NASHVILLE, Tenn. (AP) — Attorneys for the state and lawyers representing 33 death row inmates traded blame in court Monday at the outset of a trial over Tennessee's new lethal injection procedure.

Federal public defender Kelley Henry said the three-drug combination that the state plans to use can feel like chemical waterboarding, liquid fire, being buried alive or exposure to sarin gas.

"The medical proof will show those words are not hyperbole," Henry said in Davidson County Chancery Court.

Henry also said state officials secretly considered changes to the protocol for months, and just last week revealed a handful of additional amendments.

Deputy state Attorney General Scott Sutherland said Tennessee is in this situation because death penalty opponents persuaded pharmaceutical companies not to sell the previously used lethal injection drug, pentobarbital, to states for executions.

He said inmates' attorneys face the legal burden of identifying an alternative to Tennessee's three-drug method, and they haven't. He pointed out that attorneys for death row inmates opposed the use of pentobarbital in a 2015 case, but now call for its use over the three-drug combination. Attorneys for the inmates contend the state can find enough pentobarbital if officials use multiple sources.

The U.S. Supreme Court upheld a similar three-drug procedure that starts with midazolam in Oklahoma, Sutherland added. He said the Constitution doesn't require a painless death, because that would essentially outlaw the death penalty. The methods of putting someone to death that are unconstitutional, he argued, would have to be torture or other extreme options, such as disembowelment in public, burning people alive or beheading them.

"The U.S. Supreme Court, in the history of its existence, has never invalidated a state's chosen method of execution as cruel and unusual punishment," Sutherland said.

The trial has almost immediate implications: Tennessee's first execution since 2009 is scheduled for Aug. 9, and it would be the first time the state uses the three-drug combination to kill someone.

Tennessee's protocol uses midazolam as a sedative, the muscle-relaxer vecuronium bromide and then potassium chloride to stop the heart. At question is whether midazolam actually is effective in rendering someone unconscious and unable to feel pain from the other two drugs.

Similar or identical drug combinations were used in botched executions in Alabama, Arizona, Florida, Ohio, Oklahoma and Virginia, the group of attorneys has said.

A brief by the state says the risk of unconstitutional pain and suffering under the new three-drug series is minimal when administrated properly.

Henry, the public defender, also blasted the state for making changes to the state's lethal injection manual just last week, calling the move a "cynical ploy designed to gain litigation advantage." Some changes include: formally removing the pentobarbital option; saying officials can use compounded drugs; waiting two minutes after midazolam is administered to check if the inmate is conscious; and spelling out how to check consciousness.

Sutherland said the inmates' attorneys actually requested those changes.

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Previous versions of this story had an incorrect spelling of Kelley Henry's name.