AN69 membrane is not suited for diffusion, with an suggested limit at 25？mL/min dialysate flow rate. When prescribing continuous hemodialysis this threshold must be surpassed to achieve. We designed a study aimed to check if a higher dose of dialysis could be delivered efficiently with this membrane. Ten ICU patients under continuous hemodiafiltration with 1.4？m2 AN69 membrane were included and once a day we set the monitor to exclusively 50？mL/min dialysate flow rate and 250？mL/min blood flow rate and after 15 minutes measured dialysate saturation for urea, creatinine, and -microglobulin. We detected that urea saturation of dialysate was nearly complete ( ) for at least 40 hours, while creatinine saturation showed a large dispersion ( ) and did not detect any relation for these variables with time, blood flow, or anticoagulation regime. Saturation of -microglobulin was low ( ) and decreased discretely with time ( , ) and significantly with TMP increases ( , ). In our experience AN69 membrane shows a better diffusive capability than previously acknowledged, covering efficiently the range of standard dosage for continuous therapies. Creatinine is not a good marker of the membrane diffusive capability. 1. Introduction Continuous renal replacement therapies (CRRT) have changed substantially the last two decades. Developed as a practical method to treated acute kidney failure in unstable patients and based in the use of convection, in the first stages a low solute clearance capability was characteristic and subsequent changes (as an early shift from an arterial-vena to a vena-vena approach) [1] were aimed to improve performance. To raise the clearance of uremic toxins, CRRT procedures evolved to slightly different methods like continuous hemodiafiltration (CHDF) [2] or continuous hemodialysis (CHD) [3] because a supplementary diffusive transport can improve the clearance of low molecular weight toxins, such as urea [4]. Dosage delivered as convective treatment can theoretically be raised without limits but in the real practice we have a limiting factor, that is, blood flow. When this limit has been reached to augment the dialysate flow seems an attractive alternative but some early reports demonstrated that when we set the dialysate over 25？mL/min, efficiency of the treatment is seriously compromised and this effect is related to the membrane involved [5]. In our unit, the weaning from CRRT is usually performed with slow intermittent dialysis delivered with the same CRRT monitor, in sessions lasting 10–12 hours. During this weaning phase some patients
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