Determining Thresholds for Three Indices of Autoregulation to Identify the Lower Limit of Autoregulation During Cardiac Surgery*

Abstract

Monitoring cerebral autoregulation (CA) may help identify the lower limit of autoregulation (LLA) in individual patients. Mean arterial blood pressure (MAP) below LLA appears to be a risk factor for postoperative acute kidney injury (AKI). CA can be monitored in real-time using correlation approaches. However, the precise thresholds for different CA indexes that identify the LLA are unknown. We identified thresholds for intact autoregulation in patients during cardiopulmonary bypass surgery and examined the relevance of these thresholds to postoperative AKI. Design: A single-center retrospective analysisSetting: Tertiary academic medical center Patients. Data from 59 patients was used to determine precise CA thresholds for identification of the LLA. These thresholds were validated in a larger cohort of 226 patients. Methods and Main Results:Invasive MAP, cerebral blood flow velocities (CBFV), regional cortical oxygen saturation and total hemoglobin were recorded simultaneously. Three CA indices were calculated, including mean flow index (Mx), cerebral oximetry index (COx), and hemoglobin volume index (HVx). CA curves for the three indices were plotted, and thresholds for each index were used to generate threshold-and index-specific LLAs. A reference LLA could be identified in 59 patients by plotting CBFV against MAP to generate gold standard Lassen curves. The LLAs defined at each threshold were compared with the gold standard LLA determined from Lassen curves. The results identified the following thresholds: Mx (0.45), COx (0.35), and HVx (0.3). We then calculated the product of magnitude and duration of MAP < LLA in a larger cohort of 226 patients. When using the LLAs identified by the optimal thresholds above, MAP<LLA was greater in patients with AKI than in those without AKI. Conclusions:This study identified thresholds of intact and impaired CA for three indices and showed that MAP below LLA is a risk factor for AKI after cardiac surgery. 4

Continuous Time-Domain Cerebrovascular Reactivity Metrics and Discriminate Capacity for the Upper and Lower Limits of Autoregulation: A Scoping Review of the Animal Literature

“…Finally, and most important, the results from studies with animal models do not directly translate to human patients, though preliminary findings in humans support their ability to estimate the LLA. 49 , 50 …”

Pro-Con Debate: The Clinical (Ir)relevance of the Lower Limit of Cerebral Autoregulation for Anesthesiologists

“…This has been shown to be true in cardiac surgery patients. 7 Thresholds also probably differ from patient to patient or even may fluctuate in time. There are easy to adopt techniques that are helpful in assessing individual thresholds and monitoring their fluctuations in time.…”

Effect of hypertension and medication use regularity on postoperative delirium after maxillofacial tumors radical surgery

“…Scholars has found that cerebral blood perfusion [ 11 ] and cerebral blood oxygen saturation are closely related with POD, the regional cerebral blood flow measurements of the frontal, temporal and occipital cortex [ 12 ] during delirium are lower than normal state. Cerebral blood flow [ 13 ] is tightly controlled via the static and dynamic properties of cerebral autoregulation, this shows that cerebrovascular reactivity can affect the blood supply of the brain, hypertension can reduce the ability of cerebrovascular self-regulation [ 14 ], and the changes in vascular stiffness caused by hypertension will further aggravate the decrease in cerebral blood flow [ 15 ].…”