In critically ill patients, optimized strategies for red blood cells transfusion (RBCT) are still controversial. Most recent guidelines suggest that clinical practice in ICU setting should follow a restrictive approach to RBCT (i.e., hemoglonim level < 7.0 g/dL).In our previous study, oxygen extraction ratio (O2ER) has shown good performance as a marker to identify the correct timing for RBCT, potentially affecting 90-day mortality in non-bleeding, critically ill patients [11]. Moreover, our data suggested that an individualized strategy for RBCT may reduce the incidence of acute kidney injury (AKI), which is possibly related to a better delivery of oxygen and organ perfusion.

Inclusion Criteria:

• Hb levels ≤ 9.0 g/dL (as confirmed through a blood test and/or through blood gas analysis)
• Presence of an arterial line and a central venous line (either jugular or subclavian), with confirmed correct position of the catheter tip at the atrio-caval junction (allowing correct estimation of central venous saturation, ScvO2).

Exclusion Criteria:

• Age < 18 years;
• Pregnancy
• Clinical evidence of acute bleeding
• Diagnosis of haematological malignancy
• Diagnosis of sickle cell disease, or other diseases exposing the patient to chronic RCBTs
• Acquired or congenital disorders of coagulation
• Patients with ongoing AKI of stage 1 or worse and/or known chronic kidney disease (CKD) of stage G3a or worse, defined as glomerular filtration rate below 60 for a minimum of 3 months

To be shared under reasonable requests.