I. V ADDITIVE REVIEW Electrolyte Solutions and Body Fluids I. Use of Milliequivalent and Milliosmol by ANTHONY S. INGLOTT BODY FLUIDS CONTAIN PRECISE AMOUNTS of inorganic ions and organic compounds. The maintenance of delicate balances of fluids and the concentrations of the anions and cations is essential for nu- merous functions. Electrolyte solutions are liquid preparations used for the treatment of disturbances in the electro- lyte and fluid balance of the body. The distribution of fluids in the body into the three major fluid compartments is shown in Table 1. Under normal con- ditions blood plasma contains 155 milli- equivalents of cations and an equal number of anions. The distribution of the mineral elements in the adult body is described in Table 2. The subject is to be dealt with in three sections. The first part considers physical, chemical and pharmaceutical aspects in using electrolyte solutions. Isotonic solutions will be covered in the second part. The third part will deal briefly with clinical considerations. The first two sections are illustrated with mathematical examples while the clin- ical applications of electrolyte solutions are explained by discussing simple case histories. Table 1. The Three Major Fluid Compartments of the Body. Total Body Water 45 Liters 1 EXTRACELLULAR (ECF) 15 LITERS INTRACELLULAR (ICF) 30 LITERS Blood or Intra- vascular 3 liters Na:K 28:1 Inter- cellular or Extra- vascular 12 liters Na:K 28:1 Intracellular 30 liters Na:K 1:10 The Milliequivalent Disturbances in electrolyte and fluid balance in the body are adjusted by electrolyte solutions. The normal values for serum electrolytes are listed in Table 3. The concentrations of electrolyte solu- tions like the concentration of body elec- trolytes used to be commonly expressed in terms of different units, such as grams per 100 ml, volumes % W/V, and mg % W/V. The term "mg %" refers to the number of mg per 100 ml and repre- sents the older concept of measuring elec- trolytes in units of weight or physical units. More recently, a new concept of a chemical unit, the milliequivalent, is be- ing used and this concept has created some hesitance and misunderstanding of units. It is not surprising that the phar- macy often gets calls on matters con- cerning the relation between the chemical and the physical units. Although the mil- liequivalent, is now commonly used by clinicians, physicians, manufacturers and clinical laboratories to express the concern- tration of electrolytes in solution, there are still some who use another term. In these cases the pharmacist is often called upon to carry out some conversions. The following formula may be useful for such conversions. 3 To convert mg per 100 ml to mEq per liter, the following equation may be used: mg per 100 ml X 10 X valence formula weight = mEq per liter (Equation 1 ) In the case of gases such as carbon dioxide, the volume percent of the gas is multiplied by 10 and divided by 22.4, Table 2. Mineral Elements in the Adult Body* PERCENT OF BODY WEIGHT IN GRAMS (154 LB. MAN) PRINCIPAL LOCATIONS IN THE BODY Major Elements Calcium Phosphorus Potassium Sulfur Chlorine Sodium Magnesium Iron Trace Elements Manganese Copper Iodine Fluorine Zinc Molybdenum Selenium Cobalt Chromium Present but not known to be essential: aluminum, arsenic, barium, boron, bromine, lead, nickel, silicon, strontium. Calculations based on elementary composition of the body as stated by H. C. Sher- man, Chemistry of Food and Nutrition, ed. 8, New York, The Macmillan Com- pany, 1952, p. 227 1.5-2.2 0.8-1.2 0.35 0.25 0.15 0.15 0.05 0.004 0.0003 0.00015 0.00004 1050-1540 560-840 245 175 105 105 35 2.8 0.21 0.11 0.02 99% in bones and teeth 80-90% in bones, teeth Fluid inside cells Associated with protein Fluid outside cells Fluid outside cells 70% in bones and teeth l /i in hemoglobin ; stores in liver and other organs Thyroid gland Bones and teeth Part of vitamin Bu mole- cule 28