The Trend above shows the importance of automated trending when performing TCD exams. The PI may give you a day or two heads up as to the direction a patient may be trending. This can be life saving! The pulsatility index (PI) and resistant index (RI) are calculated from TCD parameters as follows: PI (PSV–EDV)/mean CBFV and RI (PSV–EDV)/PSV (Table 2).The pulsatility index is an indicator of amount of vascular resistance in distal intracranial pressure and it is used as indirect evaluation of intracranial pressure when ICP exceeding
20 mmHg. It is also found that there is a good correlation between ICP and RI but this correlation is less sensitive than PI. It should also be noted that PI is less effected by angle and therefore it is a very reproducible measurement when comparing exams over time.