Thipental is not-- repeat not-- an anesthetic; in doses used, it is a hypnotic, and does not block pain It would makes the inmate groggy, and put him to sleep, but pain can be felt. There are other drugs that can be used. High enough concentrations it is lethal, but the death process would take too long.
The Pancuronum which paralyzes muscles, is a take off p curare, favorite killer of detective writers; it is lethal-- but in higher amounts than on the point of an arrow. It does not block pain, but the inmate, paralyzed with all his muscles , cannot move, talk, and eventually cannot breath. This must be horribly painfull and terrorifying.
The Potassium Chloride or Kalium Chloride as it is also known-- stops the heart in systole, making the heart rock hard. It is used in heart surgery and its effects can be easily reversed by Sodium Chloride. Although a lethal combination, it does it poorly, and as Dr Chapman says, other drugs can do a better job.
Once the heart is stopped, unconsciousness follows within 20 seconds-- true unconsciousness-
A major problem though, is access to a vein, needed to this form of chemical garotte to work. the piddlin; around for 90 minutes to find a vein, adds to the sense of torture-- better know the inmate over the head with a two-by-four to render him/her unconscious. But then again, tha tis not "civilized". But the folks killing folks by poison miss the point; it is the most despicable form of murder. They just do not get it. And lastly, because injection cannot be made "civilized" and "painless" it cannot fit in the US and State Constitutions.
G M Larkin MD