Acid-base Disturbances and Ultrasound Markers as Biological Predictors of Maternal and Fetal Outcomes in Severe Late Onset Preeclampsia

I. Introduction / Specific Aims Preeclampsia is a major cause of maternal mortality (15-20 % in developed countries) and acute and long-term morbidity for the mother and newborn. It is a multi-system disorder characterised by abnormal vascular response to placentation, associated with increased systemic vascular resistance, enhanced platelet aggregation, activation of the coagulation system, and endothelial dysfunction. Preeclampsia is defined by a number of signs and symptoms, but is characterized by multi-organ changes that encompass the central nervous system (CNS), lungs, liver, kidneys, systemic vasculature, coagulation, and the heart .

Derived from other clinical arenas of intensive care medicine, new potential markers of disease severity in women diagnosed with preeclampsia have recently been identified. Using noninvasive point-of-care (POC) ultrasound, pulmonary interstitial edema and raised intracranial pressure were identified in 25% and 20% respectively of women showing features of severe preeclampsia. In addition, echocardiographic and laboratory studies in women diagnosed with preeclampsia indicate an incidence of diastolic dysfunction and increased left ventricular end-diastolic pressure (LVEDP) in up to 30%. These findings could have a significant impact on maternal outcome and the detailed methodology of anesthesia care for the parturient with severe preeclampsia (PreE), including the mode of anesthesia, positioning of the patient, fluid management, and hemodynamic goals.

In a recent investigation performing a comprehensive physicochemical acid/base analysis in pre-eclamptic women (AB-PreE-Trial), the presence of simultaneous hypoalbuminaemic alkalosis and hyperchloraemic acidosis was identified. In addition, investigators found indications that hypoalbuminaemic alkalosis is more marked in early versus late onset disease and is associated with mode of delivery. In other critical care arenas it has been shown that reduced albumin and acid-base abnormalities are associated with pulmonary interstitial edema, elevated intracranial pressure (ICP), and poor clinical outcomes. Venous acid-base analysis may therefore be a widely available and inexpensive marker of pulmonary interstitial edema and elevated ICP in preeclampsia, with potentially important impact on anesthesia care. Therefore, one aim is to evaluate the association between elevated base excess to changes in albumin concentration (BE(Alb)) with pulmonary interstitial edema and increased ICP (both evaluated with non-invasive ultrasound) in patients with late onset severe preeclampsia. Investigators will further evaluate for an association with urgent delivery (fetal or maternal indication).

Long-term goal will be to use findings to guide clinical decision-making by anaesthetists to identify individual patients with acute organ system failures, helping better plan anaesthetic management during Cesarean delivery. Also, the findings from a larger future study could predict maternal and fetal complications, and show differences between early- and late onset disease. This should be of significant future benefit in the South African context, where preeclampsia is a leading cause of maternal morbidity and mortality.

II. Aims