For accurate measurements of arterial blood pressure (BP), international guidelines recommend placing the automated oscillometric cuff directly on the bare upper arm. However, for various reasons, cuffs are often applied over a layer of textile. Whether this practice affects the reliability of the readings remains uncertain. Using a rigorous methodology, the CASBA study aims at addressing this issue.

Additionally, two different BP measurement algorithms are available in some oscillometric monitors. To our knowledge, no study has compared the performance of these two algorithms. This study will help determine which oscillometric algorithm should be given priority in intensive care facilities.

The automated oscillometric cuff is the predominant non-invasive method for measuring BP. For accurate measurements, international guidelines recommend placing the cuff directly on a bare upper arm. However, for reasons of convenience, hygiene, comfort, cultural or religious practices, or skin reactions, cuffs are often applied over a layer of textile. Some authors suggest this practice does not significantly affect BP readings, while other authors are more cautious or even advise against it. Prior studies are not devoid of limitations. Further research into sleeve effects on BP measurement accuracy is warranted. The present study project employs rigorous methodology and leverages invasive arterial catheters for reliable reference measurements. Additionally, the broad range of BP levels in surgical intensive care units ensures comprehensive data, including mean, systolic, and diastolic BP (MBP, SBP, and DBP).

Additionally, some oscillometric monitors incorporate two reference algorithms for BP measurement:

• Auscultatory Reference Algorithm: Calibrates oscillometric measurements to align with manual cuff and stethoscope values. This is the default setting.
• Invasive Reference Algorithm: Adjusts non-invasive BP values to approximate invasive measurements.

Health care providers are, in our experience, rarely aware of the existence of these two distinct algorithms. Although the reference auscultatory algorithm is generally recommended for routine non-invasive monitoring, such as at home or in a clinic, the invasive reference algorithm might be preferable in critical care settings. Importantly, in the absence of published studies on the subject, these considerations remain speculative.

However, it is important to determine which oscillometric algorithm should be prioritized in critical care settings, where invasive measurement serves as the reference. This will be a secondary objective of this study.

Inclusion Criteria:

• - Patients having a catheter in the radial artery.
• and with stable BP over a 5-min period (no change in invasive MBP >10% and no change in vasoactive drugs)

Exclusion Criteria:

• - Cardiac arrhythmia.
• Dysfunctional of the arterial catheter or waveform, suggesting signal over- or under-damping.
• Arm circumference > 42 cm (measured at mid-arm).
• Contraindication to BP measurement on the arm (fracture, wound, amputated limb, limb ischemia, infection, phlebitis, history of lymph node dissection, venous access on the limb preventing cuff inflation, other).
• Patient's health status requiring urgent care incompatible with study protocol.
• Asymmetry of MBP between the two arms (>5 mmHg) or inability to check it.
• Pregnant woman.
• Age <18 years old.
• Adult known to be under guardianship or legal supervision before inclusion.
• Absence of social security coverage.
• Non-French speaker patient (i.e. unable to receive study information)

Patients of a surgical intensive care unit having an arterial catheter