NASHVILLE, Tennessee. — What was expected to be Tennessee’s first execution of a woman in more than two centuries ended in an extraordinary situation Wednesday night after death row inmate Christa Gail Pike survived two doses of pentobarbital administered during an attempted lethal injection.

Pike, 50, was sentenced to death for the 1995 murder of 19-year-old Colleen Slemmer, a crime committed when Pike was 18. Her execution was scheduled at the Riverbend Maximum Security Institution in Nashville. But after prison officials administered two doses of the lethal drug, Pike remained alive. Media witnesses reported that she was still breathing and could be heard snoring behind the closed curtain of the execution chamber. She was later transported by ambulance to a hospital for medical treatment.

The Tennessee Department of Correction said officials followed every step of the state’s established execution protocol, which had been approved by the Attorney General’s Office. The protocol provides for a second dose if an inmate has not died after the first dose, but it does not specify what should happen if the second dose also fails to cause death.

The incident has been described by death penalty experts as highly unusual. Previous troubled executions in the United States have included cases in which execution teams were unable to establish intravenous access, but Pike’s case is different because she remained alive after receiving the drug intended to cause her death.

Tennessee Gov. Bill Lee ordered a comprehensive third-party review to determine exactly what happened and announced that the state’s remaining scheduled execution for 2026 would not take place. The failed attempt came only months after Tennessee halted another execution, that of Tony Carruthers, when officials spent more than an hour unsuccessfully attempting to establish an intravenous line.

Pike’s case had already attracted national attention because she was 18 when Slemmer was killed. Her attorneys had also argued that her history of severe abuse and mental health problems should have been considered in determining her sentence.

The failed execution is now raising new questions about Tennessee’s lethal injection procedures and about what happens next in Pike’s case. State officials have not publicly explained why the two doses failed, saying only that the established protocol was followed.

For now, the unprecedented outcome has transformed what was expected to be the conclusion of a decades-old death sentence into a new legal and procedural challenge for Tennessee authorities.