A nurse wearing scrubs prepares surgical instruments including swabs.

Retained swabs following invasive procedures: themes identified from a review of NHS serious incident reports


This investigation explored the patient safety risk of swabs being unintentionally retained following an invasive procedure such as surgery.

When operating on a patient, a surgeon may put swabs (pieces of gauze that come in a range of types, shapes and sizes) into the patient’s body to absorb bodily fluids such as blood. The operating theatre team count the swabs in and out, using a process known as reconciliation, to ensure all swabs are accounted for at the end of the operation. However, sometimes a swab can be unintentionally retained (left inside a patient’s body).

This type of patient safety incident is known as a ‘Never Event’ – that is, an event that NHS England considers to be wholly preventable. Unintended retention of swabs can result in negative outcomes for patients, including distress, further surgery, prolonged hospital stays and extended time off work. There is also a risk of infection and death.

To explore the issue of retained swabs, the investigation used a real patient safety incident, referred to as ‘the reference event’, as an example.

The reference event

The patient, Helen, underwent surgery to treat coronary artery disease (a type of heart disease). The procedure involved opening Helen’s chest to expose her heart and took approximately 5 hours to complete.

Following the procedure, a chest X-ray identified that a swab had been left inside Helen’s chest. Helen was returned to the operating theatre to open the wound to remove the swab. Later, another chest X-ray showed that a second swab remained in Helen’s chest, in the same location as the first. Helen returned to the operating theatre again for the wound to be opened and the second swab was removed.

The investigation

The incident was referred to the Healthcare Safety Investigation Branch by Helen’s family and the investigation sought to:

  • explore the factors associated with unintentional retained swab events following an invasive procedure (not including vaginal swabs which has previously been investigation by the Healthcare Safety Investigation Branch)
  • identify alternative safety controls to reduce the likelihood of foreign objects (such as swabs) being unintentionally retained.

The investigation produced an interim report which highlighted common themes in 31 serious incident reports (reports of investigations carried out by local healthcare trusts into patient safety incidents) where a swab was unintentionally retained following an invasive procedure. The interim report made a safety recommendation to NHS England.


  • A range of complex and interrelated system (tools, technology, organisation, task, environment, and people) factors routinely influence the reliability of the swab count and the achievability of the overall reconciliation process.
  • The reconciliation process has not been formally analysed or designed using human factors expertise (where the interactions between people and other elements of the system in which they work are explored) or any other process design expertise.
  • Other safety-critical industries assess and control risks to be ‘as low as reasonably practicable’ (ALARP), where there is not an expectation to eliminate all risk. These risk management principles have not been applied to the risk of swabs being unintentionally retained.
  • There is no accountability framework, and it is unclear who owns the risk for retained swabs and reducing the risk for retained swab events to as low as reasonably practicable.
  • Blame can be inappropriately placed on scrub practitioners and/or the surgeon when an item goes missing, rather than the reconciliation process being seen as a team activity and one that can be influenced by a wide range of interrelating factors.
  • Staff and national organisations had varying views on the roles and responsibilities for swab reconciliation; limitations in training were identified.
  • The investigation was told by various national organisations that there is a concern about removing Never Events from the NHS’s framework and how determining risk appetite (where it is accepted a level of harm will occur) will be perceived by the wider public.
  • The design of swabs does not help staff to locate, identify, or track swabs during the reconciliation process.
  • There are technologies and tools that could be used to improve the accuracy of the swab count; however, these have not been embedded into UK healthcare.
  • The technology and tools have not been formally considered using risk management principles in terms of reducing the risk to as low as reasonably practicable, or how the technology could reduce other patient safety concerns while also supporting productivity and efficiency in healthcare.
Interim report Investigation report