Abstract:Abstract: Objective?To evaluate the effect of permissive hypercapnia ventilation on the cerebral oxygen saturation and postoperative cognitive function in patients undergoing arthroscopic shoulder surgery in beach chair position (BCP).?Methods?86 ASA Ⅰ ~ Ⅲ patients, aged 60?~?79 y, weight 42?~?78 kg, underwent elective arthroscopic shoulder surgery in the beach chair position (BCP), were divided into 2 groups using random number table method: control group (group C, n?=?43, PETCO2 35 ~ 40?mmHg) and permissive hypercapnia group (group H, n?=?43, PETCO2 50?~?55?mmHg). The rSO2 was monitored by using the near infrared specrometer (NIRS). Record the regional cerebral oxygen saturation (rSO2) in the time before anesthesia (T0), 5 min after induction (T1), 5 min after BCP (T2), 5 min after ventilation (the PETCO2 was maintained at 35 ~ 40 mmHg in the group C, and 50 ~ 55 mmHg in the group H by adjusting the anaesthesia machine, the mean arterial pressure was maintained at 60 ~ 65 mmHg) (T3), 30 min after ventilation (T4), 1 h after ventilation (T5) and 5 min after supine (T6). The occurrence of cerebral desaturation event (CDE), anaesthetic resuscitation and adverse reactions. Blood samples were taken from the peripheral venous at time of T0, T6 and T7 to check the protein concentrations of Aβ-42 and S100β. Cognitive function was assessed by mini-mental state examination (MMSE) at 1 day before operation and 1 d, 7 d after operation.?Results?Compared with T0, the rSO2 in group C was significantly decreased at T1?~?T6 (P??0.05). Compared with the time before operation, the MMSE score of two groups decreased at 1?d after the operation (P?