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Critical Care Obstetrics part 9

Critical Care Obstetrics part 9 provides expert clinical guidance throughout on how you can maximize the chances of your patient and her baby surviving trauma. In this stimulating text, internationally recognized experts guide you through the most challenging situations you as an obstetrician are likely to face, enabling you to skillfully:Recognize conditions early-on which might prove life threatening, Implement immediate life-saving treatments in emergency situations, Maximize the survival prospects of both the mother and her fetus | 6 Fluid and Electrolyte Balance William E. Scorza1 Anthony Scardella2 1Division of Maternal-Fetal Medicine Department of Obstetrics Lehigh Valley Hospital Allentown PA USA 2University of Medicine and Dentistry Robert Wood Johnson Medical School New Brunswick NJ USA The physiologic effects of pregnancy on normal fluid dynamics and renal function The infusion of fluid remains a cornerstone of therapy when treating critically ill pregnant women with hypovolemia. An understanding of the distribution and pharmacokinetics of plasma expanders as well as knowledge of normal renal function and fluid dynamics during pregnancy is needed to allow for prompt resuscitation of patients in various forms of shock as well as to provide maintenance therapy for other critically ill patients. The total body water TBW ranges from 45 to 65 of total body weight in the human adult. TBW is distributed between two major compartments the intracellular fluid ICF space and the extracellular fluid ECF space. Two-thirds of the TBW resides in the ICF space and one-third in the ECF space. The ECF is further subdivided into the interstitial and intravascular spaces in a ratio of 3 1. Regulation of the ICF is mostly achieved by changes in water balance whereas the changes in plasma volume are related to the regulation of sodium balance. Because water can freely cross most cell membranes the osmolalities within each compartment are the same. When water is added into one compartment it distributes evenly throughout the TBW and the amount of volume added to any given compartment is proportional to its fractional representation of the TBW. Infusions of fluids that are isotonic with plasma are distributed initially within the ECF however only one-fourth of the infused volume remains in the intravascular space after 30 minutes. Because most fluids are a combination of free water and isotonic fluids one can predict the space of distribution and thus the volume transfused into each compartment. During .