Any patient 18 years and older who is admitted to the OHSU Hospitals ICUs with ARF, or End Stage Renal Disease (ESRD) for a diagnosis other than hyperkalemia, as the sole determinant for that level of care, will be invited to participate. The patient must have acute or chronic needs for dialytic support during their ICU stay in order to qualify for the study. Dialysis support may be provided by intermittent HD sessions, or continuous venovenous hemodiafiltration (CVVHDF) depending on the underlying hemodynamic stability of the patient.