logo of COBALT study

Cardiorespiratory Optimisation By Arteriovenous fistula ligation after transplantation (COBALT)

Randomised-controlled trial (RCT), UK-only, Multi-centre
Primary Investigator: Gavin Pettigrew
Funding: NIHR, Addenbrooke’s Kidney Patient Association, Cambridge University Hospitals NHS Foundation Trust
Sponsor: Cambridge University Hospitals NHS Foundation Trust and the University of Cambridge
Start date: 01/03/2022
End date: 14/12/2022

This is a randomised, open-labelled, interventional feasibility study of a proposed multicentre randomised controlled trial.

Research question: Should we disconnect haemodialysis fistulas in patients after they have been transplanted successfully?

Background: Kidney transplantation is the best form of treatment for most patients with kidney failure. Before they receive a transplant, patients often require a period of haemodialysis, whereby the blood is cleansed by regularly attaching the patient to an artificial kidney machine. For this, patients often have an operation to create an arteriovenous fistula, which involves joining a vein in the arm directly onto a nearby artery. Once created, the fistula vein expands and the blood flow through the vein increases markedly. While this is ideal for providing access for haemodialysis, the increased blood flow means that the heart must work harder, and studies have shown that the heart becomes bigger and its muscle thicker. Although not proven, it seems likely that these changes to the heart may contribute to the extra deaths from heart disease. This study will examine whether an operation to disconnect the fistula vein from the artery improves heart function in kidney transplant patients. As preliminary work for a much larger study, we will recruit forty consenting patients with good, stable kidney transplant function, and who still have a working fistula.

The objectives of the study are:

  • To conduct a feasibility study involving six centres that mirrors a proposed Randomised Controlled Trial (RCT)*, but that uses pre-defined cut-offs with regards to patient recruitment and retention rates to justify progression to the RCT.
  • To understand patients’ and healthcare professionals’ perceived acceptability of the proposed trial design and processes, with a view to planning strategies to optimise recruitment and retention for the main RCT.
  • To assess feasibility and acceptability of a Cardiopulmonary exercise test (CPET) in the kidney transplant population, as judged by the proportion of participants who successfully complete both tests.
  • To assess patient compliance with wearing a wrist accelerometer (activity sensor).


Participating centres:

  • Cambridge University Hospitals NHS Foundation Trust
  • Oxford University Hospitals NHS Foundation Trust
  • Royal Free Hospital
  • Queen Elizabeth University Hospital, Glasgow
  • University Hospital Coventry
  • Freeman Hospital
Contact: anna.sidders@nhsbt.nhs.uk