Clinical validation of an intra-abdominal pressure monitoring system by comparison with pneumoperitoneum pressure

In critically ill patients, intra-abdominal hypertension (IAH) is associated with organ dysfunction and increased mortality. Acute kidney injury may occur early, since the kidney is particularly vulnerable to elevated intra-abdominal pressure (IAP). Accurate and timely measurement of IAP is essential for early detection of IAH and the initiation of appropriate therapeutic interventions. Therefore, the aim of this study was to assess the accuracy of an IAP monitoring system compared to a reference standard, the CO2 insufflator, during laparoscopy. The second aim was to assess the changes in renal biomarker levels during and after increases in IAP through pneumoperitoneum. A prospective cohort study in patients undergoing laparoscopy at the University Medical Center Groningen. IAP measurements were performed with a urinary catheter using an IAP monitoring system (Accuryn® Monitoring System, Accuryn Medical) and compared to the pressure set at the CO2-insufflator system. Bland-Altman analysis was performed with accounting for repeated measures. Urine samples were collected at several time-points and Kidney Injury Molecule 1 (KIM-1), Tissue Inhibitor of Metalloproteinase 2 (TIMP-2), urinary Neutrophil Gelatinase-Associated Lipocalin (NGAL), Liver-type Fatty Acid-Binding Protein (L-FABP), and albumin-creatinine ratio were measured. Between March 2025 and January 2026, 99 measurements were performed in 29 patients. One patient (3%) underwent hemicolectomy, and 28 patients underwent endometriosis surgery (97%). Analysis showed a bias of -1.4 mmHg (95% CI (-1.96 - (-0.82)) and limits of agreement of − 5.96 mmHg and 3.2 mmHg (95% CI -6.8–3.99) between the IAP monitoring system and the CO2-insufflators. The precision was 2.3 mmHg. The levels of renal biomarkers KIM-1, TIMP-2 and albumin/Cr ratio increased during laparoscopy compared to baseline, suggesting that relatively small IAP increases during laparoscopy have a subclinical effect on the kidney. The IAP monitoring system underestimated the IAP set by the CO2-insufflator by approximately 1 mmHg. The wide limits of agreement warrant cautious interpretation. Overall, the IAP monitoring system showed reasonable accuracy and precision. The increase of several renal biomarkers during laparoscopy compared to baseline may reflect a direct effect of elevated IAP on the kidney. Similar content being viewed by others 1 Background In critically ill patients, intra-abdominal hypertension (IAH) and abdominal compartment syndrome (ACS) are conditions that lead to organ failure and increased mortality [1,2,3]. IAH is defined by a sustained intra-abdominal pressure (IAP) equal to or above 12 mmHg, and ACS is a further sustained increase in IAP above 20 mmHg in combination with new onset organ failure [4]. Both the extent and duration of elevated IAP affect organ function, in particular kidney function [5, 6]. Therefore, monitoring of IAP in the Intensive Care Unit (ICU) is crucial for early detection of IAH and timely intervention when IAH progresses to ACS [4, 7]. Many IAP measurement methods have been developed to facilitate the diagnosis of IAH or ACS. From clinical examination with a poor sensitivity of 40–60%, to indirect IAP measurements estimating the pressure in the abdominal cavity via a hollow organ, such as intragastric pressure, intra-rectal pressure, intra-esophageal pressure or intravesical pressure, have been tested [8,9,10,11]. Direct IAP measurements are invasive and therefore have a limited applicability in critically ill patients. They are mostly used in the operating theatre with a sensor in the CO2-insufflation system to establish pneumoperitoneum during laparoscopy. The current standard in critically ill patients is IAP measured indirectly via the bladder, by instilling a maximum of 25 ml of NaCl 0.9% through a urinary catheter connected to a pressure transducer [12, 13]. However, measuring IAP with this technique is time-consuming, and as a result, current clinical practices often involve sporadic intermittent measurements, limiting the ability to observe IAP changes over time. To address these limitations, continuous IAP monitoring systems have been developed. The Accuryn® Monitoring System has been validated in laboratory settings, but it awaits validation in different clinical settings [14]. This IAP monitoring system allows frequent monitoring of IAP, enabling the tracking of IAP trajectories rather than relying on isolated ‘on spot’ measurements [15, 16]. This approach facilitates early detection of sustained elevations in IAP. Elevated IAP is associated with acute kidney injury, and several pathophysiological mechanisms have been proposed [17]. Even brief periods of elevated IAP may lead to increases in kidney-specific biomarkers, suggesting subclinical renal injury [18]. However, many factors contribute to the development of acute kidney injury, making it challenging to analyze the specific impact of elevated IAP on kidney function. The first aim of this study was therefore to assess the accuracy of the Accuryn® Monitoring System compared to a reference standard, the CO2-insufflator, in a clinical setting during laparoscopy. The second aim was to assess the changes in renal biomarker levels during and after an increase in IAP through pneumoperitoneum. 2 Methods 2.1 Participants In this prospective cohort study, patients undergoing elective laparoscopy to remove endometriosis or patients undergoing laparoscopic colon surgery at the University Medical Center Groningen (UMCG) were included. Patients younger than 18 years, or those with chronic kidney disease, chronic dialysis, or a kidney transplantation in their medical history, were excluded. Eligible patients were identified by their gynecologist or surgeon during the pre-operative counselling at the endometriosis or abdominal surgery outpatient department. 2.2 Methods to measure intra-abdominal pressure The IAP monitoring system (Accuryn® Monitoring System, Accuryn Medical, Hayward, CA, USA) was used as an index method. It measures IAP in the bladder using a semi-flaccid balloon with a pressure sensor at the tip of a urinary catheter. Urine is actively drained by the Accuryn Monitoring System to empty the bladder. The urinary catheter was placed in the operating theatre after induction of anesthesia and tracheal intubation and was attached to the IAP monitoring system. Direct IAP measurement by a CO2-insufflator was used as reference standard. Two types of CO2-insufflators depending on the type of laparoscopy were used, the UHI-4 (Olympus America, Center Valley, PA, US) for standard laparoscopy and the Lexion AP50/30 (AFS MEDICAL GmbH, Teesdorf, Austria) for DaVinci robot-assisted laparoscopy. In standard laparoscopy, a target pneumoperitoneum pressure of 12 mmHg was applied. For DaVinci robot-assisted procedures, insufflation pressure was set to 12 mmHg during initial setup, after which it was lowered to 8 mmHg for the surgical procedure. During intra-abdominal pressure measurements patients were positioned in Trendelenburg according to surgery protocol. 2.3 Data collection The first IAP measurement was taken 30 min after incision and repeated after one hour, after two hours etc. until pneumoperitoneum ended. At each time-point, the CO2-insufflator pressure was recorded, and the pressure measured by the Accuryn® monitoring system, as well as the fluctuations of the CO2-insufflator. Urine samples were collected at several time-points: before the incision, one hour after the incision, at the end of surgery, one hour postoperatively and one day postoperatively. The following renal biomarkers were measured in the urine samples: Kidney Injury Molecule 1 (KIM-1), Tissue Inhibitor of Metalloproteinase 2 (TIMP-2), urinary Neutrophil Gelatinase-Associated Lipocalin (NGAL), Liver-type Fatty Acid-Binding Protein (L-FABP), and albumin-creatinine ratio. Other variables collected were age, sex, Body Mass Index (BMI), comorbidities, type of surgery, duration of surgery and duration of pneumoperitoneum. Urine samples were frozen at − 80 °C until analysis. Urinary NGAL, L-FABP, KIM-1 and TIMP-2 were measured by commercially available sandwich ELISAs according to the manufacturer’s instructions: Human Lipocalin-2/NGAL Quantikine ELISA Kit (DLCN20), Human Urinary TIM-1/KIM-1/HAVCR Quantikine ELISA Kit (DKM100) and TIMP-2 Human Quantikine ELISA kit (DTM 200), all R&D Systems (Bio-Techne, Minneapolis, MN, USA), and Human L-FABP ELISA kit (HK404; Hycult Biotech, Uden, The Netherlands). Urine creatinine (Cr) and albumin were analyzed in the central UMCG laboratory using clinical grade standard measurements. Biomarker levels were normalized using urine Cr. 2.4 Statistical analysis

are presented as medians with interquartile ranges (IQR), means with standard deviations (SD), or as counts (N) and percentages (%). Normality was assessed by visual inspection of histogram and Shapiro-Wilk test. A repeated measures correlation was performed to quantify the linear association between two methods. Data were analyzed in R version 4.4.3. Graphs were generated using Graph Pad Prism 10.2.3. Analysis of absolute agreement was calculated using the SimplyAgree package in R [19]. For the Bland-Altman style limit of agreement analysis the “agreement_limit()” function was applied. Bias was defined as the mean difference between methods, and limits of agreement (LOA) were calculated as the mean difference ± 1.96 times the SD of the differences [20]. Repeated measures per patient were accounted for by adjusting the variance of the differences. The Method of Variance Estimates Recovery (MOVER) was used to calculate 95% confidence intervals of the limits of agreement [21]. A Bland–Altman plot was used for visualization [20]. Precision was defined as the SD of the variability of the difference between methods while accounting for repeating measures. Diagnostic plots to check assumptions were created (suppl. Figures 2 and 3). Subgroup analysis was used to identify differences between CO2-insufflator types. Outliers were identified when outside of the 95% of LOA (mean difference ± 1.96 SD) based on percentage differences. Sensitivity analysis was performed to assess the influence of those outliers on primary analysis. Biomarker differences between baseline and during surgery were analyzed using t-test. Standardized effect size was calculated using Cohen’s d. Correlations between biomarker concentrations at the end of surgery and duration of pneumoperitoneum were assessed using Pearson’s or Spearman’s correlation analysis, depending on data distribution. 2.5 Sample size The sample size was chosen according to the research recommendations of the World Society of the Abdominal Compartment Syndrome (WSACS) to validate a novel IAP measurement device [22]. 3 Results Between March 2025 and January 2026, 30 patients were enrolled with a total of 106 IAP measurements (Fig. 1). The first included patient was treated as a “training patient” for protocol development and team training of this study. Three “IAP measurement errors” of the monitoring system occurred, and one measurement was missing. Ninety-nine IAP measurements in 29 patients were included in the analysis with a median of three measurements (IQR 3–4) per patient (suppl. Figure 1). The median age of patients was 35 years (IQR 32–40) with a BMI of 27.3 kg/m2 (± 4.7) (Table 1). Most patients were female (97%) and underwent endometriosis resection surgery (97%). One patient underwent a hemicolectomy. Seven patients (23%) underwent robot-assisted surgery with the CO2-insufflator AP50/30, while 22 patients (76%) underwent standard laparoscopy with the UHI-4 CO2-insufflator (Fig. 1; Table 1). Of 99 measurements in total, 19 measurements were in the robot-assisted group and 80 measurements were in the standard laparoscopy group. The median duration of the pneumoperitoneum was 150 min (IQR 123–224). The IAP of the monitoring system measured a median pressure of 9.6 mmHg (8.3–10.4) compared to 11mmHg (IQR 10.5–12) measured by the reference standard, the CO2-insufflator. The IAP monitoring system and the CO2-insufflator correlated moderately (R = 0.38, p-value: <0.001). Visual inspection of the scatterplot showed that the IAP monitoring system tended to underestimate the reference, with most observations lying below the line of equality (Fig. 2). 3.1 Agreement To analyze agreement, Bland-Altman plots were performed for visualization (Fig. 3). At visual inspection, for the majority of measurements the difference is minimal between the methods at lower IAP levels (Fig. 3a). At a medium mean IAP level of 9–12 mmHg (where most measurements took place) there was a visual underestimation of the IAP monitoring system compared to the CO2-insufflation shown, while above 12 mmHg there was an overestimation. A proportional bias and heteroscedasticity were statistically detected (p-value: <0.001, suppl. Figure 2). However, at visual inspection of the Bland-Altman, a consistent proportional bias could not be confirmed (Fig. 3). The overall bias was − 1.4 mmHg (95%CI -1.96 - (-0.82)) (Table 2). The lower limit of agreement (LOA) was − 5.96 mmHg, and an upper LOA was 3.2 mmHg (95% CI -6.8–3.99) (Table 2). In this study, two different CO2-insufflators were used (Fig. 3b and c). Most measurements of the Lexion AP50/30 were collected at 8 mmHg (during robot-assisted surgery, 95%) and most measurements of the UHI were collected at 12 mmHg (45%). The bias of the AP50/30 group was smaller (-1.1 mmHg, 95% CI -2.4–0.3) compared to the bias of the UHI group (-1.5 mmHg, 95% CI -2.2 - (-0.8)) indicating that the IAP monitoring system performed better when compared to Lexion AP50/30 reference standard or measured more accurately at lower pressure levels. The LOAs of the AP50/30 were narrower compared to the UHI-4, which underlines the better agreement of the IAP monitoring system with the reference standard (Table 2). The precision of the IAP monitoring system was 2.3 mmHg (Table 2). The highest precision was in the AP50/30 group (2.1 mmHg). 3.2 Sensitivity analysis Six outliers were identified and excluded in a sensitivity analysis (suppl. Figures 1 and 4). Removal of these observations resulted in minimal change in estimated bias (-1.2 mmHg, 95% CI − 1.7 - (-0.7)), while the limits of agreement were slightly narrower compared with the primary analysis. Following outlier exclusion, there was no evidence of heteroscedasticity (p-value: 0.20, suppl. Figure 3). 3.3 Biomarker course over time KIM-1/Cr ratio significantly increased between baseline and 1 h after the start of surgery (t(28) = -3.6, p = 0.001, Cohen’s d = − 0.68 (95% CI [− 1.08, − 0.27]). After surgery, the levels of KIM-1/Cr decreased (Fig. 4). TIMP-2/Cr ratio significantly increased during surgery compared to baseline (t(28) = -2.8, p = 0.02, Cohen’s d = − 0.46 (95% CI [− 0.84, − 0.07]). Albumin/Cr ratio significantly increased from 0.9 mg/mmol Cr (IQR 0.7–2.1). to 2.8 mg/mmol Cr (t(28) = -4.4, p < 0.001, Cohen’s d = − 0.81 (95% CI [− 1.23, − 0.39]). Urinary NGAL/Cr ratio decreased one hour after the start of surgery compared to baseline but not significantly (t(28) = 0.34, p = 0.71, Cohen’s d = 0.07 (95% CI [− 0.29, − 0.43]). L-FABP/Cr ratios were not significantly different (t(27) = 1.13, p = 0.27, Cohen’s d = 0.21 (95% CI [− 0.16, 0.59]). 3.4 Severity of pneumoperitoneum exposure Patients exposed to a 12 mmHg pneumoperitoneum had higher KIM-1 ratios and higher albumin/Cr ratio during surgery compared to those exposed to 8 mmHg, although the difference was not statistically significant (t(12) = 0.6, p = 0.57 and t(20) = 2.1, p = 0.05). There was no significant difference between TIMP-2/Cr ratio (W = 82, p = 0.82) and NGAL/Cr ratio (W = 84, p = 0.75) according to severity. L-FABP/Cr ratio was higher in the 12mmHg group compared to the 8 mmHg group, but not significantly (W = 73, p = 0.84). 3.5 Duration of pneumoperitoneum exposure The change in L-FABP/Cr ratio from baseline to the end of surgery was moderately correlated with the duration of pneumoperitoneum (ρ = 0.40, p = 0.04). Other changes in biomarkers at the end of surgery were not associated with the duration of pneumoperitoneum exposure (p > 0.14). 4 Discussion This study was the first assessing accuracy of this IAP monitoring system in a clinical setting with 99 measurements in 29 patients. The IAP monitoring system underestimated the IAP measured by the CO2-insufflator by approximately 1 mmHg. The wide limits of agreement warrant cautious interpretation and constrain the overall accuracy of the device in this study. Furthermore, the levels of renal biomarkers KIM-1, TIMP-2 and albumin/Cr ratio increased during laparoscopy compared to baseline. At mean IAP levels between 9 mmHg and 12 mmHg, the IAP monitoring system underestimated the CO2-insufflator, while at levels above 12 mmHg there was a modest overestimation. Interestingly, 12 mmHg and 8 mmHg were the target pressures of the CO2-insufflator for the majority of patients. The pattern may simply reflect variability of the IAP monitoring system, which influences both the mean and the difference in the Bland–Altman plot. Additionally, deviations from the target pressure may have reduced pneumoperitoneum, potentially contributing to higher variability, particularly in the IAP monitoring system and possibly in both methods. Furthermore, this study assumes that the type of CO2-insufflation is important when used as a reference standard. The smaller bias and the higher precision of the reference standard AP50/30, which is mainly used in robot-assisted surgery in our hospital, could be explained by a more stable pneumoperitoneum achieved with a pressure-probe positioned closer to the abdominal wall. Future validation studies should account for the specific type of insufflator. Measuring IAP timely, reliably, and precisely is essential for early diagnosis of IAH and ACS. Therefore, the assessment of clinical performance is crucial. The study by Tayebi et al. described the performance of the Accuryn® Monitoring System in an experimental in-vitro setting [14]. A negative bias was reported with a similar precision for 48-hour measurements. Although the negative bias was smaller than in our study, results from an in-vitro setting are more likely to show close agreement because they are less affected by physiological, anatomical, and environmental interference. Another experimental in-vitro study conducted by Smit et al. also showed a slight underestimation of IAP measured by this device compared to the water column pressure (suppl. abstract) [23]. The primary reference standard used for validation of a novel IAP measurement method is the intravesical method first described by Kron and recommended by the WSACS [4]. However, this method was not feasible due to the closed urinary catheter system of the Accuryn® Monitoring System. The CO2-insufflator is a commonly used alternative reference standard in literature [11, 24,25,26,27,28]. In the setting of laparoscopy, the pneumoperitoneum serves as a model for controlled IAP. However, a recent study with a similar study design compared a continuous monitoring device to CO2-insufflation and found a bias of approximately 6 mmHg with wide limits of agreement (TraumaGuard Foley catheter, Sentinel Medical Technologies, Jacksonville, FL, USA) [29]. Compared to these findings, our study showed better performance of the IAP monitoring device. However, the WSACS recommends safety margins of a bias < 1 mmHg, a precision of 2 mmHg, and limits of agreement of ± 4 mmHg [22]. When assessed against these criteria, the IAP monitoring system demonstrated only marginal performance. It should be noted, however, that these standards are primarily used in literature for bladder-to-bladder comparisons. As indicated in a previous study, the comparison between CO₂-insufflation pressure and bladder pressure may account for the observed deviation [29]. Urinary KIM-1/Cr, TIMP-2/Cr, and albumin/Cr ratio increased during laparoscopy compared with baseline. Since KIM-1 is a marker of tubular injury and TIMP-2 reflects renal tubular stress, these findings suggest that even relatively small IAP increases during laparoscopy have a subclinical effect on the kidney. These findings are consistent with Smit et al. [18] who observed significant increases in plasma NGAL during laparoscopy compared to open surgery. Future studies should aim to further elucidate the relationship of IAP increases on renal function. This study was the first to validate the Accuryn® Monitoring System using the pneumoperitoneum pressures of laparoscopy. With this clinical validation study, we were able to show a reasonable performance of the IAP monitoring system. 4.1 Limitations This study has several limitations. Our assessment covered a restricted range of IAP values, as the laparoscopic procedures were intentionally conducted at the lowest safe operating pressure and we did not assess the initial opening pressure after trocar placement. Although we do not expect a difference in performance, further studies should validate the Accuryn® Monitoring System for higher IAP [14, suppl. abstract]. Furthermore, we have assessed accuracy of the IAP monitoring system during ongoing surgery, which could have led to disturbances of stability of the pneumoperitoneum through e.g. suction or manipulation of the abdomen or bladder. Therefore, the performance of the Accuryn® Monitoring System may have been underestimated. IAP measurements were performed in Trendelenburg position, which may have influenced the results. The generalizability of this study to the ICU population is limited, as all patients were under anesthesia during IAP measurements, most patients were female, and sample size was limited. Although the validation of novel IAP measurement devices in the setting of pneumoperitoneum has been established, the comparison of measurements obtained from different anatomical sites may have influenced the study findings. Lastly, no blinding of the researcher has taken place, which increases observation bias. 5 Conclusion We assessed the accuracy of the IAP monitoring system (Accuryn® Monitoring System, Accuryn Medical) in a clinical environment using 99 paired measurements in 29 patients. The IAP monitoring system showed an underestimation of approximately 1 mmHg compared with the CO2-insufflation during laparoscopy. In summary, the IAP monitoring system showed reasonable accuracy and precision. Furthermore, the increase of several renal biomarkers during laparoscopy compared to baseline may reflect a direct effect of elevated IAP on the kidney. Data availability The dataset analyzed during the current study is not publicly available due to ethical and legal restrictions related to patient confidentiality, as the data contain potentially identifying information. The data are available from the corresponding author upon reasonable request.

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We would like to thank Jacqueline Koeze for her support in the study design and editing the manuscript. We would like to thank Rianne Jongman for her support in analyzing the urine samples. We would like to thank Just van Es-de Weerd for statistical advice. We would also like to thank Wyke Kroesen, Claas Rollman and Jülide Senem Karaca, medical students at the University of Groningen, for their support with patient enrolment during surgery. Finally, we would like to thank Vanessa Moll for her support in conceptualization of this study. Funding Franziska Günther was funded by a MD/PhD grant from the University Medical Center Groningen. No funding in cash was received for this study. Accuryn Medical (Hayward, CA, USA) provided the Accuryn® Monitoring System used in this study and were not involved in study design, data interpretation or writing this manuscript. Author information Authors and Affiliations Contributions Authors’ contributions FG: Writing – original draft, Visualization, Project administration, Methodology, Investigation, Funding acquisition, Formal analysis.HSH: Writing - Review & Editing, Project Administration: “Managed patient inclusion process and consent”, MethodologyERK: Writing - Review & Editing, Project Administration: “Managed patient inclusion process and consent"KvdT: Writing - Review & Editing, Project Administration: “Managed patient inclusion process and consent"MWN: Writing - Review & Editing, InvestigationMvM: Study design, supervising study process, Writing - Review & EditingMS: Conceptualization, Study design, supervising study process, Writing - Review & Editing, Validation. Corresponding author Ethics declarations Competing interests The authors declare no competing interests. Consent to participate Participants received written information by letter, and written informed consent to participate in this study was obtained prior to enrolment from all individual participants included in the study. Consent for publication Written informed consent for publication of anonymized data was obtained from the participant. Ethics approval The Central Ethics Review Board of the University Medical Center Groningen approved this study (CTc 20426). Additional information Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. Supplementary Information Below is the link to the electronic supplementary material. Rights and permissions Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. About this article Cite this article Günther, F., Hofker, H.S., Klinkert, E.R. et al. Clinical validation of an intra-abdominal pressure monitoring system by comparison with pneumoperitoneum pressure. J Clin Monit Comput (2026). https://doi.org/10.1007/s10877-026-01515-y Received: Accepted: Published: Version of record: DOI: https://doi.org/10.1007/s10877-026-01515-y