Assessment of fluid responsiveness in spontaneously breathing patients

Abstract

Assessment of volume responsiveness is an important issue in patients with spontaneous breathing activity. The difficulty in predicting the response to fluid infusion in this population of patients is variable and depends on the clinical situation. Three different scenarios must be distinguished: The first scenario refers to patients admitted to the emergency room for evident acute blood losses or body fluid losses. The diagnosis of hypovolemia is almost certain and the presence of clinical signs of hemodynamic instability (hypotension, tachycardia, oliguria, mottled skin, altered mental status, etc) strongly suggests that a positive hemodynamic response to volume resuscitation will occur, although these signs lack sensitivity. The degree of hypotension, of tachycardia, and of oliguria is important for estimating the degree of hypovolemia and hence the degree of urgency for initiating volume resuscitation. The second scenario refers to patients admitted to the emergency room with a high degree of suspicion of septic shock. In this situation, cardiac preload is always inadequate since relative as well as absolute hypovolemia are always present in the early phase of septic shock. The study by Rivers et al. [1] emphasized the importance of volume resuscitation in the first hours of management in this category of patients. There is no need to search for sophisticated parameters to predict volume responsiveness since a positive hemodynamic response is always present at this stage. Rather, there is a need to define parameters that can indicate whether volume infusion should be either continued or stopped because of no further expected efficacy (see the third scenario). There is also a need to define indicators of lung intolerance; however, this is not the subject of the present chapter. The third scenario refers to patients hospitalized in the intensive care unit (ICU) who experience hemodynamic instability that requires urgent therapy. In these patients, volume responsiveness is not guaranteed since they have already been volume resuscitated and continuation of volume infusion carries risks of pulmonary edema. In spontaneously breathing patients either without an endo-tracheal tube or making inspiratory efforts while receiving mechanical ventilation, prediction of volume responsiveness can be a difficult challenge. In these conditions, indices of volume responsiveness that use heart-lung interaction, such as respiratory variations in arterial pressure or in stroke volume and derived indices, are no longer reliable. © 2007 Springer Science + Business Media Inc.