Volume State Control - A New Approach

Abstract

Objective: To describe a new approach to circulating volume control in critically ill patients. Data sources: Studies in circulatory physiology, mathematical models of the circulation and open and closed loop circulation control. Summary of review: In evaluation of the volume state it may be wiser to consider the determinants of the systemic venous return rather than those of the cardiac output. These determinants include the mean systemic filling pressure, the right atrial pressure and the unknown resistance to venous return. A model based approach is advanced to determine a mean systemic filling pressure analogue (Pmsa) which accounts for variation in venous resistance. It is suggested that Pmsa is an appropriate object of volume control. Definition of a volume state provides insights for cardioactive therapy. Conclusions: Use of a Pmsa volume signal enables prolonged stable closed loop volume servocontrol. In global heart dysfunction the dimensionless variable (Pmsa - RAP)/Pmsa may be used to guide inotropic therapy.