OxiCLEAR (Oxiris Cytokines and Endotoxin Adsorption Rate) Study

This is a prospective, single-center, observational study designed to characterize the adsorption capacity and saturation dynamics of the AN69-polyethylenimine membrane (Oxiris® hemofilter) during continuous veno-venous hemofiltration (CVVH) in adult patients with septic shock.

The Oxiris® hemofilter is approved for continuous renal replacement therapy (CRRT) for up to 72 hours in patients with sepsis-associated acute kidney injury; however, in routine clinical practice the filter is commonly replaced after 12-24 hours because of concerns regarding declining adsorption efficiency. The biological basis for this practice remains insufficiently defined. This study aims to provide in vivo quantitative evidence on how endotoxin and cytokine adsorption by the Oxiris® membrane changes over time and whether cytokine clearance persists through convective transport when adsorption capacity is reduced.

The primary objective is to quantify the adsorption capacity of the AN69-polyethylenimine membrane for endotoxins and inflammatory mediators over a continuous 24-hour CVVH treatment period. Secondary objectives are to determine whether membrane adsorption efficiency declines over time in a manner consistent with saturation, to quantify cytokine clearance via convective transport into the effluent, and to evaluate whether reduced membrane adsorption is associated with clinical course and outcomes in septic shock.

Adult patients (≥18 years) with septic shock admitted to the intensive care unit of Pauls Stradiņš Clinical University Hospital will be enrolled. All patients will receive CVVH with the Oxiris® hemofilter as part of standard-of-care management. Eligibility requires fulfillment of Sepsis-3 septic shock criteria, a Dynamic Scoring System (DSS) score of 6-8, and treatment with CVVH for at least 24 hours. Baseline endotoxin concentration will be used to define the primary analytical cohort.

All patients will be treated using CVVH with the PrisMax platform and Oxiris® membrane under standardized conditions to ensure comparability of adsorption kinetics: blood flow 100-150 mL/min, filtration dose 25-30 mL/kg/h, regional citrate anticoagulation, replacement fluid 1000-1500 mL/h with 50% pre- and post-dilution, and net ultrafiltration of 0 mL/h.

Blood and effluent samples will be collected at baseline (T0) and at 1, 3, 6, 12, and 24 hours after initiation of CVVH. At each time point, inlet (arterial line) plasma, outlet (venous line) plasma, and effluent will be obtained. A total of 17 samples per patient will be collected. Samples will be centrifuged immediately and stored at -80 °C until analysis.

Endotoxin concentrations will be measured using a competitive ELISA assay with high analytical sensitivity. Inflammatory mediators, including IL-1α, IL-1β, IL-2, IL-4, IL-6, IL-8, IL-10, TNF-α, IFN-γ, MCP-1, VEGF, and EGF, will be quantified using a multiplex biochip analyzer.

For endotoxins, removal occurs exclusively via adsorption. Adsorption rate will be calculated from the inlet-outlet concentration difference multiplied by plasma flow rate and normalized to membrane surface area (U/cm²/min). For cytokines, total plasma clearance will be calculated from inlet and outlet concentrations, convective clearance from effluent concentration multiplied by effluent flow rate, and adsorptive clearance as the difference between plasma and effluent clearance. This approach allows separation of cytokine removal by adsorption and convection and enables determination of whether cytokine clearance persists when membrane adsorption capacity declines.

Clinical data will include demographics, comorbidities, SOFA and Dynamic scores, source of infection, antimicrobial therapy, hemodynamic variables, vasopressor dose, lactate, CRP, procalcitonin, renal and liver function, and CRRT technical parameters including blood flow, transmembrane pressure, and filter pressure gradients. Clinical outcomes include 28-day mortality, renal recovery, vasopressor-free days, and ICU length of stay.

The primary endpoint is the adsorption rate of endotoxins and inflammatory mediators. The primary analysis evaluates the relationship between inlet endotoxin concentration and adsorption rate across repeated time points. Pearson correlation coefficients will be calculated and transformed using Fisher's Z transformation to obtain a pooled estimate of correlation over time. A decline in this relationship will be interpreted as evidence of reduced membrane adsorption capacity consistent with saturation. Time-dependent changes in adsorption will also be analyzed using linear mixed-effects models with patient as a random effect and time, inlet concentration, transmembrane pressure, and filter age as fixed effects.

For cytokines, the relative contribution of convective versus adsorptive clearance will be modeled over time to determine whether convective transport remains effective when adsorption declines. Associations between early membrane saturation and clinical outcomes (e.g., lactate reduction, vasopressor requirements, SOFA score, renal recovery, and 28-day mortality) will be explored using mixed-effects regression, logistic regression, and Cox proportional hazards models as appropriate.

Twenty-nine patients provide sufficient power to detect clinically meaningful changes in adsorption dynamics based on preliminary correlation estimates. Continuous variables will be summarized as mean ± standard deviation or median with interquartile range, and categorical variables as counts and percentages. Missing data will be handled using complete-case analysis, with multiple imputation applied if missingness exceeds 5%.

All data will be stored in a secure electronic database with predefined range and consistency checks. Laboratory values will be verified against certified laboratory records and clinical data against ICU medical records. Standard operating procedures govern patient enrollment, sample handling, laboratory analysis, data management, and statistical evaluation.