Study objectives: Neurologic disorders belong among the most serious complications of cardiac surgery. We tested the hypothesis that combinations of hemodynamic events from apparently normal cardiopulmonary bypass (CPB) procedures are related to the development of postoperative neurologic complications and affect the impact of common clinical risk factors.
Design: Retrospective study.
Setting: Cardiothoracic surgery department in a university hospital.
Methods and patients: A multivariate statistical procedure (ie, cluster analysis) was applied to a data set of automatically recorded perfusions from 1,395 patients who had undergone coronary artery bypass grafting. One-way analysis of variance was used to select five parameters with the strongest significant correlation to postoperative neurologic complications for further cluster analysis. The dependencies in the clusters were tested against common clinical risk factors. To our knowledge, this is the first study of its kind.
Results: The following five parameters emerged for cluster analysis: mean arterial pressure (MAP); dispersion of MAP; dispersion of systemic vascular resistance; dispersion of arterial pulse pressure; and the maximum value of mixed venous saturation. Using these parameters, we found four clusters that were significantly different by CPB performance (first cluster, 389 patients; second cluster, 431 patients; third cluster; and fourth cluster, 229 patients). The frequency of postoperative neurologic complications was 0.3% in the first cluster and increased to 3.9% in the fourth cluster. Importantly, the impact of common clinical risk factors for postoperative neurologic complications was affected by the performance of the CPB procedure. For example, the frequency of neurologic complications among patients with cerebrovascular disease in their medical history was 22% in the fourth cluster, whereas it was zero in the second cluster.
Conclusions: This study shows that apparently normal CPB procedures affect the impact of common clinical risk factors on postoperative neurologic complications. Patients who underwent CPB procedures with large fluctuations in hemodynamic parameters particularly showed an increased risk for the development of postoperative neurologic complications.