Cause & Manner: Lethal Hypothermia

It was my first day on the Colorado doctor’s ski patrol and lethal hypothermia was the last thing on my mind as I floated down a perfect powder run. “Code blue, bottom of Rabbit Run,” said a voice on my radio. “Code blue; doc we need you now.”

A skier lay unconscious, not breathing, no pulse, as blizzard-like snow blew around us and the temperature dropped to 10°F (-12°C). I tried to intubate him but the frozen secretions in his throat made it impossible. A bag of intravenous fluid froze in the tubing. “Helicopter can’t come in because of the weather,” said the ski patrol guy. “You know we can’t declare him dead out here because he’s hypothermic, right?”

After hours of futile CPR, an ambulance took the 26-year-old to the nearest hospital for the official pronouncement. His cause of death turned out to be a broken neck from trying to jump over an off-trail creek. But all we knew on the snowy slope that day was that he wasn’t dead until he was warm and dead.

Lethal hypothermia is on the rise

In 2003, about 600 people per year died of hypothermia in the United States. By 2010, the number had more than doubled and was up to 1,536. Today total mortality numbers aren’t readily available, perhaps due to changing definitions and medical coding practices. But wild temperature swings, including severe cold snaps in southern states, make it likely hypothermia is a growing threat.

What we do know is that hypothermia deaths are more common than hyperthermia (heat stroke) deaths. Although lethal hypothermia is much less common than accidental death due to drug overdose or motor vehicle crash, almost every coroner or medical examiner sees hypothermia deaths.

What is Lethal Hypothermia?

The classic definition of human hypothermia is a core body temperature lower than 95.0°F (35.0°C), but there’s no set temperature at which someone dies of hypothermia. That’s one reason it’s not always easy to determine if hypothermia was an underlying or contributing cause of death.

Because the elderly, the very young, the chronically ill, and alcohol and drug users are particularly prone to hypothermia, it’s often a challenge to puzzle out which came first—a death due to natural causes or hypothermia due to excessive cold, an accidental death.

Bizarre Behaviors

Patrick Dolan, age 35, died of hypothermia during a blizzard on December 26, 1846. “As the blizzard progressed, Dolan became delirious, stripped off his clothes, and ran into the woods. Reportedly ranting that it felt “warm as a summer day,” Dolan’s Donner Party companions brought him back into the Camp of Death where he died a few hours later.

Dolan’s behavior in the throes of hypothermia is a bizarre phenomenon known as “paradoxical undressing.” Severe hypothermia affects the brain’s temperature regulation centers, making the person feel hot rather than cold. Dilation of peripheral blood vessels, no longer able to constrict in response to cold, may also play a role.

An elderly woman I’ll call Winnie lived alone and no one had seen her in person for the past week because of COVID concerns. Eventually a family member found her in her back yard with a body temperature of 41°F (5°C). Despite the cold, Winnie had removed her shoes and wore no jacket. Several abrasions and a laceration made the coroner wonder about foul play, but the injuries were superficial. The cause of death was hypothermia due to environmental exposure, manner accidental.

“Terminal burrowing” is another poorly-understood behavior in victims of severe hypothermia. Winnie’s body was found in a brushy hedge around her back yard. It can happen outdoors, as in her case, or indoors, with victims found under beds or behind furniture. Researchers hypothesize hypothermia causes the brain stem to produce “a primitive and burrowing-like behavior of protection, as seen in hibernating animals.”

As in Winnie’s case, undressing, superficial injuries, and burrowing behavior result in a confusing picture for death investigators. Was the person sexually assaulted? Was someone trying to hide the body? Understanding the physiology of lethal hypothermia can help direct investigators to the correct cause and manner of death.

Who’s at Risk for Lethal Hypothermia?

Living in a rural area doubles (women) and triples (men) the risk of death from hypothermia, according to 2022 CDC data.

The elderly, especially those over 90 years of age or with dementia, are at high risk, as are those experiencing homelessness.

Alcohol use is a frequent finding in hypothermia deaths like that of an Iowa University student in February 2021. Alcohol can cause accidents, loss of consciousness, and disorientation.

In a case I investigated a few years ago, a man in his thirties was found dead in a back yard tool shed at a stranger’s house. He had no signs of trauma but his blood alcohol was just above the legal limit and his body temperature was below 80°F (27°F). I hypothesized that he’d become confused or tired after drinking with friends the night before and had taken shelter in the shed. He was probably alive but asleep or unconscious for some hours, allowing his body to metabolize the alcohol down to the level obtained at autopsy. Unfortunately, the overnight temperature had been less than 50°F (10°C) and he succumbed to hypothermia in his sleep.

Surviving Severe Accidental Hypothermia

Sometimes—very rarely—, someone recovers after apparent death from hypothermia. That’s why doctors may not pronounce someone dead “until they’re warm.” In Norway, they know something about this. A young female skier was trapped in an icy river for almost one and a half hours. When her companions got her out, she had a temperature of 57°F (13.7°C) and no signs of life. Her companions happened to be doctors and did continuous CPR after her extraction from the ice. Several hours later, her heart began to beat on its own again as she rewarmed on cardiopulmonary bypass (heart-lung machine) at a hospital. This woman made a complete recovery.

Few are as lucky as that Norwegian skier. The average mortality rate in severe cases of accidental hypothermia is approximately 70%. It’s probably higher in the elderly and those with underlying medical conditions. Cardiac complications, including dysrhythmias and a condition known as “rewarming shock,” threaten recovery from severe hypothermia. If the patient does survive, mental function may be affected because brain cells didn’t get enough oxygen during the body’s shutdown. Prevention is a better strategy than counting on rescue and resuscitation.

Autopsy Findings in Lethal Hypothermia

If excessive cold may have played a role in the death, the coroner or medical examiner’s investigator must provide the forensic pathologist with solid scene investigation information. Documentation of ambient temperature and home heating conditions and a good history of events immediately preceding the death are key to the diagnosis.

The victim’s core body temperature must be documented at the scene. Some coroner and medical examiner offices no longer do body temperatures at scenes, which means they will miss cases of both hypo- and hyperthermia. A very few offices obtain core temperatures using the gold standard, liver temperature at the scene.

The few gross autopsy findings consistent with (but not specific for) hypothermia include a full bladder and small hemorrhages in the gastric lining. The latter are called Wischnewsky spots and can also be seen in diabetic ketoacidosis. Frequent the skin will be bright red or pink, similar to what’s seen in carbon monoxide poisoning.

Prevention and Treatment

Hypothermia is a medical emergency. Don’t let it get to that point! Any of these three resources will show you the signs to look out for and what to do and not do. For example, did you know that cotton is the worst type of fabric to wear in cold weather?