The blood flow balance: USask scientists test treatment for severe bleeding in trauma patients

Here’s a common scenario facing paramedics: a person gets injured and is bleeding heavily from a wound. Bystanders manage to control the bleeding by putting pressure on the wound until the paramedics arrive. The paramedics insert an intravenous (IV) line into the person’s arm and administer fluid to increase the patient’s blood pressure while transporting them to the nearest hospital.

Severe bleeding, or hemorrhage, is responsible for over 35 per cent of pre-hospital deaths in human patients. Paramedics treat hemorrhage on scene by applying pressure to stop the bleeding and then replacing the patient’s lost blood by giving them fluids.

This practice, which is the only option for increasing blood pressure in the field, helps to recover the dangerously low blood pressure caused by blood loss, therefore keeping oxygen flowing to the patient’s vital organs. But the downside to treating hemorrhage with fluids alone is that it can cause hypothermia and promote bleeding by disrupting blood clotting.

One way to overcome this problem may be to use vasopressors, which are drugs that make a person’s blood vessels constrict. Historically, medical professionals haven’t used these drugs to treat hemorrhage for the fear that excessive constriction would compromise blood flow to vital organs. A patient’s brain is especially vulnerable to compromised blood flow: without delivery of blood and oxygen, brain cells start to die within four to six minutes.

However, recent studies have shown that low doses of vasopressors improve blood pressure without causing too much constriction in the brain. They also have the added benefit of requiring less fluid to resuscitate, which could potentially prevent hypothermia and allows blood to clot better.

But what if first responders could combine these two treatments — fluids and vasopressors — to buy some time for their patients’ brains and save lives?

Last summer, this question motivated me to study the use of a vasopressor drug called norepinephrine during my University of Saskatchewan (USask) research job in the lab of Dr. Dylan Olver, an associate professor at the Western College of Veterinary Medicine (WCVM).

As Olver explains, he conducts cardiovascular physiology-related research that focuses on “the relationship between heart and brain function across the lifespan and heart disease spectrum.” His recent projects have focused on the coupling between heart and brain blood vessel responses to metabolic stress — such as blood loss.

Olver emphasizes that the brain uses a lot of energy, which requires constant blood flow: “The brain is a highly metabolically active organ. Even modest alterations in blood flow regulation can be detrimental for short- and long-term brain health.” 

He adds that understanding the brain blood vessel response to stress will “enable us to develop effective preventative and treatment therapies for different pre-clinical and clinical ailments that affect the brain.”

With Olver’s guidance, I designed and conducted a study to look at the difference between these two treatments for blood loss: using a combination of fluids and vasopressor (norepinephrine) in comparison to using just fluids alone.

“Norepinephrine increases blood pressure, and maintaining adequate blood pressure helps maintain blood flow to the brain — making this strategy a potential out-of-hospital treatment,” says Olver.

We tested both treatments on pigs — a common research model since pigs share many physiological similarities with humans. We specifically used low-dose norepinephrine since Dr. Olver points out that high doses of the drug may cause arteries in the brain to constrict beyond a safe amount — potentially limiting blood flow to the brain.

“Arteries outside the brain appear to be more responsive to norepinephrine, so we are interested to see if the effects of [low-dose] norepinephrine on increasing blood pressure is done without causing a decrease in blood flow to the brain,” says Olver.

Although the research is promising, my paramedic colleagues won’t be utilizing this proposed treatment strategy for some time. More studies need to be done.

“First, we need to determine if low-dose norepinephrine is effective in improving blood pressure and brain blood flow following blood loss,” says Olver. “If we can confirm that there is benefit, then conducting further research to validate these findings in humans and companion animals will be the next step.”

Kendra DuRussel of Warman, Sask., is a paramedic and a first-year WCVM veterinary student who worked as a summer research student in 2024. Her story is part of a series of articles written by WCVM summer research students.