Assessment of capillary refill time (CRT) is a cornerstone of tissue perfusion monitoring in critically ill patients.

CRT measurement is performed by applying brief and gentle pressure (for a few seconds) to a small area of skin until blanching occurs. CRT is defined as the time, in seconds, required for the skin surface to return to its initial color after release of pressure.

Although CRT is a monitoring tool used on a daily basis in emergency departments and critical care units, its practical measurement modalities remain poorly standardized and time-consuming. Consequently, there is no consensus regarding the most reproducible bedside method for CRT assessment. Moreover, repeated CRT measurements during patient management are resource-intensive in terms of medical time and may raise issues related to healthcare staff availability.

The perfusion index (PI) is a marker of tissue perfusion derived from a pulse oximetry sensor. This monitoring device is routinely used in all critically ill patients. It is placed on the finger and worn continuously, including during patient transport.

Because PI measurement is automatic and continuous, establishing its correlation with CRT could allow for more precise tissue perfusion monitoring while reducing the time burden associated with bedside assessments in critically ill patients.

Inclusion criteria :

• Adult patient.
• Admission within the previous 24 hours, or within 24 hours of the onset of a hemodynamic instability criterion (requirement for vasopressors or fluid resuscitation).
• Absence of patient objection.

Exclusion criteria :

• Legal guardianship, curatorship, or judicial protection.
• No social security coverage.
• Morphological abnormalities preventing CRT and IP measurements.

Patients admitted to a University Hospital, either to a medical or surgical intensive care unit.