Blood Pressure Excursions Below the Cerebral Autoregulation Threshold During Cardiac Surgery are Associated With Acute Kidney Injury*

Abstract

Objectives To determine whether mean arterial blood pressure (MAP) excursions below the lower limit of cerebral blood flow (CBF) autoregulation during cardiopulmonary bypass (CPB) are associated with acute kidney injury (AKI) after surgery. Setting Tertiary care medical center. Patients Four hundred ten patients undergoing cardiac surgery with CPB. Design Prospective observational study. Interventions None. Measurements and Main Results Autoregulation was monitored during CPB by calculating a continuous, moving Pearson’s correlation coefficient between MAP and processed near-infrared spectroscopy signals to generate the variable cerebral oximetry index (COx). When MAP is below the lower limit of autoregulation, COx approaches 1, because CBF is pressure passive. An identifiable lower limit of autoregulation was ascertained in 348 patients. Based on the RIFLE criteria, AKI developed within 7 days of surgery in 121 (34.8%) of these patients. Although the average MAP during CPB did not differ, the MAP at the limit of autoregulation and the duration and degree to which MAP was below the autoregulation threshold (mmHg × min/hr of CPB) were both higher in patients with AKI than in those without AKI. Excursions of MAP 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 AKI. Conclusions Excursions of MAP below the limit of autoregulation and not absolute MAP are independently associated with for AKI. Monitoring COx may provide a novel method for precisely guiding MAP targets during CPB.

A Brain–Kidney Connection: The Delicate Interplay of Brain and Kidney Physiology

“…Therefore, the authors' observation that serum creatinine elevation was associated with higher mortality should not be surprising [5]. Nevertheless, despite these limitations, this study is an extension of previously published evidence that cerebral perfusion and GFR are interconnected, with patients who experience cerebral hypoperfusion at an increased risk of renal injury and vice versa, with subsequent effects on outcome and mortality [6,7]. Without a larger study, control population, or similar validation, the clinical impact of this study remains to be seen outside the realm of physiological insights.…”

Relationship Between the Ambulatory Arterial Stiffness Index and the Lower Limit of Cerebral Autoregulation During Cardiac Surgery

“…Even though the surgical team was blinded to the LLA measurements, they could have chosen a higher MAP for patients on bypass who subjectively appeared to have an altered LLA, such as those who had hypertension that was difficult to control intraoperatively or those who appeared frail. Prior studies have shown that the duration and magnitude of BP below the LLA is associated with acute kidney injury38 and major morbidity and mortality2 after cardiac surgery. Those studies suggested that maintaining MAP within the range of cerebral autoregulation may improve postoperative outcomes.…”

Renal Failure and Heart Surgery

“…Innovative technology to determine the lower limit of the cerebral autoregulation threshold has been developed and validated at Hopkins. Excursions of MAP below the lower limit of cerebral autoregulation were independently associated with AKI [28]. Because of this, observations of cerebral perfusion may be used as a surrogate for renal perfusion.…”