The goal of this observational study is to describe characteristics of catheter related thrombosis (CRT) that persists after catheter extraction in condition of intensive care unit. The main questions it aims to answer are:

1. What is the incidence of CRT that persists after catheter extraction in patients hospitalized in the intensive care unit?
2. What are the risk factors for this phenomenon?
3. What is the fate of such a thrombus, including recanalization or the development of complications such as pulmonary embolism or post-thrombotic syndrome?

Thrombosis associated with an indwelling central venous catheter (CRT) is a significant phenomenon associated with intensive care. Its incidence can reach up to 41% in intensive care units despite adequate thromboprophylaxis. It manifests itself as the formation of a fibrin coating, thrombotic occlusion of the catheter, mural thrombosis, or complete venous thrombosis. CRT is a frequent reason for catheter removal. However, in these situations, it is not possible to reliably predict the fate of the thrombosis - whether embolization of the thrombus occurs, its removal together with the extracted catheter, or its persistence in the venous bed. Based on our previous clinical observations and studies, it can be stated that in some patients the thrombus is fixed not only to the catheter itself, but also to the venous wall at the site of catheter insertion. After its extraction, the thrombus may persist in the lumen of the vein at the site of the original puncture. The issue of CRT is almost unexplored in the field of intensive care. There are no reliable data on the true incidence of CRT (which is probably underestimated), nor are there standardized recommendations on how to deal with proven thrombosis, what risks it poses to the patient, and whether it is appropriate to perform targeted CRT screening. It is particularly important to identify how often CRT persists after catheter removal, as these patients may be candidates for anticoagulant treatment. Although this fact can significantly influence the therapy strategy both during the ICU stay and after discharge from intensive care, it is a phenomenon that has not been described in detail in the literature. Therefore, we decided to conduct a prospective observational study in which we want to address this specific problem.

Main objectives of the study:

1. To determine the incidence of venous thrombosis associated with an indwelling central venous catheter that persists in the vein after catheter removal.
2. To describe the detailed characteristics of this phenomenon in terms of risk factors for thrombosis depending on the type of catheter, insertion site, duration of insertion, and other demographic and clinical parameters. 3. To describe the course of subsequent recanalization of the thrombus and the occurrence of potential complications of thrombosis.

Inclusion Criteria:

• age over 18 years
• ICU hospitalization
• signed informed consent
• an indwelling central venous catheter planned for extraction

Exclusion Criteria:

• age under 18 years
• local pathology precluding ultrasound examination
• disagreement with participation in the study

The clinical study will include all adult patients with an indwelling central venous catheter hospitalized at the Department of Anesthesiology, Perioperative and Intensive Care Medicine of the Masaryk Hospital in Ústí nad Labem, in whom catheter removal is planned regardless of the cause, and who agreed to participate in the clinical study.

The data will be available after publishing the study. The data will be available for 10 years.

Data will be accessible publicly in university data repository.