Volume state control - a new approach.
OBJECTIVE
To describe a new approach to circulating volume control in critically ill patients.


METHODS
Studies in circulatory physiology, mathematical models of the circulation and open and closed loop circulation control.


RESULTS
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 (P(msa)) which accounts for variation in venous resistance. It is suggested that P(msa) is an appropriate object of volume control. Definition of a volume state provides insights for cardioactive therapy.


CONCLUSIONS
Use of a P(msa) volume signal enables prolonged stable closed loop volume servocontrol. In global heart dysfunction the dimensionless variable (P(msa )- RAP)/P(msa )may be used to guide inotropic therapy.
Parkin
W G
WG
Intensive Care Unit, Monash Medical Centre, Clayton, VIC, Australia.