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Ann Thorac Surg 2006;81:519-521
© 2006 The Society of Thoracic Surgeons

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Original article: Cardiovascular

Cerebral Microembolization During Antegrade Selective Cerebral Perfusion

^a Division of Thoracic and Cardiovascular Surgery, Hannover Medical School, Hannover, Germany
^b Division of Anesthesiology, Hannover Medical School, Hannover, Germany

Accepted for publication July 22, 2005.

^_* Address correspondence to Dr Kamiya, Division of Thoracic and Cardiovascular Surgery, Hannover Medical School, Carl-Neuberg-Strasse 1, 30625 Hannover, Germany (Email: hkamiya88{at}yahoo.co.jp).

	Abstract

Top Abstract Introduction Material and Methods Results Comment References

 
BACKGROUND: This study quantified the number of intraoperative microemboli in patients undergoing aortic arch surgery using selective cerebral perfusion (SCP) in comparison with those in patients undergoing ascending aortic replacement without circulatory arrest and SCP.

METHODS: A transcranial Doppler monitoring of the medial cerebral artery was performed in 15 patients undergoing proximal arch replacement with SCP (SCP group) and 15 patients undergoing replacement of the ascending aorta (control group).

RESULTS: There was no significant difference in the high-intensity transient signal counts between the SCP group and the control group at any phase. In the SCP group, 4.8% of microemboli occurred during cross-clamping, and only 0.6% occurred during SCP. In the control group, 4.6% occurred during cross-clamping. Most microemboli occurred after removing the cross-clamps in both groups; 92.2% in the SCP group and 92.1% in the control group.

CONCLUSIONS: The present study demonstrated that outbreak frequency of microemboli during SCP was very low, and thus implies that the risk of embolic event that may be caused by SCP is very low.

	Introduction

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Although it is well known that antegrade selective cerebral perfusion (SCP) is a reliable technique for cerebral protection during the repair of aortic arch aneurysm [1–3], the occurrence of accidental embolization of atheromatous debris or air bubble during SCP has been raised as one of the criticisms against this procedure [4]. However, there has been no report of evidence regarding cerebral microembolism during SCP. High-intensity transient signals (HITS), detected using transcranial Doppler ultrasonography, result from an increase in the ultrasound signal reflected from the microemboli compared with the normal level of the surrounding blood and can provide an index of microemboli entering the cerebral circulation [5, 6]. This study quantified the number of intraoperative microemboli in patients undergoing aortic arch surgery using SCP in comparison with those in patients undergoing ascending aortic replacement without circulatory arrest and SCP.

	Material and Methods

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Patients
Fifteen patients undergoing proximal arch replacement with SCP (SCP group) and 15 patients undergoing replacement of the ascending aorta (control group) were included in the study. Preoperative carotid duplex sonography was performed on all patients. Exclusion criteria were as follows: carotid artery stenosis, reoperation, and emergency operation. Patient characteristics are summarized in Table 1. The review board of our institute approved this study, the purpose of this study was explained to each patient, and informed consent for this study was obtained from all patients.

In the SCP group, the ascending aorta was clamped, and manipulation of the proximal site was performed. After the patients were cooled to a nasopharyngeal temperature of 26° to 28°C, the systemic circulation was arrested, the aneurysm was opened, and the arterial cannula was removed. With the patient in the Trendelenburg position, 15F retrograde coronary sinus perfusion cannulas (Medtronic DLP, Grand Rapids, MI) connected to the oxygenator with a separate single-roller pump head were inserted into the innominate artery and the left carotid artery. The left subclavian artery was clamped or occluded with a Fogarty catheter (Baxter Healthcare Corp, Deerfield, IL) to avoid the steal phenomenon. Cerebral perfusion was initiated at a rate of 10 mL · min^–1 · kg^–1 and adjusted to maintain a pressure of between 40 and 60 mm Hg. Then, hemiarch replacement was performed. Selective cerebral perfusion was ceased, and cardiopulmonary bypass was resumed with the perfusion cannula directly reinserted into the graft. In the control group, the ascending aorta was clamped just below the innominate artery and opened. The patients were cooled to a temperature of 28° to 30°C. Removal of air was performed in a similar manner in both groups. First, a small hole was made on the graft and the air in the heart cavity was taken out through it by inflating the lung and massaging the heart. Then, the patient was placed in the Trendelenburg position and the heart was elevated. The apical part of the heart was punctured, and the remaining air was removed. The hole made in the graft was used for continuing the air removal until the patient was weaned from cardiopulmonary bypass. The use of carbon dioxide was not applied in this study.

Transcranial Doppler Technique
A bilateral transcranial Doppler monitoring of the medial cerebral artery (Pioneer TC8080; Medilab, Germany) was performed in all the patients. For this purpose, the patients were placed in the supine position, and two 2-MHz ultrasound transducers were attached bitemporally over the preauricular transcranial window. The insonation depth was adjusted to the best possible Doppler signal. The power was set at 30%, and the range of sensitivity was individually adjusted depending on the Doppler signal. Acoustic signals were recorded for off-line analysis. The HITS, detected using transcranial Doppler monitoring, result from an increase in the ultrasound signal reflected from the microemboli compared with the normal level of the surrounding blood and can provide an index of microemboli entering the cerebral circulation. Transcranial Doppler monitoring was performed from the time of skin incision until wound closure.

Statistical Methods
Statistical analysis was performed using Student's t test for continuous variables or ² tests (Fisher's exact tests if n < 5) for categorical variables. A p value less than 0.05 was considered significant. All statistical analyses were performed using SPSS 10.0 software (SPSS Japan Inc, Tokyo, Japan).

	Results

Top Abstract Introduction Material and Methods Results Comment References

 
One patient in the SCP group died owing to multiorgan failure, and 1 in the control group died of low output syndrome. Temporary neurologic dysfunction without permanent neurologic damages occurred in 3 patients in the SCP group (postoperative confusion in 2 patients and delirium in 1 patient) and 2 patients in the control group (postoperative confusion in both patients).

The HITS count in both groups is presented in Table 2. There was no significant difference in the HITS count between the SCP group and the control group at any phase. In the SCP group, 4.8% of microemboli occurred during cross-clamping, and only 0.6% occurred during SCP. In the control group, 4.6% occurred during cross-clamping. Most microemboli occurred after removing the cross-clamps in both groups: 92.2% in the SCP group and 92.1% in the control group.

	Comment

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Up to present, there has been no study regarding the occurrence of cerebral microemboli during SCP, although this has been one of the major criticisms against SCP. The present study showed remarkably low occurrence of microemboli during SCP, accounting for only 0.6% of those that occurred during the operations. Moreover, although in one group patients underwent proximal arch replacement with circulatory arrest and SCP, and patients in the other underwent replacement of the ascending aorta without those two procedures, there was no significant difference in the total number of microemboli between the two groups.

The transcranial Doppler detects cerebral microemboli as HITS because an embolus causes an increase in the amount of reflected ultrasound compared with the amount normally caused by red blood cells [7]. Gaseous microemboli, atherosclerotic debris dislodged from the vascular wall, lipid microemboli caused by use of the cardiotomy suction and denaturation of proteins, and platelet and blood cell aggregation during cardiopulmonary bypass are considered to be possible sources of the HITS [5]. It seems that the majority of microemboli detected in the present study may be gaseous microemboli because they occurred after the removal of the cross-clamps. However, it remains unclear as to which source caused cerebral microemboli during SCP.

It is well known that these microemboli may cause cognitive impairment if they enter the cerebral circulation in significant numbers [7]. This has been studied in detail in patients who have received coronary artery bypass graft surgery. Borger and coworkers [8] reported that patients with increased perfusionist interventions, and therefore increased gaseous microemboli, had significantly worse performances on tests of learning, memory, and attention and concentration. It seems very doubtful that the very small numbers of cerebral microemboli during SCP observed in the present study could cause functional impairment of the brain, but the consequences, including postoperative cognitive impairment, should be investigated in further studies.

In conclusion, we found that the outbreak frequency of microemboli during SCP was very low, accounting only for 0.6% of the total microemboli observed during operations, and the vast majority occurred after removing the cross-clamps without relation to the use of circulatory arrest and SCP. The results of this study imply that the risk of embolic events caused by SCP is very low.

	References

Top Abstract Introduction Material and Methods Results Comment References

 

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2. Di Eusanio M, Schepens MA, Morshuis WJ, Di Bartolomeo R, Pierangeli A, Dossche KM. Antegrade selective cerebral perfusion during operations on the thoracic aortafactors influencing survival and neurologic outcome in 413 patients. J Thorac Cardiovasc Surg 2002;124:1080-1086.[Abstract/Free Full Text]
3. Kazui T, Yamashita K, Washiyama N, et al. Usefulness of antegrade selective cerebral perfusion during aortic arch operations Ann Thorac Surg 2002;74(Suppl):S1806-S1809.[Abstract/Free Full Text]
4. Okita Y, Minatoya K, Tagusari O, Ando M, Nagatsuka K, Kitamura S. Prospective comparative study of brain protection in total aortic arch replacementdeep hypothermic circulatory arrest with retrograde cerebral perfusion or selective antegrade cerebral perfusion. Ann Thorac Surg 2001;72:72-79.[Abstract/Free Full Text]
5. Abu-Omar Y, Balacumaraswami L, Pigott DW, Matthews PM, Taggart DP. Solid and gaseous cerebral microembolization during off-pump, on-pump, and open cardiac surgery procedures J Thorac Cardiovasc Surg 2004;127:1759-1765.[Abstract/Free Full Text]
6. Scarborough JE, White W, Derilus FE, et al. Combined use of off-pump techniques and a sutureless proximal aortic anastomotic device reduces cerebral microemboli generation during coronary artery bypass grafting J Thorac Cardiovasc Surg 2003;126:1561-1567.[Abstract/Free Full Text]
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This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Hiroyuki Kamiya Uwe Klima Christian Hagl Klaus Kallenbach Axel Haverich Matthias Karck Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Kamiya, H. Articles by Karck, M. Search for Related Content PubMed PubMed Citation Articles by Kamiya, H. Articles by Karck, M. Related Collections Cerebral protection