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Communications to the Editor |

Insights of Neurologic Dysfunction After Coronary Artery Bypass Grafting FREE TO VIEW

Jun Luo, MD, PhD; Akif Ündar, PhD
Author and Funding Information

Affiliations: Penn State College of Medicine, Hershey, PA,  University Hospital Maastricht, Maastricht, the Netherlands

Correspondence to: Akif Ündar, PhD, Associate Professor of Pediatrics, Surgery, and Bioengineering, Penn State College of Medicine, Department of Pediatrics–H085, 500 University Dr. PO Box 850; Hershey, PA 17033-0850; e-mail: aundar@psu.edu



Chest. 2005;127(3):1075-1076. doi:10.1378/chest.127.3.1075
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Published online

To the Editor:

We read with great interest the article by Ganushchak and associates (June 2004).1 The authors have investigated the correlation between the combinations of hemodynamic events during cardiopulmonary bypass (CPB) and the development of postoperative neurologic complications. The authors have utilized cluster analysis to review 1,395 perfusion charts, and have concluded that CPB procedures with large fluctuations in hemodynamic parameters have an increased risk for the development of postoperative neurologic complications.

We would like to make a few comments for this important investigation. First, it is well documented that the number of emboli (micro and macro) delivered during CPB has a direct correlation with the postoperative neurologic dysfunction.23 The duration of CPB also has an impact on the number of emboli delivered during CPB; the longer the duration, more emboli delivered.4 According to Table 2, the duration of CPB was much longer in one group with postoperative neurologic complications (n = 27) compared to the no-complication group (103 ± 43 min vs 82 ± 33 min, p = 0.01 [± SD]). The only way to quantify the number of microemboli during CPB is to use transcranial Doppler (TCD) monitoring. Did Ganushchak and associates use TCD monitoring during CPB?

Second, the authors have used two different hollow-fiber membrane oxygenators in this investigation. One wonders whether or not there was any significant difference between the oxygenators in 27 patients with postoperative neurologic complications. In 27 patients, did the authors calculate how many times one oxygenator was used vs the other oxygenator? Were there any significant differences between the two oxygenators?

Last, the authors have documented that the majority of patients with postoperative neurologic complications (21 of 27 patients) coincide with postoperative cardiac arrhythmias. It is not clear whether the neurologic complications were secondary to cardiac arrhythmias or not. The cause of postoperative neurologic complications in these 21 patients was probably due to ventricular arrhythmias rather the CPB procedure.5 We congratulate the authors for applying cluster analysis to this particular patient population, and we also believe that large fluctuations in hemodynamic parameters during CPB has caused significant postoperative neurologic risks.5

Ganushchak, YM, Fransen, EJ, Visser, C, et al (2004) Neurological complications after coronary artery bypass grafting related to the performance of cardiopulmonary bypass.Chest125,2196-2205. [CrossRef] [PubMed]
 
Blaut, CI Macroemboli and microemboli during cardiopulmonary bypass.Ann Thorac Surg1995;59,1300-1303. [CrossRef] [PubMed]
 
Barbut, D, Lo, YW, Gold, JP, et al Impact of embolization during coronary artery bypass grafting on outcome and length of stay.Ann Thorac Surg1997;63,998-1002. [CrossRef] [PubMed]
 
Brown, WR, Moody, DM, Challa, VR, et al Longer duration of cardiopulmonary bypass is associated with greater numbers of cerebral microemboli.Stroke2000;31,707-713. [CrossRef] [PubMed]
 
Luo, J, Zhu, X, Xiao, M, et al Clinical analyses of determinants of perioperative mortality and complications after cardiac valve replacement.Chin Circ J1996;11,159-163
 
To the Editor:

First, we thank Drs. Luo and Ündar for their comments on our investigation, and acknowledge them for recognizing the interest and importance of our article. In answer to the first comment, we like to express that we also recognize the fact that the number of emboli (micro and macro) delivered during cardiopulmonary bypass (CPB) could have an impact on the incidence of postoperative neurologic complications. Unfortunately, we were unable to use transcranial Doppler (TCD) routinely in our patients. However, a longer CPB procedure is theoretically accompanied by a higher number of emboli delivered, as was described previously.12 Therefore, although we did not use TCD, one could hypothesize that the aforementioned is confirmed by our findings as presented in Table 2. However, the large difference in number of patients in our study (27 patients with postoperative neurologic complications vs 1,368 patients without neurologic complications) made the results of the analysis of variance test suspicious. That is why we used cluster analyses, and in the sequence of these analyses the impact of duration of CPB on the development of postoperative neurologic complications disappeared. Nevertheless, microremobilization of cerebral vessels during CPB could be one of the factors explaining the significance of fluctuations in hemodynamic parameters in the increased risk for the development of postoperative neurologic complications. It is well documented that good blood flow through the brain might hasten the clearance of microemboli, and increased perfusion pressure during CPB has been proposed as a means of forcing air bubbles through the cerebral microcirculation.3 It is obvious that fluctuations in perfusion pressure could often provoke the stabilization of an embolus in a cerebral vessel and increase the duration of hypoxia and extend the area of hypoxic damage.

Second, the type of oxygenator indeed could affect the rate of microemboli during CPB4 and, in this way, be related to the incidence of postoperative neurologic complications. The two types of oxygenators used in our patients were used in sequence. Although the influence of oxygenator type on postoperative neurologic complications was beyond the scope of our study, we evaluated whether there was any significant fluctuation in the frequency of neurologic complications during the study period (between May 1996 and January 1999). This appeared not to be the case, and therefore we assumed that the type of oxygenator had no significant impact on the results as described in our article.

Third, in general, causal relations are extremely hard to prove in clinical research. In this retrospective study, we could not distinguish the sequence of events in complications development. Our results show that the development of severe postoperative neurologic events in all but the first clusters was statistically related to at least one coexistent complication. The interrelationship of these events makes the identification of the relative contribution of each single variable difficult. It is reported that the development of neurologic complications can be the result of low cardiac output syndrome (ie, severe arrhythmias).56Vice versa, cardiac injury can develop as a result of brain damage.78 Therefore, further studies are necessary to elucidate the relationship of these complications.

References
McKhann, GM, Goldsborough, MA, Borowicz, LM, Jr, et al Predictors of stroke risk in coronary artery bypass patients.Ann Thorac Surg1997;63,516-521. [CrossRef] [PubMed]
 
Brown, WR, Moody, DM, Challa, VR, et al Longer duration of cardiopulmonary bypass is associated with greater numbers of cerebral microemboli.Stroke2000;31,707-713. [CrossRef] [PubMed]
 
Edmonds, HL, Jr, Rodriguez, RA, Audenaert, SM, et al The role of neuromonitoring in cardiovascular surgery.J Cardiothorac Vasc Anesth1996;10,15-23. [CrossRef] [PubMed]
 
Georgiadis, D, Stets, R, Schorch, A, et al Doppler microembolic signals during cardiopulmonary bypass: comparison of two membrane oxygenators.Neurol Res2004;26,99-102. [CrossRef] [PubMed]
 
Mathew, JP, Fontes, ML, Tudor, IC, et al A multicenter risk index for atrial fibrillation after cardiac surgery.JAMA2004;291,1720-1729. [CrossRef] [PubMed]
 
Hogue, CW, Jr, Murphy, SF, Schechtman, KB, et al Risk factors for early or delayed stroke after cardiac surgery.Circulation1999;100,642-647. [CrossRef] [PubMed]
 
Knyshov, G, Shestunov, A, Ganushchak, I, Ivasiuk, V, Lakubiuk, S, Onishchenko, V Gas embolism of cerebral vessels in surgery with extra-corporeal circulation (clinical and pathophysiological aspects).Grud Serdechnososudistaia Khir (Russian)1991;5,33-35
 
Tung, P, Kopelnik, A, Banki, N, et al Predictors of neurocardiogenic injury after subarachnoid hemorrhage.Stroke2004;35,548-551. [CrossRef] [PubMed]
 

Figures

Tables

References

Ganushchak, YM, Fransen, EJ, Visser, C, et al (2004) Neurological complications after coronary artery bypass grafting related to the performance of cardiopulmonary bypass.Chest125,2196-2205. [CrossRef] [PubMed]
 
Blaut, CI Macroemboli and microemboli during cardiopulmonary bypass.Ann Thorac Surg1995;59,1300-1303. [CrossRef] [PubMed]
 
Barbut, D, Lo, YW, Gold, JP, et al Impact of embolization during coronary artery bypass grafting on outcome and length of stay.Ann Thorac Surg1997;63,998-1002. [CrossRef] [PubMed]
 
Brown, WR, Moody, DM, Challa, VR, et al Longer duration of cardiopulmonary bypass is associated with greater numbers of cerebral microemboli.Stroke2000;31,707-713. [CrossRef] [PubMed]
 
Luo, J, Zhu, X, Xiao, M, et al Clinical analyses of determinants of perioperative mortality and complications after cardiac valve replacement.Chin Circ J1996;11,159-163
 
McKhann, GM, Goldsborough, MA, Borowicz, LM, Jr, et al Predictors of stroke risk in coronary artery bypass patients.Ann Thorac Surg1997;63,516-521. [CrossRef] [PubMed]
 
Brown, WR, Moody, DM, Challa, VR, et al Longer duration of cardiopulmonary bypass is associated with greater numbers of cerebral microemboli.Stroke2000;31,707-713. [CrossRef] [PubMed]
 
Edmonds, HL, Jr, Rodriguez, RA, Audenaert, SM, et al The role of neuromonitoring in cardiovascular surgery.J Cardiothorac Vasc Anesth1996;10,15-23. [CrossRef] [PubMed]
 
Georgiadis, D, Stets, R, Schorch, A, et al Doppler microembolic signals during cardiopulmonary bypass: comparison of two membrane oxygenators.Neurol Res2004;26,99-102. [CrossRef] [PubMed]
 
Mathew, JP, Fontes, ML, Tudor, IC, et al A multicenter risk index for atrial fibrillation after cardiac surgery.JAMA2004;291,1720-1729. [CrossRef] [PubMed]
 
Hogue, CW, Jr, Murphy, SF, Schechtman, KB, et al Risk factors for early or delayed stroke after cardiac surgery.Circulation1999;100,642-647. [CrossRef] [PubMed]
 
Knyshov, G, Shestunov, A, Ganushchak, I, Ivasiuk, V, Lakubiuk, S, Onishchenko, V Gas embolism of cerebral vessels in surgery with extra-corporeal circulation (clinical and pathophysiological aspects).Grud Serdechnososudistaia Khir (Russian)1991;5,33-35
 
Tung, P, Kopelnik, A, Banki, N, et al Predictors of neurocardiogenic injury after subarachnoid hemorrhage.Stroke2004;35,548-551. [CrossRef] [PubMed]
 
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