乌鸦传媒

Time is running out for responders trying to locate the submersible from expedition company OceanGate that went missing on Sunday in the North Atlantic, but some still remain hopeful for a rescue.

The Titan submersible -- which had five people aboard -- lost contact about an hour and 45 minutes into its dive to the Titanic shipwreck site, which sits more than 2 miles down on the ocean floor.

It's impossible to know at this point whether the vessel is bobbing on the ocean surface somewhere, floating in the water column, or sitting on the ocean floor -- or if it succumbed to the immense pressure that exists at a depth of 12,500 feet.

But should a rescue be possible, emergency and hyperbaric medicine experts walked through the considerations and response strategies that would be appropriate.

Matthew Levy, DO, MSc, deputy director of operational medicine for the Johns Hopkins emergency medicine department in Baltimore and an expert in pre-hospital emergency care, told 乌鸦传媒 that, given the time that has elapsed, a primary consideration would be the consequences of the hypoxic environment and treating patients for hypercarbia, or a buildup of carbon dioxide in the bloodstream.

Physicians would also have to consider other physiologic stressors of having limited rations, including hypoglycemia and dehydration, he said, as well as exacerbations of any underlying chronic conditions or comorbidities.

In addition, ocean temperatures can be extremely cold, especially at depth, so responders might need to treat for hypothermia, he added.

There's also the need to assess for physical trauma that could have occurred if the vessel had a hard landing or was otherwise bumped around, he noted. That includes everything from soft tissue or musculoskeletal injuries to head injury.

Barotrauma events are also a possibility, if the participants experienced a rapid change in ascent or descent inside the vessel, particularly if the sub's pressurization equipment wasn't functioning properly. These include decompression sickness, pneumothorax, and air embolism, Levy said.

"This goes back to core dive medicine, all of those things associated with changes in depth and how quickly they occur," he said.

Decompression sickness is one of the most well-known complications of scuba diving. It's also known as "the bends" because it tends to cause severe pain in the joints. Essentially, it results from bubbles of nitrogen gas that were able to slip into tissues under compression, but become trapped if a diver ascends too quickly, Levy said.

It's difficult to imagine exactly how much pressure would be on a submersible at a depth of 12,500 feet. Scuba divers are taught that for every 10 meters (30 feet) they descend, they carry the weight of an entire additional atmosphere on them. The National Oceanic and Atmospheric Administration (NOAA) estimates that one atmosphere accounts for about 14.6 pounds per square inch (PSI) of pressure.

"If there was any kind of hull breach, the occupants would succumb to the ocean in a near instant, given the more than 5,500 PSI pressure exerted by the ocean at the depth of 3,800 meters, which is 380 times the air pressure at the surface," Nicolai Roterman, DPhil, of the University of Portsmouth in England, who is a deep-sea ecologist and lecturer in marine biology, said in a .

Levy expressed concern for the five people aboard the submersible, as well as their families, and the rescue teams that were putting themselves in harm's way to try to find the missing vessel.

Roterman urged caution about future expeditions, noting that the "deep sea is a very inhospitable place. Even the most reliable technology can fail, and therefore accidents will happen. With the growth in deep-sea tourism, we must expect more incidents like this."

"Deep-sea tourism is not without impacts on the environment," he added, "and rather like the tragedies and human detritus left on Mt. Everest, a conversation is warranted about whether this is a worthwhile human endeavor going forward."

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