In this study, the concentration of hemoglobin within the subject's blood is affected by fluid status changes. The fluid status is affected by fluid loss during surgery for hospitalized study subjects or controlled administration of fluids intravenously for healthy study volunteers. The accuracy of a noninvasive hemoglobin sensor(s) will be assessed by comparing with blood sample analysis.

Healthy Volunteers

Inclusion Criteria:

• Has physical status between ASA 1 or 2
• Able to communicate in English

Exclusion Criteria:

• Pregnant or sexually active without birth control.
• Hemoglobin less than 11g/dL
• Known alcohol or drug abuse
• Skin abnormalities affecting the digits such as psoriasis, eczema, angioma, scar tissue, burn, fungal infection
• Nail polish
• Head injury with loss of consciousness within the last year
• Known neurological and psychiatric conditions.
• Known concurrent chronic usage of psychoactive or anti-convulsive drugs within the last 90 days, or use in the last 7 days (i.e. tricyclic antidepressants, MAO inhibitors, lithium, neuroleptics, anxiolytics or antipsychotics. Except SSRIs
• Subject has any medical condition which, in the judgement of the investigator, renders them inappropriate for participation in this study, such as Reynauds syndrome
• Hypertension: Systolic BP >= 140 mmHg or Diastolic BP >= 90 mmHg
• Baseline heart rate <50 beats per minute

Surgical Subjects

Inclusion Criteria:

• Age > 18 years old
• Scheduled for surgery requiring frequent schedule blood draws as a part of their routine care

Exclusion Criteria:

• Pregnant or lactating women
• Skin abnormalities at the planed application sites that would interfere with transilluminating the finger, or other measurement sites, like burns, scar tissue, nail polish, infections etc.