The Philadelphia ExperimentSuspended animation, the stuff my childhood sci-fi movies were made of, is coming to a hospital near you – if you live in Pittsburgh. Apparently, this has been tested well enough in pigs to let the docs have a go on real patients. We’re as surprised – and excited – as you are. Let’s have a look at medical frontier meeting sci-fi, and why it might not be so far off after all.

Going live – on the dead
Of course, this isn’t exactly mainstream treatment, but seem to have been granted for 10 test subjects for a start. 10 stab or gun shot victims at the edge of life will be rapidly cooled to suspend cell activity to buy time to be and taken to surgery to fix them before rewarming and restarting them.

At the edge of life actually means dead. Inclusion is by traumatic cardiac arrest – described as loss of pulse – less than 5 mins before entering the ED or in the ED. Then, all standard life saving measures, including thoracotomy must have been performed before suspended animation is initiated. The thoracotomy is also needed to access the aorta for rapid cooling.

The trial is run by Dr. Tisherman and a short, but interesting protocol is available at here, and was recently presented in a news article here.

Inducing suspended animation
The goal is to induce deep hypothermia quickly to avoid hypoxic damage. This is done by rapidly flushing a cold crystalloid solution through the body, replacing all the blood and inducing hypothermic metabolic arrest – or, said in a cooler way, suspended animation.

There’s been a lot of studying on dogs and pigs, with promising results. Even after being in profound hypovolemic shock for up to one hour before initiation of suspended animation. There’s also been studies on different techniques and targets, showing that rapid cooling is beneficial, and that the optimal cooling target apparently is 10 degrees celcius. 15 degrees slightly worse, 5 degrees a lot worse. But all tests are small in numbers. But this is what we have so far, so rapid cooling and 10 degrees is what they’re going for in Pittsburgh.

Tests have been on anaesthetisted dogs and pigs having inflicted lethal bleeding injuries and then put on suspended animation before exsanguinating to cardiac arrest. True suspended animation is still a dream, as metabolism isn’t really arrested, merely slowed down considerably. So we aren’t going to Mars just yet, the clock is still ticking – just slower.

Suspended animation
Illustrating the concept: Full line is showing MAP, dotted line is temperature.

The goal is survival, including good neurological survival. By clamping the aorta, the cooling first focuses on the upper body, and most importantly, the brain. Neurological tests has been looking at animals retaining previously learned procedures, and how they adapt to learning new stuff. Both these parameters are good with up to 60 minutes in suspended animation, and in some settings up to 90 minutes. 120 minutes seems to be pushing it with current techniques.

The Pittsburgh experiment
And now it’s been decided the time has come for human tests. We’ll be followig the Pittsburgh Experiment, hoping it won’t be the Philadelphia Experiment‘s little sister.

It will be interesting to see if quick cooling to suspended animation is feasible in real settings with real humans, and give time and opportunity for surgeons to fix the problem, and then finally wake the persons back up with intact physiology and neurology.

The team say they’re reluctant to use the term suspended animation, as it sounds like a sci-fi movie. They probably have to say that to sound professional, but we all know they too love the term and use it every chance they get. We would.

Interview with the Pittsburgh team


Still, this is not new
Once cooled, the trials have either had subjects on no circulation, or on a low flow external circulation (ie a cardio-pulmonary bypass circuit). For the rewarming, the subjects are put on bypass, crystalloid goes out, blood goes in and is heated through the bypass system. They’re in suspended animation.

In that setting, they’re not much different from thoracic anaesthesia where thoracic aortic surgery is sometimes performed on cooled patients with the heart stopped and no bypass running. This is a kind of brief suspended animation, and quite eerie to watch. This gives the surgeons very limited time to do the repair. Cooling the patient further, and removing the blood, buys a lot of extra time.

A similar thing happens with drownings that are ‘naturally’ cooled before going into arrest. They are in state of suspended animation when they get to hospital and get rewarmed.

Other future uses
As mentioned, this treatment buys time, much like ECMO does for heart and/or lung failure, and might not be just for trauma bleedings. Safar mentions in his overview article that

“Suspended animation could also be useful when surgeons and anesthesiologists are unexpectedly losing ground with unmanageable hemorrhage during various surgical operations – and for performing otherwise infeasible cardiovascular or neurosurgical procedures.”

There are a lot of available articles on suspended animation, many (most) of them written by Peter Safar and Hasan Alam. First, though, is Tisherman’s protocol. Then a nice overview on suspended animation by Safar, followed by one of Alam’s experiments:

Emergency Preservation and Resuscitation (EPR) for Cardiac Arrest From Trauma (EPR-CAT), Tisherman,, 2011.

Suspended animation for delayed resuscitation, Safar, Curr Opin Anaesthesiol, 2002.

Learning and memory is preserved after induced asanguineous hyperkalemic hypothermic arrest in a swine model of traumatic exsanguination, Alam, Surgery, 2002.

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