title: Blood pressure excursions below the cerebral autoregulation threshold during cardiac surgery are associated with acute kidney injury.
abstract: OBJECTIVE
  To determine whether mean arterial blood pressure excursions below the lower limit of cerebral blood flow autoregulation during cardiopulmonary bypass are associated with acute kidney injury after surgery.
  
  
  METHODS
  Tertiary care medical center.
  
  
  METHODS
  Four hundred ten patients undergoing cardiac surgery with cardiopulmonary bypass.
  
  
  METHODS
  Prospective observational study.
  
  
  METHODS
  None.
  
  
  RESULTS
  Autoregulation was monitored during cardiopulmonary bypass by calculating a continuous, moving Pearson's correlation coefficient between mean arterial blood pressure and processed near-infrared spectroscopy signals to generate the variable cerebral oximetry index. When mean arterial blood pressure is below the lower limit of autoregulation, cerebral oximetry index approaches 1, because cerebral blood flow is pressure passive. An identifiable lower limit of autoregulation was ascertained in 348 patients. Based on the RIFLE criteria (Risk, Injury, Failure, Loss of kidney function, End-stage renal disease), acute kidney injury developed within 7 days of surgery in 121 (34.8%) of these patients. Although the average mean arterial blood pressure during cardiopulmonary bypass did not differ, the mean arterial blood pressure at the limit of autoregulation and the duration and degree to which mean arterial blood pressure was below the autoregulation threshold (mm Hg × min/hr of cardiopulmonary bypass) were both higher in patients with acute kidney injury than in those without acute kidney injury. Excursions of mean arterial blood pressure below the lower limit of autoregulation (relative risk 1.02; 95% confidence interval 1.01 to 1.03; p < 0.0001) and diabetes (relative risk 1.78; 95% confidence interval 1.27 to 2.50; p = 0.001) were independently associated with for acute kidney injury.
  
  
  CONCLUSIONS
  Excursions of mean arterial blood pressure below the limit of autoregulation and not absolute mean arterial blood pressure are independently associated with for acute kidney injury. Monitoring cerebral oximetry index may provide a novel method for precisely guiding mean arterial blood pressure targets during cardiopulmonary bypass.
authors.affiliation: Department of Surgery, Division of Cardiac Surgery, The Johns Hopkins University School of Medicine, Baltimore, MD, USA.
authors.forename: Masahiro
authors.initials: M
authors.lastname: Ono
authors.forename: George J
authors.initials: GJ
authors.lastname: Arnaoutakis
authors.forename: Derek M
authors.initials: DM
authors.lastname: Fine
authors.forename: Kenneth
authors.initials: K
authors.lastname: Brady
authors.forename: R Blaine
authors.initials: RB
authors.lastname: Easley
authors.forename: Yueying
authors.initials: Y
authors.lastname: Zheng
authors.forename: Charles
authors.initials: C
authors.lastname: Brown
authors.forename: Nevin M
authors.initials: NM
authors.lastname: Katz
authors.forename: Morgan E
authors.initials: ME
authors.lastname: Grams
authors.forename: Charles W
authors.initials: CW
authors.lastname: Hogue
mesh_terms: D058186:Acute Kidney Injury / Q000503:physiopathology*; D000368:Aged; D001794:Blood Pressure / Q000502:physiology*; D001921:Brain / Q000098:blood supply*; D002315:Cardiopulmonary Bypass; D003920:Diabetes Mellitus / Q000503:physiopathology; D005260:Female; D006706:Homeostasis / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D016343:Monitoring, Intraoperative; D010092:Oximetry; D011446:Prospective Studies; D012372:ROC Curve; D019265:Spectroscopy, Near-Infrared