NHS staff left a sponge in a patient after confusion caused by a tea break, an investigation has discovered.

The mistake - made during keyhole surgery - has been condemned as highlighting "major systems of care issues" in a report on how it happened by local health board NHS Lanarkshire.

It had left the patient, who has not been named, in "worsening pain" after the operation and was only fixed when the sponge was pulled out in a second procedure.

Documents obtained by The Herald under Freedom of Information Laws show NHS officials have come up with a series of recommendations over the incident, including warnings that staff changeovers during surgery should be avoided.

It is now clear when the surgery took place or at which hospital. A Significant Adverse Event Review - a formal investigation carried out in to serious mistakes - blamed the error on a breakdown in communication when workers were swapped around for "tea relief".

It concluded: "A different plan and/or delivery would, on the balance of probability, have been expected to result in a more favourable outcome i.e. systemic factors considered to have an adverse and causal influence on outcome."

The sponge left in the patient was called an endoractor, and is put through a small keyhole incision to gently make more space for surgeons to work.

The review said: "An endoractor was used during the procedure to facilitate dissection. The patient initially made a reasonable recovery post op however, there was a slight elevation in inflammatory markers towards the end of the week and the patient complained of worsening pain and.

"A repeat CT scan identified a foreign body, which was confirmed by surgeon as being the endoractor.

"The patient returned to theatre on and endoractor was successfully removed."

The investigation discovered that no-one remembered taking the sponge out and putting on the the theatre tray - everything that goes in a patient should come out again and put on a tray. There was no note put on a whiteboard in the theatre about the sponge being removed.

The investigation's author, who was anonymous, added: "There was a change of staff during the procedure due to off-duty and tea relief. This may have contributed to the lack of communication regarding the endoractor."

He or she added: "Robust communication between the floor nurse and scrub nurse is essential when additional equipment or sundries are added on during a procedure. Staff changeover during procedures should be avoided. "When it must happen, a formalised handover of information should occur."

The investigation also found that staff education for new equipment, like the endoractor, was essential and that "distraction should be minimised".

Dr Lesley Anne Smith, an associate director at NHS Lanarkshire, said: “We take the safety of our patients extremely seriously and we regret any adverse incident.

"This type of incident is incredibly rare however, should one occur, we carry out a thorough investigation with the staff involved to ensure that lessons are learned and measures are put in place to prevent similar incidents happening in the future. The findings of the investigation were made available to the patient."