The first image is taken from the transtemporal window and shows the middle cerebral artery with colour doppler and the pulse-wave doppler gate overlying the vessel. The following still image shows the resultant doppler flow pattern. As you can see the doppler flow ranges from 35cm/s to 70cm/s and is always positive, suggesting that blood flow is constant (during systole and diastole) and towards the ultrasound transducer. This is the flow pattern in a normal MCA flow state. By tracing the envelope of one cycle we can obtain the pulsatility index (PI). The PI is a numeric representation of the difference between the systolic and diastolic velocity which tends to increase as ICP increases. Clinically the PI can be used to estimate ICP, as was shown by Bellner at el, 2004. Their study found a correlation coefficient of 0.938 using the following equation ICP = [10.93 X PI] – 1.28. Using this equation our patient’s ICP would be estimated at 5.5mm Hg. Click here for a clinically relevant review of TCD applications for the intensivist. Based on this POCUS study and the incongruent results with the ICP monitor, the patient had a repeat CT scan of the brain which showed a decrease in the generalized brain edema, and less sulcal effacement from the date of admission. As such the ICP monitor was felt to have malfunctioned and was subsequently removed. The image below is the TCD of a patient with multiple strokes, dilated pupils and shows diastolic flow reversal which suggests impending cerebral circulatory arrest.