Lethal injection as its currently practiced may not be a particularly painless way to execute someone. In the medical journal The Lancet, researchers report that in 90% of the cases they examined, the executionees were not completely anesthetized to pain when they were kicked off this mortal coil and 40% may have been conscious when it happened. Since they couldn't very well ask their subjects, the researchers analyzed the post-mortem blood levels of anesthetic in 49 executed inmates. From New Scientist:
Since 1976, when the death penalty was reinstated in the US, 788 people have been killed by lethal injection. The procedure typically involves the injection of three substances: first, sodium thiopental to induce anaesthesia, followed by pancuronium bromide to relax muscles, and finally potassium chloride to stop the heart.Link
But doctors and nurses are prohibited by healthcare professionals’ ethical guidelines from participating in or assisting with executions, and the technicians involved have no specific training in administering anaesthetics.
“My impression is that lethal injection as practiced in the US now is no more humane than the gas chamber or electrocution, which have both been deemed inhumane,” says Leonidas Koniaris, a surgeon in Miami and one of the authors on the paper. He is not, he told New Scientist, against the death penalty per se.