Prone Positioning for Brain-injured Patients With Severe ARDS (ProBrain)

"TCD ultrasonography is based on the principle of the Doppler effect. According to this principle, ultrasound waves emitted from the Doppler probe are transmitted through the skull and reflected by moving red blood cells within the intracerebral vessels. The difference in the frequency between the emitted and reflected waves, referred to as the Doppler shift frequency, is directly proportional to the speed of the moving red blood cells (blood flow).~Cerebral blood flow (in cm/s) of the middle cerebral artery will be measured with TCD in blood-injured ARDS patients before and one hour after prone positioning (normal ranges: 48 to 72 cm/s)."