Page 27 - ANZCP Gazette NOVEMBER 2022

6
Perfusion 00(0)
bubble exposure on cerebral vascular function during cardiac surgery.
The finding of a preponderance of emboli entering the right versus the left middle cerebral artery in the present study is of uncertain relevance. Two studies in cardiac surgery reported results broadly confluent with ours (larger numbers of emboli entered the right cerebral circulation).18,19 However, in neither of those was the finding as convincing as reported here. The difference in exposure between cerebral hemispheres in our patient cohort may provide another means to evaluate the effect of bubbles on vascular function on an intra-patient basis, in addition to comparing groups of patients with differing total exposures.
Study limitations
This study has several limitations. First, it is a single- centre study, and thus the emboli exposures reported here may not be generalizable to other centres. Nevertheless, the confluence of our data with those reported by Chung et al.13 using identical Doppler technology is reassuring, and it is unlikely that the fundamental finding of comparatively higher emboli exposure in OCS is different in other centres. Second, we did not apply an emboli sizing algorithm to our transcranial Doppler data. However, in evaluating open- versus closed-chamber patient groups as poten- tial comparators in the analysis of cerebrovascular function, we believe this to be unnecessary. Once again, given the confluence in data describing num- bers of emboli, the size distribution of bubbles gener- ated during surgery is unlikely to be significantly different to that reported by Chung, and the entire size spectrum they reported is comprised of bubbles that previous studies show are likely to redistribute very quickly (as opposed to prolonged trapping and conse- quent ischaemia). Thus, the numbers of bubbles alone would seem a reasonable index of potential bubble harm to endothelium and compromise of vascular function. Third, we acknowledge that the counting algorithms in automated emboli detection devices are not universally accepted as completely accurate. Nevertheless, even if these ‘counts’ can only be consid- ered an ‘index of exposure’, we believe that counts from the same device remain a legitimate means of compar- ing exposure in different groups of patients (as we have done here). Fourth, the cohort was not selected ran- domly, but instead was a small sample of convenience from a large surgical population based on the availabil- ity of the principal researcher. Finally, with only one female patient, our data can only be applied to the male population, although it seems unlikely that patterns of emboli exposure would be influenced by patient gender.
Conclusion
Patients undergoing open-chamber surgery are exposed to considerably higher numbers of cerebral arterial emboli (mainly small bubbles) after removal of the aor- tic cross-clamp than those undergoing closed-chamber surgery, and more emboli enter the right MCA than the left. These results may help inform the evaluation of the pathophysiological impact of emboli exposure.
Declaration of conflicting interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The author(s) disclosed receipt of the following financial sup- port for the research, authorship, and/or publication of this article: The transcranial Doppler device was purchased with a grant from the Green Lane Research and Educational Fund. The laptop required to run the transcranial Doppler software was purchased with a Joint Anaesthesia Faculty of Auckland grant. The first author received a PhD scholarship from the Green Lane Research and Educational Fund to conduct his research.
ORCID iD
Ghazwan NS Jabur
References
https://orcid.org/0000-0002-1264-8088
1. 2. 3. 4. 5. 6. 7. 8. 9.
Kruis RW, Vlasveld FA, Van Dijk D. The (un)importance of cerebral microemboli. Semin Cardiothorac Vasc Anesth 2010; 14: 111–118.
Mitchell SJ, Merry AF. Perspective on cerebral microem- boli in cardiac surgery: significant problem or much ado about nothing? J Extra Corpor Technol 2015; 47: 10–15. Milsom FP, Mitchell SJ. A dual-vent left heart deairing technique markedly reduces carotid artery microemboli. Ann Thorac Surg 1998; 66: 785–791.
Nussmeier NA. Adverse neurologic events: risks of intra- cardiac versus extracardiac surgery. J Cardiothorac Vasc Anesth 1996; 10: 31–37.
Ono M, Joshi B, Brady K, et al. Risks for impaired cer- ebral autoregulation during cardiopulmonary bypass and post-operative stroke. Br J Anaesth 2012; 109: 391–398. Fok H, Jiang B, Chowienczyk P, et al. Microbubbles shunt- ing via a patent foramen ovale impair endothelial func- tion. JRSM Cardiovasc Dis 2015; 4: 2048004015601564. Brubakk AO, Duplancic D, Valic Z, et al. A single air dive reduces arterial endothelial function in man. J Physiol 2005; 566: 901–906.
Brucher R, Russell D. Automatic online embolus detec- tion and artifact rejection with the first multifrequency transcranial Doppler. Stroke 2002; 33: 1969–1974. Russell D, Brucher R. Online automatic discrimination between solid and gaseous cerebral microemboli with the first multifrequency transcranial Doppler. Stroke 2002; 33: 1975–1980.
NOVEMBER 2022 | www.anzcp.org 24