Stephen Warrillow shared his concerns to a Victorian Supreme Court jury on Friday as Patterson stands trial on three counts of murder and one count of attempted murder.
It's alleged she intentionally served beef Wellingtons laced with death cap mushrooms during a lunch at her Leongatha home on July 29, 2023.
Her former in-laws Don and Gail Patterson, and Gail's sister Heather Wilkinson, all died after consuming the meal.
Heather's husband Ian survived but Dr Warrillow, the intensive care director at Austin Health, told the jury it did not look like he would.
"We thought he was going to die, he was very close," Dr Warrillow said.
Mr Wilkinson was the fourth guest to be transported to Austin Health with liver failure in the days after the lunch, the doctor said.
He was already intubated and suffering from acute liver failure when doctors began rounds of activated charcoal and vitamin C treatment.
The jury was told by August 4, Mr Wilkinson's condition had deteriorated and he underwent a laparoscopy to check his bowel, although there were no significant abnormalities.
Dr Warrillow said Mr Wilkinson then made slow but significant improvements between August 5 and 7.
"It was very slow because he was coming from extreme clinical illness but he did improve," he told the jury.
Mr Wilkinson was moved from intensive care to a normal ward on August 21 and then ultimately discharged to a rehabilitation facility on September 11.
His wife's condition did not improve while at the Austin and she died of acute liver failure in the early hours of August 4.
Gail Patterson also died from the same condition later that day, while her husband Don died at 11.30pm on August 5.
Don had undergone a liver transplant but his condition continued to get "relentlessly worse" before his death, Dr Warrillow said.
Similar transplants were not undertaken for Gail and Heather as they were both too unwell, the doctor told the jury.
Dr Warrillow said the conditions of all four patients were consistent with death cap mushroom poisoning and no other causes for their illnesses were found.
He told the jury treatment for death cap poisoning was not 100 per cent effective and there were high mortality rates even with optimal care.
Mr Wilkinson was inside the courtroom to hear Dr Warrillow's evidence, while Erin Patterson appeared visibly upset as the doctor recounted Heather's condition.
She has pleaded not guilty to all charges and claims it was a terrible accident.
The trial will resume on Monday morning.
13°C