An inquest has heard how medics critically failed to recognise they had wrongly placed a breathing tube in the oesophagus on a 44-year-old woman who died in their care.

Mum-of-four Sharon Grierson, from Aspatria, died at the Cumberland Infirmary on November 14, last year, three days after she went in for elective surgery to remove a polyp from her right vocal cord.

While she underwent general anesthetist and the surgery with no issues, complications arose when the tube which was aiding her breathing was removed.

Medics tried desperately to ventilate Mrs Grierson by reinserting an endotracheal tube (ETT) - but this was twice placed wrongly in her oesophagus - a fatal error they didn't immediately spot.

She also suffered a cardiac arrest and CPR was administered.

The inquest heard how abnormal capnography readings, and at times and absence of capnography readings altogether, should have alerted them sooner to the fact that the breathing tube was not in her airway.

Capnography represents the amount of carbon dioxide - measured as end tidal carbon dioxide (etCO2) - in exhaled air, which assesses ventilation.

Pathologists said that a lack of oxygen to Mrs Grierson's brain for more than 40 minutes after the procedure had resulted in irreversible brain damage.

Dr Julian Brown, Consultant in Anesthesia and Intensive Care Medicine, who works at Southend Hospital, prepared a report at the request of Cumbria Police CID after considering witness statements.

He concluded "lapses in her care caused her death", though he did not believe gross negligence occurred.

He said: "In my opinion by far the most significant error was not the failure to manage the extubation, or the need for reintubation, or even the esophageal intubation but the failure to recognise a failed intubation."

Sam Harmel (corr) , the barrister representing Mrs Grierson's family, pressed medics as to why the lack of normal capnography readings didn't lead them to realising the tube was incorrectly placed sooner.

The team had collectively decided on a working diagnosis of hypoxia.

Dr Chris Dickson, a consultant anesthetist, was called into help as the emergency situation escalated.

Mr Harmel asked Dr Dickson, why when he arrived was the diagnosis beyond the tube being wrongly placed.

He said: "It was a very complex situation I had come into.

"This was my honest belief that we had secured the airway and something else was going on."

The coroner David Roberts said the criticism was clearly the failure to recogonise the absence of etCO2.

"It meant the possibility of the tube being in the wrong place was overlooked," he said.

Dr Dickson said no etCO2 was consistent with laryngospasm, which can occur after extubation, but on reflection he said you should expect to see an etCO2 reading "rapidly".

Instead, other signs were relied on such as fogging of the tube and chest sounds, as well a clicking sounds, usually indicating the tube was in the airway.

On two occasions Dr Glen Pinto, a specially trained year 3 (ST3), questioned the position of the tube because he was concerned about the capnography readings.

Another error was the failure to correctly administer oxygen to Mrs Grierson.

The operation was run on 50 per cent oxygen, which is usual. But during the process of removing the breathing tube, her oxygen was not turned up to 100 per cent as it should have been - an error that wasn't spotted until Dr Dickson was called in to help.

Dr Pinto was working under Dr Jenny Fraser, the hospital's lead head and neck anaesthetist, that day.

Dr Fraser assumed her trainee had turned the oxygen up when required to do so.

She said in her evidence: "I made an assumption that, being an ST3 trainee, he would have understood the requirement to keep the sevoflurane gas on and turn the oxygen up for a deep extubation.

"I accept that I should have been more precise in communicating my instruction and should have either checked his actions or operated the anaesthetic machine myself."

When asked by Mr Roberts if he accepts now that he hadn't turned up the oxygen when he should have, Dr Pinto replied: "Yes, and that was not for Dr Fraser. I should have known."

Dr Pinto explained that there are times when patients are extubated with less than 100 per cent oxygen, but added: "In Mrs Grierson's case I should have given her 100 per cent oxygen."

All medics who have so far given evidence have expressed their deepest sympathies to the family.

Dr Dickson said: "It has been a horrible event to be part of and I'm really, really sorry to the family."

Since Mrs Grierson's death the North Cumbria University Hospitals NHS Trust's medical director has issued and circulated to departments an urgent patient safety notice entitled, Management of the Airway and Breathing During Anaesthetic Crisis.

The inquest was due to last until the end of the week but was adjourned on Wednesday. An alternative date is yet to be fixed.