Predicting fluid responsiveness in mechanically ventilated patients

Fluid resuscitation is a frequent therapeutic strategy iintensive care unit. It is important to evaluate the volume status of patients and predict the fluid responsiveness before starting fluid therapy and to avoid the complication due to excessive fluid loading. But it is a challenging issue in mechanically ventilated patients. In paralytic and ventilator-dependent patients, the positive-pressure inspiration pattern which is opposing to spontaneous negative-pressure inspiration pattern in normal subjects leads to continuous and complex interaction with cardiovascular system. The results limit the efficacy of static parameters, such as central venous pressure, right atrial pressure, pulmonary capillary wedge pressure, right and left end-diastolic ventricular volume, in evaluating the volume status and predicting fluid responsiveness of ventilated patients. On the other hand, the dynamic parameters, such as systolic pressure variation, stroke volume variation, pulse pressure variation, were demonstrated to be useful in predicting fluid responsiveness of ventilated patients in clinical studies. In clinical practice, we may decide the most appropriate fluid resuscitation strategy according to these dynamic parameters as well as the individual condition of each patient, such as comorbid diseases, ventilator setting, coexisting spontaneous breathing or not, etc. and decrease the possible damage by excessive fluid loading.