{"doi":"10.2215/cjn.01770220","title":"The Elusive Promise of Bioimpedance in Fluid Management of Patients Undergoing Dialysis","abstract":"There can be little doubt that bioimpedance measurements in patients undergoing dialysis have predictive value. In a systematic review of cohort studies in which multivariable survival models were reported, 32 out of 38 found that overhydration determined by bioimpedance was associated with worse survival independently of other known predictors such as age, comorbidity, and serum albumin (1). Meta-analysis, regardless of the bioimpedance method used, found mortality to be approximately doubled in the top 15% of overhydrated patients. The increased risk is apparently independent of BP and synergistic with inflammation. Surely all we need to do is to use bioimpedance to normalize hydration in the dialysis population and many lives would be improved or prolonged. “Would that it were so simple,” to quote the amusing scene in the movie Hail, Caesar by the Coen brothers. It is of the greatest importance that using bioimpedance to guide fluid management is properly tested by appropriately designed, randomized, controlled trials. Just because an association is strong it cannot be inferred that a causal relationship exists or that it can be manipulated, especially if such manipulation might cause harm. Normalizing hemoglobin did not turn out to be the optimal strategy in this population. The evidence that bioimpedance does provide reasonably accurate estimates of tissue hydration and lean body mass is fairly good (2), particularly if multifrequency spectroscopy is used, but there are other issues to be considered. In fact, the relationship between tissue hydration and lean body mass is also affected by nutritional health. Whether deliberately starved or malnourished because of poverty, as fat and muscle mass decreases there is not necessarily a proportional reduction in the extracellular fluid. This means that even healthy individuals that are malnourished (all too commonly the case in those on dialysis) will appear to be relatively overhydrated, but it is far from clear that the removal of this relative excess in extracellular fluid would automatically improve nutrition. It should also be remembered that bioimpedance cannot distinguish between extravascular and intravascular fluid excess, and how this is partitioned will be determined by other factors, most notably serum albumin levels. This is of particular importance to patients undergoing peritoneal dialysis in whom serum albumin is influenced to a large extent by peritoneal losses and local intraperitoneal inflammation. In addition to these difficulties in interpreting the meaning of bioimpedance evidence of overhydration, it should not be forgotten that normalizing hydration status may not be without risk. Bioimpedance-guided volume depletion, when applied aggressively, may increase the risk of premature loss of residual kidney function, and there is concern associated with aggressive ultrafiltration rates in patients undergoing hemodialysis. Undertaking and reporting trials that test bioimpedance-guided management of fluid status has proved difficult. The UK Medical Research Council (MRC) advises that an intervention should be considered complex in a number of situations, many of which are encountered when evaluating bioimpedance-guided fluid management (see Table 1) (3). Among these challenges is the appropriate choice of clinical outcome, choice of bioimpedance device, the defining of an appropriate algorithm that incorporates the bioimpedance measure into what is effectively complex decision making, and the satisfactory recording of the actual decision making by clinicians during the course of the study. Despite these challenges, MRC guidance favors an experimental design when evaluating complex interventions if at all possible, and a number of trials have been reported and attempts to synthesize these results have been made (4,5). The trial reported by Tian et al. (6) in this volume of CJASN is an important addition when considering the overall pattern of findings that emerg","journal":"Clinical Journal of the American Society of Nephrology","year":2020,"id":76349,"datarank":0.0,"base_score":0.0,"endowment":0.0,"self_citation_contribution":0.0,"citation_network_contribution":0.0,"self_endowment_contribution":0.0,"citer_contribution":0.0,"corpus_percentile":null,"corpus_rank":null,"citation_count":21,"citer_count":0,"citers_with_citation_signal":0,"citers_with_endowment":0,"datacite_reuse_total":0,"is_dataset":false,"is_dataset_confidence":0.9497,"is_data_producer":false,"deposit_databanks":null,"is_oa":true,"file_count":0,"downloads":0,"has_version_chain":false,"published_date":"2020-01-01","fair_score":null,"fair_percentile":null,"algorithm_id":"datarank_citation_only_1hop_v6","ranking_scope":"data_only","authors":[{"id":398013,"name":"Simon Davies","orcid":"0000-0001-5127-4755","position":0,"is_corresponding":true}],"reference_count":13,"raw_metadata":null,"created_at":"2026-07-18T21:47:46.469293Z","pmid":"32381550","pmcid":null,"fwci":null,"citation_percentile":null,"influential_citations":0,"oa_status":null,"license":null,"views":0,"total_file_size_bytes":0,"version_count":0,"fair_f":null,"fair_a":null,"fair_i":null,"fair_r":null,"fair_zscore":null,"fair_rationale":null,"fair_model":null,"fair_agent_version":null,"fair_fulltext_source":null,"fair_has_llm":null,"fair_computed_at":null,"clinical_trials":[],"software_tools":[],"db_accessions":[],"linked_datasets":[],"topics":[]}