It has been a pleasure to read Dr. Blanco's work,1 “Cerebral circulatory arrest detected by insonation of extracranial arteries”. We know that brain death (BD) diagnosis with doppler of extracranial arteries is accepted in other countries,2 and we believe it is a useful alternative that could be considered as complementary evidence, added to clinical neurological examination. However, we would like to add two comments:

First, we believe that it is important to emphasize that the phenomenon pursued with the flow tests in BD is derived from the theory of Monro-Kelly, in which it is assumed that the intracranial content (central nervous system, cerebrospinal fluid and blood) is constant. The disruption of this equilibrium, taken to the extreme, is what causes cerebral circulatory arrest at this level. In this sense, the assessment of extracranial vessels should not replace other techniques used to complete the instrumental diagnosis of BD, such as transorbital doppler or duplex color with or without contrast, which confirm the absence of intracranial flow, the true pathophysiological responsible for the onset of the brain death process.

Secondly, we want to point out that the use of confirmatory tests in BD aims, among other objectives, to avoid the diagnostic delay that could happen if you only refer to clinical examinations. In the case presented by Dr. Blanco, he talks about a period of observation of 16h until the extracranial diastolic flow inversion pattern is captured.

Therefore, although we thank Dr. Blanco for his advice, we believe it is appropriate to recommend other BD confirmatory alternatives before using the extracranial artery flow analysis.