Q: I ran the Boston Marathon and had to leave the race at mile 15 because it was so cold and I was shivering uncontrollably. What causes this?

A: Normal body temperature is 98.6 degrees Fahrenheit (98.6 F); lower than this is hypothermia. Although failure to produce enough body heat due to certain medical conditions (such as very low thyroid levels) can occur, by far the most common cause of hypothermia is excess heat loss. Heat can be lost by:

Radiation: when the body temperature is higher than the surrounding air, heat will radiate from the patient (similar to heat radiating from a wood stove). This is usually the main mechanism of heat loss when people are at rest under normal conditions.
Evaporation: when the water in sweat or on wet clothing/skin evaporates (turns from liquid to gas), heat is lost (there is more energy in a gas than in a liquid). In addition, heat is lost in the moisture in the breath we exhale. This is usually the main mechanism of heat loss during exercise (we sweat to lose the excess heat our body generates during exercise).
Convection: this is when air blows past us and carries off body heat (and why a fan can help cool you off on a hot day).
Conduction: this is when heat transfers directly from the body to another heat conductive material that is directly in contact with it. During cold water immersion this is the reason heat loss is so extreme.

Although runners were not ‘immersed’ in water during the 2018 Boston Marathon, it was raining so hard the runners became ‘soaking’ wet. They therefore had excess heat loss from radiation (it was cold), evaporation (of their sweat and the water in their wet clothes), convection (it was windy) and conduction (it was raining so hard the water would carry some of their body heat away as it dripped off of them).

The degree of hypothermia is usually broken into stages, although the specific temperature ranges for these stages is somewhat arbitrary. For today’s discussion I will define stage 1 hypothermia as 95 to 98 F. People with this mild drop in body temperature will feel cold and begin to shiver, although they are able to stop shivering if they try. The victim may feel nauseas and their dexterity will diminish, making complex tasks difficult. Treatment is to get out of the cold, and get dry and warmed up.

Stage 2 hypothermia, 90 to 95 F, is a medical emergency. People with this pronounced a drop in body temperature will usually be shivering violently and will not have control over their shivering. Their muscle coordination will be poor, with slow labored movements. They are often confused. These symptoms may make them seem drunk. Treatment is to bring them out of the cold and to begin re-warming while arranging emergent medical care.

Stage 3 hypothermia (temperature less than 90 F) is a critical condition, with a high mortality rate. Once body temperature drops this low the patient’s shivering response stops. They will be very confused, even delirious, and their muscle coordination so limited they are unable to walk. Their exposed skin will be blue, puffy and fragile. Victims with such low body temperature are at risk for heart arrhythmias, which can be fatal. Even with prompt medical treatment 20 percent or more of patients with body temperature under 90 F die. Once body temperature drops to the low 80’s mortality climbs over 50 percent. About 1000 Americans die of hypothermia every year, most often due to immersion in cold water or prolonged exposure to extreme cold (such as winter hikers who get lost and have prolonged exposure to the elements).

When re-warming a hypothermia victim:

Bring them somewhere warm
Remove their wet clothing
Make sure they are insulated from the cold ground
Give warm fluids (if they are acting coherently)
Consider sharing body heat using skin to skin contact (insulating them only prevents heat loss, advanced stage victims need active rewarming)

But don’t:

Delay getting appropriate medical care
Rub their skin (this can damage cold, fragile skin)
Apply direct heat with heating pads or heating lamps (this can cause tissue damage)
Give them alcohol (a ‘shot of whiskey’ only works in cartoons)

Advanced medical rewarming techniques include infusing warmed fluids directly into the victim’s blood vessels, body cavity (stomach, bladder or other) lavage with warm fluids, as well as use of special warming blankets and pre-warmed air/oxygen. There are documented cases of successful resuscitation even after prolonged periods of pulselessness, leading to the medical adage “someone is not dead until they are warm and dead.”

I had the privilege of working in one of the medical tents for the 2018 Boston Marathon, and we were much busier than usual because of hypothermia induced by the weather. Many runners did not finish the race this year because of these extreme conditions.
