Distinguish heat exhaustion from heat stroke, apply emergency cooling, recognise and treat hypothermia with correct rewarming, and understand the long-term dangers of untreated temperature emergencies.
Temperature emergencies at both extremes are medical emergencies that cause death when mismanaged — or when they go unrecognised entirely. Heat stroke kills approximately 700 people in the US annually, with the number rising significantly during heatwaves in the elderly and outdoor workers. Hypothermia kills approximately 1,300 people per year in the US alone, and the majority of those deaths occur in people who were never at great cold weather risk — many occur indoors in people whose core temperature dropped slowly over days.
The fundamental challenge with temperature emergencies is that they impair the very cognitive function needed to recognise them. The heat stroke victim does not know they are not thinking clearly. The hypothermic person feels comfortable, even warm, and may remove clothing (paradoxical undressing). Recognising these conditions from the outside — in someone else — and acting correctly is what saves lives.
Painful muscle spasms caused by salt and water loss through sweating during exercise or heat exposure. The person is sweating; core temperature is normal or minimally elevated.
Treatment: Stop activity; move to a cool area; drink water or electrolyte solution; stretch and massage affected muscles. Not life-threatening, but a warning sign of more severe heat illness if activity continues.
The body is struggling with heat but has not lost control of temperature regulation.
Signs:
Treatment:
⚠️ Heat exhaustion can progress to heat stroke within minutes if the person continues in the hot environment or if cooling is inadequate. Treat heat exhaustion aggressively to prevent this progression.
Heat stroke is a medical emergency. The body's temperature regulation has failed and core temperature has risen above approximately 40°C (104°F). Uncontrolled, heat stroke causes brain damage, organ failure, and death within minutes to hours.
Two types:
| Classic Heat Stroke | Exertional Heat Stroke |
|---|---|
| Typically in elderly, unwell, or medicated people | Typically in young healthy athletes or workers |
| Develops over hours or days in heat | Develops quickly during intense exercise |
| Skin often hot and DRY | Skin often wet with sweat |
| Onset during heatwave, unventilated rooms | Onset during extreme physical exertion |
Signs of heat stroke:
⚠️ Altered mental status in the context of heat exposure is heat stroke until proven otherwise. This is the critical distinguishing sign from heat exhaustion. Call emergency services immediately.
Cooling in heat stroke must be rapid and aggressive. Every minute at high temperature causes more brain and organ damage.
Hypothermia is defined as a core body temperature below 35°C (95°F). It is classified by severity:
| Stage | Core Temp | Signs |
|---|---|---|
| Mild | 35–32°C (95–89.6°F) | Shivering, impaired coordination, confusion, fatigue, pale skin |
| Moderate | 32–28°C (89.6–82.4°F) | Shivering stops, increasing confusion, drowsiness, muscle stiffness |
| Severe | Below 28°C (82.4°F) | Unconsciousness, no shivering, very slow or absent pulse, paradoxical undressing |
Paradoxical undressing: As hypothermia deepens, peripheral blood vessels paradoxically dilate, causing a sudden sensation of warmth. Victims may remove clothing. This is a sign of severe hypothermia, not recovery.
Field assessment: In the field without a thermometer, assess severity by shivering. If the person is shivering, they are mild-moderate. If shivering has stopped in someone who was previously cold and confused, this is a dangerous sign — do not assume they are "warming up."
Afterdrop is the paradoxical fall in core temperature that can occur when peripheral warming causes cold blood to return to the core. Risk is highest when:
Prevent by rewarming the torso and head first, not the limbs.
"No one is dead until they are warm and dead." Cardiac arrest in hypothermia can be reversible with rewarming — there are documented cases of full recovery from cardiac arrest in hypothermia with very low or absent core temperature.
| Condition | Key Sign | Immediate Action |
|---|---|---|
| Heat cramps | Muscle spasm, sweating, normal consciousness | Rest, cool area, fluids, electrolytes |
| Heat exhaustion | Heavy sweating, weakness, dizziness, oriented | Cool area, lay down, cool cloths, fluids |
| Heat stroke | Altered consciousness in heat | Emergency services; aggressive cooling immediately |
| Mild hypothermia | Shivering, cold, alert | Shelter, dry warm clothes, warm drinks |
| Moderate/severe hypothermia | Shivering stopped, confused, unconscious | Gentle handling; wrap core; emergency services; CPR ready |
| Paradoxical undressing | Cold person removing clothes | Severe hypothermia; maintain insulation; emergency services |
| Afterdrop | Temperature still falling during rewarming | Rewarm core first; no vigorous activity; handle gently |
This guide provides general information on heat and cold emergencies. Heat stroke and moderate-to-severe hypothermia are medical emergencies requiring hospital-level care. Always call emergency services for suspected heat stroke or moderate-to-severe hypothermia. Prevention through awareness of environmental conditions and appropriate clothing is the most effective strategy.
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