Fluid overload traditionally has been assessed by clinical examination, but recently, bedside devices have become available that use bioimpedance as a measure of resistance and reactance in body tissues. Data from fluid overload estimates based on bioimpedance in patients on dialysis have been well-studied, but few studies exist on the use of the technology in patients with heart failure (HF) or CKD who are not on dialysis. For a report in the Journal of Cardiac Failure, Kaitlyn J. Mayne, MBChB, MRCP, and colleagues aimed to fill that gap with a systematic review of existing studies of whole-body bioimpedance in these two populations, assessing associations with mortality, cardiovascular outcomes, and/or CKD progression.

“This is the first systematic review on the topic of bioimpedance in patients with HF and non dialysis CKD,” says Dr. Mayne. “Our findings extend the established associations with mortality seen in dialysis patients with earlier-stage CKD and HF. The results provide a rationale for further testing bioimpedance in these populations.”

Measurement of Bioimpedance Data in HF & CKD

“Fluid overload is a hallmark of advanced kidney disease and HF, which causes distressing symptoms for patients and increases risk for hospitalization and death,” notes Dr. Mayne. “Clinical assessment of fluid status is subjective and not quantitative, limitations that can be addressed by technology. One such example is bioimpedance, which estimates body water and fat by measuring resistance to an electrical current applied via adhesive skin electrodes.”

Among the 31 studies of bioimpedance analyzed in the systematic review were 20 HF and 11 CKD cohorts, with two studies that enrolled more than 1,000 participants. Ten bioimpedance parameters were used in those reports—eight in the HF studies and six in the CKD studies.

“Coexistent HF is common in CKD but not well phenotyped in existing studies, which included a variety of parameters and threshold values,” says Dr. Mayne. Absolute and relative fluid overload (overhydration), as measured by the Fresenius BCM device, were the most common parameters in the CKD studies. Twenty-one studies reported single baseline measurements rather than serial measurements.

Bioimpedance Results & Clinical Outcomes

The researchers’ analysis of the literature on bioimpedance measurement in HF and CKD showed that indices of fluid overload are associated with mortality and cardiovascular disease across the range of CKD stages studied (Figure). “Fluid overload detected in earlier CKD might trigger investigation for undiagnosed HF and use of diuretic agents,” says Dr. Mayne. “We support the use of bioimpedance spectroscopy in dialysis care, particularly for patients with challenging fluid balance.”

Of the five CKD studies that reported relevant cardiovascular outcomes, the largest (751 patients) reported a 48% increased risk for atherosclerotic cardiovascular disease and 80% increased risk for HF events with a phase angle less than 5.59 degrees, indicating a higher level of fluid overload, versus at least 6.4 degrees, after adjustment for age, sex, ethnicity, and clinical site. “We suggest the use of the Fresenius BCM device and the following definitions for use in adults: moderate fluid overload (>1.1L or >7%) and severe fluid overload (>2.5L or >15%),” notes Dr. Mayne.

Future Research Needs Reflecting on the gaps in research on fluid overload and use of technology to measure it, Dr. Mayne notes the need for adequately powered randomized controlled trials to compare the use of bioimpedance spectroscopy to routine care in both pre-dialysis and CKD and HF. “The first step is to agree on a consensus approach to bioimpedance measurement and fluid overload definitions,” she adds. “The gold standard would be an adequately powered randomized controlled trial of the effects of improved fluid management on exercise tolerance, QOL, and clinical outcomes.”