Prediction of fluid responsiveness by a continuous non-invasive assessment of arterial pressure in critically ill patients: comparison with four other dynamic indices.

BACKGROUND We evaluated the ability of an infrared photoplethysmography arterial waveform (continuous non-invasive arterial pressure, CNAP) to estimate arterial pulse pressure variation (PPV). We compared the ability of non-invasive PPV to predict fluid responsiveness with invasive PPV, respiratory variation of pulse contour-derived stroke volume, and changes in cardiac index induced by passive leg raising (PLR) and end-expiratory occlusion (EEO) tests. METHODS We measured the responses of cardiac index (PiCCO) to 500 ml of saline in 47 critically ill patients with haemodynamic failure. Before fluid administration, we recorded non-invasive and invasive PPVs, stroke volume variation, and changes in cardiac index induced by PLR and by 15 s EEO. Logistic regressions were performed to investigate the advantage of combining invasive PPV, stroke volume variation, PLR, and EEO when predicting fluid responsiveness. RESULTS In eight patients, CNAP could not record arterial pressure. In the 39 remaining patients, fluid increased cardiac index by ≥15% in 17 'responders'. Considering the 195 pairs of measurements, the bias (sd) between invasive and non-invasive PPVs was -0.6 (2.3)%. The areas under the receiver operating characteristic (ROC) curves for predicting fluid responsiveness were 0.89 (95% confidence interval, 0.78-1.01) for non-invasive PPV compared with 0.89 (0.77-1.01), 0.84 (0.70-0.96), 0.95 (0.88-1.03), and 0.97 (0.91-1.03) for invasive pulse pressure, stroke volume variations, PLR, and EEO tests (no significant difference). Combining multiple tests did not significantly improve the area under the ROC curves. CONCLUSIONS Non-invasive assessment of PPV seems valuable in predicting fluid responsiveness.