The Complex Nature of Emboli Detection During Cardiac Procedures

Abstract

We thank Dr Ü ndar 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.Regarding the transcranial Doppler instrumentation used (Doppler Box X; Compumedics Gmbh): we agree that the newer generation of Doppler devices have improvements in spectral quality and emboli detection. We did not find the company's fixation device suitable for long-term use on infants and neonates in the operating room. Instead, we have devised and fabricated our own and have used it in various applications (scaling the overall size to head dimensions). Prior testing of the headset proved it was quite capable of maintaining bilateral middle cerebral artery signals with excellent stability. [2][3][4][5] We do not have the emboli discrimination option (requiring dualfrequency probes) on our system, but have watched emboli detection, discrimination, and sizing technology with great interest, including the work of Dr Ü ndar's group (eg, Clark et al and Clark et al 6,7 ). Novel signal processing methods on the raw radio frequency signal and its spectral representation are required to solve this challenging problem, with accompanying clinical studies needed to determine the pediatric health significance of these emboli parameters. 8,9 We intend to follow up with further studies to determine highintensity transient signal correlations with some of the surgical parameters identified in the letter. For the current study, we used the 1/8 inch arterial line on only a few very small patients, for which a statistical comparison with the patients using the 3/16 inch line would not have achieved valid significance. We did not monitor flow proximal to the arterial cannula with an external probe. The surgical procedure incorporated a very small open shunt with adjustment of pump flow rates accordingly to ensure proper patient flow rates. The surgical purge catheter remained closed during cardiopulmonary bypass. Average values for VAVD levels were approximately À30 mm Hg, and for venous reservoir volumes approximately 100 mL.Certainly, as the letter authors stated, emboli source and delivery during surgical procedures is complex. Multidisciplinary teams are needed to solve this problem. We are glad that a robust body of literature precedes us and that the relatively small but extremely important research community represented by World Journal for Pediatric and Congenital Heart Surgery readers will continue to work together toward improving technology to accurately identify emboli burden and characteristics during cardiac procedures.