Transcranial Doppler ultransonography as a confirmative diagnostic test in brain death: a review

Before the invention of modern technologies death was defined as the cessation of cardiac and respiratoty functions. After the advances in mechanical ventilation and cardiopulmonary resucitation techniques the term “brain death” has been used instead and with the worldwide increase in cadaveric organ transplantation this term has increasingly gained importance. Brain death is a state which is diagnosed by neurological examination in patients who fulfill some specific criteria. In patients who cannot be examined thoroughly or in whom an apnoea test cannot be performed a confirmatory test is mandatory. Diagnostic tests for brain death can either be those who show neural activity or those who evaluate cerebral circulation. The cause that leads to the development of brain death is cessation of cerebral blood flow therefore diagnostic tests which evaluate the cerebral circulation are preferred in brain death. Transcranial Doppler ultrasonography steps forward among diagnostic tests that evaluate cerebral circulation because it is non-invasive, repeatable and can be performed at bedside. In order to use transcranial Doppler ultrasonography in the diagnosis of brain death one has to have very good knowledge about the effects of increasing intracranial pressure on the Doppler spectra and the various spectral forms of cerebral circulatory arrest. In this review the utility of transcranial Doppler ultrasonography in the diagnosis of brain death will be discussed.