enrollment too slow

Pleth Variability Index (PVI) is a variable that is derived from photoplethysmography (PPG) signal. It is used as a surrogate for intravascular volume status intraoperatively. PVI can have significant amount of baseline variability which appears to oscillate at a very low frequency (5-10 minute cycles). This study aims to investigate the origin of these baseline oscillations.

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.

Inclusion Criteria:

• Neurosurgical patients for tumor resection
• neurointerventional patients
• general anesthesia with mechanical ventilation
• communicates in english (consent)
• over 18 years of age

Exclusion Criteria:

• unable to sign consent
• less than 18 years of age

Neurosurgical and neurointerventional patients will be enrolled as these patients do rarely have sudden intravascular volume changes. Neurointerventional patients typically have no significant intravascular fluid changes, but do not routinely have intra-arterial catheters. Neurosurgical patients have slow, steady fluid shifts due to mannitol administration. Since most all of these patients have intra-arterial cannulas, it allows arterial waveform data collection which can be compared to the PPG signal.