Backward component of plasma:

When the backward component is increased in volume there will be elevation in the central venous pressure. This may be inspected at the bedside by examination of the jugular venous pressure with the patient propped up to 45 . The main cause of expansion of the backward compartment is congestive cardiac failure, which may be aggrevated by overzealous fluid administration. Acute expansion of the backward compartment may occur in right heart dysfunction secondary to myocardial infarction, tricuspid valve incompetence and pulmonary embolism.

Diminishment of the backward component will cause collapse of the neck veins. If the venous return to the heart is reduced there may be inadequate ventricular filling and a low preload with a fall in cardiac output and decreased filling of the forward component. The main causes of a diminished backward component in the surgical patient are severe dehydration and haemorrhage.