Those lovely, hot, sunny days of summer are upon us. To help us to better enjoy the great outdoors, here are some pointers about heat illnesses…
Risk Factors for Heat Illness
- Heart disease
- Previous heat exhaustion or heat stroke
- Exercise in a hot environment, particularly if there is high humidity
- Lack of air conditioning or proper ventilation
- Inappropriate clothing (occlusive, heavy, or vapor-impermeable)
- Lack of acclimatization
- Decreased fluid intake
- Hot environments (inside of tents or autos in the sun, hot tubs, saunas)
Drugs & Toxins
- Antihistamines (including diphenhydramine)
- Certain motion sickness medications, such as meclizine and dimenhydrinate
- Cocaine, amphetamines and other stimulant drugs
Other Risk Factors
- Salt and/or water depletion
Types of Heat Illness
Heat cramps occur when significant salt and water losses are replaced with solutions not containing sufficient salt (sodium chloride or NaCl). Inadequate salt repletion eventually can lead to involuntary contraction of skeletal muscles. Signs of heat cramps include:
- Brief, intermittent, involuntary contractions of skeletal muscles. These cramps most commonly involve the calves, but may occur in any muscle.Usually only occur in a single muscle or muscle group, and are quite painful.
- The victim with heat cramps will classically give a history of:
- Prolonged activity in a hot environment
- Attempted hydration, typically with a non-electrolyte containing solution, such as plain water
- Poor salt/electrolyte intake
- Oral salt replacement with a 0.1% to 0.2% NaCl solution. This can be easily made with ¼ to ½ teaspoon of table salt added to a quart of water.
- Severe cases
- If not responding to the above treatment, the individual may require intravenous fluids and should be evacuated.
Heat Syncope (fainting due to a hot environment)
Syncope is the medical term for “passing out,” usually a brief loss of consciousness. Heat syncope typically occurs when a dehydrated individual stands in a hot environment for an extended period. With standing, blood pools in the legs, decreasing the amount of blood that returns to the heart. This, in combination with dehydration and dilated blood vessels from the hot environment, can decrease blood flow to the brain and cause the individual to faint. Prior to actually losing consciousness, the victim may have the following signs and symptoms:
- Vertigo / dizziness
- Dimming or graying of vision
These symptoms and the actual loss of consciousness usually resolve once the victim is horizontal, as this facilitates redistribution of blood from the legs back to the brain.
The loss of consciousness should be brief, on the order of several seconds up to 2 minutes.
Treatment to improve blood flow to the brain should be instituted
- Lie the victim flat on their back (supine)
- Elevate the feet to improve venous return back to the heart
- Loosen tight or constrictive clothing
- Remove from direct sunlight
- Move to a cool area if possible
- Have the victim drink fluids
- Assess the victim for other injuries that may have resulted from the fall
Heat exhaustion is a form of heat illness that results from a significant heat stress. Heat exhaustion is part of a continuum of heat illnesses that progress to heat stroke.
- Nausea with or without vomiting
- Rapid heartbeat and breathing
- Profuse sweating
- Cessation of all physical activity
- Liberal fluid and electrolyte replacement. With heat exhaustion, oral hydration as discussed below is appropriate.
- Remove the victim from direct sunlight into a cool, shaded area
- Restrictive clothing should be loosened
- If the victim is hyperthermic (> 38 degrees C or 100.4 degrees F), active cooling measures should be taken. In the wilderness, there are limited resources to actively cool a victim.
- The best way to cool a hyperthermic victim is through evaporative cooling. Remove most of the victim’s clothing and make them “sopping wet” with tepid water. While it may seem paradoxical to cool a hyperthermic victim with warm water, the warm temperature of the water helps to prevent the shivering reaction and keeps the skin blood vessels dilated, which allows for heat exchange. Cold water might lead to shivering and constriction of the blood vessels in the skin. However, if only cold water is available, use it.
- Fan the victim with anything that will increase air movement across the skin. This air flow will result in evaporation of water from the skin, which cools the victim.
- Shivering will increase core body temperature and should be avoided.
Oral hydration should adhere to the following guidelines:
- Cool/cold water or sports drink
- Beverage should not exceed 6% carbohydrate content. Increased carbohydrate content inhibits fluid absorption. You can dilute most sports drinks with water to achieve a better concentration.
- A general rule is that every pound lost to sweat should be replenished with 500 mL or 2 cups of fluid.
- The treatment goal for mild heat exhaustion should be 1 to 2 liters of oral fluids over 2 to 4 hours.
Heat stroke is a true medical emergency that is classically defined by the following:
- Severe hyperthermia (core temperature > 40°C or 104°F)
- Central nervous system (CNS) disturbances such as alteration in the level of consciousness, confusion, or seizures.
- Lack of active sweating
However, experience has shown that waiting for the appearance of these three symptoms is too strict and may delay critical treatment. Any person who has any of the following symptoms in a hot environment should be treated as having heat stroke:
- Unsteady gait (often one of the first manifestations of heat stroke)
- Bizarre behavior
- Coma (very late finding)
Diminished or lack of sweating is classically associated with heat stroke; however it is typically a late finding and cannot be relied upon to make an accurate diagnosis. Typically, heat stroke victims will be covered in sweat until very late stages of the illness.
The key to treatment and prevention of heat stroke is in the understanding that heat exhaustion and heat stroke are not separate entities, but are a continuum of the same illness. The onset of any alteration in mental status should alert you that a victim is suffering from significant heat illness.
The primary goal of treatment for heat stroke is to facilitate rapid cooling, which can be accomplished by evaporative cooling as discussed previously. Additionally, one may place ice packs or cold compresses in areas where large blood vessels are superficial, such as the neck, axilla, groin, and scalp Most persons will not have a rectal thermometer to measure temperature. However, it may be used when one is available.
The goal of treatment is to drop the temperature to below 40°C (104° F) as rapidly as possible
Active cooling efforts should be discontinued around 39°C (102.2°F) to avoid overshoot to a condition of hypothermia, which can occur with very successful cooling efforts.
Drink at least 4-8 ounces of water or sports drink every 15-20 minutes during mild to moderate physical activity, depending on the ambient environmental temperature and humidity.
- Hydrate with a goal of clear urine instead of a fixed amount of intake.
- Consume salt containing foods or add salt to water if exposed to heat for time periods greater than 2-3 hours, especially if using only water for hydration.
- To make a salt solution, add ¼ to ½ teaspoon of table salt to a liter of fluid. Flavored drinks that are cold are more palatable.
- Most commercially available sports drinks should be diluted with an equal amount of water for ideal electrolyte concentration.
Wear loose fitted clothing that will allow for air circulation and increased evaporation.
- Avoid direct sunlight when possible and wear light colored clothing.
- Douse with cool fluids or cool misting spray frequently.
Heat acclimatization decreases the incidence of heat injuries and improves performance in hot environments. General guidelines for acclimatization:
Adults should gradually increase the time and intensity of activity in a hot environment over 7 to 10 days.
- Children and elders require 10 to 14 days to maximize acclimatization.
- Those who are from temperate or cold climates and will be traveling into a hot environment can acclimatize by going into a sauna or steam room for increasing amounts of time each day, beginning 7 to 10 days before making the trip.
- De-acclimatization usually occurs within 1 to 2 weeks of being removed from the hot environment. In such a situation, acclimatization must be repeated if necessary.
A victim who suffers a fainting episode thought to be heat-related should only have brief loss of consciousness and recover quickly. Any victim who endures a prolonged loss of consciousness, persistent pre-syncope signs and symptoms upon awakening, more than one episode of passing out, or signs of heat stroke should be evacuated.
A victim with severe heat cramps that do not respond to oral salt solutions, or a person who suffers diffuse and multiple cramps should also be considered for evacuation, depending on the situation.
Heat exhaustion victims may not need to be evacuated:
- As long as the victim can adequately be protected from the environment.
- In mild cases, close observation in the field for development of heat stroke, as well as cessation of activities for 24-48 hours, is recommended.
If the victim develops behavioral changes, records a temperature above 39°C (102.2°F), or has a fainting episode while under observation, he should be considered a potential heat stroke victim and be evacuated immediately.
Heat stroke is a serious medical emergency, so any victim with signs or symptoms of heat stroke should be evacuated as soon as possible.