A hospital in Pennsylvania will soon begin clinical trials to put gunshot or other accident victims into a state of suspended animation while their organs are repaired. By all measures the people suspended will be dead for hours but with luck many will be brought back to life.
The first step is to flush cold saline through the heart and up to the brain – the areas most vulnerable to low oxygen. To do this, the lower region of their heart must be clamped and a catheter placed into the aorta – the largest artery in the body – to carry the saline. The clamp is later removed so the saline can be artificially pumped around the whole body. It takes about 15 minutes for the patient’s temperature to drop to 10 °C. At this point they will have no blood in their body, no breathing, and no brain activity. They will be clinically dead.
In this state, almost no metabolic reactions happen in the body, so cells can survive without oxygen. Instead, they may be producing energy through what’s called anaerobic glycolysis. At normal body temperatures this can sustain cells for about 2 minutes. At low temperatures, however, glycolysis rates are so low that cells can survive for hours. The patient will be disconnected from all machinery and taken to an operating room where surgeons have up to 2 hours to fix the injury. The saline is then replaced with blood. If the heart does not restart by itself, as it did in the pig trial, the patient is resuscitated. The new blood will heat the body slowly, which should help prevent any reperfusion injuries.
The technique will be tested on 10 people, and the outcome compared with another 10 who met the criteria but who weren’t treated this way because the team wasn’t on hand. The technique will be refined then tested on another 10, says Tisherman, until there are enough results to analyse.
No one knows how long people can be maintained in suspended animation before revival is impossible. We know from accidents where people drown in icy lakes that suspended animation can work for at least half an hour and experiments on pigs suggest no cognitive defects from revived animals suspended for up to an hour, mice have been suspended for up to six hours and roundworms for up to 24 hours. If the initial trials are successful, further experiments will likely discover ways to lengthen the period of suspended animation in humans and perhaps suggest improvements to current cryonic techniques.
Hat tip: Noah Smith.