The study has been stopped due to technical difficulties.

Passive leg raise (PLR) and fluid challenge are useful tools in assessing the fluid responsiveness. However, they require continuous monitoring of cardiac output, which is usually an invasive technique and in some cases not always available. Vascular ultrasound can be an alternative to cardiac output monitoring in a fluid status evaluation. The common carotid artery (CCA) is an easily accessible vessel. It has recently been noted that the diameter of this artery changes after an intravenous fluid bolus. It is possible that the change in the diameter of the common carotid artery during passive leg raise and fluid challenge can be a predictor of fluid responsiveness.

Inclusion Criteria:

• mechanically ventilated patients with circulatory failure, who are monitored with PiCCO and need fluid responsiveness assessment

Exclusion Criteria:

• contraindication for the volume administration (hydrostatic pulmonary edema or other evidence of fluid overload)
• contraindication for PLR test (e.g. after trauma)
• lack of possibility to examine the carotid arteries
• bilateral carotid surgery in the past
• bilateral anatomical defects of the carotid arteries
• unstable cardiac rhythm (e.g. atrial fibrillation)

Mechanically ventilated patients admitted to critical care unit.