Tuesday, November 27, 2007

Stopping Battlefield Bleeding

A polymer-filled pouch that expands when exposed to blood can quickly halt bleeding.

By Brittany Sauser

A lifesaver: The swelling hemostats (above) are designed to absorb blood and stop bleeding in severe wounds. A superabsorbent polymer inside each pouch soaks up the blood and expands, putting pressure on the walls of the wound and stemming the flow of blood. Credit: Aurora Flight Sciences

Researchers at Aurora Flight Sciences have developed a pouch that can be put inside a large, open wound to halt life-threatening bleeding within minutes. The pouch, called a swelling hemostat, resembles a beanbag and is made of a polymer-fiber mesh encased in spandex fabric. The polymer absorbs the blood, and as it does, it expands, putting sufficient pressure on the walls of the wound to stem the flow of blood. Preliminary tests have also shown that the pouch promotes clotting: only the water from the blood is absorbed, hence the natural clotting factors that exist in blood become concentrated.

The pouch would be most useful for treating wounds in areas of the body where a tourniquet could not be applied and for wounds too large and severe for haemostatic bandages. One of the main causes of soldier death in Iraq and Afghanistan is bleeding, and there are many instances on the battlefield in which this device would prove lifesaving, says Javier de Luis, chief scientist at Aurora and the principal investigator for the swelling hemostat. Furthermore, it can be worn for long periods of time without any side effects, and it can be easily removed.

Conventional methods for controlling external bleeding include applying direct pressure. This can be done by a medic or another individual compressing the wound, stuffing it with haemostatic gauzes, or applying a tourniquet. "Each one presents a unique problem, and I am not sure any of them are very effective," says George Velmahos, a professor of surgery at Harvard Medical School and chief of the division of trauma, emergency surgery, and surgical critical care at Massachusetts General Hospital (MGH). A tourniquet, for example, stops the blood circulation below the point on which it is applied, which leaves the rest of the extremity susceptible to becoming "dead muscle," says Velmahos. Recently, the U.S. Army developed an ultrasonic tourniquet to stem the flow of blood using focused beams of ultrasound. (See "An Ultrasonic Tourniquet to Stop Battlefield Bleeding.") But this method, along with others, has thermal side effects that cause damage to the surrounding tissue.

It is also very difficult to compress deep wounds, especially when bullets are flying, says Velmahos. "We need smart devices and smart materials that can stop bleeding without cutting circulation off, and without the need of a paramedic or another body being physically present. To that extent, the swelling hemostat is very useful."

The pouch initially measures about three square inches and only weighs a couple of ounces, making it easy to stuff into a first-aid kit, a backpack, or even a soldier's pocket. It is made of a polyacrylic-acid-based superabsorbent polymer powder, a standard material known to greatly swell when exposed to water, hence it can absorb the aqueous components of blood and expand. However, when the pouch is used in a wound, the expansion of the polymer particles is easily blocked by the particulates in the blood, which significantly reduces the effectiveness of the polymer in the device.

To combat this, Aurora researchers mixed the polymer with a polypropylene fiber. The fiber keeps the polymer particles evenly spaced so that they can soak up the blood quickly while expanding uniformly. The outside material is a micro-mesh spandex fabric that stretches to accommodate gel expansion. The pouch, in turn, puts pressure on the walls of the wound and stems the flow of blood through a mechanical fluid-blocking effect.