Should catheter leg bag drainage tubes be made narrower?

We worked with researchers, patients and businesses to explore whether the diameter of catheter drainage tubes could or should be reduced if this could be done without affecting the function and whilst still meeting regulatory standards.

D4D Project Lead and Organisation

Dr Alberto Marzo, University of Sheffield

When did project start?

December 2013

Clinical Requirement

It is estimated that around 5 million people in the UK suffer from severe urinary incontinence, a condition commonly associated with other long-term health conditions such as stroke, multiple sclerosis, dementia, and mobility restrictions related to ageing. Unfortunately for many sufferers there are no effective treatments available to stop the leakage and they have to use continence pads, commode toilets or bladder drainage tubes (catheters), with wearable bags to collect the urine. Around 30% of patients suffering from urinary incontinence depend on indwelling urethral catheters. Around 130,000 catheters are used per annum in the UK.

In a user survey current drainage tubes were found by some patients to be oversized and unwieldy. They are uncomfortable to wear and visible under patient clothing, thus having an impact on patient dignity and quality of life.

Our Investigations

We have used numerical and experimental approaches, including a newly developed in vitro bladder drainage model, to investigate whether drainage tube diameter could be reduced while still satisfying physiological, clinical and regulatory requirements.  Drainage tube size are closely related to the flow rates that the tube will allow.  Urinary catheters and drainage bag average flow rates are regulated by standards BS1616 and BS86692, respectively. The same standards do not place any direct constraints on drainage tubes and connector dimensions and design.

In addition to exploring whether it would be possible to reduce the diameter of tubing without losing physiological flow rates, we have also approached industry colleagues to discuss the possibility of narrow bore tubing becoming available, and what evidence would be required to support and enable such a change.


Our research has indicated that the internal diameter of tubing used in urinary drainage bags could be reduced significantly while still meeting the relevant standard. This research is under preparation for publication.

The model that we developed could prove a useful tool in developing new catheter products as it provides a quick method to test flow, before embarking on more complex and expensive analyses. It also provides a strong methodological basis for the development of a computer model of urinary catheterisation that can incorporate fluid flow, and potentially biofilm formation. Biofilm formation causes some of the greatest clinical challenges for catheter users.

The concept and preliminary findings were discussed with relevant manufacturers, who agreed that independent testing and greater evidence of the need for change would be required before they will invest into changing their ranges. There are many barriers to the development of new medical devices, and to updates of existing devices, including manufacturing changes, CE mark changes, independent clinical evidence that new devices improve on older designs and do not cause unexpected complications compared to the devices they replace, compatibility with interconnected devices, marketing changes, and the cost of changing the production processes.


This project was led by the University of Sheffield (Alessandro Melis under the supervision of Dr Alberto Marzo) in partnership with D4D at Sheffield Teaching Hospitals NHS FT and Professor Jaan Unger at the University of Applied Sciences, Hochschule Niederrhein , Germany.