Pre-eclampsia: the effect of intravenous fluid preload on atrial natriuretic peptide secretion during caesarean section under spinal anaesthesia.

Abstract

The haemodynamic effect of volume load at elective Caesarean delivery may be modulated by atrial natriuretic peptide (ANP) especially in pre-eclamptic women in whom basal ANP levels are increased. We followed the haemodynamic parameters and determined the peripheral venous levels of ANP before and after an intravenous volume preload of 1000 ml of Ringer's acetate solution, followed by a further load of the same volume under spinal anaesthesia in 7 healthy and in 6 pre-eclamptic women. During the preload period the median ANP level increased more (from 14.8 to 22.1 pmol/l, P = 0.03) in pre-eclamptic than in healthy women (from 8.0 to 8.5 pmol/l, NS); while an increment in central venous pressure (CVP) was also greater in pre-eclamptic than in healthy women. The increase in the concentrations of ANP correlated significantly (P < 0.05) with the increase in CVP in the total study group. A significant increase in ANP levels in healthy pregnant women was not seen until during the second infusion period under spinal anaesthesia; in pre-eclamptic women the levels increased further during that period. These findings concur with the theory that atrial stretch is a stimulus for ANP release. An exaggerated release of ANP in response to volume loading may aid in the adaptation of maternal circulation to volume load at elective Caesarean delivery in pre-eclamptic women.