Effect of intravenous fluid preload on vasoactive peptide secretion during Caesarean section under spinal anaesthesia

The endogenous release of the vasoactive peptides atrial natriuretic peptide and endothelin-1 may modify maternal haemodynamic responses to a rapid intravenous volume load used to prevent hypotension at elective Caesarean delivery under spinal anaesthesia. Twenty-two healthy pregnant women were examined during elective Caesarean section at term pregnancy. They were randomly assigned to receive either 2000 ml of Ringer lactate solution (crystalloid group) or 500 ml of 6% hydroxyethyl starch + 1000 ml of Ringer lactate solution (colloid group). The mean (SEM) concentration of atrial natriuretic peptide in plasma increased from 10.9 (1.5) to 24.7 (5.1) pmol.l-1 during crystalloid infusion and from 10.3 (1.4) to 28.2 (5.6) pmol.l-1 during colloid infusion. A slight decrease in endothelin-1 levels was found during colloid infusion. A significant increase in the release of atrial natriuretic peptide in response to volume load may decrease vascular tone and initiate diuresis, thereby attenuating the effect of volume load on blood pressure during elective Caesarean delivery.