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Eur J Cardiothorac Surg 2007;32:507-513. doi:10.1016/j.ejcts.2007.06.006
Copyright © 2007, European Association for Cardio-Thoracic Surgery. Published by Elsevier B.V. All rights reserved

Cognitive brain function after hypothermic circulatory arrest assessed by cognitive P300 evoked potentials

^a Department of Thoracic and Cardiovascular Surgery, University Hospital of Saarland, Homburg, Germany
^b Department of Psychiatry and Psychotherapy, University Hospital of Saarland, Homburg, Germany
^c Department of Public Health, Hokkaido University Graduate School of Medicine, Sapporo, Japan

Received 20 November 2006; received in revised form 14 May 2007; accepted 4 June 2007.

^_* Corresponding author. Address: Department of Thoracic and Cardiovascular Surgery, University Hospital of Saarland, 66421 Homburg, Germany. Tel.: +49 6841 1632000; fax: +49 6841 1632005. (Email: h-j.schaefers{at}uniklinikum-saarland.de).

Background: The role of hypothermic circulatory arrest (HCA) in cardiovascular surgery is controversial and assumed to result in neurocognitive dysfunction that is not always detected by standard clinical observation. We assessed cognitive P300 visual evoked potentials (P300) in patients undergoing either HCA or coronary artery bypass grafting (CABG) to elucidate whether HCA was associated with postoperative cognitive decline. Methods: Thirteen patients undergoing either aortic arch replacement (n = 4) or pulmonary thromboendarterectomy (n = 9) using HCA (mean: 28 ± 11 min, 22 ± 2 °C) were studied. They were compared to 13 patients undergoing on-pump CABG. P300s were measured 1 day before and 1 week after the operation. We assessed an area under the curve (AUC) between 280 and 600 ms and center of this area [Ct (time), Cv (voltage)]. The ratio of these parameters acquired by target (TG) and non-target (NTG) stimulus (TG/NTG) was calculated to assess concentration on TG stimulus and defined as concentration index (CI: CI(AUC), CI(Ct), and CI(Cv)). Results: There was no significant difference in preoperative characteristics between groups. There were neither strokes nor hospital deaths. Preoperatively, the HCA group could not concentrate on target stimulus as well as the control group in frontal leads (CI(AUC) and CI(Cv) were lower in HCA group than in control group). However, the HCA group could concentrate on target stimulus better than the control group postoperatively because postoperative CI(AUC) (pre-operation: 1.1 ± 0.5 to post-operation: 1.7 ± 0.4, P = .02) and CI(Cv) (1.1 ± 0.4 to 1.6 ± 0.4, P = .01) were significantly improved in the HCA group, whereas these were significantly impaired in the control group (CI(AUC): 1.6 ± 0.6 to 1.3 ± 0.4, P = .03, CI(Cv): 1.5 ± 0.5 to 1.2 ± 0.3, P < .01). Postoperative CI(Ct) in the HCA group were significantly impaired in all leads. The duration of HCA did not correlate with any values of postoperative P300. No specific trends were observed in either preoperative or postoperative P300 values between patients with or without postoperative temporary neurological dysfunction (one in each group). Postoperative improvement of CI(AUC) and CI(Cv) in Fz lead were found in 85 and 69% in the HCA group and 23 and 23% in the control group, respectively (CI(AUC): P < .01, CI(Cv): P < .05). Conclusions: P300 detected no significant neurocognitive impairment due to the relatively brief period of HCA (approximately 28 min).

Key Words: Hypothermic circulatory arrest • Neurocognitive dysfunction • P300 visual evoked potentials • Aortic arch replacement • Pulmonary thromboendarterectomy