In 2022, only 6% of patients in stage 5 chronic kidney disease (CKD) in France were treated with peritoneal dialysis (PD), which highlights its relatively low adoption rate [1]. Automated peritoneal dialysis (APD), however, remains a cornerstone therapy for managing end-stage kidney disease (ESKD), offering flexibility and effectiveness in achieving fluid and solute clearance [2][3][4][5][6]. APD provides several benefits, particularly for patients requiring urgent initiation of dialysis, as it has been associated with a lower incidence of PD-related complications compared to urgent start of hemodialysis [7].

However, challenges persist in the effective use of APD, particularly in addressing negative daytime ultrafiltration (UF) when icodextrin is used [8][9][10][11]. Icodextrin, a complex polysaccharide solution, is widely used in PD for its ability to sustain UF during long daytime dwell periods and reduce glucose-related complications [11][12][13][14][15][16]. Nonetheless, negative UF or UF failure during the long dwell remains a significant clinical challenge, potentially leading to fluid overload and associated morbidities [8][10][11].

According to the International Society for Peritoneal Dialysis (ISPD), UF failure is defined as a net UF of less than 400 mL after a 4-hour dwell with glucose/dextrose 3.86%/4.25%, or less than 100 mL with glucose/dextrose 2.27%/2.5% [17]. Several factors contribute to UF variation under icodextrin, including patient membrane characteristics, hydrostatic and osmotic pressures, dialysate composition, and metabolic factors [8–10,18,19]. Lambie et al [8]closely examined these influences, emphasizing the importance of individualized management.

Another critical factor can be the intraperitoneal pressure (IPP), the pressure exerted within the abdominal cavity [20]. IPP is influenced by factors such as the volume of fluid in the peritoneal cavity, patient morphology, posture, and abdominal muscle tone [21,22] [21][22]. IPP measurement, first described by Durand et al.[22][23][24] in the 1990s, is a simple and non-invasive procedure. It involves placing the patient in a supine position and estimating the pressure by measuring the height of the dialysate column in tubing connected to the catheter, using the mid-axillary line as the reference point [22][23][24]. For a patient in a supine position, IPP typically ranges between 8 and 18 cmH2O for an infused peritoneal volume of 2 L [23][24].

Our study aimed to analyze the occurrence of negative daytime UF during icodextrin long dwell in patients undergoing APD, focusing specifically on this occurrence and identifying potential associated factors.

The results of our analysis on UF volume during the long dwell with icodextrin in APD highlight interesting dynamics. Notably, IPP emerges as the primary determinant of interest. However, it is crucial to acknowledge that our small cohort size likely limited the statistical power of this study, restricting our ability to capture the complexity of the interactions fully.

The clinical impact of IPP variation is still poorly documented in the literature, with many existing studies being constrained by small sample sizes and methodological limitations. For instance, Imholz et al. [18]demonstrated that increases in IPP led to a reduction in net UF, primarily due to enhanced lymphatic absorption. Similarly, Díaz et al. [25]reported that IPP influences PD efficiency by decreasing UF and solute clearance. Moreover, Durand et al. [23],24] [23][24] found that even a modest increase of 1 cmH2O in IPP could decrease total UF by 70 mL after two hours, primarily due to increased lymphatic reabsorption.

In addition, in 2009, Lambie et al. highlighted that intraperitoneal and extraperitoneal hydrostatic pressures, as well as osmotic pressures, were key factors influencing the direction and quantity of UF. Specifically, high intraperitoneal hydrostatic pressure, and thus high IPP, favors fluid reabsorption that can result in negative UF, while high plasma colloidal osmotic pressure favors UF [8].

Moreover, our findings, while not statistically significant, suggest a possible dynamic between BMI and daytime UF. Several studies have demonstrated a correlation between BMI and IPP, with Castellanos et al. and Dejardin et al. [20,21] both observing that higher BMI correlates with elevated IPP. This suggests that patients with higher BMI may be more likely to experience increased IPP, potentially contributing to negative UF. Further, larger studies should tend to investigate the potential interaction between BMI and IPP, and its impact on UF volumes.

We also observed a potential link between the prescribed volume of the last injection and daytime UF. Specifically, higher prescribed volumes appeared to be associated with more negative daytime UF, although the results were not statistically significant. This association may be mediated by IPP, as an increase in prescribed volume could elevate IPP, thus influencing UF. Current guidelines recommend individualized PD prescriptions, focusing on fluid balance, nutritional and metabolic aspects, and small molecule clearance [26]. While the ISPD does not recommend routine IPP measurement, we believe it could serve as a valuable tool for optimizing PD prescriptions [24–26]. Measuring IPP could assist in adjusting the amount of fluid used during PD to prevent complications. Regular monitoring of IPP may help identify at-risk patients and guide clinical management. In cases of UF failure or fluid overload, IPP measurement can be especially useful for diagnosing UF losses, assessing the patient’s tolerance to intraperitoneal fluid, and optimizing treatment strategies. At the University Hospital of Caen, IPP is routinely measured at the onset of PD. In cases of elevated IPP, PD prescriptions are reassessed by reducing the infused volumes. This approach helps ensure that IPP levels are appropriately managed, potentially improving UF outcomes.

Another compelling finding in our analysis was that, while the results were not statistically significant among diabetic patients, five out of seven achieved positive UF. Previously, Ahmad et al. [13]conducted a retrospective study comparing UF variations in 17 diabetic and 23 non-diabetic patients undergoing APD. Their results suggest that icodextrin may be more effective for UF in diabetic patients, although the underlying mechanisms remain unclear.

In our sample, we found that patients with negative daytime UF exhibited a higher level of residual renal function. This observation leads us to consider whether negative ultrafiltration might be linked to fluid reabsorption, which could contribute to a state of relative hypervolemia and, in turn, explain the increased urine volume observed in these patients.

Finally, we observed that the use of hypertonic solutions during night-time exchanges was lower in the negative daytime UF group. Hypertonic solutions are commonly used to enhance UF by increasing the osmotic gradient. Additionally, it was noted that residual diuresis was greater in this group. We hypothesize that patients with negative daytime UF may have more preserved renal function, better volume control, and consequently less need for hypertonic solutions to achieve UF.

Several limitations must be considered when interpreting the results of this study. The primary limitation is the small sample size, which reduces the statistical power of the analysis and may impair our ability to detect significant differences between the groups. This highlights the necessity for larger, more comprehensive studies to confirm and refine our findings. We also assumed that averaging the daily UF volume over a week would help reduce variability within patients. UF calculations were performed using Sharesource ^® . Furthermore, this study utilized a retrospective observational design, which inherently restricted our ability to establish causal relationships between the variables. Despite our efforts to control for known confounders, there may still be unmeasured variables that could have introduced bias into our results. It is essential to recognize this observational nature when interpreting our findings, as we cannot definitively infer causality. Additionally, the study was conducted at a single center, which may limit the generalizability of our conclusions. The characteristics of our sample and the specific institutional environment might not accurately represent broader patient populations or clinical settings. Therefore, caution should be exercised when applying our results to other contexts, and further replication of these findings in diverse populations and settings is necessary. Measuring peritoneal pressure on day four may also lead to overestimated values, as the abdominal wall may not fully adapt to the presence of fluid, particularly in cases involving significant intraperitoneal volume. Lastly, while we have attempted to account for various confounding factors, there remains the possibility that unmeasured variables—including detailed medical histories, individual health behaviors, and sociodemographic factors—could have influenced the outcomes. These factors were not included in our analysis, and their potential impact should be considered when interpreting our findings.

In conclusion, this retrospective, single-center observational study investigated the occurrence of negative daytime UF in APD using icodextrin and examined potential factors influencing this outcome. Although our findings were not statistically significant, likely due to the limited sample size, they suggest a possible association between increased IPP and negative daytime UF. While routine measurement of IPP is not currently recommended in clinical practice, our results underscore its potential importance in optimizing treatment. We advise centers that do not routinely measure IPP to consider evaluating it in cases of negative daytime UF. This will help ensure that IPP levels are not excessively elevated, and adjusting peritoneal dialysis prescriptions by reducing infused volumes in such instances may enhance patient outcomes. Given the limitations of our study, particularly the small cohort size, further research is necessary to better understand the clinical implications of IPP and its role in UF during APD.

Srouji T.: Contributed to the conceptualization of the study, performed statistical analysis, and wrote the manuscript.

Boyer A.: Contributed to the conceptualization of the study, performed statistical analysis, and revised the manuscript.

Lanot A., Béchade C., Lobbedez T.: Contributed to the design of the study.

This study was approved by the Local Research Ethics Committee, CLER, of the University Hospital of Caen (ID 3793).

This retrospective observational study is based on data from patients followed at the University Hospital of Caen. In accordance with current regulations, individual patient consent is not required. Approval from the Local Research Ethics Committee (CLER) is sufficient.

The authors declare that no financial support was received for the research, authorship, or publication of this article.

The authors have none to declare.