Research Article: Lethal Injection for Execution: Chemical Asphyxiation?

Date Published: April 24, 2007

Publisher: Public Library of Science

Author(s): Teresa A Zimmers, Jonathan Sheldon, David A Lubarsky, Francisco López-Muñoz, Linda Waterman, Richard Weisman, Leonidas G Koniaris, Clifford J Woolf

Abstract: BackgroundLethal 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 FindingsWe 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.ConclusionsWe 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.

Partial Text: 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].

North Carolina lethal injection protocols were determined from Department of Corrections drug procurement records and testimony of prison personnel participating in the process. Times to death were determined from North Carolina Department of Corrections documents including the Web site [8], official statements, and corroborating news and eyewitness reports. Start times were available for 33 executions, of which 19 could be independently confirmed. The North Carolina warden pronounces death after a flat line is displayed on the electrocardiogram (ECG) monitor for 5 min, thus time to death was calculated from start time to pronouncement of death less 5 min. Dosages were calculated from postmortem body weights taken from Reports of Investigation by the North Carolina Office of the Chief Medical Examiner. Information regarding the California protocol and execution logs and Florida and Virginia executions were obtained through available court documents [9,10,11]. Data are expressed as mean ± standard deviation. One-way ANOVA with Tukey’s multiple comparison test was used for statistical analysis.

Most US executions are beset by procedural problems that could lead to insufficient anesthesia in executions. This hypothesis has been supported by findings of low postmortem blood thiopental levels and eyewitness accounts of problematic executions. Herein we report evidence that the design of the drug scheme itself is flawed. Thiopental does not predictably induce respiratory arrest, nor does potassium chloride always induce cardiac arrest. Furthermore, on the basis of execution data and clinical, veterinary, and laboratory animal studies, we posit that the specified quantity of thiopental may not provide surgical anesthesia for the duration of the execution. Thus some inmates may experience the sensations of pancuronium-induced paralysis and respiratory arrest.