Intraoperative volume optimisation

Abstract

The accurate estimation of effective intravascular volume is of great importance in patients after major vascular procedures. The main goal of achieving an adequate preload is to improve the ability of the left ventricle to cope with alterations in contractility or afterload and maintain cardiac output. Because major surgical procedures are associated with imperceptible fluid losses, blood loss, large amounts of intravenous fluids, and underlying cardiovascular pathology, patients may have either inadequate or excessive preload postoperatively. Volume status is particularly difficult to assess during the early recovery period during which mechanical ventilation is still necessary. There are several reasons why conventional haemodynamic monitoring may give a poor indication of changes in intravascular volume. During anaesthesia, hypovolaemia occurs frequently without being accompanied by tachycardia. This is because baroreflexes are depressed by anaesthetic agents and because the volume receptors in the right atrium are unloaded by the decreased venous return.