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October 04, 2020
10/4/2020 12:00:00 PM - 10/4/2020 1:00:00 PM
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Characterizing Precordial Doppler Audio Changes In Patients Receiving Agitated Saline Injection During Echocardiography
Nikolaus Gravenstein, M.D., Anthony Destephens, M.Eng., Cesar Cardoso, Student, Meghan M. Brennan, M.D., John Peterson, M.D., Ferenc Rabai, M.D.
University of Florida, Gainesville, Florida, United States
Disclosures: N. Gravenstein: None. A. Destephens: None. C. Cardoso: None. M.M. Brennan: None. J. Peterson: None. F. Rabai: None.

Precordial Doppler ultrasound is one of the many tools anesthesiologists can use to monitor for venous air embolisms (VAE) during high risk procedures. Due to the noisy environment of the operating room and the divided attention of the anesthesiologist, such an event may be easy to miss early on despite having a precordial Doppler monitor in place. Incorporation of a software component that could independently monitor the precordial Doppler ultrasound and alert the anesthesiologist of a possible VAE via Doppler signal interrogation would provide an excellent opportunity for earlier detection and treatment of a VAE. Therefore, the goal of this study is to characterize the various potential Doppler sound qualities of VAE so that an alert for the anesthesia provider can be created.


After IRB approval, 13 consenting patients undergoing elective bubble studies for other indications were enrolled. A precordial Doppler ultrasound (MedaSonics® Versatone® Model D8) was placed over the right atrium/ventricle of the study participant’s heart in coordination with the echocardiography team prior to injection of the agitated saline. The Doppler audio was continuously recorded before, during and after the injection of agitated saline. The echo video clips that were recorded as part of the bubble study were used as a visual reference for when the microbubbles were present in the heart. The recordings were then analyzed to determine if there were any quantifiable Doppler signal intensity differences before, during and after injection of agitated saline.


A paired t-test was used to compare pre and post injection normalized Doppler intensity. Mean normalized standard deviation of post injection sound intensity, 0.0312 was significantly higher than that of pre-injection, 0.00586, (p-value 0.0065, mean difference: 0.025 SE: 0.00831).


Standard deviation of the mean was chosen as the method to compare changes in Doppler intensity due to the symmetry the data had with the x axis (the average intensity over time would have been near 0). The standard deviation of the Doppler data between patients was high, which we suspect is a result of a probe placement, variability of patient surface anatomy and variability of agitated saline quality. We also noted that despite clear heart sounds pre-injection of agitated saline, Doppler probe placement on the patient’s right sternal border sometimes failed to produce significant changes in doppler audio intensity. Probe placement on the patient’s left sternal border was able to consistently pick up high quality heart sounds and significant changes in doppler audio. Despite a high standard deviation, the results show a clear and quantifiable distinction between absent vs present bubbles on echocardiography with an average fivefold increase in standard deviation of normalized Doppler intensity between pre and post agitated saline injections. Future work includesidentifying other possible Doppler audio characterization parameters for VAE as well as creating and testing Doppler monitoring software for VAE.
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