Sections View Full Chapter Figures Tables Videos Full Chapter Figures Tables Videos Supplementary Content +++ INTRODUCTION ++ Fluid and electrolyte homeostasis is maintained by feedback mechanisms, hormones, and many organ systems, and is necessary for the body’s normal physiologic functions. Disorders of sodium and water, calcium, phosphorus, potassium, and magnesium homeostasis are addressed separately in this chapter. +++ DISORDERS OF SODIUM AND WATER HOMEOSTASIS ++ Total body water (TBW) ranges from 45% to 60% of body weight depending on sex and age and is distributed primarily into two compartments: intracellularly (ICF; two-thirds [67%] of TBW), and one-third (33%) is contained in the extracellular space. Effective osmoles are solutes that cannot freely cross cell membranes, such as sodium and potassium. Addition of an isotonic solution to the extracellular fluid (ECF) does not change ICF volume because there is no change in effective ECF osmolality. Adding a hypertonic solution to the ECF decreases ICF volume, whereas adding a hypotonic solution increases it. Table 76-1 summarizes the composition of commonly used IV solutions and their expected distribution into the ECF and ICF compartments. Hypernatremia and hyponatremia can be associated with conditions of high, low, or normal ECF sodium and volume. Both conditions are most commonly the result of abnormalities of water metabolism. It’s important to understand the difference between dehydration (loss of TBW producing hypertonicity) and hypovolemia (volume depletion due to a symptomatic deficit in ECF volume). ++Table Graphic Jump LocationTABLE 76-1Composition of Common IV SolutionsView Table||Download (.pdf) TABLE 76-1 Composition of Common IV Solutions Distribution Solution Dextrose g/dL (kcal/L) [Na+] (mEq/L or mmol/L) [K+] (mEq/L or mmol/L) [Cl−] (mEq/L or mmol/L) Other (mEq/L or mmol/L) Osmolality (mOsm/kg or mmol/kg) Tonicity % ECF % ICF Free water (mL/L) Dextrose 5% in water 5 (170) 0 0 0 — 253 Hypotonic 33 67 1000 mL 0.2% NaCla 0 34 0 34 — 68 Hypotonic 50 50 750 mL 0.45% NaClb 0 77 0 77 — 154 Hypotonic 67 33 500 mL 0.9% NaClc 0 154 0 154 — 308 Isotonic 100 0 0 mL Lactated Ringer’sd 0 130 4 105 Lactate 28 Ca 4.8 273 Isotonic 97 3 0 mL Plasma-Lyte Ae 0.44 (21) 140 5 98 Acetate 27 Mg 3 294 Isotonic 100 0 0 mL Plasma-Lyte 148e Normosol-R (pH 6.6) 0 140 5 98 Acetate 27 Mg 3 294 Isotonic 100 0 0 mL Normosol-R (pH 7.4) 3% NaClf 0 513 0 513 — 1026 Hypertonic 100 0 –2331 mL aAlso referred to as quarter normal saline.bAlso referred to as half normal saline.cAlso referred to as normal saline.dAlso referred to as LR; also available commercially as Dextrose 5% LR.ePlasma-Lyte A pH 7.4; Plasma-Lyte 148 pH 5.5.fHypertonic solution; results in osmotic removal of water from the ICF.One g/dL is equivalent to 0.1 g/L; one kcal/L is equivalent to 4.18 ... Your MyAccess profile is currently affiliated with '[InstitutionA]' and is in the process of switching affiliations to '[InstitutionB]'. Please click ‘Continue’ to continue the affiliation switch, otherwise click ‘Cancel’ to cancel signing in. Get Free Access Through Your Institution Learn how to see if your library subscribes to McGraw Hill Medical products. Subscribe: Institutional or Individual Sign In Username Error: Please enter User Name Password Error: Please enter Password Forgot Username? Forgot Password? Sign in via OpenAthens Sign in via Shibboleth