Patients allocated to the HPI group will receive haemodynamic monitoring using the Acumen IQ sensor (Edwards Lifesciences, Irvine, CA, USA) connected to the radial arterial line. The Acumen IQ system provides all parameters available with the FloTrac sensor, plus additional advanced metrics including dynamic arterial elastance (Ea_dyn), the rate of ventricular pressure change (dP/dt), and the Hypotension Prediction Index (HPI).

The HPI is a machine learning-derived value ranging from 0 to 100 that represents the probability of MAP falling below 65 mmHg within the next 15 minutes. When HPI exceeds 85, the system generates an alert and displays a secondary screen presenting real-time haemodynamic parameters and suggested interventions. Haemodynamic management in the HPI group will follow a structured protocol incorporating both predictive (HPI-triggered) and reactive (MAP-based) components.

Patients allocated to the FloTrac group will receive haemodynamic monitoring using the FloTrac sensor (Edwards Lifesciences, Irvine, CA, USA) connected to the radial arterial line. The FloTrac system provides continuous measurements of cardiac output (CO), cardiac index (CI), stroke volume (SV), stroke volume index (SVI), stroke volume variation (SVV), systemic vascular resistance (SVR), and systemic vascular resistance index (SVRI) based on arterial pressure waveform analysis.

Haemodynamic management in the FloTrac group will follow a structured protocol designed to maintain MAP ≥ 75 mmHg while avoiding excessive hypertension (target MAP ≤ 100 mmHg).

The investigators hypothesise that HPI-guided haemodynamic management, when implemented with protocol refinements to mitigate hypertensive overcorrection, will reduce the burden of intraoperative hypotension compared with standard APCO monitoring in patients undergoing major abdominal aortic surgery. Secondary objectives include evaluation of postoperative organ injury, assessment of intraoperative hypertension as a safety outcome, and characterisation of fluid and vasopressor requirements. By testing this hypothesis in a rigorously designed, adequately powered trial, the investigators aim to clarify whether predictive haemodynamic monitoring offers clinically meaningful advantages over current reactive approaches in this high-risk population.

The primary outcome is the time-weighted average of mean arterial pressure below 65 mmHg (TWA-MAP < 65 mmHg) during the period from induction of anaesthesia to departure from the operating theatre.

At least one of the following:

• Acute kidney injury (AKI) according to KDIGO criteria

• Myocardial injury after non-cardiac surgery (MINS), defined as troponin elevation ≥ assay-specific 99th percentile upper reference limit

• Stroke (new focal neurological deficit confirmed by neuroimaging)

• Postoperative respiratory failure will be defined as a composite endpoint reflecting clinically relevant impairment of gas exchange or ventilation in the early postoperative period. It will be considered present if at least one of the following criteria is met within 7 days after surgery or before ICU discharge:

  1. Prolonged invasive mechanical ventilation, defined as failure to extubate within 48 hours after the end of surgery;
  2. Unplanned reintubation with initiation of invasive mechanical ventilation due to respiratory failure (hypoxaemia, hypercapnia, or inability to maintain adequate ventilation) after initial extubation; or
  3. Unplanned initiation of non-invasive ventilation or high-flo