The different studies conducted to date reveal high incidences of acute renal failure (ARF) in hospitalized patients, and particularly among critically-ill patients.1 Moreover, since ARF in the critical patient is associated with multiorgan dysfunction syndrome (MODS), the mortality rate among such individuals is much higher (35–53% depending on the source) than in patients without ARF admitted to the Intensive Care Unit (ICU).2,3 Even the need for renal replacement therapy (RRT) in the critical patient has been shown to be an independent predictor of mortality.4,5

In recent years there have been many changes in RRT which in turn have led to important improvements. Since the publication in the year 2000 of the article by Ronco et al.,6 in which increased dialysis doses were correlated to improved survival, continuous RRT mainly has been designed to apply high convective dialysis doses to the patient, and this subsequently has led to the introduction of new catheters and machines allowing such high flows.

Despite the knowledge obtained, the improvements in the management of these patients, and the years of experience gained in the use of renal replacement techniques, the mortality rate remains high in these patients. This could be explained by the fact that the patients treated today are older, with increased comorbidities and in more serious condition than in the past.5 Indeed, given the current characteristics of the patients, the needs for intermittent hemodialysis (IHD) at discharge have increased.7–9

Among those patients who survive, most will recover from failure with good quality of life at discharge, while 5–20% will require IHD after leaving hospital.4

The primary objective of this study was to describe the characteristics of the patients admitted to the ICU with ARF and who required RRT, and to analyze the evolutive changes of the patients and of the treatment received over the years. The secondary objective was to identify the risk factors associated to mortality and the recovery of renal function in the study cohort.

The present study shows that the survival of critical patients requiring RRT due to renal failure has improved over time. All the patients were treated according to the homogeneous protocol used in our Unit, with variability being limited to changes in the therapy provided in accordance with the literature published during these years and the improvements in the global treatments provided in our Unit.

Although the global mortality of our patients has been similar to that described in the literature, the main finding in our study was the decrease in mortality observed despite the fact that these are older patents, with increased comorbidity and in very serious condition (APACHE II>20). These findings are in contrast to the published data affirming that mortality in patients with ARF remains high despite the medical advances, because of the greater age of the patients, greater comorbidity, and a more serious patient condition.5

While old, several publications offer results similar to our own.12,13 Turney et al.14 compared patients with ARF (admitted or not to the ICU) treated in two different time periods, and reported a decrease in mortality rate from 51% to 42%, despite an increase in age and in the seriousness of the patient condition. Bisenbach et al.15 in turn compared three consecutive time periods and likewise found a progressive drop in mortality rate from 69% to 54% and 48%, despite an increase in patient age.

In addition to the decrease in mortality, we recorded a significant reduction in the days of therapy between the two time periods. In our case, considering similar characteristics in both groups and knowing that most patients presented ARF secondary to septic shock, we attributed the decrease in mortality and in days of therapy to implementation of the treatment recommendations established from publication of the sepsis management guides.10

This is justified by the greater number of cases of ARF originating in the community during the second time period, which would correspond to the septic patients admitted during that period.

Of note is the observation that despite the decrease in days of therapy and in mortality, the number of patients dependent upon IHD at discharge was higher in the recent period. This is probably related to the larger number of patients with exacerbated chronic renal failure, older age and a greater number of RFs for the development of renal failure.

Although this may be incongruent, fewer days of therapy but more patients requiring IHD at discharge could be explained by the small number of patients needing RRT at discharge from the ICU, together with the fact that many of these patients will not require IHD prior to hospital discharge.

These conclusions are complex and may be due to the difficult and scant definition of the concepts of ARF and exacerbated chronic renal failure.

Regarding the applied technique, it is well known that the article published by Ronco et al. in the year 20006 led to important changes in the management of our patients, with the incorporation of an increased use of convection, and a decrease in diffusion. Furthermore, the Acute Dialysis Quality Initiative, on occasion of its third consensus conference, recommended a dose of 35ml/kg/h in septic patients (evidence level II and degree of recommendation C).16

This caused many Units to replace their RRT machines with systems characterized by higher ultrafiltration flows, and consequently involving higher pressures, and to the great increase in the utilization of convective therapy. A decade later, in 2008 and 2009,17,18 two studies have been published where despite the limitations involved, the efficacy and safety of the treatment applied in recent years has been questioned, and even new concepts have emerged such as “dialytrauma”–causing us to reflect upon and analyze how the high dialysis doses affect our patients and the rest of their treatment (antibiotics, nutrition, etc.).19 At present, this has led us to assess the dialysis dose requirements of our patients on a daily basis, introducing changes according to their evolution over time.

On analyzing the mortality predictors in our study population, one of the variables correlated to increased mortality was creatinine upon admission–with higher values among the survivors. Since most of the patients were septic cases, we probably could deduce that since these subjects had higher creatinine levels, they were placed on dialysis earlier (though in our work, and as a limiting element of the study, the RRT starting time was not documented).

Recently, however, Chou et al.20 have published a propensity score analysis of the relationship between the RIFLE criteria11 and the early or late start of replacement therapy. The authors conclude that the mentioned classification is a poor predictor of the benefits of early or late initiation of RRT in the septic patient.

The other important finding in our study was that the therapy provided is independently associated with increased mortality–the provision of intermittent therapy only being a protective factor against mortality compared with continuous treatment or a combination of both techniques (OR 0.77). Ours is an observational study; this result therefore cannot be inferred from the logistic regression analysis. Despite adjustment for the APACHE II score and age, there are very important limitations; given the protocol used in our Unit, it was obvious that those patients who were only subjected to intermittent treatment, as less seriously ill individuals, also suffered lesser mortality.

Regarding the predictors of the recovery of renal function at discharge from the ICU, our findings are not very different from those published to date.4,5,7 At discharge from the ICU, only 21.4% of the patients required IHD, and if from these we exclude the chronic cases (basal creatinine>1.8mg/dl), then the percentage drops to 11%.

In our case, elevated creatinine values upon admission represented a risk factor for dependency upon IHD at discharge (OR 1.98). On the other hand, ARF versus exacerbated chronic renal failure was identified as a protective factor, in the same way as continuous techniques as RRT versus the group of patients receiving both treatment modes.

Another important limitation appears here, since the group of survivors did not include the patients who died, and the great majority of those who died did so while receiving treatment with continuous techniques. The patients only subjected to continuous treatment and which improved were therefore more likely to recover better renal function than the patients who were previously on IHD. Here again, however, we cannot infer that the continuous techniques are related to improved recovery of renal function.

Our study has a number of important limitations. A first limitation is the complexity of the variables and of the definitions involved–a situation still in wait of improvement after all these years of research in the field of renal failure. On the other hand, the time of the start of RRT has not been registered, and no analysis has been made of the evolution of the SOFA score of the patient in the ICU, or of other severity scores at the time of initiation of RRT. As a result, no extrapolation can be made to the APACHE II score of the same patient 24h after admission to the ICU.

Despite the results of the regression analysis, we cannot independently relate the different techniques to patient mortality and/or the recovery of renal function, since this is an observational study, and the protocol used in our Unit precludes such inference.

Lastly, another important limitation is the fact that no registry has been made of the complications of RRT, for although such complications are well defined and are few, they could also have been analyzed according to the technique used.

In conclusion, critical patients requiring RRT have shown lower mortality rates in recent years, and require fewer days of therapy. This situation is probably attributable to improvements in the global management of these patients, since many other factors in addition to RRT influence patient outcome.

The authors declare that they have no conflicts of interest.