John: Haemodialysis is the most common treatment for kidney failure globally, but problems can arise with access to the patient’s bloodstream. A new Cochrane Review from January 2016 examines the evidence for preventing one of these problems, the development of a stenosis. The lead author of the review, Pietro Ravani, from the University of Calgary in Canada, describes the findings in this Evidence Pod.

Pietro: In order for a patient to receive haemodialysis, we need reliable access to their bloodstream. An arteriovenous access, i.e. a fistula or a graft in the arm, is considered the best means of achieving this. A fistula is a vein that is surgically connected to an artery; while a graft is a plastic conduit placed under the skin to connect an artery with a vein. However, over time, these tend to develop a narrowing, which is called a stenosis. This reduces blood flow and the quality of the dialysis, and can lead to clotting in the access or its loss. As a consequence, guidelines recommend regular screening using diagnostic tests, physical examination or both to identify and treat problems, in the hope that early correction of stenosis can maintain the functionality and openness of the access, and prolong its use. Our review examines the evidence for correcting stenosis pre-emptively, before the access became dysfunctional, or waiting and correcting the stenosis only if the access became dysfunctional; and, after considering this carefully, we are not able to support the pre-emptive strategy.
We included 14 trials, with nearly 1400 participants randomised to either a pre-emptive correction of an access stenosis or a deferred correction. Overall, we found that pre-emptive stenosis correction is more likely to prevent access clotting but does not improve the longevity of the arteriovenous access. When we assessed the effects of pre-emptive correction separately in fistulas and grafts, we found more favourable results in people using fistulas, but the studies are small and of very low quality suggesting that better outcomes they found may have been due to chance or bias, rather than true effects of the pre-emptive strategy. We also found that a pre-emptive stenosis correction strategy may increase the number of access-related procedures and procedure-related adverse events, including infections and mortality. 
In summary, our research provides evidence-based data that do not support access surveillance and pre-emptive correction of stenosis in an arteriovenous access, particularly in people using grafts. Although pre-emptive stenosis correction may reduce the risk of access loss in fistulas, it might also increase the risk of procedure-related adverse events and healthcare costs. Large, multicentre clinical trials are needed, with a focus on people using fistulas, to clarify potential harms and expected benefits of routine access surveillance and pre-emptive correction of access stenosis.

John: If you’d like to read more about the existing evidence base described by Pietro, and watch for updates of the review should those large trials be done, you can find the full review easily by going to Cochrane library dot com and running a search for 'pre-emptive correction and access stenosis'.