75-OR

Abstract

Objectives Hypertensive disorders of pregnancy continue to be amongst the leading causes of severe maternal morbidity and mortality, and of maternal admissions to the intensive care unit (ICU). There is debate about the optimal monitoring and treatment for these women, particularly in regard to circulatory management. A restrictive fluid strategy is widely advocated, which conflicts with the widely held belief that the circulating volume is contracted in pre-eclampsia. This belief has been erroneously reinforced by use of the central venous pressure (CVP) as a measure of the volume state. Methods The Guytonian concept of the mean systemic filling pressure (Pms) provides a solution to this paradox. The Pms is the pressure in the systemic circulation when the heart is stopped, arguably the true measure of the volume state. It is about 7 mmHg in normal non-pregnant humans [Guyton, 8th Edtn, 1991]. It is possible to measure an analogue of Pms, (Pmsa), using commonly measured circulatory variables [Parkin, 1999]. We used a Guytonian model of the circulation to review published data, using a cohort of normal pregnant/postpartum women [Clark, 1989] and a pre-eclamptic cohort [Cotton, 1988]. Results Our results show the Pmsa to be elevated in normal pregnancy versus postpartum (10.79 vs 9.58, a 12.6% difference) and elevated further in pre-eclamptic pregnancy (13.86, 29% higher than the normal pregnant group). Conclusions This approach shows that the maternal volume state in pre-eclampsia is often elevated, contrary to previous teachings. When viewed in combination with recent echocardiographic insights this model helps to explain some of the hemodynamic management paradoxes that these women present. These include the marked susceptibility to pulmonary edema seen with even minimal volume administration. Most importantly, it provides a sound physiological basis for the restrictive fluid strategy that is currently recommended. Disclosures T.M. Crozier: None. E.M. Wallace: None. G.W. Parkin: Consultant, Commercial Interest: Applied Physiology.