The present study was designed to assess, in a population of patients admitted to the intensive care unit and already carrying an indwelling arterial catheter, the ability of combined continuous (ClearSight™) and intermittent (automatic cuff) non-invasive monitoring to detect low mean BP (<65mmHg). The intra-arterial measurement will be the reference measurement. As secondary objectives, the investigators will assess the ability of combined continuous (ClearSight™) and intermittent (automatic cuff) non-invasive monitoring to detect stage 2 hypertension, and to detect changes in BP during a cardiovascular intervention (as clinically indicated but not imposed by the study protocol). Additionally, the accuracy of both devices against the current international standard (ISO standard) will be assessed.

The measurement of arterial blood pressure (BP) is of paramount importance when caring for critically ill patients, as BP, especially mean BP, is the driving force of blood flow through all the organs. The reference method is the invasive method that measures BP continuously and directly in an artery (most often the radial artery), through an indwelling arterial catheter. A popular, less invasive method, most often used in emergency situations or during the first hours of care in the intensive care unit (ICU), is the non-invasive oscillometric method (NIBP) using an arm cuff (some have shown that the cuff could also be placed around the calf, just above the ankle), that provides only intermittent measurements. In between the above 2 techniques, the place of continuous non-invasive BP monitoring devices using a different technology (plethysmography and volume clamp technique) and a cuff placed around a finger is uncertain. It would be interesting to evaluate whether the 2 non-invasive techniques (using arm or finger cuff) can be advantageously combined either to replace invasive monitoring or to reinforce non-invasive monitoring (in patients in whom an arterial catheter is not envisaged). In the critically ill patient, reliable detection of low BP is often the most important task assigned to BP monitoring devices, at least in the initial phase of management. It is conceivable that if the finger cuff (ClearSight™ device) was not infallible in measuring BP, low BP could still be detected sufficiently reliably by the finger cuff (even with weak accuracy), giving an early warning. The arm measurement could then confirm hypotension in a robust, on-demand manner, since the ability of the arm cuff to detect hypotension has already been demonstrated. The ability to detect hypotension using a combined non-invasive approach (finger and arm cuff) has never been explored with the ClearSight™ device. This combined approach could similarly detect high blood pressure or a rapid change in BP as a result of cardiovascular intervention. In addition, the automatic cuff cannot always be placed around the arm (presence of wounds, burns, fractures or surgery of the upper limb, venous catheter, etc.) for intermittent NIBP measurements, and is then placed around the calf. However, this commonly observed practice exposes the NIBP measurement to less accuracy. The finger cuff could be an alternative to the calf cuff. However, the accuracy of finger measurement has never been compared to the accuracy of oscillometric measurement at the calf.

Inclusion Criteria:

• Patient hospitalised in one of the three recruiting intensive care units
• Patient already carrying an indwelling arterial catheter
• Stable BP over a 5-min period: no variation of mean BP above 10% and no change in vasopressor therapy

Exclusion Criteria:

• Brachial circumference > 42 cm.
• Any local fracture, wound, ischemic injury, infection, amputation, thrombophlebitis, that could prevent inflating a cuff around the arm or a finger
• Need of emergency therapy not compatible with the BP measurements schedule
• Asymmetry of mean BP between right and left arm (> 5 mmHg)
• Pregnancy
• Age < 18 years
• Patient under curatorship or guardianship