There is increasing evidence that renal replacement therapy (= continuous veno-venous hemodialysis) generates cerebral microembolism which is detectable on transcranial Doppler ultrasound.

The aim of this study is to monitor patients with transcranial Doppler under two conditions: during hemodialysis and in a hemodialysis-free interval (in each period cerebral embolic load is detected during 30 minutes).

The study hypothesis is that during hemodialysis the cerebral embolic load is significantly higher than in the hemodialysis-free interval.

Inclusion Criteria:

• Renal replacement therapy (continuous veno-venous hemodilalysis) on the in-house intensive care unit
• Age > 18yrs and < 90yrs

Exclusion Criteria:

• Absent informed consent
• Preexistent neurological morbidity
• Neurocognitive disturbances
• Carotid artery stenosis > 70%
• Patent foramen ovale
• Treatment with other extracorporeal devices
• Cardial pathology (valvular heart disease, prosthesis, endocarditis)
• Pregnancy, drug abuse
• Inclusion in an other clinical study
• Allergy against materials of the medical device used in the study (transcranial Doppler) or temporal skin/bone lesions

The study population incloses patients who are in renal failure needing renal replacement therapy under intensive care conditions.