The purpose of this study is to assess validity of extended duplex ultrasound examination for diagnosis of proximal deep vein thrombosis performed by general intensive care unit nurses in the critically ill patients.

Critically ill patients hospitalized in the intensive care unit are in increased risk of proximal deep vein thrombosis despite thromboprophylactic measures. Diagnostic method of the first choice is Point-of-Care ultrasound examination. This method is usually performed by a trained intensive care physician. However, if this examination could be performed by trained nurses, its availability would be greatly increased. The results of the investigator's pilot study showed that general nurses are able to diagnose proximal deep vein thrombosis in critically ill patients by compression ultrasound test with a sensitivity of 88,9 % and a specificity of 99 %. Before implementation of this examination into the optional competencies of general nurses, the results need to be confirmed in a larger group of patients. This is the goal of proposed clinical study.

In this prospective observational study, the patients will be investigated by extended duplex ultrasound (compression ultrasound test combined with colour doppler imaging in the range from the groin to the popliteal region) by a trained nurse and on the same day, the examination will be repeated by a trained physician - intensivist. The results of the examinations of each patient will be blinded until both tests will be performed.

Inclusion Criteria:

• Inpatients
• Critically ill patients hospitalised in the intensive care unit for more than 72 hours

Exclusion Criteria:

• Known deep vein thrombosis
• Contraindication of ultrasound examination
• Refusal of ultrasound examination by patient

Adult critically ill patients.