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.
