Accuracy of ankle versus arm oscillometric non-invasive blood pressure in detecting hypotension during shoulder surgery in the beach-chair position: A prospective observational study.

Background and Aims: Accurate blood pressure monitoring is crucial in the beach-chair position (BCP), which poses a risk of cerebral hypoperfusion. This study compared arm and ankle non-invasive blood pressure (NIBP) with invasive arterial blood pressure (IBP) for detecting hypotension. Methods: This prospective observational study included 36 adults undergoing shoulder surgery in the BCP after obtaining written informed consent. The primary objective was to evaluate the diagnostic performance of arm and ankle NIBP in detecting hypotension at IBP. Secondary objectives assessed agreement with IBP using Bland-Altman analysis (BAA) and clinical risk using error grid analysis (EGA). Results: A total of 1088 paired NIBP-IBP readings were analysed, of which 326 were hypotensive. Arm mean arterial pressure (MAP) identified hypotension more accurately than ankle MAP, with a higher area under the curve of 0.83, 95% confidence interval (CI) 0.81-0.86 versus 0.72, 95% CI 0.70-0.76, Conclusion: In the beach-chair position, both ankle and arm NIBP are unreliable for detecting hypotension and invasive arterial monitoring should be preferred when accurate blood pressure assessment is vital.