitoring for hypovolemic and cardiogenic

shock, Maintaining a patent air way, 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.

PROGNOSIS

Elevated creatine phosphokinase (CPK)

Elevated liver enzymes,

Metabolic acidosis

are predictors of multiorgan dysfunction

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.

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, con

fusion, a core (rectal) temperature exceeding 38°C (100.4°F), increased pulse rate, and moist skin, Hyperventilation and respiratory alkalosis

HEAT EXHAUSTION

Treatment Placing the patient in a cool and shaded

environment and providing hydration (1-2 L over 2-4 hours) and salt replenishment—orally 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.

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

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.

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

HEAT SYNCOPE

Treatment

Recumbency, cooling, and rehydration.

Preexisting medical conditions should be

monitored and treated if necessary

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").