A vulnerable female patient in respite care died after a nurse mistakenly binned a vital part of her breathing tube, an inquest heard.
Emily Bushaway, who suffered with a rare neuro-degenerative disease, was left unable to breathe properly after a small section of her ventilator's "whisper valve" was discarded.
Nurse Katie Philips said she had been following 21-year-old Emily's care plan when she correctly changed and then discarded a length of used flex tubing in a bin.
But in error - and unknown to her at the time - she had also removed part of the attached whisper valve, which cleared Emily's build-up of cardon dioxide generated as a side effect of her condition.
Although with 20 years in nursing, Miss Philips told Oxford Coroner's Court she had never before had to change a whisper valve, and had no formal training on that type of ventilator.
Recording a narrative verdict on Wednesday, Oxfordshire coroner Darren Salter said Emily's "accidental death was contributed to by neglect" because the hospice's care plan was inadequate.
He is also writing to the Government agency which regulates medical equipment about the "alarming" fact the two-part valve could appear to be correctly assembled when it was not.
Mr Salter ruled that Emily (pictured) became "unwell and unresponsive" at the home, and died shortly afterwards at John Radcliffe Hospital.
He added that part of the whisper valve had been "unintentionally removed and discarded by a nurse" which meant the patient was left unable to exhale properly.
The coroner is preparing a report to the Medicines and Healthcare products Regulatory Agency (MHRA) to express concerns of a lack of "colour-coding" or similar design, which would "flag up" if a piece of the valve was missing.
In evidence, the court heard the ventilator's message log had shown air-flow alarms had been triggered three times in 13 minutes just before Emily's father Mark Greener arrived to pick her up on May 14 2016.
Describing his impression of the unfolding scene, Mr Greener claimed staff's response at Helen & Douglas House hospice, Oxford, to his daughter's rapidly deteriorating situation was "woeful", and it was he who spotted the valve was missing.
Giving her account, Miss Philips said when she saw the valve she had no idea what it did, was "not confident" changing it, and had no formal training on use of that ventilator.
She described getting "a feeling" something was wrong with Emily about an hour after changing the tube.
Emily was diagnosed, aged six, with the life-limiting and "relentlessly progressive" condition Niemann-Pick disease type C (NP-C), and later had a tracheotomy to allow her to breathe.
Unable to talk, walk or look after herself, she needed highly specialised care at the family's Letchworth home in Hertfordshire and was seen daily by intensive-care trained nursing staff.
Her younger sister Sarah also has the same rare hereditary disease, which affects only about 700 worldwide.
Doctors provided Emily with a Nippy ventilator in early 2016 which attached directly to a flexible breathing tube connected to her windpipe.
Describing in court changing the breathing tube, known as an Edith-flex, Miss Philips said: "I threw the tube in the bin because it wasn't needed and I got another Edith-flex tube, and fitted it.
"I thought in fact the bit discarded was all part of the same thing because it all came together."
When she replaced the tube with a new section of flex, she added it "slotted back perfectly", adding "the machine did not alarm".
Examination of the machine found it to be in good working order.
Mr Greener rushed into his daughter's room and described her looking "awful", and saw her fingernails and lips had turned blue.
When he noticed part of the whisper valve was missing and asked home staff where it was, he claimed one nurse's response was "what's that?"
Giving evidence, he said: "They were woeful. I may as well have been the ambulance."
He added: "I walked in there and they were standing there doing nothing."
Emily had stayed at the respite home, Douglas House, in the previous two years without incident.
Because of his daughter's new ventilator, Mr Greener told the coroner how he had three separate phone conversations with the home's staff and was "assured they were competent".
Emily's main daytime nurses, many of whom had looked after her for years, then visited the respite home to talk staff through her needs.
Mr Greener, who was present at that handover, said the whisper valve was "one of the biggest checks you do - it's simple".
However, statements showed a variety of opinions about the whisper valve care process among Douglas House nurses, with one saying it had "taken us ages to work it out".
A post-mortem investigation found Emily died of "severe respiratory compromise due to a failure of the ventilator function".
The Crown Prosecution Service ruled out any criminal proceedings on Monday but the Care Quality Commission (CQC) is still investigating, the court heard.
The coroner also asked the hospice for evidence of what improvements it has made - although a new draft CQC report has identified it is making good progress.
In a statement following the inquest Emily's parents Lisa and Mark said: "We had complete faith in the care home we had chosen for Emily and believed she was being looked after under the highest of standards.
"To walk in that day and see our daughter so poorly was absolutely unexpected and a memory that will haunt forever.
"Emily was cared for at home with us, alongside trained nurses who came in to help support her.
"She was only in the care home for a five night respite, so we could redecorate her bedroom in time for her return.
"Our beautiful daughter's health was improving and she was gradually being weaned off her ventilator because she was doing so well.
"We are utterly devastated and bereaved at the tragic loss of our daughter."
The family's lawyer, Tim Deeming, from legal firm Slater and Gordon, said Emily's had been a "tragic avoidable death", which had shocked her family.
He added: "Nothing can mask the pain the family have, and are still going through, but we hope this inquest will help put effective measures in place to safeguard other families throughout the country, and make sure the highest standard of care is delivered everywhere."
Copyright (c) Press Association Ltd. 2017, All Rights Reserved. Picture (c) Slater & Gordon / PA Wire.