Louella Fletcher-Michie, 24, the daughter of Holby City star John Michie, took class A party drug 2-CP at Bestival in Dorset on September 10 2017, and died in woodland an hour before her 25th birthday.
She was given drugs by her on-off boyfriend Ceon Broughton, 29, and died as her parents rushed to help her, it is alleged.
Broughton, of Enfield, north London, denies manslaughter and supplying the drug.
The jury at Winchester Crown Court on Monday heard that Ms Fletcher-Michie was the first recorded death caused by 2-CP.
Professor Charles Deakin, a consultant in cardiac anaesthesia and intensive care at Southampton General Hospital, told the court he was “very confident” she would have “stood a very good chance of surviving” if she had been given early medical care.
“As long as she’s actually breathing when medical services arrive, the chances of her surviving are very high,” he said.
The court previously heard that Ms Fletcher-Michie was found dead by a security steward in the woodland, 400 metres from the festival’s hospital tent, at around 1am.
A post-mortem examination found “2-CP toxicity” and traces of ketamine and MDMA.
The jury has been shown a 50-minute video of Ms Fletcher-Michie, taken by Broughton, in which she shouts: “This is the best trip I have ever f****** had.”
But as her condition deteriorated, Broughton ignored pleas from her family to seek help and continued to film even after she was dead, the court heard.
Asked to analyse the clips by police, Prof Deakin said Ms Fletcher-Michie appeared “agitated and confused” and was “probably hallucinating”.
According to Prof Deakin’s written statement, at 8.15pm she appeared to be making “incoherent noises”, was not “aware of her surroundings” and was “seriously unwell and in need of urgent medical care”.
By 11.24pm, he concluded, there were “no signs of life” and “Louella’s skin appears a bluey-grey colour which is consistent with someone who has effectively stopped breathing”.
He added: “Her mouth was open and her eyes were rolled back, in all probability she was actually deceased at that stage.”
Prof Deakin, who has 30 years’ experience of pre-hospital care, accepted in court it was hard to tell, given the quality of the clips, but “it is very likely she has died at that time”.
He said sedative drugs, breathing support and monitoring of blood pressure could have been used to treat Ms Fletcher-Michie at the scene.
The court heard that 2-CP is a “relatively new drug” that starts affecting users one to three hours after being taken, with them returning to normal after 20 hours.
Prof Deakin said people who take stimulant drugs risk being affected by increased heart rate and respiratory failure.
He said it was “very likely” that Ms Fletcher-Michie had a “high heart rate” - exacerbated by MDMA in her system - and eventually became “exhausted” by the effects of the 2-CP.
Prof Deakin said there were “no previously documented deaths from 2-CP”, but a US newspaper article suggested two out of seven people treated in hospital after taking the drug at a festival went into cardiac arrest.
Cross-examining, Broughton’s lawyer Stephen Kamlish QC claimed Prof Deakin had changed his witness statement following an initial draft and discussions with a police officer.
Mr Kamlish said Prof Deakin’s first report claimed it was “not possible to say beyond reasonable doubt that early medical intervention would have been able to save Louella’s life”.
The report added: “However, I do believe that on the balance of probabilities, medical intervention at any time to 9.10pm is likely to have saved Louella’s life.”
Mr Kamlish asked Prof Deakin: “Today is the first time that you have said that Louella could have been saved as long as she was still breathing.”
In response Prof Deakin told the court he had asked to “clarify and expand” on his evidence in his second report which had not changed any meaning in what he had said.
He added: “I have never claimed that survival was a foregone conclusion.”
The trial continues.