Zusammenhang zwischen Blutdruck und mittels Nahinfrarotspektroskopie gemessener zerebraler regionaler Sauerstoffsättigung bei Operationen in Beach-Chair-Position mit permissiver Hypotonie

Background: Severe cerebral ischaemia in orthopaedic patients undergoing shoulder surgery in beach chair position has been attributed to an inappropriately low systolic blood pressure. As a consequence it is currently recommended that the systolic blood pressure should not drop by more than 20% below the preoperative value measured in the supine position. The aim of our study was to show the effects of a drop in systolic blood pressure of more than 20% on cerebral oxygen saturation (rSO₂) measured by near-infrared spectroscopy (NIRS) based on slope deviations of the regression lines for both parameters. Methods: Included were 70 patients without cardiovascular health problems. Systolic blood pressure and rSO2 values were measured in beach chair position and mean values determined. Decreases in rSO2 of >20% or an absolute value <50% were defined as a cerebral desaturation event (CDE). The slope of the regression lines between systolic blood pressure and rSO2 was used to describe correlation differences between rSO2 and systolic blood pressure values of patients with and without CDE. Results: In patients without CDE, the median systolic blood pressure decreased by 41.9 mmHg (Q1: 32,4; Q3: 50,2; n=32) and by 47.2 mmHg (Q1: 37.5; Q3 55.7; n=27; p=0.29) in patients with CDE. The slope of the regression line was 0.11 (Q1: 0.05, Q3: 0.20; n=32) for patients without pathological rSO2 values and 0.22 (Q1: 0.16, Q3: 0.36; n=27; p<0.01) for patients with CDE. The receiver operating characteristic (ROC) curve for the different slope of the regression line for patients with or without CDE resulted in an area under the curve of 0.74. Conclusion: Permissive hypotension in the beach chair position led to a CDE in some cardiovascular healthy patients (n=27) while others were unaffected (n=32). Both groups revealed no significant difference in systolic blood pressure. The significantly smaller slope of the regression line in patients without CDE indicates a comparatively lower dependence of rSO2 on systolic blood pressure relative to patients with CDE.