11/21/2023 0 Comments Transcranial doppler courses![]() ![]() After the Doppler probe is placed in the transtemporal window, the anatomical points used to determine the vascular structures forming the Willis polygon are the sphenoid bone, the petrous part of the temporal bone and the cerebral peduncles. However, in clinical practice, usually only one window can be used. It is divided into three parts as the anterior, middle and posterior. The examination is made above the arcus zygomaticus through the squamous part of the temporal bone between the external auditory canal and the orbital area. Some criteria are used to define the basal arteries of the brain that constitute the Willis polygon in the TCD: (1) direction of Doppler probe and depth of insonation, (2) blood flow approaching or moving away from the Doppler probe and (3) evaluation of the response of blood flow to carotid compression in cases where it is not possible to distinguish between the anterior and posterior blood circulation ( 14). Even though each acoustic window has advantages for different arteries and indications, detailed TCD examination should include the evaluation of all acoustic windows, and the blood flow velocities of the arteries forming the Willis polygon should be examined ( 13). ![]() Acoustic windows used in the TCD application are transorbital, transtemporal and suboccipital windows ( 14). These acoustic windows are the thinnest parts of the skull bone. TCD ultrasound examination should be performed from acoustic windows where sound waves can easily pass through the skull. Low-frequency colour TCD ultrasound probe Transcranial Doppler (TCD) ultrasonography, a method used to evaluate cerebral blood flow by ultrasonography, is non-invasive, can be performed at bedside, repeatable and does not require opaque substances therefore, it is a reliable method for detecting cerebral circulatory arrest ( Table 1) ( 1, 3, 5, 8, 9). The main disadvantages of this method are the need to get the patient out of the intensive care unit and the use of contrast agent ( 4– 8). Cerebral angiography used to evaluate cerebral blood flow is accepted as the gold standard method in the diagnosis of brain death. The main limitations of the tests in which neural activity is evaluated include artefacts and being influenced from metabolic changes and drugs. Tests used to evaluate neural activity are EEG and evoked potentials. Similarly, in our country, the regulation of organ and tissue transplant services published in 2012 recommended a ancillary test that evaluates brain circulation in cases where apnoea test is not performed ( 1– 6).Ĭerebral blood flow or neural functions are evaluated with the ancillary tests used in the diagnosis of brain death. In the AAN guideline, additional testing is recommended to confirm brain death in cases where neurological evaluation is not possible. Finally, in 2010, the American Academy of Neurology (AAN) published an updated evidence-based guideline to detect brain death. The Harvard Report was first published in 1968 and was widely accepted in the medical field. They have determined in this group of patients the absence of spontaneous respiration, deep coma status, lack of reflexes, low blood pressure and loss of activity in electroencephalography (EEG).Īs a result of the developments in organ transplantation, interest in brain death has increased, and organ transplantation from the donor who had brain death in 1963 for the first time has caused the need for regulation in the diagnosis and detection of brain death. In the definition in a group of patients under mechanical ventilator support, the term ‘Le coma de passe’ was used in the same way as in the current definition. In the historical course, brain death was first defined by Mollaret and Goulon in 1959. Brain death is the irreversible loss of clinical functions of the brain and brainstem. ![]()
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