Use of the Hypotension Prediction Index Algorithm (HPI) for the Prevention of Intraoperative Hypotension (IOH) in Adult Patients Undergoing Spinal Surgery: Study Protocol for a Randomized Clinical Trial

The study is a Prospective Randomized clinical trial. Adult patients (>18y) undergoing spinal surgery in the prone position under general anesthesia will be included.

The patients will be randomized using a computer-generated, permuted block randomization with a 1:1 allocation into two groups.

Intervention group: in this group, the HPI algorithm will be used in order to prevent hypotensive episodes Control group: in this group standard anesthetic care will be provided. Hypotensive episodes will be treated with vasoactive agents and fluids.

All patients will receive the same type of anaesthesia (TIVA with propofol) and monitoring including Patient State Index (PSI), non-invasive monitoring of blood pressure, SpO2, continuous electrocardiographic monitoring, ETCO2 and urinary output. Additionally, invasive continuous measurement of the patient's blood pressure will be available via radial artery catheterization. The arterial catheter will be connected to both the standard monitor and the platform which includes the HPI software. Arterial blood gas testing will be performed on an hourly basis.

Intraoperative recordings include PSI values, hemodynamic parameters every 10-15 minutes and urinary output every hour. Hemodynamic parameters will also be collected electronically from the monitor. The total doses of propofol, opioids/sedatives, fluids and vasoactive agents will also be recorded, as well as the estimated blood loss.