Thermoregulation, Fluid Balance, and Risk Factors for Environmental Illness Practice Questions

25 multiple-choice questions on Thermoregulation, fluid balance, and risk factors for environmental illness for paramedic and EMT students, from Chapter 39 (Environmental Emergencies). Read each question, pick your answer, then tap Show answer to check it and read the explanation.

25 practice questions

1. In a conscious, healthy adult, the most powerful defense against heat and cold is behavior, such as seeking shelter. This defense is lost in a patient who:

   1. A. Is intoxicated or has dementia
   2. B. Takes a daily beta-blocker
   3. C. Has well-controlled diabetes
   4. D. Is well acclimatized to hot weather
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   Answer: A. Is intoxicated or has dementia

   Behavioral responses such as moving to shade or shelter, changing clothing, and drinking fluids are more powerful than physiologic responses. Intoxication, dementia, psychiatric illness, injury, and immobility remove them, which is why these patients are overrepresented in environmental emergencies. A beta-blocker or diabetes can blunt physiologic responses but does not take away the ability to seek shelter, and acclimatization strengthens rather than removes heat defenses.

2. At rest in a cool, still room, most body heat is lost by:

   1. A. Conduction
   2. B. Evaporation
   3. C. Radiation
   4. D. Respiration
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   Answer: C. Radiation

   A resting person in a cool environment loses most heat as infrared radiation from exposed skin to cooler surroundings. Evaporation becomes the dominant route during exercise or when air temperature approaches skin temperature.

3. When air temperature is higher than skin temperature, the only effective way the body can still lose heat is:

   1. A. Radiation to the air
   2. B. Convection to moving air
   3. C. Conduction to the ground
   4. D. Evaporation of sweat
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   Answer: D. Evaporation of sweat

   Radiation, convection, and conduction move heat only from warmer to cooler objects, so in hot air they add heat. Evaporating sweat removes heat regardless of air temperature, as long as the air is not saturated.

4. Evaporative cooling becomes much less effective when the:

   1. A. Wind speed is high and gusty
   2. B. Relative humidity is high
   3. C. Air is cool and very dry
   4. D. Patient is lying flat and still
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   Answer: B. Relative humidity is high

   Sweat cannot evaporate into air that is already nearly saturated with water vapor, so above about 75% humidity it drips off without cooling. Wind actually speeds evaporation by moving saturated air away from the skin.

5. Heat loss by conduction is the transfer of heat:

   1. A. By air currents moving across the skin
   2. B. By direct contact with a cooler object
   3. C. As infrared energy to the surroundings
   4. D. As water changes from liquid to vapor
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   Answer: B. By direct contact with a cooler object

   Conduction requires direct contact, such as lying on cold ground or sitting in cold water. Air currents carrying heat away describe convection, not conduction.

6. A hunter fell into a lake at 10°C (50°F). He loses heat much faster than he would in air of the same temperature because water:

   1. A. Blocks the normal shivering response
   2. B. Stores less heat than still air
   3. C. Conducts heat about 25 times faster
   4. D. Greatly increases radiant heat loss
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   Answer: C. Conducts heat about 25 times faster

   Water conducts heat roughly 25 times faster than still air, so immersion cools the body rapidly. Shivering still occurs in cold water; it simply cannot keep up with conductive loss.

7. A climber stands on an exposed ridge in a 40 km/h (25 mph) wind. The mechanism most increasing his heat loss is:

   1. A. Conduction
   2. B. Radiation
   3. C. Respiration
   4. D. Convection
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   Answer: D. Convection

   Moving air strips away the warm layer next to the skin; this is convection and is the basis of wind chill. Conduction needs direct contact with a cold surface, such as snow or wet ground.

8. Breathing cold, dry air causes heat loss mainly because the inhaled air must be:

   1. A. Warmed and humidified
   2. B. Filtered of particles
   3. C. Cooled to body temperature
   4. D. Separated from nitrogen
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   Answer: A. Warmed and humidified

   Each breath of cold, dry air is warmed and saturated with water before exhalation, which costs heat and fluid. This respiratory loss rises at altitude and in cold, dry climates.

9. A man who has lain on a concrete floor since a fall last night has lost heat mainly by:

   1. A. Radiation to the ceiling
   2. B. Conduction to the floor
   3. C. Evaporation of sweat
   4. D. Convection to still air
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   Answer: B. Conduction to the floor

   Prolonged direct contact with a cold, dense surface such as concrete drains heat by conduction. Insulating the patient from the ground is therefore a first step in any cold patient.

10. The body's earliest response to a falling core temperature is:

    1. A. Skin vasoconstriction
    2. B. Vigorous shivering
    3. C. Increased sweating
    4. D. A slower resting heart rate
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    Answer: A. Skin vasoconstriction

    Constricting skin vessels keeps warm blood in the core and is the first, cheapest defense. Shivering follows when vasoconstriction alone cannot hold the temperature.

11. Shivering can raise the rate of heat production to about:

    1. A. 10 to 15 times the resting rate
    2. B. Half again the resting rate
    3. C. 2 to 5 times the resting rate
    4. D. The same as the resting rate
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    Answer: C. 2 to 5 times the resting rate

    Intense shivering increases metabolic heat production several-fold but consumes glucose and glycogen quickly. Shivering fails as fuel runs out or as core temperature falls toward 30 to 32°C (86 to 90°F).

12. A hiker caught in cold rain and wind at 10°C (50°F) becomes confused and clumsy. Regarding hypothermia, you should know that:

    1. A. It needs a core below 32°C (90°F)
    2. B. It needs air below 5°C (41°F)
    3. C. Wet clothing keeps heat in better
    4. D. It can occur well above freezing
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    Answer: D. It can occur well above freezing

    Wet clothing and wind greatly increase conductive and convective heat loss, so hypothermia often develops at temperatures well above freezing, especially with exhaustion or inadequate clothing. Hypothermia begins when the core falls below 35°C (95°F), not 32°C, no minimum air temperature is required, and wet clothing loses most of its insulation. Remove wet clothing, insulate, add a vapor barrier, and shelter from the wind.

13. Heat acclimatization over 10 to 14 days of exercise in heat produces:

    1. A. Earlier sweating with less sodium lost
    2. B. Less sweat and a higher core set point
    3. C. A lower plasma volume and heart rate
    4. D. Loss of thirst and of sweat production
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    Answer: A. Earlier sweating with less sodium lost

    Acclimatized people start sweating sooner, sweat more, conserve sodium, and expand their plasma volume. A higher core set point is not part of acclimatization.

14. A worker sweating heavily in the heat may lose about how much fluid per hour?

    1. A. 5 to 6 L
    2. B. 1 to 2 L
    3. C. 50 to 100 mL
    4. D. 200 to 300 mL
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    Answer: B. 1 to 2 L

    Sweat rates of 1 to 2 L/hour are common during heavy work in heat, and acclimatized people can sweat even more. Without replacement, dehydration reduces sweating and cardiac output and raises core temperature.

15. Thirst is an unreliable guide to fluid needs during heavy work in heat because it:

    1. A. Overstates fluid loss
    2. B. Appears before sweating
    3. C. Rises with acclimatization
    4. D. Lags behind fluid loss
    Show answer

    Answer: D. Lags behind fluid loss

    Workers who drink only when thirsty during hours of heavy work in heat usually replace only part of their sweat loss (voluntary dehydration), so occupational guidance (NIOSH 2016) recommends drinking at regular intervals, about one cup (240 mL) every 15 to 20 minutes during moderate work, rather than waiting for thirst. Thirst understates, not overstates, the deficit. Thirst follows fluid loss; it does not appear before sweating. Acclimatization improves fluid balance and does not make thirst unreliable. The setting matters: for endurance athletes, the WMS exercise-associated hyponatremia guideline recommends drinking to thirst, because scheduled overdrinking causes hyponatremia. (NIOSH 2016 heat criteria document; WMS 2019 EAH update.)

16. During a heat wave, which person is at increased risk of heat illness because of body build?

    1. A. A lean, fit long-distance runner
    2. B. A slender, acclimatized laborer
    3. C. A man with severe obesity
    4. D. An adult of average weight at rest
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    Answer: C. A man with severe obesity

    Obesity reduces the body surface area relative to mass, adds insulation, and increases the work of moving, so heat is produced more and lost less effectively. Obesity is also associated with lower fitness and cardiovascular disease, which further limit heat tolerance. Lean, fit, or acclimatized people tolerate heat better.

17. A severely hypothermic man feels very cold, but your standard thermometer reads only "LO" at 34°C (93°F). The best interpretation is that:

    1. A. His temperature is exactly 34°C
    2. B. He is mildly hypothermic at most
    3. C. His temperature may be far lower
    4. D. The reading rules out severe hypothermia
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    Answer: C. His temperature may be far lower

    Many standard clinical thermometers cannot read below about 34 to 35°C, so a severely hypothermic patient may show only the device's minimum value. A reading of LO gives only an upper limit, so it cannot show that he is mildly hypothermic or rule out severe hypothermia. Use a low-reading thermometer if available, and otherwise stage hypothermia by clinical findings such as level of consciousness and shivering.

18. A 74-year-old woman on furosemide and metoprolol is found confused in an apartment without air conditioning. Her medications raise her risk of heat illness because they:

    1. A. Increase sweating and sodium loss
    2. B. Raise her hypothalamic set point
    3. C. Cause widespread skin vasodilation
    4. D. Reduce volume and blunt heart rate
    Show answer

    Answer: D. Reduce volume and blunt heart rate

    Diuretics deplete plasma volume and beta-blockers limit the tachycardia needed to send blood to the skin, so both impair heat loss. Neither raises the hypothalamic set point; that is how fever works.

19. A hunter is choosing clothing for a wet, cold day. The poorest choice for the layer next to his skin is:

    1. A. Cotton
    2. B. Wool
    3. C. Polyester
    4. D. Polypropylene
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    Answer: A. Cotton

    Cotton absorbs water and loses most of its insulating value when wet, so it speeds heat loss ("cotton kills"). Wool and synthetic fibers such as polyester and polypropylene keep more insulation when damp and move moisture away from the skin.

20. Alcohol increases the risk of hypothermia mainly because it:

    1. A. Raises metabolism and burns glucose stores
    2. B. Dilates skin vessels and impairs judgment
    3. C. Causes shivering to start sooner than usual
    4. D. Blocks the conduction of heat to the ground
    Show answer

    Answer: B. Dilates skin vessels and impairs judgment

    Alcohol causes cutaneous vasodilation, suppresses shivering, causes hypoglycemia, and impairs the judgment that would lead a person to seek shelter. The feeling of warmth it produces is misleading.

21. A 30-year-old with extensive healed burn scars over his chest and back is working outdoors on a hot day. He is at higher risk of heat illness because the scarred skin:

    1. A. Reflects most of the sun's heat
    2. B. Sweats much more than normal skin
    3. C. Cannot sweat normally
    4. D. Has extra blood flow for cooling
    Show answer

    Answer: C. Cannot sweat normally

    Full-thickness burns and skin grafts destroy sweat glands, so large scarred areas cannot cool by evaporation, and patients with extensive burn scars are at higher risk of heat illness. Scars do not reflect heat or increase sweating.

22. A 30-year-old runner finishing a marathon in mild weather drank water at every station. She is confused, nauseated, and has a normal temperature. The most likely cause is:

    1. A. Exertional heat stroke
    2. B. Heat exhaustion from dehydration
    3. C. Hypoglycemia from glycogen loss
    4. D. Exercise-associated hyponatremia
    Show answer

    Answer: D. Exercise-associated hyponatremia

    Drinking more hypotonic fluid than is lost in sweat dilutes serum sodium and causes cerebral edema, with confusion and seizures. A normal temperature argues against heat stroke, although sodium and glucose should both be checked.

23. The heat index combines air temperature with:

    1. A. Wind speed
    2. B. Relative humidity
    3. C. Solar radiation level
    4. D. Altitude above sea level
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    Answer: B. Relative humidity

    The heat index estimates how hot it feels when humidity limits sweat evaporation. Wind speed combined with temperature gives the wind chill, which applies to cold exposure.

24. Which situation best fits the usual definition of a wilderness EMS call?

    1. A. A hiker hurt 4 hours' carry from a road
    2. B. A golfer who collapses on a city course
    3. C. A cyclist hurt on a rural road near town
    4. D. A swimmer at a lifeguarded public beach
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    Answer: A. A hiker hurt 4 hours' carry from a road

    Wilderness EMS is defined by the setting: remote or austere locations with limited resources and prolonged access and evacuation, so that the crew must give extended care. Courses and systems commonly use a threshold of more than 1 hour (some use 2 hours) to definitive care, and the WMS/NAEMSP wilderness EMS work stresses delay and austerity rather than a fixed number; a 4-hour carry-out qualifies under any of these definitions. Being outdoors is not enough: a golfer on a city course, a cyclist on a rural road near town, and a swimmer at a guarded public beach can all reach an ambulance and hospital quickly, so ordinary EMS care applies. (WMS/NAEMSP 2017 wilderness EMS joint project; WMS definition of wilderness medicine.)

25. Which person is at greatest risk of both heat and cold illness?

    1. A. A fit 25-year-old office worker
    2. B. A 40-year-old acclimatized roofer
    3. C. A 16-year-old swimmer in summer
    4. D. A frail 85-year-old living alone
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    Answer: D. A frail 85-year-old living alone

    Older adults have blunted thirst, sweating, shivering, and vasoconstriction, take medications that impair thermoregulation, and may be unable to leave a hot or cold home. Social isolation delays discovery.