Pleth variability index to monitor the respiratory variations in the pulse oximeter plethysmographic waveform amplitude and predict fluid responsiveness in the operating theatre

Background. Respiratory variations in pulse oximetry plethysmographic waveform amplitude (Delta POP) can predict fluid responsiveness in mechanically ventilated patients but cannot be easily assessed at the bedside. Pleth variability index (PVI) is a new algorithm allowing for automated and continuous monitoring of Delta POP. We hypothesized that PVI can predict fluid responsiveness in mechanically ventilated patients under general anaesthesia. Methods. Twenty-five patients were studied after induction of general anaesthesia. Haemodynamic data [cardiac index (CI), respiratory variations in arterial pulse pressure (Delta PP), Delta POP, and PVI] were recorded before and after volume expansion (500 ml of hetastarch 6%). Fluid responsiveness was defined as an increase in CI >= 15%. Results. Volume expansion induced changes in CI [2.0 (SD 0.9) to 2.5 (1.2) litre min(-1) m(-2); P < 0.01], Delta POP [15 (7)% to 8 (3)%; P < 0.01], and PVI [14 (7)% to 9 (3)%; P < 0.01]. Delta POP and PVI were higher in responders than in non-responders [19 (9)% vs 9 (4)% and 18 (6)% vs 8 (4)%, respectively; P < 0.01 for both]. A PVI > 14% before volume expansion discriminated between responders and non-responders with 81% sensitivity and 100% specificity. There was a significant relationship between PVI before volume expansion and change in CI after volume expansion (r=0.67; P < 0.01). Conclusions. PVI, an automatic and continuous monitor of Delta POP, can predict fluid responsiveness non-invasively in mechanically ventilated patients during general anaesthesia. This index has potential clinical applications.