Hypotension After Cardiac Operations Based on Autoregulation Monitoring Leads to Brain Cellular Injury

Abstract

Background: Individualizing blood pressure targets could improve organ perfusion compared with current practices. In this study we assess whether hypotension defined by cerebral autoregulation monitoring vs standard definitions is associated with elevation in the brain-specific injury biomarker glial fibrillary acidic protein plasma levels (GFAP).

Methods: Plasma GFAP levels were measured in 121 patients undergoing cardiac operations after anesthesia induction, at the conclusion of the operation, and on postoperative day 1. Cerebral autoregulation was monitored during the operation with the cerebral oximetry index, which correlates low-frequency changes in mean arterial pressure (MAP) and regional cerebral oxygen saturation. Blood pressure was recorded every 15 minutes in the intensive care unit. Hypotension was defined based on autoregulation data as an MAP below the optimal MAP (MAP at the lowest cerebral oximetry index) and based on standard definitions (systolic blood pressure decrement >20%, >30% from baseline, or <100 mm Hg, or both).

Results: MAP (mean ± standard deviation) in the intensive care unit was 74 ± 7.3 mm Hg; optimal MAP was 78 ± 12.8 mm Hg (p = 0.008). The incidence of hypotension varied from 22% to 37% based on standard definitions but occurred in 54% of patients based on the cerebral oximetry index (p < 0.001). There was no relationship between standard definitions of hypotension and plasma GFAP levels, but MAP of less than optimal was positively related with postoperative day 1 GFAP levels (coefficient, 1.77; 95% confidence interval, 1.27 to 2.48; p = 0.001) after adjusting for GFAP levels at the conclusion of the operation and low cardiac output syndrome.

Conclusions: Individualizing blood pressure management using cerebral autoregulation monitoring may better ensure brain perfusion than current practice.

Figure 1

Cerebral oximetry index (COx) results obtained during cardiopulmonary bypass placed in 5mmHg bins. Optimal MAP was defined as that MAP with the lowest COx. As MAP moves away from the optimal MAP, COx increases indicating trends towards pressure dependent changes in cerebral blood flow. In this example, the optimal MAP is 80 mmHg. (Black Arrow)

Figure 2

Box and whisker plot comparing plasma GFAP levels on post-operative day 1 for patients who had average MAP (ICU) above the optimal MAP, and patients who had average MAP (ICU) below the optimal MAP.(p<0.001) The horizontal line in the shaded box represents the median value, and the shaded box represents the interquartile range. The error bars below and above the shaded area represents ±1.5× the interquartile range; points beyond the error bar are outliers.

Figure 3

Box and whisker plot comparing the product of magnitude and duration of MAP below optimal MAP (AUC

Figure 4

Spearman's correlation ratio between plasma GFAP levels on postoperative day 1 and the product of magnitude and duration of blood pressure below the optimal MAP. (r=0.31, p<0.001)