Assessment of fluid responsiveness in patients under spontaneous breathing activity.

To assess fluid responsiveness in patients under spontaneous breathing activity ventilation remains a challenge for intensive care physicians. Much of the knowledge on heart-lung interactions and dynamic indexes of fluid responsiveness may not be useful for these patients. Historically, the most frequently used variables to guide fluid responsiveness on this population have been the static preload indexes. However, more recently, dynamic indexes from less invasive devices are being often used, even though their usefulness on spontaneously-breathing subjects remains controversial. The purpose of this article was to review evidences on the assessment of fluid responsiveness in patients under spontaneous ventilation. A search in literature showed poor evidence for use of static variables, such as filling pressures and ventricular end-diastolic volumes. Dynamic indexes, such as pulse pressure variation and other indexes had not been appropriately tested during spontaneous ventilation. Favorable results were found with central venous pressure variation and with transthoracic echocardiography or transesophageal Doppler dynamic indexes, especially when associated to passive lower limb elevation. We conclude that although central venous pressure variation and echocardiography variables could aid bedside clinicians in assessing fluid responsiveness during spontaneous ventilation, more studies on this subject are definitely required.