The purpose of this study is to evaluate the effects of hypercapnia on hemodynamics and cerebral oxygenation during shoulder arthroscopy.

The patients are randomly allocated to receive normocapnia or hypercapnia . After the 70º sitting position, record the mean arterial pressure (MAP), heart rate, and regional oxygen saturation (rSO2).

Inclusion Criteria:

• patients undergoing elective shoulder arthroscopic surgery

Exclusion Criteria:

• a history of age > 65 years, morbidly obesity (BMI > 30 kg/m2), diffuse lung disease, uncontrolled systemic hypertension, intracranial disease, cardiovascular and cerebrovascular disease.