A central venous catheter (CVC) is a thin plastic tube placed into one of the body's large veins, typically in the neck or near the clavicle. CVCs are crucial for administering medications, fluids, and secure blood samples. Although CVCs are an essential tool in healthcare, there are certain risks and complications associated with their use. CVCs can affect the body's coagulation system, potentially leading to the formation of blood clots at the site of the catheter. This can result in serious complications, and in some cases, increased morbidity and mortality. Despite the known risk of blood clot formation with catheter use, it is still do not fully understand why clots occur or how a newly inserted catheter affects the coagulation system.

The aim of this randomized controlled trial is to compare four different central venous catheters and their impact on the coagulation system.

Eighty eight patients ≥18 years of age, who require a CVC and agree to participate in the study will be randomly assigned to one of the four predetermined, commonly used, central venous catheters. Two blood samples will be taken from the newly inserted catheter. The first blood sample (Sample 1) will be collected within seconds after catheter insertion without pre-flushing the catheter with saline. The second blood sample (Sample 2) will be taken after the catheter has been flushed with at least 10 ml saline and the initial blood discarded. All samples will be taken from the distale lumen without any connectors. Samples 1 and 2 will then be analyzed to measure how the coagulation system is affected after contact with the inside surface of the CVC. The blood samples will also be compared between the different catheter types and in overall cohort irrespective of group .

The study could provide valuable information on how the coagulation system is affected after catheter insertion. This knowledge could help improve preventive measures to reduce the risk of blood clot formation and ensure safer blood sampling for patients with venous catheters.

This is a randomized controlled trial, designed to evaluate coagulation activation in response to four different commercially available central venous catheters (CVCs), all with similar internal surface areas. The study focuses on comparing changes in coagulation parameters, primarily clotting time (CT), measured using rotational thromboelastometry (ROTEM® NATEM), as well as additional ROTEM variables and standard coagulation markers.

Participants are included based on clinical need for central venous access, and are randomized using REDCap to receive one of four CVC types:

1. MERITMEDICAL Careflow™ Two-Lumen Catheter (7 Fr, 150 mm, polyurethane, OD 2.4 mm)
2. ARROW Two-Lumen Catheter (7 Fr, 160 mm, polyurethane, OD 2.5 mm)
3. ARROWg+ard Blue Plus® Two-Lumen Catheter (8 Fr, 160 mm, polyurethane, OD 2.8 mm, chlorhexidine/silver sulfadiazine coating)
4. Multicath 2 Expert UP Two-Lumen Catheter (7.5 Fr, 160 mm, polyurethane shaft embedded with silver ions, OD 2.5 mm)

Blood samples will be collected at two time points for each participant:

• Sample 1: Immediately after catheter insertion, before flushing
• Sample 2: After at least 10 ml saline flush and discard protocol

All catheters will be inserted without pre-procedural filling with saline.

Blood will be collected into Vacuette® CTAD tubes (Greiner Bio-One, Kremsmünster, Austria) containing sodium citrate, theophylline, adenosine, and dipyridamole, designed for hemostatic testing. The tubes will be inverted eight times immediately after blood collection and kept at 37°C until processing. ROTEM® analysis will be performed within 3 hours of blood collection. After the ROTEM® analysis, the remaining blood will undergo centrifugation at 4000g for 15 minutes, and 600-700 µL of plasma from each sample will be transferred into cryotubes, which will be immediately frozen and stored at -80°C for further analysis.

Laboratory and ROTEM® Analyses

ROTEM® analyses will be performed on whole blood using recalcified non-activated thromboelastometry (NATEM), in accordance with the manufacturer's instructions. Each test will be run for 60 minutes, measuring the following variables:

Clotting Time (CT) - time to initial fibrin formation Clot Formation Time (CFT) - speed of thrombus development Alpha Angle (α-angle) - kinetics of clot formation Maximum Clot Firmness (MCF) - measure of final clot strength

Routine Plasma-Based Coagulation Assays:

Prothrombin Time-International Normalized Ratio (PT-INR) Activated Partial Thromboplastin Time (aPTT)

The following coagulation markers will also be assessed:

Factor VII (FVII) and Factor XII (FXII) Thrombin-Antithrombin Complex (TAT)

Inclusion Criteria

Participants must meet all of the following criteria to be included in the study:

1. Clinical indication for the placement of a two-lumen central venous catheter with length 150-160 mm.
2. Age ≥18 years.
3. Signed informed consent.

Exclusion Criteria

Participants meeting any of the following criteria will be excluded:

1. Current use of anticoagulants or platelet inhibitors, except: Prophylactic low molecular weight heparin (LMWH), double prophylactic dose of LMWH, Acetylsalicylic acid (ASA).

2. Prothrombin complex (pK/INR) outside the normal range (0.9-1.2), platelet count <50 × 10⁹/L or haemoglobin < 80 g/L, if already available.

3. Known coagulopathic conditions, including but not limited to:

   • Activated protein C (APC) resistance,
   • Hemophilia A or B,
   • Vitamin K deficiency,
   • Disseminated intravascular coagulation (DIC),
   • Antiphospholipid syndrome,
   • von Willebrand disease, Other known congenital or acquired bleeding disorders.

De-identified individual participant data (IPD) underlying the study results will be made available upon reasonable request. Data will be completely anonymized prior to sharing, in accordance with applicable data protection regulations. Requests from both academic researchers and commercial entities (e.g., device manufacturers) will be considered. All requests will undergo review to assess scientific validity and compliance with ethical standards.

Data will be available starting 6 months after publication of the primary results and will remain available for 5 years.

Access will be granted to researchers or organizations submitting a methodologically sound proposal. Approval is at the discretion of the study investigators, subject to compliance with applicable regulations and ethical considerations.

Assossors of routine and complementary coagulation assays are masked