MyTEMP trial: Is this the end of “cooled dialysis”?

The MyTEMP trial is a triumph. In years to come it will be thought of as a ground-breaking clinical trial for people on maintenance haemodialysis and an exemplar of how trials should be conducted in this population. Why? Well, not because it tested a new compound and showed overwhelming effectiveness, but rather it definitively answered a question that clinicians have thought about for years. It refuted established practices and should change guidelines and patient care overnight.

So, what was the MyTEMP trial all about? Cardiovascular disease remains the leading cause of death for people on dialysis, in part driven by the processes of haemodialysis and ultrafiltration. One of the clearest signs of cardiovascular compromise for people on haemodialysis is the development of symptomatic intra-dialytic hypotension or “going flat” on dialysis. This scenario is well recognised by dialysis clinicians and represents circulatory failure, usually towards the end of dialysis, and often in the context of large volume or rapid ultrafiltration. Episodes of intra-dialytic hypotension associate strongly with adverse cardiovascular outcomes and one of the established practices to mitigate these episodes (and improve cardiovascular outcomes) has been to lower the temperature at which patients dialyse, typically by around 1°C lower than body temperature. The established theory is that being colder causes peripheral vasoconstriction, improves afterload, helps maintain cardiac output and offsets circulatory collapse. A perfectly reasonable theory that was backed up by nice mechanistic studies, observational data and small trials, and not unreasonably “cooled dialysis” has been recommended in international and national haemodialysis guidelines as a way of managing patients prone to intra-dialytic hypotension.

The MyTEMP trial, which published in the Lancet at the end of 2022, showed definitively that lowering the temperature at which patients dialyse to 0.5-1°C below body temperature (though no lower than 35.5°C) did not reduce major adverse cardiovascular events, compared to standard treatment at 36.5°C. Moreover, patients in the intervention arm who dialysed at the lower temperature had significantly more unwanted side-effects from being colder during dialysis and there was no difference in rates of intra-dialytic hypotension. Why are the authors so convinced of the study finding? Well, apart from anything else this is the largest ever trial of patients on haemodialysis recruiting over 15,000 people and the study design was exemplary. This was a pragmatic, two-arm, open-label cluster randomised trial where randomisation occurred at a centre level, meaning all patients at a centre randomised to lower temperature dialysis received exactly that and outcomes were compared to patients at centres randomised to dialysis at a standard temperature. A total of 84 centres across Canada took part in this study and outcomes were captured through linkage to provincial registry data. This is hugely pragmatic, enormously efficient and extremely cost-effective. The study team must be commended on this land-mark trial, which really sets the bar for trials in this population in the future – big, pragmatic and inclusive. It gives evidence of the highest quality to guide clinical practice and gives hope that in the coming years we will be able to build an evidence base with similarly pragmatic trials.

So, does MyTEMP signal the end for “cooled dialysis”? Well, clinicians may feel it is still appropriate to try in certain situations on an individual basis, but we can be confident now that cooled dialysis does not improve outcomes as we had hoped and impacts a patient’s dialysis experience. For these reasons practices and guidelines should be changed.

A digest of the MyTEMP study can be read here.