[Transcranial Doppler in anesthesia and intensive care].

Transcranial Doppler sonography (TCD) is a non invasive technique whereby ultrasonic signals may be recorded from the basal cerebral arteries by using a low frequency probe. Three routes can be used: the transtemporal approach, which studies the anterior, middle and posterior cerebral arteries; the transorbital approach, which evaluates the ophthalmic artery and the carotid canal; and the sub-occipital approach, which assesses the basilar, posterior cerebral and intracranial vertebral arteries. Normal reference values for Doppler parameters have been established for these arteries. Many factors influence them, such as the diameter of the examined blood vessel, PaCO2, cerebral blood flow and cerebrovascular resistances. There are numerous clinical applications of TCD. In anaesthesia, monitoring with this method is useful during cardiopulmonary bypass, controlled hypotension, or carotid endarterectomy. After subarachnoid haemorrhage, the degree of vasospasm can be assessed by TCD. Monitoring cerebral blood flow velocities in intensive care provides important information for the treatment of patients suffering from meningitis, or experienced a head injury, or another ischaemic-anoxic disease. The field of clinical applications of TCD is increasing greatly, but the results must always be carefully interpreted, taking into account the data of other investigations.