This clinical investigation will investigate whether Hypotension Decision Assist (HDA) is a feasible, safe and effective patient clinical decision support system to enhance an anaesthetist's ability to manage a patient's cardiovascular system when undergoing surgery. If successful, this study will provide evidence that the use of HDA facilitates beneficial outcomes for patients who have this device used.

In this study participants who are due to undergo elective major surgery and have an arterial line as part of their standard care will be invited to have the additional monitoring device (HDA) included as part of their care. Agreeing participants will have demographic, contact and medical history information necessary to conduct the study recorded, including a record of their intraoperative arterial line measurements.

After completing the consent process participants will receive intraoperative monitoring with Hypotension Decision Assist in addition to their standard care. The HDA monitor will be attached to the patient vital signs monitor, which will in turn be attached to the blood pressure transducer. All sampled arterial line data collected by the patient vital signs monitored will be automatically transmitted in real time to the HDA device via a serial cable attached to a digital export port of the vital signs monitor. HDA will process this input data to display, in graphical and numeric format, vital signs data and physiological parameters derived from the arterial wave form data including: Mean Arterial Pressure (MAP), systolic and diastolic blood pressure, heart rate and changes in heart rate, cardiac output and systemic vascular resistance.

The output from the study will be compared to the primary and secondary outcomes to evaluate the performance and safety of the device and to evaluate whether HDA improves control of the cardiovascular system from the anaesthetists' perspective.

Inclusion Criteria:

• Adults (≥18 years) due to undergo elective surgery who are likely to have an arterial line sited as part of their standard intraoperative care.
• Recruitment after booking for surgery with sufficient time to read, understand and question study patient information prior to attending for surgery.
• Ability and willingness to provide informed consent
• Expected duration of anaesthesia > 60 minutes
• Intra-arterial monitoring is part of routine clinical care

Exclusion Criteria:

• Inability to provide informed consent
• No arterial line planned as part of their intraoperative care
• Aged < 18 years of age
• Patients with aortic regurgitation
• Patients fitted with an intra-aortic balloon pump (IABP)
• No other intra-arterial pressure management system in use
• Concurrent participation in another experimental intervention or drug study