RBC Transfusion Improves Cerebral Oxygen Delivery in Subarachnoid Hemorrhage

Abstract

Objective Impaired oxygen delivery due to reduced cerebral blood flow (CBF) is the hallmark of delayed cerebral ischemia (DCI) following subarachnoid hemorrhage (SAH). Since anemia reduces arterial oxygen content, it further threatens oxygen delivery increasing the risk of cerebral infarction. Thus, SAH may constitute an important exception to current restrictive transfusion practices, wherein raising hemoglobin could reduce the risk of ischemia in a critically hypoperfused organ. In this physiologic proof-of-principle study we determined whether transfusion could augment cerebral oxygen delivery, particularly in vulnerable brain regions, across a broad range of hemoglobin values. Design Prospective study measuring CBF and oxygen extraction fraction (OEF) using 15O-PET. Vulnerable brain regions were defined as those with baseline oxygen delivery < 4.5 ml/100g/min. Setting PET facility located within the Neurology/Neurosurgery Intensive Care Unit. Patients 52 patients at risk for DCI after aneurysmal SAH with hemoglobin 7–13 g/dl. Interventions Transfusion of one unit of red blood cells (RBCs) over one hour. Measurements and Main Results Baseline hemoglobin was 9.7 g/dl (range 6.9–12.9) and CBF was 43±11 ml/100g/min. After transfusion, hemoglobin rose from 9.6±1.4 to 10.8±1.4 g/dl (12%, p < 0.001) and oxygen delivery from 5.0 (IQR 4.4–6.6) to 5.5 (4.8–7.0) ml/100g/min (10%, p=0.001); the response was comparable across the range of hemoglobin values. In vulnerable brain regions, transfusion resulted in a greater (16%) rise in oxygen delivery associated with reduction in OEF, independent of Hgb level (p=0.002 vs. normal regions). Conclusions This study demonstrates that RBC transfusion improves cerebral oxygen delivery globally and particularly to vulnerable regions in SAH patients at risk for DCI across a wide range of hemoglobin values and suggests that restrictive transfusion practices may not be appropriate in this population. Large prospective trials are necessary to determine if these physiologic benefits translate into clinical improvement and outweigh the risk of transfusion.

Differential cerebral hemometabolic responses to blood transfusions in adults and children with sickle cell anemia

“…Prior work with PET has demonstrated that blood transfusions reduce OEF in anemic patients with subarachnoid hemorrhage along a similar physiological mechanism as proposed in this study (ie, increase in oxygen content of blood without a decrease in blood flow) . Previous work in SCA using 133 Xenon inhalation found reduced CBF in a small cohort ( n = 2) of patients after transfusion therapy compared with nontransfused patients, but the posttransfusion CBF remained higher than in age‐matched control volunteers .…”

Regional cerebral tissue oxygen saturation changes following blood transfusion in neuro‐intensive care unit patients – a pilot observational study

“…In this regard, physicians are attempting to incorporate other physiological parameters like ScvO 2 to decide on RBC transfusion. In a prospective study, cerebral blood flow and metabolism were studied, using 15 O 2 positron emission tomography-computerized tomography (PET CT), in 42 SAH patients requiring single-unit pRBC transfusion (Dhar et al, 2017). Patients had a baseline haemoglobin of 7-13 g dL −1 .…”

Lessons from the CONSCIOUS-1 Study

“…Anemia and transfusion are common after aSAH and were reviewed by Leroux [ 53 ]. Hemodilution used to be recommended to improve cerebral blood flow but now it is believed that it increases cerebral blood flow simply to maintain rather than improve brain oxygen delivery [ 54 ]. Indeed, anemia has been associated with poor outcome, although transfusion has as well [ 55 ].…”

“…Avoiding anemia could avoid the need for transfusion, which has deleterious effects such as organ injury and increased risk of infection [ 55 ]. Transfusion, however, been shown by positron emission tomography to be one of the best methods to increase brain oxygen delivery [ 54 ]. We analyzed anemia, defined as hemoglobin < 10 g/dL, at different times after aSAH (at hospital admission before aneurysm securing, one to 3 days post-aneurysm securing and during the peak DCI window 5 to 9 days after admission) in CONSCIOUS-1 [ 34 ].…”