Clot Forming Dressings
Over the past few years several new clot-forming dressings have been developed to help control severe life-threatening bleeding. This market has been driven primarily by the military for war efforts in Iraq and Afghanistan. There are many aspects of providing emergency care in the military setting that are quite different from those in the civilian arena.
One of the most obvious differences is the set of massive injuries that can occur from improvised explosive devices (IED’s). These devices can rip through vehicles producing shrapnel that can cause deep penetrating wounds and even sever limbs. The depth of these wounds can produce life-threatening arterial bleeding which can be very hard to control. Thus, the new dressings containing blood-clotting compounds to help rapidly form blood clots which seals off the bleeding arteries.
Venous versus arterial bleeding – a quick review of the circulatory system:
The heart is a two-sided pump. Blood returning to the heart enters the right side into the right atrium. As the heart contracts, the blood in the right atrium is pushed through the tricuspid valve into the right ventricle. From there it is pumped through the pulmonary valve into the vasculature of the lungs, which is referred to as the pulmonary circulation.
In the lungs, carbon dioxide leaves and oxygen enters the blood. The freshly oxygenated blood now returns to the heart and enters the left atria. As the heart contracts, this blood is pushed through the mitral valve into the left ventricle and then through the aortic valve into the aorta.
The heartbeat, pulse, propels the blood down the length of the aorta. The aorta divides into smaller arteries, then into even smaller arterioles, and finally into the smallest vessels, the capillaries. It is in the capillaries where the oxygen exchange occurs, nutrients are delivered, and carbon dioxide and waste products are picked up. The capillaries then merge together to make larger venules; they merge into veins, which merge into the vena cava that empties the blood into the right atrium of the heart, completing the loop of the systemic circulation. The blood returning to the heart via the venous circulation is under very low pressure, 5 –10mm Hg pressure, as opposed to blood leaving the heart and entering the arterial circulation, which is under much higher pressure 100+mmHg pressure. Because of this, arteries are buried deep under muscles, lying against the bones to protect them from possible injury. As a result, arterial bleeding is unusual; the wound has to penetrate deeply into the tissues to reach and injure the arteries.
Venous bleeding is under low pressure as it flows out of a wound and can be easily controlled with direct pressure and simple pressure dressings. However, arterial bleeding, being under high pressure, can squirt out of the wound and be very difficult to control. Arterial bleeding will require several techniques in addition to direct pressure: Applying digital pressure by plugging the hole in the artery with a finger, using a tourniquet to shut off the blood supply to the entire limb, or using a clot forming dressing.
There are two different compounds that are currently being used to promote blood clotting in severe life-threatening arterial bleeding, Chitosan and Zeolite.
Chitosan is a polysaccharide (a polymer or chain of d-glucosamine sugars) that is found in the exoskeletons of shrimp, lobsters, and crabs. This polymer is a naturally occurring bioadhesive that rapidly binds charged surfaces together. Thus, it promotes aggregation of platelets in the blood to clot off the bleeding arteries. Chitosan is the active compound used in Celox and HemCon products. Celox comes as a powder that can be put directly into wounds, or, like HemCon it comes imbedded in the dressings that are applied directly to the wounds.
Zeolite on the other hand,, is a mineral, a microporous aluminosilicate, that is extremely absorbent. It is imbedded in the dressings that are applied to the wounds. Being very absorbent the aluminosilicate quickly forms stable blood clots in the bleeding arteries. Zeolite is used in QuikClot brand hemostatic dressings.
Studies have shown that both of these products are very effective and are presently used by the various militaries. The only down side of Chitosan-based products is that they have to be monitored over time as the clots that form at the site of the injury will begin to deteriorate after about 2 hours and bleeding can resume. Neither of these products is dangerous to the human body.
In the typical, everyday urban situations, these clot-forming dressings are rarely needed as arterial bleeding is rarely encountered and venous bleeding can always be controlled with direct pressure and pressure bandages. But in long-term wound care outside an hour or whenever arterial bleeding occurs, these products can not only be life-saving, but they can prevent the need to use a tourniquet.