In December, the BC Ambulance Service (BCAS) in Canada became the latest in a growing number of HEMS operators worldwide to carry blood — packed red blood cells (PRBCs) — on board its helicopters.

Transfusing patients in the air is nothing new. Western militaries have shown the efficacy of the practice during the latest round of unpleasantness in Afghanistan and Iraq, especially to victims of traumatic blunt force injuries. Civil HEMS operators began carrying it aboard on an experimental basis in the mid-1980s and at least one, in Texas, has made it standard equipment since 2002.

Now the practice is spreading worldwide — albeit slowly — after numerous studies have shown the benefits pumping O-negative into accident victims, especially those who have gone into cardiac arrest. When properly administered, O-negative — the universally accepted WD40 of the human circulatory system — oxygenates the organs and appears to provide greater patient benefit than just keeping the plumbing running with bags of saline.

"We know that the sooner patients receive blood products, the better the chance of a positive medical outcome," said Dr. Erik Vu, a physician and BCAS critical care paramedic.

A major study released last year in Australia concluded that "early packed red blood cell transfusion accompanied by fresh frozen plasma, while limiting crystalloids, confers a survival benefit in major trauma." The extent of that benefit is hard to measure, but it could be an increased survival rate of up to 30 percent compared to crystalloid therapy alone, according to some of the data.

However, "properly administered" are the key words here.

Blood on board must be stored in a specialized cooler and kept at a set temperature range — no lower than 36 degrees F and no higher than 46. However, the blood must be warmed to body temperatures before infusion to prevent patient hypothermia. Blood can be properly stored aboard the helicopter for up to 72 hours, and most blood products have a shelf life of 42 days if returned to hospital controls.

The question remains as to how much blood to carry on board. The typical complement on EMS helicopters that carry is two units, but a growing school of thought is that number should be bumped to at least four to adequately deal with internal hemorrhaging and related shock caused by blunt force trauma. PRBCs should also be given in combination with fresh frozen plasma on a ratio between 1:1 and 1:2.

None of this comes cheap, especially if EMS helicopters need to be fitted with blood chillers and warmers that run off either the aircraft inverter or an independent power source onboard. And the bean counters will have a field day with this, given that PRBCs are administered in only 4 to 10 percent of all HEMS flights when available, and that much of the patient benefit data is preliminary.

But there is enough data to suggest that having PRBCs on board can make the difference between life and death. That's good enough for me.