Pulse pressure variation and ARDS

Fluid management is a crucial issue in patients with acute respiratory distress syndrome (ARDS). Assessment of preload responsiveness should help to define the best fluid strategy. Arterial pulse pressure variation (PPV), which represents the amplitude of the respiratory changes in arterial pulse pressure, is considered as a marker of preload responsiveness in patients mechanically ventilated and fully adapted to their ventilator. The good ability of PPV to predict fluid responsiveness has been confirmed in various clinical situations (sepsis, operative and post-operative periods). However, there are a number of limits of using PPV (e.g., spontaneous breathing activity, cardiac arrhythmias, low tidal volume ventilation, low lung compliance), which are particularly important in ARDS. Clinical studies have confirmed the poor reliability of PPV in predicting fluid responsiveness in patients with ARDS, ventilated according to the currently recommended lung protective strategy. Although a PPV >10-12% still keeps its good predictive value, a lower PPV (<10%) is far to guarantee fluid unresponsiveness since many false-negative cases can be encountered in this setting. Thus, performance of alternative preload responsiveness tests such as passive leg raising or end-expiratory occlusion tests, is necessary when low PPV values are measured. This review addresses the meaning of PPV, its conditions of use and its limits in ARDS patients.