David Kroll explains the original three drugs proposed for lethal injection:
- a sedating drug to render the condemned unconscious (barbiturates such as sodium thiopental or pentobarbital)
- a neuromuscular blocking drug to cause paralysis of all muscles except the heart (such as pancuronium or vercuronium bromide)
- a lethal dose of potassium chloride to arrest the heart
He then addresses the drugs in reverse order:
Among the various salt ions that allow our bodies to function, one of the most tightly regulated is potassium. It’s required for all manner of nerve signals, proper brain functioning, and for the constant beating of the heart. The body keeps most of our potassium in cells with only a small fraction present in our blood. A large dose of potassium chloride introduced into the bloodstream, like that used in executions, would irreversibly paralyze the heart.
If given alone without the other drugs, the high concentration of potassium chloride would be terribly painful, akin to fire or electricity coursing through the veins.
Pancuronium, vecuronium, or other neuromuscular blocking agents
These drugs are modern relatives of the South American arrow poison, curare. They work by blocking the chemical signals from the brain and spinal cord that tell our muscles to contract. They act precisely where these nerves end at our muscles, hence the term neuromuscular blocker.
These drugs are most often used during surgery to allow a breathing tube to be inserted into the patient and to prevent involuntary muscle contractions during surgery. But the high dose used in executions is intended to stop the offender from breathing while also ensuring that the condemned appears completely still to the audience.
If given without the other drugs, it would be like having the worst night terror imaginable. You would experience oxygen hunger from being unable to breathe but be unable to move, all while being fully conscious.
Thiopental, pentobarbital, or other barbiturates
Barbiturates were first created in the early 1900s and were used intravenously throughout much of the last century to induce anesthesia, producing a loss of consciousness and an inability to perceive pain. They were then usually followed by an inhaled anesthetic for the maintenance of anesthesia. At lower doses, barbiturates were used to relieve anxiety in the years before the introduction of the safer benzodiazepine drugs: Librium (chlordiazepoxide) and Valium (diazepam).
For anesthesia, the barbiturates have largely been replaced by other safer drugs, usually in a combination that includes following: midazolam (Versed), an opioid like fentanyl, and a general sedative-hypnotic drug like propofol.
If given alone without the other drugs, a high dose of barbiturate alone could kill a person just fine. But it would take anywhere from 30 to 60 minutes. In fact, many drugs will cause death within an hour or two. However, corrections officials sought for execution to be rapid. This is why the sedating barbiturate was used in combination with the neuromuscular blocker and the potassium chloride.