Comparing Pleth Variability Index (PVI) Measurements at Different Sensing Locations

Inclusion Criteria: * 18 years of age or older * Undergo any type of surgeries under general anesthesia in UCI Medical Center * Mechanically ventilated during surgery * Arterial line placement is preferred but not required * Agree to sign the consent and HIPAA forms Exclusion Criteria: * Less than 18 years of age * Pregnant women * Refused to sign the consent and HIPAA forms * Receive vasoactive medication prior to surgery * Has these conditions: hypotension, hypothyroidism, moderate or poorly controlled hypertension, chronic poorly-controlled diabetes, heart failure patients, and patients with active airway flow obstruction, left ventricular dysfunction, intra-cardiac shunts, right ventricular dysfunction, atrial fibrillation, arrhythmias * patients with surgeries at or around site of sensor placement * Subject has skin abnormalities affecting the digits such as psoriasis, eczema, angioma, scar tissue, burn, fungal infection, substantial skin breakdown, nail polish or acrylic nails that would prevent monitoring of SpO2 levels during the study