Acute renal failure (ARF) is a frequent and serious condition encountered in intensive care units (ICUs), often requiring renal replacement therapy (RRT) for metabolic waste elimination, electrolyte balance restoration, and volume regulation [1] . Among the various RRT modalities, intermittent hemodialysis (IHD) and continuous veno-venous hemofiltration (CVVH) are the two most widely used techniques, each with distinct operational mechanisms and clinical applications [2] .

IHD is a widely established technique that uses a dialyzer to remove toxins and excess fluids over relatively short sessions (typically 3 - 4 hours) performed multiple times per week. It operates on the principle of diffusion, where solutes move across a semi-permeable membrane driven by concentration gradients. However, the rapid fluid and solute shifts associated with IHD can lead to hemodynamic instability, hypotension, and electrolyte imbalances, particularly in critically ill patients [3] .

In contrast, CVVH is a continuous therapy that provides slow and steady solute and fluid removal over 24 hours or longer. This technique relies on convection rather than diffusion, utilizing hydrostatic pressure to remove solutes through ultrafiltration. CVVH is generally preferred for hemodynamically unstable patients due to its gradual fluid removal and better hemodynamic tolerance. However, it requires specialized equipment, continuous anticoagulation, and extended monitoring, making it resource-intensive [3] .

Despite their widespread use, the optimal choice between IHD and CVVH in ICU settings remains debated. Several studies have explored their comparative efficacy and tolerability, but conclusions have been inconsistent. For instance, Ronco et al. [4] . suggested that continuous therapies like CVVH might provide superior hemodynamic stability in critically ill patients, reducing the risk of intradialytic hypotension. On the other hand, Gaudry et al. [5] . and the AKIKI and IDEAL-ICU trials [6] found no significant survival benefit between IHD and CVVH, emphasizing the need for individualized treatment decisions based on patient-specific factors [5] . Moreover, meta-analyses by Schneider et al. [7] . and Zhao et al. [8] . indicated that while CVVH may reduce the need for early treatment interruptions due to instability, it does not necessarily improve long-term survival or renal recovery.

Given these discrepancies, further comparative evaluation is warranted to refine ICU management strategies and improve patient outcomes. This study aims to assess the clinical indications, hemodynamic tolerability, and impact on biological parameters and survival between IHD and CVVH in critically ill patients. A clearer understanding of these modalities could aid in optimizing renal replacement therapy decisions in intensive care settings.

This single-center study compared the hemodynamic tolerance and efficacy of two extra-renal replacement therapy (ERT) techniques in the intensive care unit: continuous veno-venous hemofiltration (CVVH) and intermittent hemodialysis (IHD). CVVH was found to be the predominant modality, and it is used in around 69% of patients ( Figure 1 ). Although there is no consensus on the choice of renal replacement technique in the ICU, both options are prescribed to varying degrees. A 2010 survey of resuscitators by the European Society of Intensive Care Medicine found that 92.6% were responsible for prescribing RRT. Of these, half reported using both intermittent hemodialysis and continuous renal replacement therapy techniques, although the majority favored CVVH [9] . Conversely, a French prospective observational multicenter cohort study, which included 1360 patients, showed that 40% of patients were initially treated with CVVH and 60% with IHD [10] . Other studies, mainly based on a randomized controlled trial design with proportional inclusions for each group, do not necessarily reflect resuscitators’ spontaneous choice between these two techniques.

The patients’ clinical data were comparable, irrespective of the EER technique used. They were elderly (mean age 67) and had comorbidities such as hypertension, diabetes, chronic renal failure and ischemic cardiomyopathy ( Table 1 ). This profile is like that of patients admitted to intensive care requiring EER, as described in the literature [11] [12] .

The main indications for EER, in order of frequency, were electrolyte disorders, intricate indications, hypervolaemia and metabolic disorders ( Figure 2 ). These results are in line with those reported in the literature, where the most frequently observed indications include anuria, acute lung oedema, metabolic acidosis, hyperkalaemia and uraemic syndrome [13] [14] .

The primary endpoint of this study was hemodynamic tolerance, particularly regarding intermittent hemodialysis (IHD). Variations in mean arterial pressure (MAP) and heart rate (HR) were analyzed during IHD sessions ( Figure 3 ). It was observed that patients undergoing IHD showed significant fluctuations in MAP and HR, possibly indicating hemodynamic instability. No other variable, apart from the technique used, was associated with these fluctuations in multivariate analysis. However, there was no early interruption of sessions for hemodynamic instability in patients undergoing IHD, in contrast to patients undergoing CVVH, among whom 14% had to interrupt their sessions for hemodynamic instability. CVVH is generally preferred in hemodynamically unstable patients, as it may be associated with better hemodynamic tolerance [15] - [18] . However, a systematic review of randomized clinical trials comparing hemodynamic parameters between CVVH, IHD and hybrid therapy in patients with acute renal failure revealed no significant differences between the groups [19] .

With regard to the efficacy of the two techniques, notably in terms of recovery of renal function, measured by creatinine at discharge from intensive care, and the need to continue dialysis after resuscitation, the study showed a significantly lower discharge creatinine in the CVVH group (245 vs. 389 µmol/l, p = 0.026) ( Figure 7 ) and a higher proportion of patients requiring continued dialysis after resuscitation in the HDI group (88% vs. 66%) ( Table 3 ). Although this difference was not statistically significant, these results suggest a potentially superior efficacy of CVVH, especially as the proportion of patients with chronic renal failure was higher (94%) in the CVVH group ( Table 1 ). These findings are also corroborated by other studies in the literature, including an analysis of 16 French observational studies, which suggested a higher rate of dialysis dependence in survivors who initially received IHD compared with those treated with CVVH (RR 1.99 [95% CI 1.53 - 2.59], I2 = 42%) [7] . However, this trend was not confirmed by the 7 randomized trials included in the same analysis, which showed no significant differences between the two modalities [7] .

In terms of survival, assessed by death rate, the analysis revealed that hemodialysis was associated with a higher survival rate than CVVH, with a statistically significant difference (p = 0.024) ( Figure 4 ). Clinical factors associated with death included older age, with a mean of 67.5 years in deceased patients versus 62.5 years in survivors. In addition, arterial hypertension was present in 69.5% of deaths, heart failure in 34.7%, and renal failure in a notable proportion of cases ( Figure 5 and Figure 6 ). However, in multivariate analysis, only the treatment modality significantly influenced the mortality rate. These observations are also reported in the literature, notably in a meta-analysis of the effects of different EER modalities on recovery of renal function and survival in patients with acute renal failure. This analysis revealed higher ICU mortality in patients who received CVVH compared with those who received IHD [8] . Although not methodologically comparable, a secondary analysis of two randomized trials also showed that the 60-day Kaplan-Meier-weighted mortality rate was 54.4% in the CVVH group versus 46.5% in the IHD group (weighted HR 1.26, 95% CI 1.01 - 1.60) [5] . Another meta-analysis including five French studies, involving 1045 patients treated with CVVH and 1416 with HDI, showed no significant difference in mortality risk between the two modalities (HR = 1.10 [95% CI 0.95 - 1.27], p = 0.21), with moderate heterogeneity (I2 = 63%, p = 0.03) [20] . However, in our study, CVVH was associated with exclusive use of noradrenaline, longer ICU stays and more frequent invasive ventilation. This suggests that this modality is used to manage more severe patients. These results testify to the variability observed in terms of efficacy and survival between the two modalities, probably due to patient-specific indications and the severity of their clinical condition.

In contrast to established knowledge, our study found that a high SOFA score was associated with a reduced risk of mortality. This paradoxical finding may be explained by the fact that patients with higher SOFA scores were the most critically ill and predominantly received CVVH, which emerged in our study as a protective factor against mortality. This suggests that CVVH may act as a mortality-protective factor, independent of patient severity. Consequently, the improved survival observed in patients with higher SOFA scores might not reflect a lower intrinsic mortality risk but rather the potential benefits conferred by CVVH in managing critically ill patients.

This hypothesis is supported by findings from a study published in Membranes, which examined the impact of ultrafiltration rates during CVVH in patients with severe sepsis. The study demonstrated that, among patients with a SOFA score ≥15, a higher ultrafiltration rate was significantly associated with improved 90-day survival compared to standard ultrafiltration rates. These results suggest that specific CVVH modalities may offer survival benefits even in the most severely ill patients, potentially explaining the observed association between high SOFA scores and reduced mortality in our study [21] .

This study shows that CVVH, thanks to its better biological stabilization, is suitable for hemodynamically unstable patients, while IHD, effective in stable patients, is associated with a better survival rate. The choice of technique must be individualized according to clinical profile. These results need to be confirmed by prospective studies to guide ICU strategies.

The study was conducted in accordance with ethical standards, with informed consent obtained from all participants or their legal representatives.