Disorders due to Heat
¨There is a spectrum of heat-related illnesses:
¤heat syncope
¤heat cramps
¤heat exhaustion
¤heat stroke
Hyperthermia
¨Hyperthermia results from the body's inability to maintain normal internal temperature through heat loss
¤Risk factors include inhibition of sweat production or evaporation
¤Use of drugs that reduce sweating
¤Obesity, skin disorders (miliaria),
¤Reduced cutaneous blood flow, dehydration, hypotension, reduced cardiac output
¤increase metabolism or muscle activity, prolonged seizures, and withdrawal syndromes
Heat Syncope or Collapse
¨Exercise-associated postural hypotension is usually the cause of this: it may occur during or immediately following exercise
¨Sudden collapse or unconsciousness result from
¤volume depletion and coetaneous vasodilatation
¤consequent systemic and cerebral hypotension.
¨There is usually a history of prolonged vigorous physical activity.
¨Typically, the skin is cool and moist, the pulse is weak, and the systolic blood pressure is low.
¨Treatment consists of rest and recumbency in a cool place and fluid and electrolyte rehydration by mouth (or intravenously if necessary).
Heat Cramps
¨Fluid and electrolyte depletion may result in slow, painful skeletal muscle contractions ("cramps") and severe muscle spasms lasting 1–3 minutes, usually of the muscles most heavily used
¨Cramping results from dilutional hyponatremia as sweat losses are replaced with water alone.
¨The skin is moist and cool.
¨The muscles are tender, hard and lumpy, and muscle twitching may be present.
¨The patient is alert, with stable vital signs, and may be agitated and complaining of pain.
¨The body temperature may be normal or slightly increased.
¨There is almost always a history of vigorous activity just preceding the onset of symptoms
¨The patient should be moved to a cool environment and given oral saline solution (4 tsp of salt per gallon of water) to replace both salt and water
¨The patient may have to rest for 1–3 days with continued dietary salt supplementation before returning to work or resuming strenuous activity in the heat
Heat Exhaustion
¨Heat exhaustion results from prolonged strenuous activity with inadequate water or salt intake in a hot environment.
¨ It is characterized by sodium depletion, or isotonic fluid loss, dehydration, with accompanying cardiovascular changes.
¨The diagnosis is based on symptoms and a rectal temperature over 37.8 °C, increased pulse (> 150% of the patient's normal) and moist skin.
Heat Exhaustion- Symptoms
¨Symptoms are similar to those associated with heat syncope and heat cramps
¨Additional symptoms include nausea, vomiting, malaise, myalgias, hyperventilation, thirst, and weakness.
¨Central nervous system symptoms include headache, dizziness, fatigue, anxiety, paresthesias
¨Hyperventilation secondary to heat exhaustion can cause respiratory alkalosis; lactic acidosis may also occur due to poor tissue perfusion.
¨Heat exhaustion may progress to heat stroke if sweating ceases and mental status declines.
¨Treatment consists of
¤moving patient to a shaded, cool environment,
¤providing adequate hydration (1–2 L over 2–4 hours),
¤salt replenishment—orally, if possible—and
¤active cooling (i.e., fans, cool packs) if necessary.
¤Physiologic saline or isotonic glucose solution should be administered intravenously when oral administration is not appropriate.
¤Indications for intravenous 3% (hypertonic) saline are the same as for the other causes of severe hyponatremia.
¤At least 24 hours of rest and rehydration are recommended
Heat Stroke
¨Heat stroke is a life-threatening medical emergency.
¨The hallmarks of heat stroke are
¤cerebral dysfunction
¤core temperature over 40 °C and
¤absence of sweating
¨Two forms: classic and exertional.
¨Classic heat stroke occurs in patients with impaired thermoregulatory mechanisms
¨Exertional heat stroke occurs in healthy persons undergoing strenuous exertion in a hot or humid environment
¨Persons at greatest risk are the very young, the elderly, the chronically debilitated, and those taking medications that interfere with heat-dissipating mechanisms (ie, anticholinergics, antihistamines, phenothiazines)
¨Associated with high morbidity and mortality from cerebral, cardiovascular, hepatic, or renal damage.
¨In a study of heat stroke patients, in-hospital mortality was 62.6%.
Clinical Findings
Symptoms and Signs
¨dizziness, weakness, emotional lability, confusion, delirium, blurred vision, convulsions, collapse, and unconsciousness
¨The skin is hot, initially covered with perspiration; later it dries
¨The pulse - strong initially, Blood pressure slightly elevated at first, but hypotension later
¨The core temperature is usually over 40 °C
Treatment
¨Treatment is aimed at reducing the core temperature rapidly (within 1 hour) while supporting organ system function.
¨Care must be taken to avoid shivering which will increase internal heat production and inhibit effectiveness of cooling
¨ Benzodiazepines may be used to suppress shivering.
¨Evaporative cooling is a noninvasive, effective, quick and easy way to reduce temperature.
¨The patient is undressed and the entire body sprayed with lukewarm water (20 °C) while large fans circulate the room air.
¨The patient should be in the lateral recumbent position or supported in a hands-and-knees position to expose as maximum skin surface to the air.
¨Alternatively, the use of cold wet sheets accompanied by fanning may be used.
¨Inhalation of cool air or oxygen, and infusion of cool intravenous fluids are also effective.
¨Treatment should be continued until the rectal temperature drops to 39 °C.
¨Close monitoring, including vital signs, temperature, and cardiac rhythm, should continue for 24 hours.
¨The patient should also be monitored for potential complications of electrolyte abnormalities, acute renal failure due to rhabdomyolysis, cardiac arrhythmias, coagulopathy, hepatic failure, acute respiratory distress syndrome (ARDS), hypoglycemia, seizures, and infection.
¨Intravascular volume status should be assessed and managed.
¨Hypovolemic and cardiogenic shock must be carefully distinguished, since either or both may occur.
¨Oral or intravenous fluid administration must be provided to ensure a high urinary output (> 50 mL/h).
¨Fluid output should be monitored through the use of an indwelling urinary catheter.
HYPERTENSION:http://hypertensioninhuman.blogspot.com/
HYPERTENSION:http://hypertensioninhuman.blogspot.com/
