The purpose of this study is to investigate whether a validated sensor that is able to measure how much oxygen-carrying molecules called hemoglobin using pulse hemoglobin and Pleth Variability Index (PVI)] are in your blood during surgery can help your doctors manage how much fluid and possibly blood you need to get during your surgery. The hope of the study is that the device may provide an early indication you are having bleeding and this may mean you need to be treated with a transfusion. Our current method of checking this is by getting a blood sample for analysis. The investigators hope is that this device may be able to alert the clinician of the need for blood or fluids without a blood draw being needed.

Inclusion Criteria:

• Subjects must be >18 years old;
• must be having a major surgical procedure;
• The pre-operative estimation of blood loss must be at least 15% of the total blood volume

Exclusion Criteria:

• Does subject have hemoglobinopathy;
• cardiac arrhythmias producing irregular rhythms;
• severe pulmonary disease;
• procedures where loss of more that 10 to 15% of total blood volume is unlikely;
• subject refusal

The study population will be adults more than 18 years old that are scheduled for a major surgical procedure.