Public release date: 29-Apr-2008
Intravenous administration of isotonic fluids is the standard emergency treatment in the U.S. for patients with severe blood loss, but UC San Diego bioengineering researchers have reported improved resuscitation with a radically different approach. Building on earlier studies in humans that have shown benefits of intravenous fluids that are eight times saltier than normal saline, the researchers combined hypertonic saline with viscosity enhancers that thicken blood.
Reporting in the journal Resuscitation in an article that is available online, the researchers describe dramatic increases in beneficial blood flows in the small blood vessels of hamsters with the combined hypertonic saline and viscosity enhancement approach. The fluid was given to animals after as much as half of their blood was removed to simulate human blood losses on the battlefield, in traffic accidents and in operating rooms.
The team led by Marcos Intaglietta, a professor of bioengineering at the Jacobs School of Engineering, reported that the new approach sharply improved the animals’ functional capillary density, a key measure of healthy blood flow through tissues and organs.
“Of course, trauma physicians want to get the blood flowing as soon as possible, and increasing the viscosity of blood may not make any sense to them,” said Intaglietta. “However, our results are highly suggestive that increasing viscosity rather and partially restoring blood volume is a better way to increase blood flow through tissues. These findings also are consistent with recent discoveries showing that higher shear forces of more viscous blood leads to dilation of small blood vessels.”
Treating blood loss is a critical medical issue because trauma is the leading cause of death among North Americans 1 to 44 years old. Whether injured on the freeway or wounded in battlefield, loss of 40 percent or more of a patient’s blood is immediately life-threatening. Physicians and emergency workers must act quickly.
The majority of trauma deaths are due to severe brain injury or a dangerous condition resulting from blood loss called hypovolemic shock. When too little blood flows through the body’s organs, the heart begins beating rapidly, the skin becomes cold and pale, blood pressure plummets, and patients exhibit mental confusion. Hypovolemic shock can progress within a matter of one or two hours to organ failure and death.
The bible of trauma physicians and emergency workers, the Advanced Trauma Life Support (ATLS) guidelines, emphasize that physicians first control bleeding and then provide limited fluid resuscitation, a strategy known as “permissive hypotension” until control of hemorrhage is obtained. The ATLS guidelines, developed by the American College of Surgeons and adopted in more than 30 countries, were modified to lower the volume of isotonic fluids given after several studies demonstrated that sudden increases in blood pressure (without immediate bleeding control) would “pop” clots that the body forms to control bleeding.
Over several decades, studies involving humans and animals have evaluated hypertonic saline (up to 7.5 percent sodium chloride) versus isotonic saline (0.9 percent sodium chloride). Given intravenously, hypertonic solutions act like magnets, drawing fluid from tissues into the bloodstream, thereby increasing blood volume. Such hypertonic saline has not received the approval of the Food and Drug Administration for clinical use in the United States. Therefore, it is not part of ATLS guidelines.