Well, to look at the the he standard sequence of chemicals used in a typical lethal injection is:
- A large dose of sodium pentothal, a barbituate, is injected, resulting in rapid unconsciousness (typically within 1-3 min).
- Pancuronium bromide, a neuromuscular blocker (prevents nerve impulses from affecting muscles) is injected. This stops all muscle activity, including breathing, which is regulated by the nervous system. The heart, however, continues beating as long as there is still oxygen in the blood. The procedure could be stopped at this point, and the condemned would still eventually die of suffocation.
- Potassium chloride is injected, altering the balance of ion concentrations between the blood and the muscles, preventing contracted muscles from relaxing. Once the potassium chloride makes its way through the veins to the heart, it seizes up, and cardiac arrest results in seconds.
The argument about pain suffered by the condemned revolves around the last two drugs used. First, the argument is made that most states have banned pancuronium bromide from being used to euthanize animals. That’s only partly true, though, as such bans only prohibit the use of pancuronium bromide as the sole drug in the procedure, since it only causes paralysis and the animal would remain conscious while slowly suffocating. However, pancuronium bromide is also commonly used on surgery patients to prevent any involuntary movement which might interfere with the surgeon’s work. The difference is, patients are first anesthatized and kept unconscious with a sedative, and then placed on a respirator before the drug is administered. Likewise, the condemned is already unconscious when this paralyzing agent is given.
Potassium chloride, while it will instantly stop the heart, also causes intense pain if injected into a conscious individual, since it is a concentrated salt solution and burns the veins it travels through. There are accounts of people screaming in pain after accidentally injected with potassium chloride, but again, the condemned is already unconscious.
The argument against this procedure, however, is that sodium pentothal is a short-term anesthetic, and in clinical use, typically wears off in 7-10 minutes (all three injections are typically done in less than 5 minutes). The possibility is raised, then, that by the time the potassium chloride is injected, the condemned may have regained consciousness, but be unable to move or speak because of the pancuronium bromide. If this were the case, he would feel excruciating pain upon injection of the potassium chloride, and for another minute or so until lack of blood flow to the brain caused unconsciousness and then death.
However, there are two other things to keep in mind. The dose of sodium pentothal given is over ten times that which would be used in a clinical setting, so the condemned is unlikely to regain consciousness as soon as death penalty opponents would like you to belive. Furthermore, by the time the potassium chloride is injected, the pancuronium bromide has prevented the condemned from breathing for so long that even if the sodium pentothal wears off, lack of oxygen will prevent him from regaining consciousness. So, while simply injecting potassium chloride would cause an excruciating death, the other drugs ensure that the condemned cannot possibly be conscious at that point, and the most pain he can possibly feel will be that of the IV needles being inserted.
