**8. Conclusion**

Cerebral circulatory changes are often found in ICU daily practice and can lead to secondary tissue damage. Hypoxia, ischemia, intracranial hypertension, traumatic brain injury, stroke, kidney or liver failure, and sepsis can impair CAR. Since CAR mechanisms have been impaired, CBF passively follows MAP changes, which in turn compromise CPP.

A number of factors can influence the CBF and its regulation, so the monitoring and control of these factors by TCD can help adjust CBF to brain metabolic demands.

TCD has the advantage of allowing bedside access to brain hemodynamic modifications, whether intermittent or serial and continuous monitoring. The disadvantage of the method is given by operator dependence and intensive training requirement, so that it can be applied in practice by physicians with clinical expertise in various primary or systemic diseases that affect the CNS.
