Determination of CPPopt in two exemplary patients. The pressure reactivity index (PRx) is plotted against cerebral perfusion pressure (CPP). PRx values >0.2 indicate impaired pressure reactivity. Patient (A) reaches the PRx minimum for CPP values around 103 mmHg (black star). The patient (B) has the optimal CPP around 87 mmHg (black star). Error bars indicate standard errors.