Doctors at Vancouver's St. Paul's Hospital came across something highly illogical when they tried to put an arterial line into a patient about to undergo surgery: his blood was dark green.

The green blood — reminiscent of the Vulcan blood found in Mr. Spock of Star Trek fame — came as a bit of a shock to Dr. Alana Flexman and her colleagues, who report on the unusual case in this week's issue of the journal The Lancet.

The 42-year-old man was already a bit of a medical departure. He had fallen asleep while kneeling, and developed compartment syndrome in both legs.

The potentially dangerous condition involves a buildup of pressure in deep muscle tissue — in this case in the legs — and unless the pressure was relieved, permanent nerve damage could have been sustained.

As surgical staff prepared the man for the middle-of-the-night emergency operation, Flexman and a colleague attempted to insert a line into a wrist artery.

Arterial lines are used to monitor blood pressure during an operation; any blood that flows when the line is inserted into the artery should be vivid red, the sign it has been oxygenated.

But in this case, which occurred in October 2005, it was not.

"During insertion, we normally see arterial blood come out. That's how we know we're in the right place. And normally that blood is bright red, as you would expect in an artery," Flexman said in an interview Thursday.

"But in his case, the blood kept coming back as dark green instead of bright red.

"It was sort of a green-black. … Like an avocado skin maybe."

The reaction in the room? "We were very concerned, obviously," said Flexman, who is training in anesthesia at the hospital.

Medication drug may be green cause

Samples were rushed off to the lab, which quickly ruled out a dangerous condition called methemoglobin, in which the hemoglobin in the blood can't bind to oxygen.

While the lab worked, so did the operating team. The man came through the surgery well.

The next day, the lab reported it had detected sulfhemoglobin, a condition thought to be triggered by some medications.

"It's so rare that we don't have a perfect understanding how it happens, but some drug donates a sulphur group that binds to the hemoglobin molecule and prevents it from binding to oxygen," Flexman explains. "And that gives it the green colour."

She and her colleagues believe the condition may have been brought on by the man's migraine medication, sumatriptan, which he was taking in higher-than-advised doses, though they can't prove it.

Green blood can be found in some forms of life such as some marine worms. But it is a condition normally associated with science fiction and not medical texts.

Mr. Spock, the Enterprise's science officer in the famous TV series, was said to have the green blood of his father, who belonged to the race of pointy-eared, logic-seeking Vulcans.

According to Star Trek lore, however, Vulcans have green blood because the oxidizing agent in their blood is copper, and not iron.