Lethal Injection for Execution: Chemical Asphyxiation?

Teresa A Zimmers,Jonathan Sheldon,David A Lubarsky,Leonidas G Koniaris,Linda Waterman,Francisco López-Muñoz,Richard Weisman

doi:10.1371/journal.pmed.0040156

Teresa A Zimmers, Jonathan Sheldon + Show 5 more

Open Access

https://doi.org/10.1371/journal.pmed.0040156

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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.

Highlights

In the United States, lethal injection can be imposed in 37 states and by the federal government and military
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

Summary

Introduction

In the United States, lethal injection can be imposed in 37 states and by the federal government and military. The protocols currently used in the US contain three drugs: an ultrashort-acting barbiturate, thiopental (which acts as an anesthetic, but does not have any analgesic effect); a neuromuscular blocker, pancuronium bromide (which causes muscle paralysis); and an electrolyte, potassium chloride (which stops the heart from beating). Each of these drugs on its own was apparently intended by those who derived the protocols to be sufficient to cause death; the combination was intended to produce anesthesia death due to respiratory and cardiac arrest. The researchers here wanted to investigate the scientific basis for the protocols used

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