Adrenalin can save a heart but hurt the brain. Canadian research aims to find best dose for a potent drug

When Dan Shire's heart stopped beating in 2016, it led to a race against time to save his life.

Shire's wife heard him struggling to breathe in the middle of the night. Then she ran to the phone to call 911, started CPR, and waited minute-by-painful-minute for first responders to show up.

Once paramedics arrived at the couple's Pickering, Ont., home, they used a defibrillator on Shire four times, then tried a potent medication in an attempt to restart his heart.

That drug, epinephrine — also called adrenalin — is given intravenously every three to five minutes, up to an average of six milligrams. It stimulates blood flow by squeezing the blood vessels, which can, in some cases, help get someone's heart beating again. 

But researchers worry there's a dangerous ripple effect: When you save someone's heart, you can hurt their brain. Studies suggest higher doses of epinephrine might actually cause neurological damage.

In Shire's case, he survived his episode of cardiac arrest and now leads a largely normal life. But the 67-year-old does have cognitive impacts such as short-term memory issues and some difficulty with complex tasks like driving. He's not sure how much of that is from his heart stopping — cutting off oxygen to his brain for the better part of 16 minutes — or the dose of epinephrine he was given.

To give cardiac arrest patients the best chance at not only survival, but also a high quality of life, Canadian researchers have launched a massive, years-long trial to find the "sweet spot" for epinephrine usage. 

"There could be a tendency that [first responders] are erring on the side of giving you as aggressive a treatment as possible to save your life in that moment," said Shire. 

"A month later, you might find yourself in the position where you had too much epinephrine, and now have problems with cognitive outcomes."

Dubbed EpiDose, the randomized controlled trial involves paramedic teams in B.C., Ontario, and eventually more provinces. Each time those teams encounter a patient with cardiac arrest, they'll randomly provide either a higher or lower dose of epinephrine. 

Then researchers will track the results, not just to see which lives are saved, but to find out about their brain function afterwards.

It's the latest in a set of ongoing studies on epinephrine from a research team co-led by Dr. Steve Lin, the interim chief of emergency medicine at St. Michael's Hospital, a part of Unity Health Toronto.

The team is hoping to include data on nearly 4,000 randomly-selected patients — a process that could take five to six years.

Lin said the researchers are proposing a new "ceiling" for the standard dose, if the results suggest that a lower dose of two milligrams in total works just as well or better than the current standard of six milligrams. His team will then be contacting survivors to see how their bout of cardiac arrest impacted their life, including their later neurological function.