An inquest into the death of a 45-year-old woman who failed to regain consciousness after a routine back operation has been told that doctors do not know what caused her "to suffer a devastating brain injury with no possibility of recovery".

Patricia Kelly, from Castletreasure, in Douglas in Cork City, died on 17 December 2015 after being in a coma for 22 months at Cork University Hospital following an operation on two discs in her neck on 11 February 2014.

Ms Kelly's sister-in-law Margaret Kennedy told Cork City Coroner Philip Comyn that Patricia went in for a day procedure and never came home. 

"All we want to know is what happened to her so that we can give clear answers to her son Michael, who is now 12 years old."

Ms Kennedy told the inquest that her sister-in-law, who was a diabetic and had a history of hypertension, suffered a simple fall in November 2013 but needed an urgent operation.

Patricia's husband John dropped her off expecting to pick her up later in the day but was told at 12.30pm that she was not waking up.

When the family arrived at the hospital, all they were told was that the operation had gone well but no explanation was given as to why she was not waking up.

Ms Kennedy said Patricia's seven-year-old son Michael kept asking when his mother would wake up and come home. 

"The difficulty for all of us was that we didn't have an answer for Michael as to what had happened to his mum".

Ms Kelly never regained consciousness and remained in a coma at CUH for 22 months until her death on 17 December 2015.

Clinical nurse specialist Mary Frances Davey told Cork City Coroner's court that she met Ms Kelly the day before the operation to assess her at the pre-admission clinic at CUH.

She said Ms Kelly's heart rate and blood pressure levels were within known parametres.

Ms Kelly had a BMI level of 42 and as it was over 40, she discussed it with anaesthetist Dr Frank Loughnane.

She agreed, when asked by family barrister Brian Leahy, that 42 was "quite high". 

She also noted that Ms Kelly was on "quite a considerable amount" of medication and as per protocol she told her not to take her insulin and oral hypoglycaemic medication ahead of the operation, having briefed her on fasting times and when to stop drinking liquid.

Dr Loughnane told the court that he would answer many questions in a day and does not remember this case in particular, but said when asked about Ms Kelly's suitability for the operation given her BMI of 42, he does not believe he would have suggested an alternative course.

Coroner Comyn noted that while Ms Kelly was told not to take her insulin and hypoglycaemic medication ahead of the operation, she was not instructed to discontinue an ACE inhibitor she was taking (to treat high blood pressure) as is done in Beaumont hospital.

Dr Loughnane said there is broad disagreement in the medical community as to whether they should or should not be taken prior to surgery. 

In general, in CUH it is not discontinued. 

Theatre staff nurse Ginalyn Arellano said she noticed nothing out of the ordinary during surgery. 

Afterwards, when Ms Kelly was moved to a trolley she noticed her legs were twitching which she thought was a sign of her waking up. She said it can sometimes take people a while to wake up.

Consultant neurosurgeon George Kaar said Ms Kellly had been urgently referred to him after an 11-week history of neck and shoulder pain and described the surgery as "uneventful".

He said during his initial meeting with Ms Kelly he explained that because of her weight and her diabetes she was at an increased risk and she would have to weigh up the decision to operate.

He offered his condolences to the family with whom he said he has had many meetings.

Dr Osman Ahmed, who was the senior anaesthetist register under the supervision of Dr Brian O'Donnell on the day said in his statement read out in court that both of them met the patient beforehand and made out a plan noting her history, her BIM of 42, and that she was on a range of medicines.

He said there was nothing unusual about the operation although he did note that there was a drop in her oxygen saturation level which came back up, and a drop in her blood pressure.

He became concerned when she did not come out from the anaesthetic and alerted Dr O'Donnell. 

Dr O'Donnell said he found her deeply unconscious and while all her vitals were unremarkable, he was concerned she may have suffered a brain injury and she was taken for a CT scan.

The Coroner asked him if an alarm should have gone off during surgery when her oxygen saturation level seemed to have been below 94% for over an hour. 

Dr O'Donnell said it would not be unusual for someone with a BMI of over 40 to have adapted to a slightly lower oxygen level.

CUH Consultant neurologist Dr Daniel Costello told the court that he initially thought her comatose state was due to a slow wearing-off of pain medication for her back but an MRI conducted the following day was found to be very abnormal showing extensive areas of injury to the brain which was irreversible.

He said it was clear she had suffered an acute injury to the brain but there were no obvious signs of what caused this.

Asked if he knew what caused her brain injury, he replied: "I don't, is the honest truth. I don't know why she suffered such a severe injury based on the data to hand."

The inquest will resume at 11am tomorrow.