Is there a large population of people with chronic kidney disease who use haemodialysis regularly?

The prevalence of patients with end-stage renal disease is rapidly growing. This is partly due to the progressive ageing of the population and the increasing prevalence of other comorbidities such as obesity, diabetes mellitus and hypertension. For instance, in 2015 there were approximately 690,000 patients with end-stage renal disease just in the US, and this prevalence is expected to rise by 11–18 per cent in 2030 (https://tinyurl.com/sh6fmt9).

What contributes to reduce exercise capacity in this population?

Several factors and physiological mechanisms contribute to reduced exercise capacity, commonly observed in this patient population. This includes the comorbidities that these patients usually present, such as obesity or diabetes, and other conditions, malnutrition or anaemia for example. However, one of the major causes is the low level of physical activity of these patients, which is much lower than that of healthy individuals.

Has exercise during dialysis been promoted for some time?

Numerous meta-analyses have assessed the effects and safety of physical exercise during dialysis sessions. Based on dozens of studies, their results support the benefits that these interventions can provide not only on exercise capacity, but also in other relevant outcomes—blood pressure, quality of life, or even dialysis efficiency. Rather than voluntary intradialytic exercise, you investigated neuromuscular electrical stimulation to induce the exercise involuntarily.

Why would that be necessary?

As commented above, many dialysis patients have an excessively low physical capacity and are frail. This, together with some methodological limitations (some patients may find it difficult to perform exercise while seated in a semi-recumbent position during haemodialysis sessions), hinders applying voluntary exercise (eg, semi-recumbent leg-cycling, strength training). Neuromuscular electrical stimulation, the application of intermittent electrical stimuli to generate involuntary muscle contractions, might serve as an exercise mimetic for these patients.

How much evidence did you find when you searched for trials of intradialytic electrical stimulation?

The evidence on the benefits of electrical stimulation on other frail patient populations is quite strong and therefore it could be hypothesised that electrical stimulation might also be effective on dialysis patients. However, evidence on this topic is still emerging. In our research, we could find eight randomised controlled trials that applied intradialytic electrical stimulation on about 200 patients. Of these trials, seven had been published in the last five years, which highlights the novelty of this type of intervention.

Which outcomes improved with the stimulation?

After reviewing these eight trials we found evidence for improvements on functional capacity and handgrip, and lower limb muscle strength. Insufficient evidence was found to support its benefits on other outcomes such as quality of life, muscle mass, or biochemical variables. 

Did the papers also report whether using the stimulation during dialysis was safe and practical?

This is probably one of the most important issues. No major adverse events were observed, which reinforces the safety of this intervention. It must be noted, however, that electrical stimulation programs should be individualised to ensure their safety and clinical effectiveness.

What should research in this area focus on now?

More research is warranted on the effects of intradialytic electrical stimulation on haemodialysis patients, as the benefits observed in our meta-analysis need to be confirmed on long-term randomised controlled trials conducted in larger cohorts. In addition, scarce evidence is available on whether superimposing electrical stimulation onto voluntary exercise training could maximise the benefits provided by any of these strategies alone. The field of intradialytic electrical stimulation is an emerging one and much work remains to be done.

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>> Pedro L Valenzuela is a researcher at the Department of Systems Biology, University of Alcalá (Madrid). His work is mainly focused on the functional/physiological effects of physical exercise on populations at risk of muscle wasting and functional decline, notably hospitalised older adults and dialysis patients.