Plethysmography as a Useful Intraoperative Monitor

Data from both the traditional invasive cardiac monitors and the Nonin will be collected simultaneously. The investigators will analyze Nonin data for peak and trough variation with respiration, area under the curve, time from trough to peak, and slope, and compare these to data collected from the invasive monitors to look for correlations in clinically important parameters such as blood pressure, central venous pressure, cardiac output, etc.