[Assessment of cardiovascular preload and response to volume expansion]. 
Volume expansion is used in patients with hemodynamic insufficiency in an attempt to improve cardiac output.  Finding criteria to predict fluid responsiveness would be helpful to guide resuscitation and to avoid excessive volume effects.  Static and dynamic indicators have been described to predict fluid responsiveness under certain conditions.  In this review we define preload and preload-responsiveness concepts.  A description is made of the characteristics of each indicator in patients subjected to mechanical ventilation or with spontaneous breathing.