CTICU Device Study CRUISE

Investigators will compare predictors of preload responsiveness, including pulse pressure variation (PPV) and stroke volume variation (SVV), and arterial dynamic elastance (Eadyn) in all patients and estimates of cardiac output (CO) in patients with an indwelling pulmonary artery catheter. in 50 intensive care unit, intubated patients during the patient's normal course of treatment using their usually present invasive monitoring devices for the first 8 hours following cardiac surgery. The primary goal of the study will be to compare PPV, SVV and Eadyn measured by the non-invasive monitors ClearSight, CareTaker and CNAP versus a reference standard that uses invasive arterial pressure waveform data, which in this case will be the LiDCO monitor \& FloTrac monitor. Investigators will calculate accuracy, precision and concordance of each of the parameters measured during steady state conditions and after specific interventions including the administration of crystalloid fluid boluses and changes in vasoactive or inotropic medications. As a secondary objective, investigators will compare measures of CO by the same non-invasive monitors with the pulmonary artery catheter as a reference standard during the same conditions as above (i.e., steady state conditions, and before/after interventions). CO will therefore be only compared in patients that have a pulmonary artery catheter in place.