Sources of Variability in the Detection of Cerebral Emboli with Transcranial Doppler During Cardiac Surgery

Abstract

Using intensity thresholds higher than the optimal for embolus detection decreases HITS counts. Choosing a threshold depends on the type of method used for measuring the signal intensity. Uniform threshold criteria and comparative studies between different Doppler devices are necessary for making clinical trials more comparable.

Cerebral Emboli Detected by Transcranial Doppler During Cardiopulmonary Bypass Are Not Correlated With Postoperative Cognitive Deficits

“…5,8,9,13 Some studies have found that patients undergoing CABG with higher HITS counts were more likely to experience cognitive deficits 1,2,5,6 or higher rates of frontal lobe dysfunction, 16 but others have found that there is no correlation between HITS counts and neurological symptoms or cognitive deficits. 6,8,17 Several methodological issues may account for the variability among these studies, including small sample sizes, 1,6 differences in intensity thresholds used to detect HITS, 13 artery location (carotid versus middle cerebral artery), 1,8,12 unilateral or bilateral recordings, 2,8,12 type of ultrasound device, 13,18 quality of TCD recordings, 18 inconsistency of signal reviewing techniques (automatic versus manual), 13,18 and the effects of several confounding variables such as the duration of CPB and core body temperature. 2 We sought to overcome these limitations by studying a large number of low-risk patients undergoing †HITS were recorded unilaterally in the left common carotid artery.…”

“…who was unaware of the results of the cognitive assessment and patient treatment allocation reviewed the TCD recordings and classified ultrasonic signals into true or equivocal HITS, Doppler speckles, and artifacts according to preestablished criteria. 13 Only true HITS were considered in the final counts of HITS. The quality of the TCD recording was assessed using a 5-point scoring scale.…”

“…Our TCD equipment and reviewing procedures have been previously described. 12,13 Only embolic signals identified in the middle cerebral arteries with relative intensities Ͼ8 dB (intensity threshold) were accepted. Bilateral middle cerebral artery counts of HITS were grouped into periods that included the following surgical maneuvers: cannulation; defined from the time of aortic cannulation to before CPB initiation, CPB onset; from CPB initiation to immediately before the application of the aortic crossclamp, aortic X-clamp-on; from aortic crossclamping to immediately before declamping, aortic X-clamp-off; from aortic declamping to before aortic side-clamping, side clamp-on; from the application of the aortic side clamp to immediately before its release, side clamp-off; from aortic side clamp release to the end of CPB, and decannulation; from the time of CPB termination to immediately after aortic decannulation.…”

Distinguishing Air From Solid Emboli Using Ultrasound: In‐Vitro Study of the Effect of Doppler Carrier Frequency

“…Transcranial Doppler (TCD) has been used to detect emboli in the cerebral circulation during cardiopulmonary bypass (CPB) and cardiac surgery through the identification of high‐intensity transient signals or HITS 1,2 . Despite the wide use of TCD for embolus detection, accurate differentiation of solid from air emboli with this technology has not been achieved 3 .…”

Cerebral Microembolization After Bioprosthetic Aortic Valve Replacement

“…Such physiological inference can be obtained by transcranial Doppler (TCD) examination, 12 and by measurements of inhibition of platelet-induced aggregation. 13,14 Previous studies 12,15 have documented that TCD can reliably and noninvasively detect and quantify emboli in the cerebral circulation, by recognizing brief transient increases in the intensity of the ultrasound signal designated as microembolic signals (MES), which indicate the presence of air or solid emboli in the cerebral circulation. Similarly, several tests of platelet function have been used to evaluate the efficacy and safety of a combined therapy based on aspirin and oral anticoagulants.…”