Origin of intravascular fluid recruited by vasodilatation during epidural anaesthesia

Arterial hypotension during induction of epidural anaesthesia is caused by peripheral vasodilatation and promotes intravascular fluid distribution. The excess fluid in the blood may result from either diffusion across the capillaries or enrichment of the fluid that is routinely infused intravenously to prevent severe hypotension. These alternatives were assessed in 40 urology patients who received 10 ml kg-1 of Ringer acetate solution without or with 0.5% glucose during onset of epidural anaesthesia. The result shows that arterial hypotension (systolic pressure down by > 25%) promoted mild dilutional hypoglycaemia when the infusion was glucose-free (-6% in hypotensive vs. +2% in normotensive) and hyperglycaemia when glucose was given (+15% in hypotensive vs. +7% in normotensive). The consistent deviation of the blood glucose level towards the concentration of the infused fluid suggests that the excess intravascular fluid associated with epidural-induced hypotension is derived directly from the ongoing infusion rather than by transcapillary transport.