Abstract
The effects of changes in position on systemic and cerebral circulation were studied in nine patients undergoing cervical spine operation in the sitting position under neuroleptanesthesia supplemented with diazepam and nitrous oxide, 50% in oxygen. Hemodynamic variables which include cardiac output, mean arterial pressure, mean pulmonary arterial pressure, pulmonary capillary wedge pressure, central venous pressure, and internal jugular venous pressure were measured and cerebral circulatory index (CCI) was calculated from arterial-jugular venous oxygen content difference before and after changes in position. When patients were placed to the sitting position from supine position before surgery, cardiac index (CI) decreased by 11% and systemic vascular resistance (SVR) increased by 34%. Cerebral perfusion pressure (CPP) and CCI were 82±5 (means±SEM) mm Hg and 17±1ml blood/ml O2 in the supine position, and 76±4mmHg and 15±1ml blood/ml O2 in the sitting position, respectively. After replacing the patients to the supine Position at the end of operation, CI increased by 14% and SVR decreased by 16%. CPP and CCI were 78±5mmHg and 17±2ml blood/ml O2 in the sitting position, and 86±6mmHg and 16±1ml blood/ml O2 in the supine position, respectively. There were no significant changes in either CPP or CCI with positioning. From these results, it was suggested that cerebral oxygen supply was adequate with positioning, if CPP was maintained above 76mmHg.
