Evaluation of Metabolic Acid-base Abnormalities in Pre-eclamptic Women Applying the Stewart-Fencl Approach

Studies evaluating acid/base imbalances are scarce in pre-eclamptics, and tools to thoroughly evaluate them are lacking. The detection of metabolic acidosis has been proposed as a diagnostic criterion for a severe disease state8, 11, however other studies entirely reject the presence of any metabolic acid-base disorder in pre-eclampsia10. One reason for this controversy may lie in the fact that no study performed a full comprehensive acid base analysis. Whereas some measured plasma pH, HCO3 and BE8, 11 others focused on AG1 or AG and HCO32, 10 only. Merely one study corrected the AG for low albumin1, and no study focused on independent variables. While some of the cited reports were based on retrospective chart review without differentiating mild and severe disease state1, 2, the few prospective studies available were of low sample size including a total number of 311 or 98women with severe pre-eclampsia. As indicated above, it is totally legitimate to use the traditional approach to describe changes in hydrogen ion concentration and HCO3. The Henderson-Hasselbach equation does differentiate well between respiratory and metabolic acid-base changes. However, it is unable to quantify metabolic causes15. SBE quantifies net change in metabolic acid-base status in vivo, but does not tell us about mechanisms16. The AG is insufficient to detect unmeasured anions17, 18, but when corrected for low albumin it does not detect all unmeasured cations16.

Intravascular volume depletion and disorders of electrolytes and albumin are common findings in pre-eclampsia1, 2 and the impact of such disorders on acid-base homeostasis has been increasingly acknowledged in the last decade3, 19. Decreased serum albumin has an alkalizing effect on plasma, resulting in hypoalbuminemic alkalosis. Furthermore, derangements in volume, sodium and chloride homeostasis, as well as the accumulation of unmeasured anions, are common findings in pre-eclampsia7 and may result in multiple acid-base disorders. The presence of hyponatremia or hyperchloremia has an acidifying effect on blood pH, whereas hypernatremia or hypochloremia lead to alkalosis. The accumulation of unmeasured anions, such as lactate or uric acid, will lead to acidemia, if not otherwise compensated3, 20.

We hypothesize that with comprehensive analysis, clinically significant and complex metabolic derangements might be discovered in pre-eclamptics that will potentially impact their care plan. To our knowledge, this will be the first time that the Stewart-Fencl methodology will be used to determine causes of acid-base status in pre-eclamptics, which takes into account the multiple, potentially opposing, electrochemical disturbances observed in this patient population.

Specific Aims

Aim 1: Prevalence