Carbon Dioxide Insufflation On The Number And Behavior Of Air Microemboli In Open-Heart Surgery - Response

and Behavior of Air Microemboli in Open-Heart Surgery To the Editor: Although useful neuropsychological (NP) benefits may result from the recent report by Svenarud et al1 of a reduction in air microemboli in a randomized controlled trial of CO2 insufflation during single-valve surgery, there are a number of issues relating to cerebral microemboli, valve versus coronary bypass surgery, and NP outcome that are not adequately addressed in this paper. A number of studies have linked cerebral microemboli to NP outcome, but the relationship between the two remains unclear. Other factors such as inflammatory response and altered cerebral blood flow must also be considered. Neville et al2 compared 193 patients having coronary artery bypass surgery with 73 patients having valve replacement surgery and confirmed previous findings that there were more microemboli detected during valve surgery but there was no difference found in NP outcome. Their result suggests that the number of microemboli may not always be the most significant determinant of NP outcome. Additionally, Svenarud et al1 only measured microemboli within the heart and ascending aorta, and these may not correlate with cerebral microemboli. I would be interested to know why Svenarud and colleagues1 did not assess cerebral microemboli when they have done so in the past.3 They quote two papers from the same group4,5 as evidence that air microemboli are harmful, but both papers are flawed. Taylor et al5 assume that the microemboli they detect are air, but this is unproven, and the technology to distinguish gaseous from particulate microemboli has not yet been used clinically. Borger et al4 found that the group with fewer than 10 interventions had less NP impairment after surgery; however, this group also had significantly shorter cross-clamp and cardiopulmonary bypass times. A further flaw was the failure to perform actual microemboli counts such that Borger et al4 were not able to make a direct correlation between the microemboli count and NP outcome. How did Svenarud et al1 count microemboli on a 2-dimensional image over time? Counting cerebral microemboli as they appear sequentially on a Doppler recording is relatively straightforward. However, when microemboli are “whirling around in the left ventricle and left atrium,”1 it must be very difficult to keep track of which microembolus is which for a whole minute and not doublecount any. It is not adequately explained how the microemboli were counted so that their methods could be repeated by others.