The importance of residual renal function

A recent review in this month's AJKD by Perl and Bargman describes the increasingly recognized importance of residual renal function in dialysis patients' prognoses.  Although the benefits of residual renal function are most obvious in patients undergoing peritoneal dialysis (see the CANUSA and ADEMEX studies), apparently there are also convincing associations between residual renal function and mortality in hemodialysis populations.  For instance, in this 2001 AJKD study by Shemin et al, the ability to produce >100 cc of urine a day in 114 chronic hemodialysis patients was independently associated with a 65% decrease in the risk of death.  The mechanism of how such residual renal function gives a survival advantage is unclear, but one favored explanation is that the kidney's ability to clear "middle molecules" (something which is lacking in current hemo- and peritoneal dialysis therapies) helps remove toxins which are critical for the pathogenesis of cardiovascular disease. 

This brings up a whole host of questions which challenges our current management of ESRD patients.  Should all ESRD patients be put on ACE-inhibitors or ARBs in order to retain whatever minimal renal function they have?  Should we be less cavalier about prescribing prolonged courses of gentamicin for ESRD patients with gram-negative infections?  Should I avoid giving iv contrast to ESRD patients in order to avoid contrast nephropathy, or should I specifically arrange to have dialysis immediately after iv contrast is given in order to dialyze it off?  I find this latter point to be a great source of confusion, and sometimes contention, between house staff and nephrologists regarding when to schedule dialysis in reference to a cardiac catheterization or other heavy iv contrast-requiring procedure.  I don't know if there are any clear answers dictating what we should do in these situations, but perhaps there will be more conclusive guidelines in the future.