• Masahiro Ono, George J Arnaoutakis, Derek M Fine, Kenneth Brady, R Blaine Easley, Yueying Zheng, Charles Brown, Nevin M Katz, Morgan E Grams, and Charles W Hogue.
• Department of Surgery, Division of Cardiac Surgery, The Johns Hopkins University School of Medicine, Baltimore, MD, USA.
• Crit. Care Med.. 2013 Feb 1;41(2):464-71.

ObjectivesTo 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.SettingTertiary care medical center.PatientsFour hundred ten patients undergoing cardiac surgery with cardiopulmonary bypass.DesignProspective observational study.InterventionsNone.Measurements And Main ResultsAutoregulation 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.ConclusionsExcursions 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.

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