We read with interest the article by Enevoldsen and Vistisen about the predictive model of intraoperative hypotension. Regarding the criticism the authors made about what they named “gray-zone outcome,” we would like to provide some comments.

The Hypotension Prediction Index is a new parameter provided by the Hemosphere platform from Edwards Lifesciences (USA). The platform shows also other parameters: systolic, diastolic, and mean arterial pressure; the markers of fluid responsiveness (stroke volume variation and pulse pressure variation), and their ratio, dynamic elastance (pulse pressure variation/stroke volume variation ); and the increase of pulse pressure over time (dP/dt, i.e., the increase of blood pressure in one second, the slope). The latter parameter (dP/dt) is well correlated with the left ventricle elastance and reflects cardiac contractility,.2–7 

The alarm level of the index has been set by the manufacturer at 85/100, but we believe the anesthetist should check the cardiovascular...

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