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 Med. 2007;4(4) 

In This Article

Abstract and Introduction


Background: Lethal injection for execution was conceived as a comparatively humane alternative to electrocution or cyanide gas. The current protocols are based on one improvised by a medical examiner and an anesthesiologist in Oklahoma and are practiced on an ad hoc basis at the discretion of prison personnel. Each drug used, the ultrashort-acting barbiturate thiopental, the neuromuscular blocker pancuronium bromide, and the electrolyte potassium chloride, was expected to be lethal alone, while the combination was intended to produce anesthesia then death due to respiratory and cardiac arrest. We sought to determine whether the current drug regimen results in death in the manner intended.
Methods and Findings: We analyzed data from two US states that release information on executions, North Carolina and California, as well as the published clinical, laboratory, and veterinary animal experience. Execution outcomes from North Carolina and California together with interspecies dosage scaling of thiopental effects suggest that in the current practice of lethal injection, thiopental might not be fatal and might be insufficient to induce surgical anesthesia for the duration of the execution. Furthermore, evidence from North Carolina, California, and Virginia indicates that potassium chloride in lethal injection does not reliably induce cardiac arrest.
Conclusions: We were able to analyze only a limited number of executions. However, our findings suggest that current lethal injection protocols may not reliably effect death through the mechanisms intended, indicating a failure of design and implementation. If thiopental and potassium chloride fail to cause anesthesia and cardiac arrest, potentially aware inmates could die through pancuronium-induced asphyxiation. Thus the conventional view of lethal injection leading to an invariably peaceful and painless death is questionable.


In the United States, lethal injection can be imposed in 37 states and by the federal government and military. The origin of the lethal injection protocol can be traced to legislators in Oklahoma searching for a less expensive and potentially more humane alternative to the electric chair.[1] Both the state medical examiner and a chairman of anesthesiology appear to have been consulted in writing of the statute. The medical examiner has since indicated that no research went into his choice of drugs -- thiopental, pancuronium bromide, and potassium chloride -- but rather he was guided by his own experience as a patient.[2] His expectation was that the inmate would be adequately anesthetized, and that although each individual drug would be lethal in the dosage specified, the combination would provide redundancy. The anesthesiologist's input relating to thiopental was written into law as "the punishment of death must be inflicted by continuous, intravenous administration of a lethal quantity of an ultra-short-acting barbiturate in combination with a chemical paralytic agent",[3] although in practice Oklahoma uses bolus dosing of all three drugs.[4,5] Texas, the first state to execute a prisoner by lethal injection, and subsequently other jurisdictions, copied Oklahoma's protocol without any additional medical consultation.[1]

Although executioners invariably achieve death, the mechanisms of death and the adequacy of anesthesia are unclear. Used independently in sufficiently high doses, thiopental can induce death by respiratory arrest and/or circulatory depression, pancuronium bromide by muscle paralysis and respiratory arrest, and potassium chloride by cardiac arrest. When used together, death might be achieved by a combination of respiratory arrest and cardiac arrest due to one or more of the drugs used. Because thiopental has no analgesic effects (in fact, it can be antianalgesic),[6] and because pancuronium would prevent movement in response to the sensations of suffocation and potassium-induced burning, a continuous surgical plane of anesthesia is necessary to prevent extreme suffering in lethal injection.

Recently we reported that in most US executions, executioners have no anesthesia training, drugs are administered remotely with no monitoring for anesthesia, data are not recorded, and no peer review is done.[7] We suggested that such inherent procedural problems might lead to insufficient anesthesia in executions, an assertion supported by low postmortem blood thiopental levels and eyewitness accounts of problematic executions. Because of a current lack of data and reports of problems with lethal injection for executions, we sought to evaluate the three-drug protocol for its efficacy in producing a rapid death with minimal likelihood of pain and suffering.


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