An article from the NYTimes that appeared early this month...
Critics Say Execution Drug May Hide Suffering
By ADAM LIPTAK
NASHVILLE, Oct. 1 — At the Riverbend Maximum Security Institution here, through a set of double doors next to several vending machines, a gurney stands ready to deliver prisoners to their executions by lethal injection.
Just about every aspect of the death penalty provokes acrimonious debate, but this method of killing, by common consensus, is as humane as medicine can make it. People who have witnessed injection executions say the deaths appeared hauntingly serene, more evocative of the operating room than of the gallows.
But a growing number of legal and medical experts are warning that the apparent tranquillity of a lethal injection may be deceptive. They say the standard method of executing people in most states could lead to paralysis that masks intense distress, leaving a wide-awake inmate unable to speak or cry out as he slowly suffocates.
....The chemical, pancuronium bromide, has been among those specified for use in lethal injections since Oklahoma first adopted that method of execution in 1977. Only now, though, is widespread attention starting to focus on it.
.....Pancuronium bromide paralyzes the skeletal muscles but does not affect the brain or nerves. A person injected with it remains conscious but cannot move or speak.
...."The subject gives all the appearances of a serene expiration when actually the subject is feeling and perceiving the excruciatingly painful ordeal of death by lethal injection," the judge, Ellen Hobbs Lyle, wrote, describing the worst-case scenario. "The Pavulon gives a false impression of serenity to viewers, making punishment by death more palatable and acceptable to society."
....The American Veterinary Medical Association condemns pancuronium bromide when it is the sole chemical used or when it is used in combination with the usual animal euthanasia drug, sodium pentobarbital. That is because, an association report in 2000 said, "the animal may perceive pain and distress after it is immobilized."
....Lethal injection is now the dominant way Americans are executed. It is used in all 38 states that have the death penalty except Nebraska, which uses electrocution. In 10 states, prisoners may choose between lethal injection and a second method, including hanging, firing squad, electrocution and lethal gas.