London - Humans have been placed in "suspended animation" for the first time as part of a medical trial, doctors claim.
The technique involves replacing a patient’s blood with ice-cold saline solution, in effect freezing them in time because it results in most brain and heart activity stopping.
In this state the body needs less oxygen to survive and this gives doctors extra time to save patients already close to death. After being in suspended animation for up to two hours, they are warmed up and their heart fully restarted.
Trials of the revolutionary technique called emergency preservation and resuscitation (EPR) were carried out in the US on trauma patients – with gunshot or stab wounds, for example – who had only a five percent chance of surviving
Dr Samuel Tisherman, of the University of Maryland School of Medicine, told a symposium in New York that his team had placed at least one patient in suspended animation, but he did not say whether they or any others had survived.
He described the process as "a little surreal", New Scientist reported. At normal body temperatures, when a person’s heart stops beating, they can survive for only around five minutes before cells die from lack of oxygen.
But in suspended animation – when body temperature is reduced from a normal 37C to 10C – chemical reactions in the cells slow down or stop so they need less oxygen. This buys surgeons more time to try to save the patient.
The trial was given the go-ahead by the US Food and Drug Administration, which exempted the doctors from requiring patient consent as the participants’ injuries were likely to be fatal and there was no alternative treatment.
The team had discussions with the local community and placed adverts in newspapers describing the trial, pointing people to a website where they could opt out in advance.
The trials were inspired by animal studies that showed pigs with acute trauma could be cooled for three hours, operated on and resuscitated. Dr Tisherman said: "We felt it was time to take it to our patients. Now we are doing it and we are learning a lot as we move forward with the trial. Once we can prove it works here, we can expand the utility of this technique to help patients survive that otherwise would not."
Dr Tisherman’s talk was entitled Suspended Animation, but he stressed that he was not exploring ways to preserve astronauts for deep space missions. "I want to make clear that we’re not trying to send people off to Saturn," he told New Scientist. "We’re trying to buy ourselves more time to save lives."
Doctors are still working to understand how the time a person is in suspended animation can be extended.
An effect called reperfusion injuries can occur when a person is warmed up, which involves chemical reactions that can damage the cell – a risk that increases the longer they are without oxygen.
Drugs could be used to extend the time a person is suspended, but Dr Tisherman explained that "we haven’t identified all the causes of reperfusion injuries yet".