Prediction of Fluid Responsiveness Using Dynamic Preload Indices During Arthroscopic Shoulder Surgery in the Beach Chair Position

The beach chair position (BCP) has been commonly used for shoulder arthroscopic surgery. Hemodynamic instability is frequently encountered problem associated with BCP. In addition, high rates of cerebral desaturation events have been reported during surgery in BCP. Although fluid loading could alleviate hypotension associated with BCP, it may lead to volume overload. As an alternative to static indices, dynamic preload indices such as pulse pressure variation (PPV) and stroke volume variation (SVV) were reported to be sensitive predictors of fluid responsivness in several surgical condition. The investigators will examine the abilities of PPV and SVV to predict fluid responsivness during shoulder arthroscopic surgery in BCP. Using transesophageal echocardiography (TEE), the investigators will directly estimate the change of cardiac output during BCP.