Bioengineering for New Medical Treatments: Protective Hypothermia Could Improve Odds of Surviving Cardiac Arrest or Stroke

An ice slurry, delivered through an endotracheal tube, would fill the lungs – cooling the lungs and the heart, nestled between the lungs, and rapidly lowering their temperatures. The area surrounding each carotid artery also could be filled with the slurry through a hypodermic syringe. The blood passing through these "heat exchangers" would cool rapidly, and chest compressions would be used, in the case of cardiac arrest, to induce blood flow to the brain.

More than 90 minutes is required for external cooling (immersion in ice bath) to lower the core temperature of the brain from 37°C to 25°C. With internal cooling, the core of the brain reaches 25°C in 10 minutes.

Victims of cardiac arrest have a very poor chance for survival outside a hospital – less than one in fifty. In minutes, oxygen-deprived cells in the heart and brain begin to die: when they do, the victim cannot recover, even with the best care.

Doctors have known for centuries that cold can slow cell damage caused by a lack of oxygen to the brain. Rapid, localized cooling improves cell survival rates, but external cooling methods – from applying cold wraps to immersion in an ice bath – take an hour or more to cool the brain. It must be done in 10 minutes or less to minimize damage.

In collaboration with physicians from The University of Chicago's Section of Emergency Medicine, Argonne researchers are working on a way to provide rapid, internal cooling of the heart and brain. An Argonne-engineered ice slurry could be used to induce localized hypothermia, which slows cell death. The slurry could be delivered by paramedics to the lungs, which act as heat exchangers to cool the blood. If necessary, the slurry also could be injected via a hypodermic syringe into the subcutaneous tissue along the outside of the carotid arteries for additional cooling.

Research was required on two fronts to develop the slurry concept.

1. Heat transfer modeling by Argonne researchers confirmed that external cooling could not provide the required temperature decrease in the brain quickly enough to minimize damage but that internal cooling could.
2. Argonne engineered highly fluid slurries using chemicals compatible with human tissues and worked with The University of Chicago to develop methods/equipment for slurry delivery.

Tests conducted at The University of Chicago with the Argonne slurry revealed that internal cooling methods can provide brain and heart cooling rates that are more than 20 times faster than those provided by conventional methods.

Patent applications for the slurry technology have been filed. Argonne and the University are continuing their research, under funding from a private firm, to develop procedures and equipment for slurry production and delivery that could be used by paramedics. The company has an option to license the medical cooling technology.

Next Steps

Efforts are underway to develop ice slurry of even greater ice particle content, conduct additional tests, further improve the slurry delivery devices, and engineer the slurry production and delivery equipment that eventually would be used by paramedics. As with any new medical treatment, extensive testing and clinical trials will be necessary before the new protective hypothermia method is approved for general use.

Argonne's expertise in nanofluids technology is also being used to broaden the use of slurries beyond cooling by developing magnetic medicated particle slurries that could be transported through blood vessels to targets and held in position by magnetic forces applied from outside the body.

Researchers found that roughness of ice particles is a key factor, as shown here through a microscope.. (Left) Ice particles formed by simply freezing water are very rough and elongated, and tend to "clump", resulting in poor fluidity. (Center) Ice particles formed by shaving or crushing ice are more round but still rough. (Right) The smooth ice particles formed by adding a freezing point depressant or warm water, which melts away surface roughness, have excellent fluidity and resist clumping and freezing together.

For More Information

• Bioengineering for New Medical Treatment: Nanofluids: Tiny "Magic Bullet" May Help Treat Disease . . .Microscale Heat Transfer Devices: Cooling the Chaos

For more information, contact Argonne's Office of Technology Transfer (800-627-2596, partners@anl.gov).