Early initiation of dialysis : mortality and renal function recovery in acute kidney injury patients

Palavras-chave: diálise, insuficiência renal, lesão renal aguda, mortalidade.

The timing of dialysis initiation in AKI has been discussed since its introduction over 50 years ago.1][12] According to this concept, dialysis should be started in asymptomatic patients when BUN reaches 100 mg/dl.Some years later, Gettings et al. 13 showed that survival rate was significantly increased among post-traumatic AKI patients who were started on dialysis when BUN < 60 mg/dl compared to those who starting dialysis when BUN > 60 mg/dl (39% vs. 20.3%;p = 0.041).In a meta-analysis, Seabra et al. 14 suggested that early dialysis may be associated with improvement in survival among AKI patients, whereas Bagshaw et al. 15 demonstrated that late dialysis initiation might be associated with longer length of stay and higher risk of dialysis dependence on discharge.
Based on the values established in the literature, the primary goal of this study was to evaluate mortality among patients with AKI who were started on dialysis at different BUN levels.

methods
This retrospective study was performed at Botucatu Medical School Hospital, São Paulo, Brazil, over a 5-year period.Inclusion criteria were patients older than 18 years, with AKI 16 caused by presumed Acute Tubular Necrosis (ATN), no symptoms of uremia, and underwent dialysis for longer than 48 hours.In all cases, dialysis had been indicated due to progressively increasing BUN levels associated or not with metabolic acidosis (pH < 7.2), hypervolemia and hyperkalemia (K > 6.5 mEq/L).Exclusion criteria were AKI of other etiologies, patients who started dialysis with BUN > 150 mg/dL for any reason, renal transplantation, pregnancy, ATN-ISS 17 ≥ 0.9, and continuous renal replacement therapy (CRRT).
According to BUN levels at the time of initiation of dialysis, patients were allocated into Group I (G 1): BUN ≤ 75 mg/dl or Group II (G 2): BUN > 75 mg/dl.
The prognostic scores used were APACHE II 18 and ATN-ISS 19 obtained at the time of ICU admission and at the first nephrology evaluation, respectively.Based on ATN-ISS, patients were classified as low (< 0.3), intermediate (0.3 -0.7) or high risk (> 0.7).
Patients were followed up until they died, or recovered renal function, or received dialysis for over 30 days.
ATN etiology was classified as ischemic (due to low cardiac output or hypovolemia), nephrotoxic (associated with drugs or heme pigments) 19 or septic 20 (sepsis or septic shock).ATN was excluded in patients with pre-renal, post-renal or known or suspected diagnosis of vasculitis, glomerulonephritis or acute intersticial nephritis (on the basis of clinical history, physical examination, urinalysis and hematologic tests and renal ultrasonograph). 19ypervolemia was considered in patients with positive fluid balance 3 days before nephrology consultation, presented one of the following criteria: clinical sign (edema), bilateral lung infiltrates on the chest radiograph or need to increase the fraction of inspired oxygen in patients on mechanical ventilation.
Renal function recovery (partial or complete) was defined as no need for dialysis after up to 30 days of follow up.
This study was reviewed and approved by the local Committee of Research Ethics.

Statistical analysis was performed using Stata version 8.2 (Stata Corp,College Station, Tex).
Data were expressed as mean ± SD or median, according to the normality of their distribution.Categorical data were expressed as frequency (%).Differences in clinical and laboratory parameters between groups were evaluated by Student's t-test or the Mann-Whitney test.Chi-square test or Fisher's exact test were used to compare as proportions.The outcome event was death.Univariate analysis was performed and the variables with significant associations were candidates for multivariable analysis.Multivariable logistic regression was performed using backward variable selection, with p < 0.25. 21ignificance level was set at p < 0.05 for all analyses.
Early initiation of dialysis: mortality and renal function recovery in acute kidney injury

Results
Of the 700 patients assessed, 333 required dialysis.Of these, 247 (74.2%) were excluded according to the study criteria.The remaining 86 patients were assigned to GI (23) or G II (63).
Main clinical and laboratory characteristics of the patients were similar, as shown in Table 1.Clinical signs of hypervolemia were more frequent in G I (65.2% and 14.3%; p < 0.05).
There was no difference among the dialytic methods between groups.Peritoneal dialysis was perfomed in 52.8% in GI and 68.2% in GII.Hemodialysis was performed in 43.5% in GI and 20.7% in GII.Both methods were performed in 4,3% in GI e 11.1% in GII.Regardless of the dialytic method used, 44.8% of the dialysis sessions were quantified by Kt/V urea, 22 and no difference per session (GI = 0.6 ± 0.2 and GII = 0.5 ± 0.1) or per week (GI = 4.1 ± 1.0 and GII = 3.5 ± 0.4) was observed.Follow-up length and dialysis duration were similar in both groups (18 ± 12 and 17 ± 14 days; 12 ± 9 and 11 ± 8 days) By the end of the follow-up, overall mortality rate was 61.6%.In GI, mortality was lower than in GII (39.1% and 68.9%, respectively -p < 0.05).Among survivors, the rate of renal function recovery was higher in GI (71.4%) compared with GII (36.8%, p < 0.05).
Figure 1 shows the distribution of GI and GII patients according to ATN-ISS.Among the patients with intermediate severity scores, mortality rate was lower in GI (22.2%) than in GII (76%; p < 0.05).This did not occur in patients classified as low or high severity.Delivered Kt/V urea per session (0.54 and 0.49, respectively) and per week (3.9 and 3.4) was similar in two groups.
Table 2 shows the univariate analysis of the clinical and lab variables associated with death.Age > 60 years, peritoneal dialysis, ATN-ISS > 0.3, and BUN > 75 mg/dl at dialysis indication, were associated with death.Sepsis was associated with higher mortality, although no statistically significant difference was observed.
Multivariate analysis showed that sepsis, age > 60 years, peritoneal dialysis and BUN > 75 mg/dl at dialysis initiation were independently associated with mortality (Table 3).
Prognostic scores were not included in these analyses.

dIscussIon
The majority of studies on the timing of initiation of renal replacement therapy have used BUN levels to indicate dialysis, although its use is flawed because it may reflect other situations not related to kidney  function such as gastrointestinal hemorrhages, inadequate supply of nutritional substrates and hypercatabolic states. 8Gettings et al. 13 demonstrated that patients with post-traumatic AKI who were submitted to dialysis with BUN < 60 mg/dl had higher survival when compared with patients that initiated dialysis with BUN > 60 mg/dl (39% vs. 20.3%,p < 0.05).The authors also stratified patients according to BUN levels and showed that the difference in survival remained in patients with BUN levels above and below 70 mg/dL (37% vs. initiation.Patients in the early dialysis group had BUN ≤ 76 mg/dL and patients in late group had BUN > 76 mg/ dL.Although there was no statistical difference between the two groups in mortality rate after 14 days (80% and 75%, respectively) and 28 days (65% and 59%), patients from the late group had approximately double the risk of mortality than those in the early group. 235][26] According to Seabra Early initiation of dialysis: mortality and renal function recovery in acute kidney injury but this did not occur when severity was higher or lower (ATN-ISS < 0.3 or > 0.7).This finding suggests that early dialysis may be more beneficial to patients with moderate levels of severity because patients with lower severity levels can achieve spontaneous clinical recovery and those with higher severity show high risk of death regardless of the timing of dialysis initiation.Paganini et al. 35 found similar results when analyzing prognostic scores and delivered dialysis doses.
Multivariate analysis showed that mortality was associated with advanced age, sepsis, peritoneal dialysis and BUN > 75 mg/dl at dialysis initiation.The results concerning peritoneal dialysis should be interpreted carefully because data from literature are conflicting. 36,37owever, it should be considered, that all types of dialytic treatment may intensify the insult or delay renal function recovery.Moreover, further studies should investigate other indicators for dialysis in AKI patients, as biochemical and clinical evolution (trends), 9 because BUN levels can be influenced by many factors.
This study had some limitations such as its retrospective design, reduced number of patients and performed in a single center.Furthermore, other aspects as patient nutritional status and correction of the acid-base balance were not assessed.reported complete renal recovery in 57% of survival patients who were treated with dialysis, but they did not evaluate BUN levels prior to dialysis.Gettings et al. 13 found no difference in the rate of renal function recovery between early (100% of survivors) and late dialysis (91.6% of survivors).Bagshaw et al., 15 in an observational prospective study using several criteria for the definition of early dialysis, showed that late dialysis (timing relative to hospital and ICU admission) was associated with longer duration of renal replacement therapy, longer hospital stay and higher risk of dialysis dependence, although when late dialysis was stratified by serum urea there was no difference in hospital mortality.Other investigators, such as Mehta et al., 28 Augustine et al. 29 and Palevsky et al. 30 did not mention the use of initiation timing to minimize the impact of dialytic therapy on renal recovery in AKI.
][33][34] In this study, delivered dialysis doses were not measured in all cases.Nonetheless, the two groups were similar in delivered dialysis dose, regardless of the method employed and it was very close to those reported in the literature, 27,29 suggesting that the difference in survival between the two groups was not associated with the delivered dialysis dose, but with the benefits of early dialysis initiation.
In this study, mortality was assessed according to ATN-ISS severity.Among patients with a moderate severity score (ATN-ISS between 0.3 and 0.7), mortality rate was lower when dialysis was initiated early,

Figure 1 .
Figure 1.Distribution of the patients submitted to dialysis according to different ATN-ISS values.

tAble 1
Oliguria: urine output 24 hs < 400ml.Data expressed as median or mean ± SD.Early initiation of dialysis: mortality and renal function recovery in acute kidney injury

tAble 2 univariatE
18.4%; p = 0.035) In 2006, the Program to Improve Care in Acute Renal Disease (PICARD), a multicenter observational study, analyzed the timing of intermittent hemodialysis and CRRT analysis of dEath-rElatEd variablEs in patiEnts submittEd to dialysis