Intraoperative Pleth Variability Index (PVI) Variability

PVI is derived from the infrared photoplethysmography signal. Intraoperatively during mechanical ventilation it reflect fluid responsiveness which is a surrogate endpoint of intravascular volume. PVI signal appears to have significant baseline variability which can not be explained by rapid changes in intravascular fluid volume. The baseline PVI changes also appear to oscillate at a very low frequency, much below any previously identified spontaneous vascular oscillations. The aim of this study is to investigate weather the PVI variability originates from changes in the infrared photoplethysmography signal or if they are possibly due to the algorithm calculating PVI.