Near Infrared Spectroscopy (NIRS) as Transfusion Indicator in Neurocritical Patients

Neurocritical ill patients are frequently transfused. Red blood cell transfusion (RBCT) in these patients has been associated with deleterious effects, including higher rates of nosocomial infections, multi-organ failure, and mortality. Therefore, it seems crucial to avoid any unnecessary RBCT. Most critically ill patients tolerate hemoglobin levels near 7 g/dL without an increase in morbidity or mortality rates. In this regard, a recent sub-analysis of TRICC trial has showed that TBI patients may tolerate hemoglobin levels as low as 7 g/dL, but other studies including neurocritical patients suggested that severe anemia may worsen clinical outcome. Therefore, optimal hemoglobin levels in neurocritical care patients remain largely unknown. Some textbooks and guidelines recommend to transfuse these patients to reach hemoglobin levels near to 10 g/dL, despite the lack of a solid scientific background supporting this target. Even though it has not been demonstrated, hemoglobin-based RBCT prescription could result in over- or under-transfusion in neurocritical patients. Alternatively, it has been suggested that more physiological transfusion triggers, using direct signals coming from the brain, will progressively replace arbitrary hemoglobin-based transfusion triggers in the neurocritical patients [65]. At the neurocritical units, patients are often monitored by using non-invasive methods, such as near infrared spectroscopy which indirectly measures regional cerebral oxygen saturation (rSO2). Changes in rSO2 values have been shown to directly correlate with changes in erythrocyte mass, thus increasing with RBCT and decreasing with blood losses. Moreover, rSO2 values also show a good correlation with clinical outcome and other variables which are often monitored in TBI patients. The purpose of this study is to ascertain as to whether rSO2 levels are more efficacious than conventional hemoglobin levels in guiding RBCT in patients admitted to a neurocritical care unit.