Background: Beach chair position (BCP) is used in arthroscopic shoulder operations for its advantages. The BCP together with deliberate hypotension used to decrease intraoperative blood loss during arthroscopic shoulder procedures, this may have risk to cause postoperative neurological insults. Dexmedetomidine and esmolol are used to induce deliberate hypotension. Near-infrared spectroscopy (NIRS) provides a non-invasive technique of continuous monitoring of regional cerebral tissue oxygen saturation (rScO 2 ). In this study we evaluate the prevalence of rScO 2 during hypotensive anesthesia induced by intra-operative infusion of either dexmedetomidine or esmolol in patients undergoing elective arthroscopic shoulder surgery in the BCP. Patients and methods: Fifty patients scheduled for elective arthroscopic shoulder surgery under general anesthesia with hypotensive technique in BCP, randomly assigned into two equal groups, dexmedetomidine group (D Group) and esmolol group (E Group) according to the drug used for deliberate hypotension. MAP, HR, BIS and rS c O 2 were recorded before induction of anesthesia T 0 , post-induction of anesthesia T 1 as baseline, 5 min after BCP T 2 , 5 min after starting the studied drug T 3 , 30 min T 4 , 60 min T 5 , 90 min T 6 , 5 min after stopping the studied drug T 7 , 5 min after return to supine T 8 and after extubation T 9 . Results: In D group there was significant decrease in Lt.rs c o 2 and Rt.rs c o 2 , at T2 to T7 compared to T1. In E group there was significant decrease in Lt.rs c o 2 and Rt.rs c o 2 at T2, to T7 compared to T1. In D group two patients had CDEs compared to five patients in E group. Conclusion: In patients undergoing shoulder arthroscopic surgery under general anesthesia, the BCP significantly decreases rS c O 2 , with further slight decrease of rS c O 2 with dexmedetomidine and esmolol induced hypotension with no affection of postoperative cognitive function with both drugs. Dexmedetomidine and esmolol are safe drugs with better safety of dexmedetomidine over esmolol.

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