Respiratory variations in pulse oximeter waveform amplitude are influenced by venous return in mechanically ventilated patients under general anaesthesia

Background and objectives: Respiratory variations in pulse oximetry plethysmographic waveform amplitude (Delta POP) are related to respiratory variations in arterial pulse pressure (Delta PP) in the critical care setting. The aims of this study were to test the hypothesis that in mechanically ventilated patients undergoing general anaesthesia, Delta POP calculation is feasible and can detect changes in preload. Methods: Twenty-five mechanically ventilated patients were studied immediately after induction of general anaesthesia. Haemodynamic data (mean arterial pressure [MAP], central venous pressure [CVP], Delta PP and Delta POP) were recorded at baseline, before and after tilting the patient from anti-Trendelenburg to Trendelenburg position in order to induce preload changes. Results: Change from anti-Trendelenburg to Trendelenburg position induced changes in MAP (5 8 +/- 9 to 67 +/- 10 mmHg, P < 0.05), CVP (4 +/- 4 to 13 +/- 5 mmHg, P < 0.05), Delta PP (14 +/- 8 to 7 - 5916, P < 0.05) and Delta POP (17 +/- 12 to 9 +/- 5%, P < 0.05). There was a significant relationship between Delta POP in anti-Trendelenburg position and percent change in MAP after volume expansion (r = 0.82; P < 0.05). Conclusions: Delta POP can be determined in the operating room and is influenced by changes in preload. This new index has potential clinical applications for the prediction of fluid responsiveness.