Their bare arms are strapped to boards projecting from the sides of the gurney. Trained technicians then insert a catheter into a vein in each arm, a process that sounds much simpler than it often is. Once the catheters are in place tubes carrying saline solution are connected to the catheter ends and the prisoner is either wheeled into the execution chamber or the curtains surrounding it are drawn back to allow the witnesses to see the procedure. There is a short interval between each chemical during which saline solution is injected to clean the IV line and prevent a chemical reaction blocking it. Typically the actual injections will take from three to five minutes to complete.
Sodium thiopental is a short acting barbiturate which causes unconsciousness quite quickly.
Pavulon is a muscle relaxant that paralyses the diaphragm and thus arrests breathing whilst Potassium chloride finishes the job by causing cardiac arrest. In most cases the prisoner is unconscious about a minute after the Sodium thiopental has been injected and is dead in around eight minutes, with no obvious signs of physical suffering. In some states a fully automated lethal injection machine is used that runs off a 12 volt battery. It injects the chemicals in the right order and amount once the catheters are in place. This considerably assists matters and avoids the problems of mixing of the chemicals which can lead to a reaction causing precipitation which makes them impossible to inject.