Suspended Animation in Humans

At the University of Maryland Medical Centre in Baltimore, Dr. Samuel Tisherman’s surgical team has started suspended animation trials on humans with critical injuries such as gunshot wounds or stab wounds. The technique is called Emergency Preservation and Resuscitation (EPR), and it has the potential to save the lives of patients that suffer cardiac arrest due to acute traumas or critical injuries. The major cause of fatality in these patients is severe hemorrhage which leads to cardiac arrest. The current standard treatment for cardiac arrest with acute traumas is called Emergency Department Thoracotomy (EDT). In EDT, the chest is opened to locate the thoracoabdominal site of hemorrhage and preserve blood supply for the heart and brain by clamping the descending thoracic aorta (Søreide, Petrone, & Asensio, 2007). Unfortunately, the survival rate after EDT is less than 8% (Rhee et al., 2000). This is due to profound hemorrhage, the rapid exsanguination from major vascular injuries, and the short time interval between cardiac arrest and brain ischemia (Rhee et al., 2000). Within 5 minutes of ischemia the brain starts to develop permanent damage due to neuronal cell death and secondary injury occurs in the hours and days after the cardiac arrest if the patient survives (Sekhon, Ainslie, & Griesdale, 2017). Furthermore, the heart becomes damaged after 20 minutes of ischemia (Tisherman et al., 2017). Therefore, Dr. Tisherman and his team developed EPR as a way to prolong the time frame between cardiac arrest and brain ischemia giving surgeons a longer time frame to locate and repair critical injuries. In animal studies, EPR increased the rate of survival after hemorrhagic and exsanguination injuries as compared to standard procedures (Rhee et al., 2000; Wu et al., 2006). Therefore, EPR may improve the survival rate in humans as well. 

The EPR technique induces hypothermia in order to decrease oxygen metabolism in tissues reducing the risk of brain and cardiac damage from exsanguination. In EPR, the patient’s entire body is cooled to a temperature of 10°C by infusing the body with cooled saline using closed-chest cardiopulmonary bypass (CPB) (Tisherman et al., 2017). Then the surgical team can locate the site of hemorrhage and repair it. Once the site of hemorrhage is repaired and hemostasis is achieved, slowed reperfusion and rewarming of the body (to 34°C) can be initiated using CPB (Tisherman et al., 2017). This mild hypothermia is maintained for an additional 12 hours, and then the patient is allowed to return to normal core body temperature (37°C) (Tisherman et al., 2017). The major risk associated with induced, prolonged hypothermia is blood coagulation as platelet function becomes abnormal below 34°C (Patt, McCroskey, & Moore, 1988). If severe coagulation during ERP occurs, the patient is fully returned to normal core body temperature immediately following the procedure to prevent complications (Tisherman et al., 2017). Otherwise, several studies have shown that hypothermia for less than 2 hours is safe, and there are no neurological deficits associated with it (Behringer et al., 2003; Iyegha et al., 2010; Nozari et al., 2004). Therefore, the EPR technique is very promising for the treatment of critical and traumatic injuries with severe hemorrhaging. If human trials of EPR are successful, then the technique could revolutionize the field of trauma surgery. 

References 

Behringer, W., Safar, P., Wu, X., Kentner, R., Radovsky, A., Kochanek, P. M., ... & Tisherman, S. A. (2003). Survival without brain damage after clinical death of 60–120 mins in dogs using suspended animation by profound hypothermia. Critical care medicine, 31(5), 1523-1531. doi: 10.1097/TA.0b013e3181d3cbc0

Iyegha, U. P., Greenberg, J. J., Mulier, K. E., Chipman, J., George, M., & Beilman, G. J. (2012). Environmental hypothermia in porcine polytrauma and hemorrhagic shock is safe. Shock, 38(4), 387-394. doi: 10.1097/SHK.0b013e3182657a21

Nozari, A., Safar, P., Wu, X., Stezoski, W. S., Henchir, J., Kochanek, P., ... & Tisherman, S. A. (2004). Suspended animation can allow survival without brain damage after traumatic exsanguination cardiac arrest of 60 minutes in dogs. Journal of Trauma and Acute Care Surgery, 57(6), 1266-1275. doi: 10.1097/01.ta.0000124268.24159.8b

Rhee, P. M., Acosta, J., Bridgeman, A., Wang, D., Jordan, M., & Rich, N. (2000). Survival after emergency department thoracotomy: review of published data from the past 25 years. Journal of the American College of Surgeons, 190(3), 288-298. doi: 10.1016/s1072-7515(99)00233-1

Tisherman, S. A., Alam, H. B., Rhee, P. M., Scalea, T. M., Drabek, T., Forsythe, R. M., & Kochanek, P. M. (2017). Development of the emergency preservation and resuscitation for cardiac arrest from trauma clinical trial. Journal of Trauma and Acute Care Surgery, 83(5), 803-809. doi: 10.1097/TA.0000000000001585

Sekhon, M. S., Ainslie, P. N., & Griesdale, D. E. (2017). Clinical pathophysiology of hypoxic ischemic brain injury after cardiac arrest: a “two-hit” model. Critical care, 21(1), 90. doi: 10.1186/s13054-017-1670-9

Søreide, K., Petrone, P., & Asensio, J. A. (2007). Emergency thoracotomy in trauma: rationale, risks, and realities. Scandinavian Journal of Surgery, 96(1), 4-10. doi: 10.1177/145749690709600102

Wu, X., Drabek, T., Kochanek, P. M., Henchir, J., Stezoski, S. W., Stezoski, J., ... & Tisherman, S. A. (2006). Induction of profound hypothermia for emergency preservation and resuscitation allows intact survival after cardiac arrest resulting from prolonged lethal hemorrhage and trauma in dogs. Circulation, 113(16), 1974-1982. doi: 10.1161/CIRCULATIONAHA.105.587204