Most High-Intensity Transient Signals Are Not Associated With Specific Surgical Maneuvers

Abstract

<jats:sec><jats:title>Background:</jats:title><jats:p> Mortality after congenital heart defect surgery has dropped dramatically in the last few decades. Current research on long-term outcomes has focused on preventing secondary neurological sequelae, for which embolic burden is suspected. In children, little is known of the correlation between specific surgical maneuvers and embolic burden. Transcranial Doppler ultrasound is highly useful for detecting emboli but has not been widely used with infants and children. </jats:p></jats:sec><jats:sec><jats:title>Methods:</jats:title><jats:p> Bilateral middle cerebral artery blood flow was continuously monitored from sternal incision to chest closure in 20 infants undergoing congenital heart defect repair or palliative surgery. Embolus counts for specific maneuvers were recorded using widely accepted criteria for identifying emboli via high-intensity transient signals (HITS). </jats:p></jats:sec><jats:sec><jats:title>Results:</jats:title><jats:p> An average of only 13% of all HITS detected during an operation were correlated with any of the surgical maneuvers of interest. The highest mean number of HITS associated with a specific maneuver occurred during cross-clamp removal. Cross-clamp placement also had elevated HITS counts that significantly differed from other maneuvers. </jats:p></jats:sec><jats:sec><jats:title>Conclusions:</jats:title><jats:p> In this study of infants undergoing cardiac surgery with cardiopulmonary bypass, the great majority of HITS detected are not definitively associated with a specific subset of surgical maneuvers. Among the measured maneuvers, removal of the aortic cross-clamp was associated with the greatest occurrence of HITS. Future recommended research efforts include identifying and confirming other sources for emboli and longitudinal outcome studies to determine if limiting embolic burden affects long-term neurological outcomes. </jats:p></jats:sec>

Invited Commentary: After the Clamp Comes Off: A Golden Opportunity to Decrease Cerebral Air Embolization

“…As bypass concludes, flow through the lungs increases and expels remnant air sequestered within the pulmonary veins. In the current study, termination of bypass was associated with a few instances of “large outliers” of HITS, 1 presumably showers of bubbles emerging late from the lungs.…”

“…In this issue, Twedt and colleagues present a study of bilateral transcranial Doppler (TCD) brain monitoring in a series of infants undergoing cardiac surgery with cardiopulmonary bypass. 1 Often performed in a unilateral fashion, intraoperative TCD assesses blood flow velocity in the middle cerebral artery and provides surveillance for cerebral embolization in the form of high-intensity transient signals (HITS). [2][3][4] This study sought to correlate the occurrence of HITS with specific surgical maneuvers related to the performance of cardiopulmonary bypass.…”

“…As the present authors describe, their group has an interest in improving TCD methodology, 1 with the implied goal of improving patient outcomes. The use of TCD can provide actionable feedback which may prompt real-time, potentially beneficial intervention.…”

The Complex Nature of Emboli Detection During Cardiac Procedures

“…We thank Dr Ündar and Mr Dan for their interest and comments on our recent publication, 1 “Most-high intensity transient signals are not associated with specific surgical maneuvers” in their recent Letter to the Editor. We are happy to provide a few comments and answers to questions posed in their letter.…”

Optimization of CPB Circuits and Techniques Minimize the Total Number of Intraoperative Emboli Delivery in Congenital Heart Surgery Patients

“…Among the measured maneuvers, removal of the aortic cross-clamp was associated with the greatest occurrence of HITS." 1 Twedt and his colleagues utilized the new generation of the Transcranial Doppler (TCD) device, which has significant advantages over previous generations of TCD devices used to detect the high-intensity transient signals (HITS) in infants undergoing cardiac surgeries with cardiopulmonary bypass (CPB) procedures. This new generation of TCD device (Doppler Box X; Compumedics Gmbh) allows continuous monitoring of cerebral blood flow velocity at the bilateral middle cerebral arteries and also includes an infant transducer stabilization device to safely secure both transducers on the infant's head.…”