• Konrad Chachula, Florian Lieb, Florian Hess, Joellen Welter, Nicole Graf, and Alexander Dullenkopf.
• Institute for Anesthesia and Intensive Care Medicine, Spital Thurgau Frauenfeld, Frauenfeld, Switzerland.
• BMC Anesthesiol. 2020 Oct 24; 20 (1): 271.

BackgroundThe beach chair position that is commonly used in shoulder surgery is associated with relative hypovolemia, which leads to a reduction in arterial blood pressure. The effects of patient positioning on the accuracy of non-invasive continuous blood pressure monitoring with the ClearSight™ system (CS-BP; Edwards Lifesciences, Irvine CA, USA) have not been studied extensively. Our research aim was to assess agreement levels between CS-BP measurements with traditional blood pressure monitoring techniques.MethodsFor this prospective self-controlled study, we included 20 consecutively treated adult patients undergoing elective shoulder surgery in the beach chair position. We performed Bland-Altman analyses to determine agreement levels between blood pressure values from CS-BP and standard non-invasive (NIBP) methods. Perioperative measurements were done in both the supine (as reference) and beach chair surgical positions. Additionally, we compared invasive blood pressure (IBP) measurements with both the non-invasive methods (CS-BP and NIBP) in a sub-group of patients (n = 10) who required arterial blood pressure monitoring.ResultsWe analyzed 229 data points (116 supine, 113 beach chair) from the entire cohort; per patient measurements were based on surgical length (range 3-9 supine, 2-10 beach chair). The mean difference (±SD; 95% limits of agreement) in the mean arterial pressure (MAP) between CS-BP and NIBP was - 0.9 (±11.0; - 24.0-22.2) in the beach chair position and - 4.9 mmHg (±11.8; - 28.0-18.2) when supine. In the sub-group, the difference between CS-BP and IBP in the beach chair position was - 1.6 mmHg (±16.0; - 32.9-29.7) and - 2.8 mmHg (±15.3; - 32.8-27.1) in the supine position. Between NIBP and IBP, we detected a difference of 3.0 mmHg (±9.1; - 20.8-14.7) in the beach chair position, and 4.6 mmHg (±13.3; - 21.4-30.6) in the supine position.ConclusionsWe found clinically acceptable mean differences in MAP measurements between the ClearSight™ and non-invasive oscillometric blood pressure systems when patients were in either the supine or beach chair position. For all comparisons of the monitoring systems and surgical positions, the standard deviations and limits of agreement were wide.Trial RegistrationThis study was prospectively registered at the German Clinical Trial Register (www.DRKS.de; DRKS00013773 ). Registered 26/01/2018.

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