Blog entry by Arif Khwaja
There is increasing interest in frequent haemodialysis (whether nocturnal or daily) as a result of the frequent daily dialysis study which demonstrated that frequent HD was superior to thrice weekly HD with respect to the composite endpoint of death and left ventricular mass. Its worth pointing out here that there was no significant difference in death between the two groups and its perhaps not surprising that LVMI was better in the daily dialysis group given the tighter volume control. One thing that is not mentioned as much is the higher incidence of vascular access problems in the frequent dialysis group. Now a post-hoc analysis of the two FHN trials by Daugiridas in this months Kidney International highlights some important concerns about the apparently deleterious impact of frequent hemodialysis on residual kidney function (RKF). They showed that in the Nocturnal Trial 63 patients had significant RKF at baseline. In the frequent dialysis group, urine volume had declined to zero in 52% and 67% of patients at months 4 and 12, respectively, compared with 18% and 36% in controls. In contrast in the daily dialysis trial dialysis frequency did not impact on RKF - however the range of RKF was narrower in this study and patients with a Kidney urea clearance (Kru) >3 ml/min/35 liters estimated body water were excluded which thus may have limited the capacity to detect differences.
Its important not too read too much into such post-hoc analyses, that werent powered to evaluate the impact on RKF. Furthermore there are all sorts of methodological issues with how best to measure KRF as pointed out by Professo Farrington in an accompanying editorial. However notwithstanding these limitations the study raises important questions that need to be considered -
i) the increasing vogue for frequent dialysis in the literature needs to be tempered by a better understanding of the potential risks such as negative impact on RKF and vascular access. Hypotension, volume depletion, inflammation may all be mechanisms by which frequent dialysis negatively impacts on RKF.
ii) how frequent is frequent and is there a frequency of dialysis (say 4X week) which may offer the benefits of frequent dialysis without the adverse consequences? clearly we simply dont know the answer to this but like much of the nephrology there probably needs to be a paradigm shift away from uniform therapy for all ( say thrice weekly dialysis) to individualised therapy which takes into account factors such as comorbidity, likelihood of transplantation and RKF. Like many nephrologists I now have some patients on 4 -5 times a week dialysis with others and some only on twice a week dialysis. The thrice weekly standard dialysis prescription maybe suitable for many but certainly not all patients. Thus finding easier ways of measuring RKF may then allow us to individualise therapy appropriately. Trying to get timed collections of urine in patients on dialysis can be fiendishly difficult.
iii) The choice on dialysis seems to be between tight fluid and BP control (with resulting anuria) or a more 'hydrated' state with better preservation of RKF. Farrington argues that we should be trying to do both but the reality is at the moment we simply have no real idea of how to manage volume in the haemodialysis patient and what we are trying to aim for. Whilst overhydration appears to be harmful and asociated with adverse outcomes defining normohydration is not something we are able to easily do. The Tassin approach to fluid management may work in Tassin but Im not sure how translatable this is to other clinical settings and populations.Tools such as bioimpedance measurement may help but these have yet to transition from the research arena to the dialysis floor.