Automated, continuous and non-invasive assessment of pulse pressure variations using CNAP system.

Non-invasive respiratory variations in arterial pulse pressure using infrared-plethysmography (PPV) are able to predict fluid responsiveness in mechanically ventilated patients. However, they cannot be continuously monitored. The present study evaluated a new algorithm allowing continuous measurements of PPV (PPV) (CNSystem, Graz, Austria). Thirty-five patients undergoing vascular surgery were studied after induction of general anaesthesia. Stroke volume was measured using the Vigileo/FloTrac. Invasive pulse pressure variations were manually calculated using an arterial line (PPV) and PPV was continuously displayed. PPV and PPV were simultaneously recorded before and after volume expansion (500 ml hydroxyethylstarch). Subjects were defined as responders if stroke volume increased by ≥15 %. Twenty-one patients were responders. Before volume expansion, PPV and PPV exhibited a bias of 0.1 % and limits of agreement from -7.9 % to 7.9 %. After volume expansion, PPV and PPV exhibited a bias of -0.4 % and limits of agreement from -5.3 % to 4.5 %. A 14 % baseline PPV threshold discriminated responders with a sensitivity of 86 % (95 % CI 64-97 %) and a specificity of 100 % (95 % CI 77-100 %). Area under the receiver operating characteristic (ROC) curve for PPV was 0.93 (95 % CI 0.79-0.99). A 15 % baseline PPV threshold discriminated responders with a sensitivity of 76% (95 % CI 53-92 %) and a specificity of 93 % (95 % CI 66-99 %). Area under the ROC curves for PPV was 0.91 (95 % CI 0.76-0.98), which was not different from that for PPV. When compared with PPV, PPV performs satisfactorily in assessing fluid responsiveness in hemodynamically stable surgical patients.