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Red cell exchange transfusions lower cerebral blood flow and oxygen extraction fraction in pediatric sickle cell anemia

Kristin P. Guilliams, Melanie E. Fields, Dustin K. Ragan, Cihat Eldeniz, Michael M. Binkley, Yasheng Chen, Liam S. Comiskey, Allan Doctor, Monica L. Hulbert, Joshua S. Shimony, Katie D. Vo, Robert C. McKinstry, Hongyu An, Jin-Moo Lee and Andria L. Ford

Key points

  • Exchange transfusion lowers global CBF and OEF in SCA, suggesting transfusions reduce infarct risk by relieving cerebral metabolic stress.

  • In SCA, OEF is highest in the deep white matter, where infarct risk is high; transfusion reduces the volume of tissue with elevated OEF.

Abstract

Blood transfusions are the mainstay of stroke prevention in pediatric sickle cell anemia (SCA), but the physiology conferring this benefit is unclear. Cerebral blood flow (CBF) and oxygen extraction fraction (OEF) are elevated in SCA, likely compensating for reduced arterial oxygen content (CaO2). We hypothesized that exchange transfusions decrease CBF and OEF by increasing CaO2, thereby relieving cerebral oxygen metabolic stress. Twenty-one children with SCA on chronic transfusion therapy (CTT) had MRIs before and after exchange transfusion. Arterial spin labeling and asymmetric spin echo sequences measured CBF and OEF, respectively, which were compared pre- and post-transfusion. Volumes of tissue with OEF above successive thresholds (36, 38, 40%), as a metric of regional metabolic stress, were compared pre- and post-transfusion. Transfusion increased Hb (9.1 to 10.3 g/dL, p<0.001) and decreased Hb S (39.7 to 24.3%, p<0.001). Transfusion reduced CBF (88 to 82.4 ml/100g/min, p=0.004) and OEF (34.4 to 31.2%, p<0.001). At all thresholds, transfusion reduced the volume of peak OEF found in the deep white matter, a location at high infarct risk in SCA (p<0.001). Reduction of elevated CBF and OEF, both globally and regionally, suggests that CTT mitigates infarct risk in pediatric SCA by relieving cerebral metabolic stress at patient and tissue-specific levels.

  • Submitted June 19, 2017.
  • Accepted December 4, 2017.