The goal of this clinical trial is to demonstrate the importance of arterial pressure measurement sites during major abdominal surgeries. This randomized controlled trial will compare arterial pressure measurements obtained from radial artery catheterization (the current standard method of monitoring) with those obtained from brachial artery catheterization (a more accurate reflection of central arterial pressure). At the end of the study, we are looking to answer the following questions:

1. Does arterial pressure measurement sites influence the amount of vasopressors that is administered during major abdominal surgeries?
2. What are the instances where there is a difference between peripheral (radial catheter) and central (brachial catheter) monitoring and what are the risk factors leading to the appearance of this radial-brachial pressure gradient?
3. With the data collected, can artificial intelligence based analysis help predict the reliability of a radial monitoring and help guide clinicians on choosing a peripheral versus central arterial pressure monitoring site? All adult participants who are scheduled for elective major abdominal surgeries and meeting our inclusion criteria will be approached and included if they consent. Participants will be randomized 1:1 in the intervention group and the standard of care group. In the intervention group, the brachial arterial line will be used intraoperatively to guide vasopressor and fluid administration. A radial line will also be installed to measure the radial arterial pressure simultaneously, but will not be used to guide hemodynamic management. In the standard of care group, both lines will be installed just like in the intervention group, however, it is the radial arterial line that will guide fluid and vasopressor administration. In both groups, the anesthesia protocol will be standardized and the anesthesiologist will be blinded to the arterial pressure measurement site.

Inclusion Criteria:

• Patients between 18 and 90 years of age;
• Major abdominal surgery via laparoscopy or laparotomy under general anesthesia - with or without concomitant use of regional or neuraxial anesthesia;
• Expected anesthesia time of more than 120 minutes.

Exclusion Criteria:

• Known peripheral severe vascular disease with subclavian artery stenosis,
• Significant arterial gradient between arms with preoperative non-invasive bloop pressure measurements (>25 mm Hg of systolic blood pressure or 10 mm Hg of mean arterial pressure);
• Inability or contraindications to insert arterial line on either arm (arteriovenous fistula, surgical sterility);
• Known allergies, intolerance, other medical conditions that precludes the use of prescribed general anesthesia protocol for this trial;
• Inability to communicate in French or English.

IPD might not be shared depending on the ethical consideration of sharing the information. We are currently working on a central database for perioperative research data collected at our institution, which will structure all IPD. Depending on the advancement of this initiative, we might enable IPD.