Heat Illness

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Heat Illness

• LA Wilson MD, FACEP

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Heat Illness- Topics

• Epidemiology
• Pathophysiology heat transfer, response to heat
  stress, path to heat illnesses.
• Clinical features of heat illness
• Treatment and Prevention

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Heat Illness

• Most common cause of environmentally related
  death in the U.S. during the past decade
• More than floods, tornadoes, lightning,
  hurricane, cold, or winter related fatalities

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Heat Illness

• Annual heat related deaths 1 per million in ages
  5-44 years
• 5 per million for the population over 85 years of
  age
• 400 heat related deaths per year in the US over
  the past 10 years

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Risk Factors for Heat Illness

• Hot, humid environmental conditions
• Dehydration
• Use of heavy equipment or clothing
• (football or hockey uniform)
• High-intensity exercise
• Short-term illness or fever
• Eating disorders
• Obesity

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Risk Factors for Heat Illness

• Deconditioning
• Certain medications (e.g., diuretics)
• Chronic or long-term diseases (e.g., diabetes)
• Alcohol consumption
• Other substance abuse (heroin, cocaine, Ecstasy)
• Recent move to hot, humid environment
• Elderly and very young
• Acclimatization

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Medication and Heat Illness

• Medications that interfere with heat loss
• Antipsychotics, tranquilizers, anticholinergics,
  antiparkinsonian agents, cardiovascular meds
  (beta blockers, calcium channel blockers,
  vasodilators, diuretics), sleep aids, stimulants

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Thermoregulation

• Metabolic Heat Environmental Heat
• Body Temperature

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Heat Transfer

• Radiation
• Conduction Convection
• Evaporation

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Radiation

• Main heat loss at low temperature
• In hot weather causes heat gain
• 100-250 ckal/hr heat burden from sun light
  possible

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Conduction

• Kinetic energy of warm surface (skin) transferred
  to less kinetically active molecules of a cool
  surface (solid objects, water or air)
• Conduction normally accounts for less than 3 of
  the bodies heat loss
• In still air, the air next to the skin will
  rapidly warm to the skin temperature- insulator
  zone

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Convection

• Allowing for air movement, and thus replacing the
  warm air with cooler air will result in a more
  rapid conductive heat loss
• Conduction coupled with convection may account
  for 15 of heat loss
• Heat loss by conduction in water is 32 times more
  efficient than in air at the same temperature

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Evaporation

• Primary heat loss in high temperatures
• Basal levels 600 ml of water loss through
  respiration and sweating daily
• 25 of heat loss in cooler temperatures
• 100 at higher temperatures
• High humidity impairs heat loss by evaporation

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Evaporation

• Dependent on adequate hydration
• 1 dehydration impairs heat dissipation and the
  physiological responses
• Each 1 body weight loss to dehydration results
  in a core temperature increase of 0.1-0.3 degrees
  C (0.18-0.54 deg F)
• Well acclimatized and trained athletes will
  hypohydrate and produce sweat at a more rapid
  rate than can be absorbed through the GI tract.

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Physiological Response to Heat Stress

• Temperature regulation fails as temperature
  deviates from the normal
• 35 C (95 F) gtcore temperature gt 40 C (104 F)
• May sustain with body temperature as high as 42 C
  (107.6 F) for short times without ill effects
• Highest core temperature of heat stroke survivor
  was 46.5 C (115.7 F)

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Physiological Heat Response

• Vasodilatation (mainly in skin)
• Increased sweating
• Decreased heat production
• Behavioral heat control

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Vasodilatation

• Skin blood flow increase from 0.2L/min to max of
  8L/min
• Cardiac out put increase of 3L/min/1 degree C
  elevation

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Sweat and Heat production

• Cholinergic and catecholamine stimulation by
  elevated temperature increase sweating
• Anterior hypothalamus signals the posterior
  hypothalamus to decrease body heat production
  primarily by inhibiting shivering

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Behavioral Responses

• Dressing appropriately
• Finding cooler environments

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Acclimatization

• Maximized at 7-10 days
• Primarily improved sweating, enhanced skin blood
  flow, improved cardiovascular function and reset
  the thermoregulatory set point

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Heat Injury

• Three processes
• Increased heat production
• Increased external heat gain
• Decreased heat loss

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Non-exertional (classic) heat injury

• Periods of high environmental heat stress
• Slow rise in heat burden allow volume and
  electrolyte abnormalities to develop
• Elderly and the young at risk
• Those with psychological, physiological,
  pharmacological impairment at risk

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Confinement Hyperpyrexia

• July 2000- June 2001
• 1960 nonfatal and 78 fatal heat injuries to
  children left in closed vehicles on hot days
• Many of the deaths related to confinement in cars
  or trucks

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Exertional Heat injury

• Physically fit participating in athletic events
• Jobs performed in high heat stress conditions
  such as military or fire fighters
• Basal heat production is 60 kcal/hr per square
  meter (100 kcal/hr for average 70 kg man).
• With exertion the rate can increase by a factor
  of 20.

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Heat Related Illnesses

• Heat Edema
• Prickly Heat
• Heat Cramps
• Heat Tetany
• Heat Syncope
• Heat Exhaustion
• Heat Stroke

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Heat Cramps

• Involuntary spasmodic muscle contractions,
  commonly of the calves, but other muscles
  possible.
• Occurs most commonly several hours after vigorous
  physical activity but may occur with or without
  exercise.
• Related to relative deficit in fluids, sodium and
  potassium
• Treatment is fluid and electrolyte replacement
• Two salt tabs (650 mg each) in a quart of water
  delivers 0.1 saline solution.

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Heat Tetany

• Carpal Pedal spasm resulting from
  hyperventilation- common result from short
  exposures to extreme heat stress

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Heat Syncope

• Orthostatic hypotension due to vasodilatation,
  decreased motor tone and perhaps fluid loss.
• Common in non-acclimatized persons in heat stress
  environments

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Heat Exhaustion

• Nonspecific symptoms resulting from volume
  depletion and sometimes salt depletion
• Weakness, Malaise, Nausea, vomiting, headache and
  myalgias
• Hypotension, tachycardia, tachypnea, diaphoresis
  and syncope
• Temp range from normal to 40 C (104 F)

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Heat Exhaustion

• Treatment
• Fluid resuscitation, electrolyte replacement
• Careful hydration when co-morbidities exist such
  as CHF

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Heat Exhaustion vs. Heat Stroke

• Classical differentiation includes
• Anhidrosis
• CNS changes
• Core temp gt 40 C (104 F)

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Heat Exhaustion vs. Heat Stroke

• Exertional heat stroke victims may perspire
• Defining CNS changes is subjective
• There is no temperature threshold for heat stroke

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Heat Stroke

• End organ damage- hepatic enzyme elevation may be
  used to define heat stroke
• Hepatic enzyme elevation may be delayed

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Heat Stroke

• Hyperpyrexia and CNS dysfunction should have heat
  stroke in the differential.

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Heat Stroke Dif DX

• Drug toxicity
• Drug or Alcohol withdrawal syndromes
• Serotonin Syndrome
• Neuroleptic Malignant Syndrome

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Heat Stroke Dif DX

• Infections- Sepsis, other systemic infections,
  Meningitis
• Endocrinopathies (DKA, Thyroid Storm)
• Neurologic Status epilepticus, brain hemorrhage

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Heat Stroke and the CNS

• Cerebellum susceptible Ataxia may be seen early
• Virtually any neurological signs are possible
  Babinski, posturing, hemiplegia, seizure, coma
• Cerebral edema is common
• Lower temperature for longer do more poorly than
  higher temperature for short periods

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Heat Stroke Diagnosis

• Diagnosis of exclusion
• Evaluate all the possible causes, and treat as
  appropriate

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Resuscitation

• ABCD, E
• Fluid resuscitation is paramount
• Assess for end organ damage CBC, CMP, UA,
  myoglobin,
• Cooling

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Cooling

• Evaporative
• Immersion
• Ice packing- hypothermia blanket
• Cold gastric lavage
• Cold peritoneal lavage

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Morbidity and Mortality

• End organ damage
• Muscular rhabdomyolysis, shivering
• Neurological delirium, seizures, coma cerebral
  edema and death
• Cardiac heart failure
• Pulmonary edema, ARDS
• Renal oliguria ARF
• GI diarrhea hepatic failure, GI hemorrhage

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Morbidity and Mortality

• End organ damage
• Metabolic hypokalemia, hypernatremia
  Hyperuricemia, hyperkalemia, hypocalcemia lactic
  acidosis highly correlated with morbidity and
  mortality
• Hematologic thrombocytopenia, DIC

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Prevention

• Avoid strenuous out door activity during heat
  stress periods
• Light colored, loose clothing
• Increase carbohydrate and decrease protein
• HYDRATE, HYDRATE, HYDRATE
• Avoid Alcohol

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Prevention

• Do not take salt tablets
• Avoid direct sun exposure
• Use the shade

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Public Prevention

• Pay attention to environmental conditions
• Air conditioning and heat breaks
• Emphasize hydration
• Social services to the home bound and chronically
  ill
• Acclimatization
• Educate parents, coaches, teachers

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