A hospital has changed its procedures after a guide wire was left inside a young patient during surgery.
The implement was discovered on a chest X-ray 12 hours after the procedure at Royal Stoke University Hospital.
The Trust which runs the hospital said the wire had come from a central venous catheter (CVC) containing more of the wires than usual.
Since the "never event", a report said, a checklist to count surgical equipment must now be completed by two people.
Following its investigation, a report to the University Hospitals of North Midlands (UHNM) NHS Trust board also said central venous catheter (CVC) sets containing two guide wires have been removed from the paediatric intensive care unit (PICU).
A CVC is described by Great Ormond Street a soft plastic tube which goes through a vein in the neck into the right side of the heart providing access to the heart.
The report said there were several brands of CVC sets on the unit, with different numbers of wires "which may have caused some confusion."
It said it had been assumed there were two guide wires before starting the procedure, but there was actually a third in the set.
"This was a difficult patient, and the medical team acted appropriately in providing treatment for this patient," the report added.
"It has identified the need to check equipment with another member of staff before starting a procedure, as well as at the end."
A trust spokesman told the Local Democracy Reporter Service: "Although there was no harm to this patient, we take all incidents of this nature extremely seriously.
"We work hard to understand why each incident occurs and how we can improve our practices."
A "never event" is categorised by the Department of Health as a mistake so serious it should never happen.
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