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The use of continuous cerebral oximetry as a diagnostic tool to reduce the incidence of stroke in a high risk population / by Peter S. Scherkenbach, B.S.

by Scherkenbach, Peter S.

Cardiopulmonary bypass -- Adverse effects

Cerebrovascular Accident.

Neurologic examination

vi, 83 leaves : ill. ; 29 cm.

Committee chairperson: Dr. Larry Fennigkoh.

Committee members: Dr. Lisa Milkowski, Dr. Vincent Canino, Michael Gough.

Introduction -- Mechanisms of neurologic injury -- Risk factors for neurologic injury -- Neuromonitoring alternatives -- Purpose -- Cerebral -- Background -- Cerebral oxygenation -- Delivery of oxygenated hemoglobin -- Cerebral oxygen consumption -- Correlation of rCVOS and neurologic outcome -- Origin of the baseline -- Validity of transcranial NIRS -- Cost reduction with neuromonitoring -- Materials and methods -- Model for patient selection and evaluation -- Perioperative management -- Monitoring physiologic parameters -- Perfusion protocol -- Neurologic assessment -- Statistical analysis -- Results -- Discussion -- Physiologic parameters correlate with rCVOS -- Limitations of the GLM -- Multimodality neuromonitoring -- Appendices A- Instructions for authors B- SLMC database information C- Institutional review and patient informed consent documents D- Physiologic correlation data E- Raw data for general linear model (GLM).

The occurrence of neurologic deficits of patients undergoing cardiac procedures is an area of much discussion. Since neurologic dysfunction remains one of the major contributors to patient morbidity following cardiac procedures, there is a necessity to alleviate the brain injury incurred. This study focused on reducing the stroke rate in the cardiac surgery patient requiring cardiopulmonary bypass (CPB).

The hypothesis tested was aimed at evaluating whether the stroke rate at St. Luke's Medical Center (Milwaukee, Wisconsin) could be reduced using the Somanetics INVOS® 4100 Cerebral Oximeter (Troy, MI) to evaluate intervals of cerebral ischemia and subsequently modify the perfusion and operative technique to adjust for the malady. The study was also intended to evaluate whether hospital and intensive care unit (ICU) stay was lengthened by the occurrence of neurologic dysfunction. Secondary explorations into collected cerebral oximeter data were investigated to ascertain possible correlation between the cerebral saturation waveforms and the patients' physiologic parameters. This was done to identify possible trends that were useful in predicting cerebral saturation and to evaluate the success of the perfusion interventions.

Risk scores and risk factors were obtained from a cardiac patient database at St. Luke's Medical Center using a stepwise multiple logistic regression. Patients were included into the study based upon a risk score that was used to determine whether to place those patients into a category termed as high risk for stroke. Seven independent risk factors were discovered and represented by odds ratios. The odds ratios demonstrated that a particular risk was more likely to have a stroke by a number of times greater than the average.

Patients who were included into the study exhibited risk factors that set the sum of the odds ratio greater than or equal to 9.0. This value was selected because the sum of the odds ratios above 9.0 placed those patients in a category where the risk of stroke was approximately 11.4%. The patients were all monitored using the Somanetics INVOS® 4100 cerebral oximeter (Troy, MI) and subsequently managed with the implemented perfusion protocol. A patient population from June 1996 to July 1998 served as a historic control.

The procedures included in this study were limited to coronary artery bypass grafts and valvular procedures. Redo operations were not excluded, however, concurrent carotid endarterectomy and aortic aneurysm repairs were excluded from this study. Thirty subjects were enrolled in the study. Two patients were excluded from the statistical analysis: one was for a carotid endarterectomy added late into the scheduling, and the second was for a concomitant ascending aortic aneurysm repair on an aortic valve replacement.

The 28 patients that remained in the study for postoperative evaluation exhibited no signs of a cerebral vascular accident. This data when compared to the historic control showed moderate statistical significance (χ2=3.555, ρ=0.059). Six patients that had been noted for exhibiting signs of transient neurologic dysfunction (e.g. cognitive deficits, confusion, or dementia), showed a statistically significant increase in hospital stay (ρ=0.042) and ICU stay (ρ=0.012). The results of this clinical evaluation show some evidence that neurologic injury can be reduced using the Somanetics INVOS® 4100 Cerebral Oximeter as a neuromonitoring technique.

Although the tested hypothesis was not statistically significant at the ρ=0.05 level, the trend may indicate a reduction in stroke rate. Valuable information was gathered correlating the patient's physiologic parameters and cerebral saturation as indicated by the Somanetics INVOS® 4100 cerebral oximeter. This information could be used to validate the diagnostic device and give credence to the interventions that were implemented to alleviate the ischemic intervals. Further research is necessary to support these results.

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