Hypovolemia and Fluid Responsiveness

Traditionally, fluid responsiveness has been assessed by graded volume loading, but this may easily lead to fluid overload. Whether to provide a fluid bolus is a critical decision of the utmost importance in the emergency and ICU setting. Cardiac filling pressures are poor predictors of preload and neither central venous pressure nor pulmonary artery occlusion pressure can be used to predict fluid responsiveness in patients who breathe spontaneously or in patients on positive pressure ventilation. The echocardiographic appearance of a full-blown picture of hypovolemia is consistent with a small hyperkinetic fast-beating heart. Passive leg raising has been proposed as a preload-modifying maneuver without any potentially harmful fluid infusion. This maneuver is the only reliable way to predict fluid responsiveness for the patient who breathes spontaneously. The only way to avoid useless or even harmful fluid load is simply to challenge the Frank–Starling relationship. The echocardiographic methods used to predict fluid responsiveness in mechanically ventilated patients are described. Echocardiography, with all the vital information on cardiovascular functional anatomy it provides, has become the best tool to assess volume status, predict fluid responsiveness, and guide fluid therapy in the emergency and ICU setting.