The study seeks to compare PVI (pleth variability index) with SVV (stroke volume variation) in mechanically ventilated patients in the ICU.
The purpose is to see if fluid volume status and response can be assessed using a totally noninvasive method: the pulse oximeter.

Inclusion criteria: 
1. Adults
2. Mechanically ventilated without spontaneous respirations
3. No sustained arrhythmias (PVCs, Afib..)
4. Patient connected to a FloTrac as part of their treatment

Exclusion Criteria
1. Less than 18 years old
2. Presence of spontaneous breathing
3. Absence of a Flotrac
4. Sustained arrhythmias