Thirty-four death-row inmates in Tennessee are challenging the state's lethal injections protocols. On Wednesday, their attorneys asked the state Supreme Court to let them challenge Tennessee's backup method of execution as well: the electric chair.

Here is a look at some of the chief issues involved:

___

PENTOBARBITAL AVAILABILITY

Attorneys for the inmates say pentobarbital, Tennessee's lethal injection drug, is impossible to obtain. Drug companies have stopped selling it or even its main ingredient, according to an affidavit from University of Utah College of Pharmacy professor James H. Ruble. That means compounding pharmacists will not be able to make it for the state.

And the American Pharmacists Association recently adopted a policy discouraging its members from providing drugs for lethal injections, saying that runs contrary to the role of pharmacists as health care providers.

___

THE ELECTRIC CHAIR

If Tennessee cannot obtain pentobarbital, the backup method of execution is the electric chair. The inmates claim Tennessee's electrocution protocol is unconstitutional and violates evolving standards of decency.

Deputy Attorney General Jennifer Smith argued in court on Wednesday that inmates should not be allowed to challenge the constitutionality of the electric chair until Tennessee officially certifies that it cannot obtain lethal injection drugs. That's something that may never happen, she said.

Smith said even if pentobarbital is unavailable, the state could choose to execute with a different lethal drug.

The Tennessee Department of Correction commissioner has broad discretion to modify the lethal injection protocol, she argued. "There's no indication the department will not make every reasonable effort to carry out executions by lethal injection."

___

PROTOCOL HOLES

Several of the justices expressed concerns that Tennessee's execution protocols do not require prison officials to notify the inmates if they intend to put them to death by the electric chair, rather than lethal injection. If the state were to keep it a secret until the last moment, inmate's attorneys might not have time to challenge the use of the chair.

"Here's your problem," Justice Cornelia Clark told Smith. "There's a state protocol for lethal injection and there's a state protocol for electrocution. There's a big hole in the middle."

___

EXECUTIONS STALLED

Tennessee last executed a prisoner in 2009. Since then, legal challenges and problems obtaining lethal injection drugs have stalled new executions.

In 2013 and 2014, the state tried to jump-start the process with a new one-drug lethal injection method and the reinstatement of the electric chair as a backup. Beginning in December 2013, the Supreme Court set new execution dates for 11 inmates. Since then, one has died in prison, and the execution dates for the other 10 have been postponed because of legal challenges to the new methods.

Faced with similar challenges, Oklahoma recently enacted a law allowing execution by nitrogen gas as a backup to lethal injection. Utah reinstated the firing squad.