There is no evidence for any benefit of ischaemic conditioning during cardiovascular surgeries and guidelines supporting the practice in these settings are premature, argue Australian researchers in a new meta analysis.
The simple technique – an intermittent inflation of a blood pressure cuff to cut off blood flow to a limb – is a relatively new practice.
Senior Director of the Renal and Metabolic Division in the George Institute, Professor Martin Gallagher told the limbic it has been advocated in some guidelines as a safe and inexpensive way of stemming the effects of injury including myocardial ischaemia, acute kidney injury, and stroke after early studies found some evidence of benefit on biomarkers and surrogate endpoints like troponin and creatine kinase.
But doubt remains about the clinical validity of those results after the publication late last year of larger and higher powered studies that found an “incongruous lack of benefit” on combined cardiovascular event endpoints, he said.
“The data that’s out there now suggests that if there is an effect upon mortality its vanishingly small. Based on our study the number needed to treat to prove mortality benefit was 18,000 – that’s a huge number of events and our view is [a mortality benefit] that is probably never going to be proven. We would argue that clinical trials that focus on mortality as the primary endpoint are probably of limited utility going forward.”
He thinks that early support for the practice in some countries like India, China and Europe where they are already using ischaemic conditioning before heart surgery or as a treatment following heart attack is premature and reminiscent of the initial excitement about renal denervation and its effect on blood pressure.
“That was embraced very quickly – most cardiology units in Sydney had renal nerve ablation capabilities set up within two years and our experience with that led us to have some degree of scepticism here.”
In the meta analysis, Professor Gallagher and colleagues analysed findings from 89 randomised studies.
They found that ischaemic conditioning had no effect on all cause mortality regardless of the clinical setting in which it was used.
But there’s still scope for investigating the technique in other areas, Professor Gallagher suggests.
The study found that ischaemic conditioning may reduce the rates of some secondary outcomes including stroke and acute kidney injury (AKI), although the quality of evidence was low and benefits seemed to be confined to nonsurgical settings and to mild episodes of acute kidney injury only, Professor Gallagher said.
“The fact that the effect size diminished as the kidney injury got worse is a cause of some concern – it suggests that some of the signals around AKI, like changes in creatine, might not be important to patient outcomes. However, there certainly is a signal there and I think that needs to be clarified and future studies should look at more severe and higher risk patients for AKI with more significant injury.”
While he acknowledged that the technique is simple, cheap and has not yet been found to cause harm he remains cautious for now.
“If you’re running a cardiology unit or a stroke unit you could do this without major investment in infrastructure. You’re probably not doing much harm either but you have to bear in mind that there is an opportunity cost.
“As healthcare gets more complex the more small interventions add cost and complexity into healthcare – even if they don’t cost very much in and of themselves they add complexity and they add scope for error.”