Beyond Kt/V: a review argues dialysis adequacy should be judged by what it does for the heart

The argument

Dialysis adequacy has long been measured by urea clearance (Kt/V), treatment time and small-solute removal. But cardiovascular disease is the leading cause of death in people on dialysis, and raising the urea-based dose did not improve survival or major cardiovascular outcomes. Dr. Carmine Zoccali and colleagues argue that a dialysis prescription should be judged by whether it reduces cardiovascular stress: fluid swings, fast ultrafiltration, potassium shifts, the long interdialytic interval and repeated myocardial stunning. This is a narrative review, not a systematic one.

How they rate the options

• High-volume online hemodiafiltration: the strongest survival evidence, for stable patients on thrice-weekly in-center dialysis, provided high convection volumes are reached. The mechanism is uncertain: in CONVINCE, C-reactive protein did not differ between groups, and achieved convection volume may partly mark healthier patients and better units.
• Medium cutoff dialyzers (expanded hemodialysis): "persuasive biology, incomplete proof." Better removal of larger middle molecules, but no proof of fewer cardiovascular events. In CARTOON (80 patients, one year), arterial stiffness and echocardiography did not differ from online HDF.
• Dialysate potassium: a strong rationale for limiting both the potassium build-up between sessions and the electrical instability during them. In a crossover trial in hyperkalemic patients with implanted heart monitors, a 3.0 mmol/L potassium bath plus a binder on non-dialysis days, compared with a 2.0 mmol/L bath, was associated with less atrial fibrillation. Definitive outcome trials are lacking.
• Dialysate sodium: a balancing act. In trials with cardiac MRI in home and self-care hemodialysis, lower dialysate sodium improved fluid status but did not change left ventricular mass, and increased intradialytic hypotension. The authors say the trend toward lower sodium should be reassessed until large outcome trials report.
• Frequent, nocturnal and home hemodialysis: the best evidence is for left ventricular mass, blood pressure and phosphate; harder outcomes remain uncertain, and the Frequent Hemodialysis Network nocturnal trial did not meet its coprimary outcomes. In that trial, among patients with residual function at baseline, urine output had stopped by 12 months in 67% on frequent nocturnal dialysis versus 36% on conventional dialysis.
• Incremental dialysis: may preserve residual kidney function in selected incident patients, but most of the supporting data are observational, and healthier patients tend to be the ones chosen for it.

Why it matters

The review's practical idea is phenotype: matching the prescription to the dominant cardiovascular problem, such as an arrhythmia-prone patient with large potassium gradients, or a volume-overloaded patient with left ventricular hypertrophy. It asks for multicenter, adequately powered trials with endpoints matched to each mechanism: loop recorders for potassium strategies, cardiac MRI and objective volume measures for sodium and volume strategies. It suggests large dialysis organizations are well placed to run such trials, with independent governance, blinded adjudication and full reporting.

Caveats

Study selection was interpretive, with no formal risk-of-bias assessment or evidence grading. Two of the six authors list Fresenius Medical Care as their affiliation, and the lead author lists the Renal Research Institute first; the manuscript's conflict-of-interest statement reads "None." Fresenius Medical Care makes hemodiafiltration equipment (our note, not stated in the paper). The review is nonetheless cautious about how hemodiafiltration works and evenhanded about medium cutoff membranes.

Disclosure: Dr. Wael Hussein serves on the Fresenius Medical Care US Home Medical Advisory Board.

The source: Zoccali C, Strippoli G, Locatelli F, Mallamaci F, Usyat L, Stuard S. Beyond Kt/V: Redefining Dialysis Adequacy as Targeted Cardiovascular Risk Reduction. Nephrol Dial Transplant. Advance article, 2026. doi:10.1093/ndt/gfag223 Read the original

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