When lethal injection was proposed and accepted in 1977 by Oklahoma state medical examiner Jay Chapman as a human method of killing inmates, the word seemed to go out of the side of barbaric executions by hanging or electric chair. The shot is based on an anesthetic, ultrashort-acting sedative and a paralytic compound.

This cocktail should stop the heart and induce a rapid and painless death, being at the time redundant: if one chemical does not kill the inmate, one of the other two will do it.
But a new research reveals that incorrect dosage is not only painless for the executed, but it can also induce a slow death due to the asphyxiation determined by total paralysis.

The team included the molecular biologist Teresa Zimmers of the University of Miami Miller School of Medicine, a surgeon, an anesthesiologist and a lawyer and registered the data offered by the only two states that show records of the executions: North Carolina and California (the latter being forced by court order to do so), meaning 41 out of 891 lethal injections made in US to date.

These states employ various dosages of sodium thiopental (an anesthestetic), pancuronium bromide (a general paralyzer) and potassium chloride (this salt stops the heartbeat). They are injected in doses designed to kill condemned inmates. The dosages differ from state to state, but not from mate to mate, neglecting their body measurements (weight and height). That's why in North Carolina the executed died on average in nine minutes and in California two to eight minutes following the injection of potassium chloride.

"When potassium chloride was added, it didn't seem to change the time of death," Zimmers notes.

The levels of thiopental could have been not enough to make the procedure painless as revealed by vets, who developed accurate dosage guidelines for killing painless animals.
Sometimes, in human executions less thiopental dosage is used than for killing just 50 % of mice. Monkeys could recover in many cases from such doses.

"The way that thiopental is administered, it would be an unacceptably low dose if the inmate was a pig scheduled for euthanasia," said Zimmers.

"We are doing it successfully in animals and we're doing it successfully because they've taken a hard look at it. When you do it with animals, there is no pain. It's likely there is with people." signaled co-author Jon Sheldon, criminal defense attorney in Virginia.

Finally, the slow death is induced by the bromide, which kills by asphyxiation, as breathe muscles are paralyzed.

"In such case death by suffocation would occur in a paralyzed inmate fully aware of the progressive suffocation and potassium-induced sensation of burning," the researchers write.

"This idea that this is a painless procedure is completely wrong. It's just invisible because the person is paralyzed." said Zimmers.