title: A retrospective analysis of the effect of blood transfusion on cerebral oximetry entropy and acute kidney injury.
abstract: OBJECTIVE
  Acute anemia is associated with both cerebral dysfunction and acute kidney injury and is often treated with red blood cell transfusion. We sought to determine if blood transfusion changed the cerebral oximetry entropy, a measure of the complexity or irregularity of the oximetry values, and if this change was associated with subsequent acute kidney injury.
  
  
  METHODS
  This was a retrospective, case-control study of patients undergoing cardiac surgery with cardiopulmonary bypass at a tertiary care hospital, comparing those who received a red blood cell transfusion to those who did not. Acute kidney injury was defined as a perioperative increase in serum creatinine by ⩾26.4 μmol/L or by ⩾50% increase. Entropy was measured using approximate entropy, sample entropy, forbidden word entropy and basescale4 entropy in 500-point sets.
  
  
  RESULTS
  Forty-four transfused patients were matched to 88 randomly selected non-transfused patients. All measures of entropy had small changes in the transfused group, but increased in the non-transfused group (p<0.05, for all comparisons). Thirty-five of 132 patients (27%) suffered acute kidney injury. Based on preoperative factors, patients who suffered kidney injury were similar to those who did not, including baseline cerebral oximetry levels. After analysis with hierarchical logistic regression, the change in basescale4 entropy (odds ratio = 1.609, 95% confidence interval = 1.057-2.450, p = 0.027) and the interaction between basescale entropy and transfusion were significantly associated with subsequent development of acute kidney injury.
  
  
  CONCLUSIONS
  The transfusion of red blood cells was associated with a smaller rise in entropy values compared to non-transfused patients, suggesting a change in the regulation of cerebral oxygenation, and these changes in cerebral oxygenation are also associated with acute kidney injury.
authors.affiliation: 1 Department of Anesthesiology, University of Michigan, Ann Arbor, MI, USA.|2 Department of Anesthesiology, Mercy St. Vincent Medical Center, Toledo, OH, USA.
authors.forename: Milo
authors.initials: M
authors.lastname: Engoren
authors.affiliation: 3 Department of Information Technology Services, Promedica Health System, Toledo, OH, USA.
authors.forename: Russell R
authors.initials: RR
authors.lastname: Brown
authors.affiliation: 1 Department of Anesthesiology, University of Michigan, Ann Arbor, MI, USA.
authors.forename: Anna
authors.initials: A
authors.lastname: Dubovoy
mesh_terms: D000208:Acute Disease; D058186:Acute Kidney Injury / Q000097:blood* / Q000150:complications; D000740:Anemia / Q000097:blood / Q000150:complications / Q000628:therapy; D006348:Cardiac Surgical Procedures; D002315:Cardiopulmonary Bypass; D016022:Case-Control Studies; D002560:Cerebrovascular Circulation; D003404:Creatinine / Q000097:blood; D019277:Entropy; D017707:Erythrocyte Transfusion; D006801:Humans; D010092:Oximetry; D010100:Oxygen / Q000097:blood*; D012189:Retrospective Studies
chemical_list: D003404:Creatinine; D010100:Oxygen
keywords: complexity; entropy; kidney injury; oximetry; transfusion