Image of patient hand in hospital bed

Residual drugs in intravenous cannulae and extension lines


The national investigation

Our investigation looked at the risks to patients when intravenous (IV) drugs are retained in cannulae and extension lines.

Some drugs, such as those used in anaesthesia and pain management, can cause patients to stop breathing. After administration, these drugs should be flushed through cannulae and extension lines to make sure no residual quantities of the drugs are left.

Despite the issuing of multiple safety alerts over the past ten years, residual drugs in cannulae and extension line events continue to happen. When these events involve drugs that cause the patient to stop breathing, there is a risk of hypoxic brain injury (where the brain is damaged after a period where it does not get enough oxygen) or death.

A cannula is a plastic tube that is inserted into a patient’s vein to administer medicines. Cannulae are available in a range of sizes and design types which vary between hospital departments and wards.

Extension lines may be connected to the cannula to increase the number of access points to allow multiple medicines to be given at the same time. Cannulae are subject to careful infection prevention and control oversight as these devices can be a route through which infection is caused.

Reference event

The investigation was launched after concerns were reported to HSIB by a consultant anaesthetist at a district general hospital where a patient had stopped breathing several hours after undergoing an anaesthetic.

It’s thought that a quantity of the drug Suxamethonium - a muscle relaxant - was retained in their cannula after the procedure. The cannula containing the drug was flushed on the ward by a nurse preparing to administer intravenous paracetamol around three hours after the patient had returned from his procedure.

The event was witnessed by a doctor who immediately started manual ventilation. The patient began to breathe spontaneously a few minutes later and suffered no physical harm. However, they have been left with a significant psychological impact following their experience of being awake but unable to move or breathe.

Investigation summary

This investigation:

  • Explored the design, procurement and change management of intravenous consumables, such as cannulae and extension lines.
  • Observed how checklists are used in the theatre and non-theatre setting to ensure that cannula flushing is undertaken.
  • Examined medicines safety, management and governance arrangements. This may include prescribing arrangements, record keeping, medicines dosage and presentations, and reporting of incidents.
  • Sought to identify safety recommendations.

Addendum to report (June 2021)

The investigation report discusses HSIB’s intention to develop and issue a safety recommendation around identifying medicines that present a high risk if inadvertently retained in cannula and/or extensions lines, and to assess and strengthen the mitigations in place for each identified medicine.

At the time the investigation report was published (March 2021), key stakeholders had limited capacity due to COVID-19 pressures to discuss this recommendation.

In May 2021, HSIB discussed the potential recommendation with NHS England and NHS Improvement, the Royal Pharmaceutical Society, the Royal College of Anaesthetists, and the Centre for Perioperative Care.

The stakeholders were unified that the proposed recommendation was unlikely to make a significant change to the current system and believe that flushing is the key mitigation to preventing residual drugs in intravenous cannulae and extension lines.

The stakeholders agreed that work to strengthen the process of flushing cannulae and extension lines was important and this would provide a greater improvement to patient safety than commencing activities exploring/highlighting risks with specific drugs.

A recommendation to the Royal College of Anaesthetists, and the Centre for Perioperative Care around strengthening the process of flushing has already been published as part the main investigation report in March 2021.