Defining the boundaries of bedside pulse contour analysis: dynamic arterial elastance.

Assessment of vasomotor tone is essential in defining appropriate resuscitation strategies for the hypotensive patient. Although changes in mean arterial pressure to cardiac output define arterial resistance, resistance is only one component of vasomotor tone. Compliance is the other component. The reciprocal of compliance is arterial elastance (Ea). Importantly, dynamic Ea can be estimated by the pulse pressure variation to stroke volume variation relation. Dynamic Ea is only one component of vasomotor tone, however, and increases in pulse pressure may not be proportional to increases in mean arterial pressure. Also, devices that use the arterial pressure pulse to calculate the stroke volume have an inherent bias that is different amongst devices based on their transfer function algorithms. The use of dynamic Ea for clinical decision-making thus needs to be validated separately for different devices and types of patients.