Influence of the site of measurement on the ability of plethysmographic variability index to predict fluid responsiveness

Plethysmographic variability index (PVI) is an accurate predictor of fluid responsiveness in mechanically ventilated patients. However, the site of measurement of the plethysmographic waveform impacts its morphology and its respiratory variation. The goal of this study was to investigate the ability of PVI to predict fluid responsiveness at three sites of measurement (the forehead, ear, and finger) in mechanically ventilated patients under general anaesthesia. We studied 28 subjects after induction of general anaesthesia. Subjects were monitored with a pulmonary artery catheter and three pulse oximeter sensors (the finger, ear, and forehead). Pulse pressure variation, central venous pressure, cardiac index (CI), and PVI measured at the forehead, ear, and finger (PVIforehead, PVIear, and PVIfinger) were recorded before and after fluid loading (FL). Subjects were responders to volume expansion if CI increased >15% after FL. Areas under the receiver-operating curves to predict fluid responsiveness were 0.906, 0.880, and 0.836 for PVIforehead, PVIear, and PVIfinger, respectively (P