whether or not to provide dialytic support and when to start are two dilemmas for clinicians managing patients with a sudden decline in renal function . earlier initiation is thought to be associated with better control of uremia , acidemia , electrolyte imbalances , and volume accumulation . however , the appreciation of the effect of time of initiation depends on what is considered early versus late . various studies have considered early versus late time of dialysis initiation based on arbitrary thresholds of traditional serum biomarkers or time from intensive care unit ( icu ) admission or from the diagnosis of acute kidney injury ( aki ) . the study by shiao and colleagues   in a recent issue of critical care provides support that early start may be beneficial and offers an additional approach to identifying a starting point for dialysis . although a recent meta - analysis that included four randomized controlled trials and 19 observational studies conducted over four decades suggested that early dialysis initiation may have a beneficial effect on survival , what constitutes early versus late has yet to be defined . two main approaches have been used for stratifying early and late . in most studies , levels of solutes ( blood urea nitrogen [ bun ] and serum creatinine ) have been used to define cutoffs for early and late dialysis initiation , showing variable results on different patient populations . in post - traumatic patients , bun levels of less than 60 mg / dl at dialysis initiation were associated with a 20% absolute reduction in mortality . wu and colleagues   found a bun level of less than 80 mg / dl to be predictive of mortality in patients requiring dialysis for acute liver failure after surgery . in the general icu population , a large observational study ( program to improve care in acute renal disease , or picard ) showed an increased risk of mortality in patients with higher bun concentrations ( > 76 mg / dl ) . however , a recent randomized single - center clinical trial in 106 critically ill patients with oliguric aki   demonstrated that despite early dialysis at a bun level of less than 48 mg / dl in comparison with 105 mg / dl for late dialysis , there was no difference in outcomes . these findings suggest that bun levels are relatively insensitive as a target criterion for starting dialysis . a second approach was used in the beginning and ending supportive therapy for the kidney ( b.e.s.t . kidney ) study , in which investigators included in the analysis a stratification of early or late based on time to initiate dialysis from icu admission , besides the absolute urea and creatinine , and relative change in urea and creatinine . although absolute or delta bun levels were insensitive in predicting mortality , the analysis by time from icu admission showed a more than twofold increase in the odds of hospital mortality . however , in two recent , large , randomized controlled trials of dialysis dose , time to initiate dialysis was assessed from icu admission and was not associated with outcomes . though using heterogeneous definitions of early initiation , these large observational cohorts and small randomized trials suggest that there may be a survival advantage to an early start for dialysis . they also highlight the need for better parameters to define the need for dialysis and the delineation of what is early and late . in the postoperative setting , the timing and type of renal insult are more homogenous , providing an opportunity to ascertain the benefits of earlier dialysis initiation when the event associated with aki is known . urine output of less than 100 ml during the first 8 hours after bypass surgery was a criterion to initiate dialysis regardless of solute clearance . mortality rates appeared to be dramatically reduced in both studies in the early dialysis groups . similar findings were seen in a small study of 21 patients treated with prophylactic perioperative hemodialysis . in the study of shiao and colleagues , 98 patients who required dialysis in the postoperative period of abdominal surgery were categorized as early or late dialysis initiation based on the estimated glomerular filtration rate criteria of the rifle ( risk , injury , failure , loss , and end - stage kidney disease ) classification ( simplified rifle , or srifle ) . the earlier initiation group had lower icu and hospital mortality rates than the late initiation group . these results suggest that the severity of renal injury may provide a better parameter than arbitrary values of traditional serum biomarkers ( bun and serum creatinine ) for initiating dialysis . the rifle and acute kidney injury network classification systems are validated criteria for the severity of aki but may not be the ideal parameters of early or late , as previously pointed out by bellomo and colleagues . the relationship of rifle classes at initiation and outcomes is subject to other influences that need to be considered . for instance , in the cohort of shiao and colleagues , cardiac failure was an independent risk factor for in - hospital mortality . by their definition of cardiac failure ( low cardiac output with a central venous pressure of greater than 12 mm hg and a dopamine equivalent of greater than 5 g / kg per minute ) , it is reasonable to assume that cardiac failure was a surrogate marker of fluid overload . shiao and colleagues found a lower prevalence of chronic kidney disease ( ckd ) in the late dialysis group , confirming data showing that an earlier identification of aki among patients with prior ckd could modify the process of care delivered to these patients . thus , the time to recognize aki , the severity and response to injury , and the contribution of non - renal factors may all influence the timing of initiation . timing of dialysis initiation is a potentially modifiable factor that may play an important role in determining patient outcomes . based on current knowledge , we would recommend assessing patients for changes in renal function and using dialysis to support organ function and prevent complications rather than waiting for complete renal shutdown prior to renal replacement . future research in this field is desperately needed and should include a combination of clinical and emerging biomarkers to inform these decisions . we look forward to doing away with comparisons of early versus late dialysis and focusing on improving outcomes with timely interventions of renal support individualized to patient need . aki : acute kidney injury ; bun : blood urea nitrogen ; ckd : chronic kidney disease ; icu : intensive care unit ; rifle : risk , injury , failure , loss , and end - stage kidney disease .
acute kidney injury ( aki ) is now well recognized as an independent risk factor for increased morbidity and mortality , particularly when dialysis is needed . 
 the wide variation in dialysis utilization contributes to a lack of consensus on what parameters should guide the decision to start dialysis . while the association of early initiation of dialysis with survival benefit was first demonstrated four decades ago , few studies in the modern era of dialysis have addressed time of dialysis initiation . though listed as one of the top priorities in research on aki , 
 timing of dialysis initiation has not been included as a factor in any of the large , randomized controlled trials in this area .