The episode, to air Nov. 11, will follow every moment of guest star Liotta's hospital visit. He plays an alcoholic ex-con with cirrhosis of the liver and a host of other problems.
The real-time narrative is a first for the NBC emergency room drama. "ER" has previously experimented with different structures, but the series' famous live broadcast in 1997 wasn't in real time.
"In a way, this is the inverse of that," co-producer David Zable told The Associated Press Thursday. "We also have never tracked one patient the whole time through the show."
The trademark "ER" style is one of crosscutting and story lines that intertwine with each passing gurney. The editing allows "ER" to sometimes skip over the uglier or more mundane aspects of emergency room treatment.
Zable, who wrote the Nov. 11 episode, says: "We really had to mine each moment for drama."
The season premiere of "ER," which continues last season's cliffhanger car accident ending, will air Sept. 23.