Tennessee death row inmate Christa Pike was unconscious, intubated and on a ventilator on Thursday night, after authorities failed to execute her by lethal injection, her lawyers say in court filings.

Pike, 50, was injected with two lethal doses of pentobarbital on Wednesday but remained alive. She was then sent to hospital in an ambulance.

Pike remained critically ill and was being treated at a hospital in Nashville, Tennessee.

Lawyers for Pike, who was sentenced to death in 1996 for the murder of Colleen Slemmer, are seeking to have her sentence commuted after the failed execution attempt.