The alert Monday morning from the Baltimore City Fire Department said the body of an unidentified female had been pulled from the Inner Harbor and sent to the medical examiner to determine her cause of death.

Witnesses reported seeing the dive team retrieve her from water that was probably a bit warmer than the air temperature, around 32 degrees.

Only, she wasn’t dead. First responders later said they were able to resuscitate her.

But how?

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“Basic physiology,” said Dr. Samuel Tisherman, director of the surgical intensive care unit at the University of Maryland Medical Center, who is conducting research into surgical uses of hypothermia at the center’s Shock Trauma Center.

“The cold is protective because the colder you are, the less your organs and cells need oxygen and blood flow to survive,” he said. “Slowing things down buys us time to save somebody.”

Indeed, people have been known to survive more than an hour in cold water or under snowbanks, he said.

The temperature sweet spot isn’t precise, but needs to be cold. The U.S. Coast Guard, which saved more than 5,500 people last year during search and rescue calls, sets it at about 60 degrees.

Of course, there are a lot of variables. If the water is too warm, there’s no protection. And the cold certainly doesn’t assure survival.

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The Guard says the cold can kill someone in the first three minutes at 60 degrees. The shock can cause the heart to stop or lead someone to lose their ability to fully control their breathing, leading the person to take water into their lungs and drown.

In 30 minutes, particularly if someone is trying to swim, the rapid cooling can cause the heart and lungs to labor too much and lead to cardiac arrest. This can happen even before hypothermia, where the body loses more heat than it makes, also shutting down the respiratory, nervous and organ systems.

Someone’s physical condition matters too, said Tisherman, also a professor in the University of Maryland School of Medicine’s department of surgery.

“Don’t fall or jump in cold water if you have a heart condition,” he said.

That said, there are instances where doctors want to make someone extra cold to save them. Tisherman and others at the Shock Trauma Center have been involved in a study, unique in the U.S., where trauma patients are cooled using the same principles.

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When someone is shot or stabbed and loses a lot of blood, the doctors have been chilling them to that 55- to 60-degree range. Surgeons then put patients on a heart-lung machine to maintain enough oxygenated blood to the body while they repair wound sites and transfuse new blood.

This is being performed on people who have a chance of survival but wouldn’t likely survive using traditional methods.

Survival doesn’t necessarily mean there isn’t long-term damage, however, with these patients or the woman who was pulled from the harbor, Tisherman added. There can be long-term harm to the lungs, heart, and most alarmingly, the brain, from being deprived of enough blood and oxygen. He said the emergency responders who initially thought she was dead must have seen some sign, perhaps a weak pulse, that made them work to revive her and take her to a hospital for further care.

The Baltimore City Fire Department reported that she was in critical condition Monday evening. Officials did not respond to request for comment on her condition Tuesday or how often they save someone in similar circumstances. Dozens of people have fallen in the harbor in the past decade, according to media reports.

And while Tisherman doesn’t normally advocate falling in ice-cold water, he did have a few words for people who plan to jump in the Chesapeake Bay on purpose this weekend as part of the Maryland State Police’s Polar Bear Plunge fundraiser.

Don’t do it if you have a heart condition. And for everyone else, “Get in and get out and get warm.”

Meredith Cohn is a health and medicine reporter for The Baltimore Banner, covering the latest research, public health developments and other news. She has been covering the beat in Baltimore for more than two decades. 

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