Cerebral autoregulation after subarachnoid hemorrhage: comparison of three methods

Abstract

In patients after subarachnoid hemorrhage (SAH) failure of cerebral autoregulation is associated with delayed cerebral ischemia (DCI). Various methods of assessing autoregulation are available, but their predictive values remain unknown. We characterize the relationship between different indices of autoregulation. Patients with SAH within 5 days were included in a prospective study. The relationship between three indices of autoregulation was analyzed: two indices calculated using spontaneous blood pressure fluctuations, Sxa (based on transcranial Doppler) and TOxa (based on near-infrared spectroscopy); and transient hyperemic response test (THRT) where a brief compression of the common carotid artery is used. The predictive value of indices was assessed using data from the first 5 days. Overall there was only moderate correlation between indices. However, both Sxa and TOxa showed good accuracy in predicting impaired autoregulation evidenced by a negative THRT (area under the curve (AUC): 0.788, 95% CI: 0.723 to 0.854 and AUC: 0.827, 95% CI: 0.769 to 0.885, respectively). All indices proved accurate in predicting DCI when 0- to 5-day data were used (AUC: 0.801, 95% CI: 0.660 to 0.942; AUC: 0.857, 95% CI: 0.731 to 0.984, AUC: 0.796, 95% CI: 0.658 to 0.934 for THRT, Sxa, and TOxa, respectively). Combining all three indices had 100% specificity for predicting DCI. While multiple colinearities exist between the assessed methods, multimodal monitoring of cerebral autoregulation can aid in predicting DCI.

Figure 1

Example of monitoring performed on day 5 after ictus. Middle panel shows impaired autoregulation using Sxa (black line), TOxa (gray line), with values of indices close to +1. Similarly, the lack of a hyperemic response in THRT indicates impaired autoregulation (insert top panel). There is relatively good correlation between Sxa and TOxa (r=0.68). The patient developed delayed cerebral ischemia on day 9. ABP, arterial blood pressure; Sxa, transcranial Doppler autoregulation; THRT, transient hyperemic response test; TOxa, near-infrared spectroscopy-based autoregulation.

Figure 2

Scatter plot of Sxa (top) and TOxa (bottom) dichotomized to THRR ⩽1.09 and THRR >1.09 with superimposed reference lines of optimal sensitivity and specificity as defined by the respective ROC curves (right): 0.05 for Sxa and 0.13 for TOxa. Similar accuracy for Sxa and TOxa in identifying impaired autoregulation as evidenced by THRR⩽1.09 can be seen. AUC, area under the curve; Sxa, transcranial Doppler autoregulation; THRR, transient hyperemic response ratio; TOxa, near-infrared spectroscopy-based autoregulation.

Figure 3

FV plotted against ABP bins shows an autoregulation curve with the LLA at 80 mm Hg and ULA at 120 mm Hg (vertical dashed lines) (A). When indices of autoregulation are plotted using the same ABP bins, LLA and ULA can be defined as the ABP level at below and above which the respective indices indicate impaired autoregulation. In all cases, the LLA is visible at 80 mm Hg (B–D). However, there are discrepancies between the indices with respect to the ULA. There is no clear ULA when THRR is used (B), while the ULA is shifted to the left when TOxa is used (D) compared with Sxa (C). ABP, arterial blood pressure; FV, flow velocity; LLA, lower limit of autoregulation; Sxa, transcranial Doppler-based index of autoregulation; THRR, transient hyperemic response ratio; TOxa, near-infrared spectroscopy autoregulation; ULA, upper limit of autoregulation.

Figure 4

Autoregulation indices dichotomized into DCI and non-DCI groups with superimposed threshold for impaired autoregulation obtained from the respective ROC curves (0.05 for Sxa, 0.13 for TOxa and 1.09 for THRR). ROC curve analysis showing the ability of autoregulation indices from the first 5 days to predict DCI. AUC, area under the curve; DCI, delayed cerebral ischemia; ROC, receiver operator characteristic; Sxa, transcranial Doppler-based index of autoregulation; THRR, transient hyperemic response ratio; TOxa, near-infrared spectroscopy-based index of autoregulation.