RT Book, Section A1 Hanna, Melisha G. A1 Bock, Margret A2 Hay, Jr., William W. A2 Levin, Myron J. A2 Deterding, Robin R. A2 Abzug, Mark J. SR Print(0) ID 1153310654 T1 Fluid, Electrolyte, & Acid-Base Disorders & Therapy T2 Current Diagnosis & Treatment: Pediatrics, 24e YR 2018 FD 2018 PB McGraw-Hill Education PP New York, NY SN 9781259862908 LK accessmedicine.mhmedical.com/content.aspx?aid=1153310654 RD 2022/05/28 AB Total body water (TBW) constitutes 50%–75% of the total body mass, depending on age, sex, and fat content. After an initial brisk postnatal diuresis, the TBW slowly decreases to the adult range near puberty. TBW is divided into the intracellular and extracellular spaces. Intracellular fluid (ICF) accounts for two-thirds of the TBW and extracellular fluid (ECF) for one-third. The ECF is further compartmentalized into plasma (intravascular) volume and interstitial fluid (ISF).