Knowing the 'clotting profile' can save lives in an emergency
It's a dog owner's worst nightmare: The dog has been hit by a car and is losing blood fast. He's rushed to the veterinary hospital where, thanks to a study on blood clotting at the Cummings School of Veterinary Medicine at Tufts University, his life may be spared.
The first line of treatment for dogs in severe shock has long been the administration of intravenous fluids, such as saline, to restore those the body has lost. The amount required to stabilize a dog varies, depending his size and blood loss. But thanks to a study on blood clotting at the Cummings School of Veterinary Medicine at Tufts University, veterinary hospitals now have a better chance of saving his life.
"Coagulopathy is the inability to form the blood clots that are necessary to stop bleeding," said Daniel Chan, DVM, a specialist in emergency and critical care at the Cummings School. "Whenever trauma to a dog's blood vessels or organs causes initial bleeding, the body's way to stop bleeding is to form clots. The process is initiated by clotting factors - circulating proteins within the blood." However, when veterinarians have to administer large amounts of IV fluids, they dilute the clotting factors and the dog may continue to bleed. "Coagulopathy usually translates into the dog needing several very costly plasma or whole blood transfusions to replenish these important clotting factors," said Dr. Chan. Both whole blood and plasma are collected from canine blood donors.
Because little had been known about the amount of fluid required to cause coagulopathy, Dr. Chan recognized the need for a preliminary
study measuring clotting times in blood diluted with IV fluids. "Rather than subject dogs to the potentially harmful amounts of IV fluids, we did an in vitro - an artificial environmental - study that mimicked conditions that occur in practice."
Dr. Chan and his team incrementally diluted canine blood with various fluids and measured clotting times at each dilution. They used saline, plasma or hetastarch - a synthetic substance used as a plasma replacer. "Hetastarch is perhaps 50 times more expensive than saline, but plasma or blood may be several hundred times more expensive," Dr. Chan said. "However, a lesser volume of hetastarch is required to achieve fluid resuscitation. Essentially, it is a more concentrated fluid than saline but much like plasma, which is what hetastarch is meant to mimic."
Normally, veterinarians use one "blood volume" of fluid - about 90 milligrams per kilogram of body weight for saline and 20 milligram per kilogram of body weight for hetastarch - in normal resuscitative efforts. Dr. Chan's study showed that one blood volume of any of the recommended fluids will not significantly delay clotting times. However, as larger amounts are administered, especially hetastarch, serious abnormalities in blood clotting can occur.
"The development of such coagulopathies can be quite serious and may result in death," said Dr. Chan. "However, if recognized in time and appropriately treated, coagulopathy can be reversed and a dog's life can be saved."
The study suggests veterinarians should recognize the possibility of dilutional coagulopathy whenever dogs require massive IV fluid resuscitation, Dr. Chan said. "Clotting profiles should be determined for these dogs. Should clotting abnormalities be detected, the administration of fresh frozen plasma is the treatment of choice."
Additional studies are needed now to investigate how frequently clotting abnormalities occur and to determine how veterinarians can best prevent coagulopathy from occurring.
Funding for the Cummings' study was provided by Synbiotics Corp., which makes portable clotting time analyzers used in many veterinary practices, including the Cummings School's emergency clinic. The devices allow veterinarians to precisely determine whether a given blood sample can form a blood clot in a test tube and the number of seconds it takes to form the clot. Each dog's "clotting profile" is based upon this information.
The analyzers work by mixing certain substances with a blood sample and detecting when the blood clots, said Dr. Chan said. "The shorter the amount of time it takes to form a clot, the better. If the clotting time is prolonged, the dog may require a transfusion. The sooner we can determine whether a transfusion is needed, the sooner the dog can receive treatment."
Elissa Wølfson is a free-lance writer in Ithaca, NY