The purpose of the study is to determine if the less invasive monitors are as reliable for measuring heart function in patients undergoing liver transplantation as the more invasive pulmonary artery.

Pulmonary artery catheter (PAC)is considered the gold standard in monitoring of heart function during orthotopic liver transplantation (OLT). Placement of PAC is very invasive (it passes thorough the heart chambers and into the pulmonary artery) and its benefits on the outcomes have not been proven. This study compares two newer FDA approved much less invasive devices to the PAC. The two new devices assess the heart function based either on the peripheral arterial waveform alone (Vigileo, Edwards Lifesciences)or the combination of peripheral arterial waveform and chemical indicator dilution (LiDCO, Cambridge, UK).

Inclusion Criteria:

• Patients over 18 years of age
• Scheduled for liver transplantation
• Patient undergoing vascular surgery where invasive arterial pressure is indicated (control subjects)

Exclusion Criteria:

• We will exclude patients taking lithium based medication
• Patients who weigh less than 40 kg; AND
• Patients who are pregnant

20 subjects will be enrolled in this observational study in the Liver Transplant Group; 10 patients in the Other Surgery Control Group for a total of 30 subjects. Patients will be recruited from the Operating Room schedule. Written, informed consent will be obtained from each subject prior to surgery. All participants will be informed that they may decline to participate in, or withdraw from, the study at any time.