Inclusion Criteria:

1. Patient is in hospital for study indicated treatment.
2. Patient is able to comply with the study procedure.
3. Patient must require an indwelling radial or a femoral artery catheter.
4. Patients with an American Society of Anesthesiologists Risk Score >= 3.
5. Lee Risk Index >/= 2 (Hypertension and Pre-diabetic metabolic state).
6. Patient must be 40 kg or heavier.
7. Patient has consented to be in the trial.
8. Patient's height and weight can be accurately obtained prior to study start.
9. Patient's ability to undergo major surgery with an anticipated blood loss > 500 ml.

Exclusion Criteria:

1. Patients with contraindications for the placement of radial, femoral, or other arterial cannula.
2. Patients with contraindications for the placement of central venous cannula.
3. Patients being treated with an intra-aortic balloon pump.
4. Patients with aortic valve regurgitation.
5. Patients with atrial fibrillation.
6. Female patients with a known pregnancy confirmed by urine pregnancy test.
7. Patient is currently participating in an investigational drug or another device study that has not completed the primary endpoint or that clinically interferes with the study endpoints.