Assessment of the physiologic characteristics of the Inferior Vena Cava (IVC) provides a rapid distinction between low and high volume states and offers the clinician a rapid, noninvasive way to guide resuscitation in critically ill patients. The distensibility index is the difference between the IVC maximum diameter (during inspiration on mechanical ventilation) and the minimum diameter (during expiration on mechanical ventilation) divided by the maximum diameter. A ratio more than 18% indicates the need of fluid resuscitation.
