A new US study suggests that some prisoners executed by lethal injection die from asphyxiation while conscious, paralyzed and in pain.

The study is published in the journal PLoS Medicine.

Dr Leonidas Koniaris and colleagues from the University of Miami in Florida, USA, reviewed data on executions from two US states, North Carolina and California, and assessed the medical literature on the three drugs that are used to administer lethal injections.

They concluded that the lethal injection system used to execute prisoners may not be working in the way intended.

The lethal injection is a cocktail of three drugs, each of which is supposed to be fatal on its own, according to those who originally designed the method.

-- Drug number 1 is a barbiturate: thiopental. This is an anesthetic but not a painkiller (analgesic).
-- Drug number 2 is a a neuromuscular blocker: pancuronium bromide. This paralyses the muscles, including those that control breathing.
-- Drug number 3 is an electrolyte: potassium chloride. This stops the heart beating.

These three drugs combined are supposed to cause death by rendering the prisoner unconscious and then inducing respiratory and cardiac arrest. However, the researchers suggest that the doses are not tailored to the individual prisoner, for instance to adjust for body weight.

Reports on a number of recent executions reveal that some prisoners take many minutes to die, and others become very distressed, because the method is not working as intended.

Dr Koniaris and colleagues say their findings suggest that in some cases the dose of the anasthetic, thiopental, is not sufficient to cause death and may even not be enough to keep the prisoner unconscious for the duration of the execution.

They also suggest that the dose of potassium chloride is sometimes not enough to stop the heart, which results in prisoners being conscious while the paralysis brought about by the pancuronium bromide asphyxiates them.

The research team concluded that:

"The conventional view of lethal injection leading to an invariably peaceful and painless death is questionable."

"We concluded that the original design of the lethal injection drug protocol itself is flawed," said Dr Teresa A. Zimmers, research assistant professor of surgery at the Miller School of Medicine and lead author of the report.

"The drug protocol is based on little clinical and scientific data and contradicts clinical veterinary practice," she added.

Dr Koniaris and colleagues mention that the current regimens for lethal injection in the US are derived from one designed by Oklahoma legislators and appear to be founded on personal opinion rather than independent research.

In an accompanying editorial titled "Lethal injection is not humane", the journal's editors discuss these findings and their reason for publishing them.

They declare that their intention is not to encourage further research to "improve" lethal injection methods.

"As editors of a medical journal, we must ensure that research is ethical, and there is no ethical way to establish the humaneness of procedures for killing people who do not wish to die", they write.

Explaining that "The data presented by Koniaris and colleagues adds to the evidence that lethal injection is simply the latest in a long line of execution methods that have been found to be inhumane", they argue that this strengthens the constitutional case for abandoning executions altogether in the US.

Lethal injection is used as a capital punishment to execute prisoners in a number of countries, most notably the US and China.

It is also used in euthanasia for patients with terminal or chronically painful conditions.

"Lethal Injection for Execution: Chemical Asphyxiation?"
Teresa A. Zimmers, Jonathan Sheldon, David A. Lubarsky, Francisco López-Muñoz, Linda Waterman, Richard Weisman, Leonidas G. Koniaris.
PLoS Medicine Vol. 4, No. 4, e156
doi:10.1371/journal.pmed.0040156