This observational study aims to identify the incidence and importance of discrepancies between measurements of intraoperative invasive and noninvasive blood pressure monitoring in patients undergoing non-cardiac surgeries under general anesthesia . The main questions it aims to answer are :

• The importance of the differences, in mmHg, between the non-invasive and invasive blood pressure measurements (NIBP-IBP) on systolic, diastolic and mean arterial pressure.
• Identify the predictive factors associated with these differences.

The monitoring of arterial blood pressure, invasively or noninvasively, is a requirement for perioperative hemodynamic and anesthesia management to optimize the administration of fluids and vasopressors. Numerous trials have highlighted the consequences of intraoperative blood pressure variability regarding the risk of serious complications and postoperative mortality associated with organ ischemia, and bleeding. Precisely, intraoperative hypotension (MAP <65 mm Hg) has been associated with cardiac complications as well as acute kidney injury. While no optimal intraoperative blood pressure targets has been established to minimize perioperative complications, a recent comprehensive literature review established recommended mean arterial pressure (MAP), and blood pressure (BP) targets within 100% to 120% of BP baseline with MAP ≥60 mm Hg if the patient presented low baseline (systolic BP <90 mm Hg or diastolic BP <50 mm Hg), and MAP within 90% to 110% BP baseline and ≈65 to 95 mm Hg for normal baseline (systolic BP 90-129 mm Hg and diastolic BP 50-79 mm Hg) patients.

Invasive blood pressure monitoring by arterial catheterization is the gold standard in intraoperative hemodynamic management. While providing continuous blood pressure readings allowing for dynamic and constant monitoring, clinically relevant transducer inaccuracies have been documented, present in up to 30% of patients. Within patients of the same study, comparison of invasive and noninvasive blood pressure demonstrated considerable overestimation of systolic blood pressure and underestimation of diastolic blood pressure.

Oscillometric blood pressure monitoring is noninvasive, quick, and effortless.Despite its convenience, the oscillometric monitoring of blood pressure does not allow for continuous blood pressure measurement, possibly delaying or missing the recognition of hypotensive episodes. Moreover, oscillometric devices can tend to inaccurately measure blood pressure in comparison to invasive monitoring methods. In intraoperative and critical care settings, studies have shown oscillometric devices' tendencies to overestimate low blood pressure, failing to accurately detect hypotensive episodes, thus demonstrating the superiority of invasive monitoring methods.

The discrepancies between invasive and noninvasive methods of blood pressure monitoring have been described in prior studies. It has been determined that noninvasive blood pressure tended to be greater than invasive blood pressure in 56.1% of systolic measurements, and 67.3% of diastolic measurements for the same patient. Furthermore, noninvasive blood pressure readings tend to overestimate mean arterial pressure for low blood pressure values, and to underestimate mean arterial pressure for high blood pressure values.

Considering the consequences associated with even short intraoperative hypotensive episodes, the discrepancies between noninvasive and invasive blood pressure monitoring are not negligible. Currently, little is known about the relation between these discrepancies and contextual elements linked to the patient or the surgery.

Therefore, this prospective observational trial aims to identify the incidence of gradients between intraoperative noninvasive and invasive blood pressure monitoring and extract key relationships between the occurrence of these gradients and the patient's comorbidity profile, the monitor's parameters and artifacts, and the perioperative chronology.

Study duration: 12 months

Study Center: Maisonneuve-Rosemont Hospital, Integrated University Health and Social Services Centre (CIUSSS) de l'Est de l'Ile de Montreal (CEMTL), University of Montreal, Montreal, Quebec, Canada.

Adverse Events: there is very little risk involved with participation in this study, side effects that may be associated with the use of intra-radial canula for invasive blood pressure measurement.

Inclusion Criteria:

• Fully consented, adult patients above 18 years old;
• Undergoing surgery of duration time expected at least 60 minutes using general anesthesia;
• Supine positioning during the surgery;
• Surgery requiring an arterial line;
• Both arms available for instrumentation during the surgery.

Exclusion Criteria:

• Atrial fibrillation, multifocal atrial tachycardia, or any other irregular hear rythm;
• Gradient of mean arterial pressure between the two arms greater than 5 mm Hg, as measured during the recruitment process.

Adult patients undergoing non-cardiac elective surgery expected to last at least 60 minutes, under general anesthesia, and to require an arterial line.