An Observational, Prospective, Non-randomized Multi-centre Cohort Feasibility Study of the Hypotension Prediction Index (HPI) in Patients Undergoing Lung Resections With the Use of One-lung Ventilation.

The Hypotension Prediction Index (HPI) is a hemodynamic score designed specifically for prediction of the intraoperative hypotension (IOH) episodes. It is based on an algorithm programmed into Edwards Lifesciences HemoSphere monitor clinical platform (Irvine, CA, USA). The HPI is based on a continuous analysis of an arterial pressure waveform. It is processed in addition to the FloTrac algorithm via proprietary Acumen IQ Sensor and uses an artificial intelligence technology. After internal validation, the algorithm was prospectively, externally and clinically validated in general surgical, perioperative patients, cardiovascular surgical patients, and mechanically ventilated COVID-19 ICU patients.

As opposed to conventional monitoring systems, which display physiological parameters in real life, an HPI algorithm detects the earliest changes, multivariate variability and interactions in the physiologic inter-related data on preload, afterload, and contractility to deliver an index predicting an upcoming hypotensive event. Variables used by the patent-protected algorithm to calculate HPI are as follows: heart rate variability (changes in heart rate/changes in MAP); arterial pressure waveform complexity (approximate waveform entropy, sample waveform entropy, frequency domain measure of higher order harmonics); preload parameters (pulse pressure variation PPV, stroke volume variation SVV); contractility parameters (slope of the ascending part of the pressure waveform above time, dP/dt); and afterload parameters (SVR, dynamic arterial elastance Eadyn), but their relative contribution to final index is not revealed.

Final index values of HPI range from 1 to 100, with increasing numbers representing a greater likelihood of an impending hypotensive event. These events are defined as mean arterial pressure (MAP) <65 mmHg occurring for over one minute. HPI values predict the occurrence of hypotension five to fifteen minutes before the event, with sensitivity and specificity in both time-frames of greater than 80%. In most studies, a value of 85 HPI predicts a hypotensive episode, and this value is arbitrarily preprogrammed into the HemoSphere monitor to alert the clinician and allow proactive responses to minimize or even entirely prevent intraoperative hypotension.

Parameters used and incorporated into the HemoSphere monitor can guide a clinician in the optimal management of IOH. These "secondary screen" variables include the left ventricular contractility parameter (dP/dt), dynamic preload parameter (SVV) and afterload parameter dynamic arterial elastance Eadyn.

Maximal left ventricular (LV) pressure rise (LV dP/dt max) is a classical marker of LV performance and systolic function. It is conventionally defined as the change in pressure in the left ventricular cavity over the isovolumetric contraction period and it originally requires LV catheterization. In clinical practice a surrogate peripheral arterial pressure waveform is used to estimate dP/dt value and to predict the need for inotropic support.