The Displacement of Serum Water by the Lipids of Hyperlipemic Serum. A New Method for the Rapid Determination of Serum Water 1

Abstract

In the course of studies on lactescence of serum, it was found that the insoluble lipids displaced serum water to a degree which was occasionally great enough to be of considerable practical importance. The immediate consequence of this displacement was the finding of spuriously low concentrations of water-soluble components of serum, although their concentrations were normal when repeated on sera from which the insoluble lipids had been removed by ultracentrifugation.These observations clearly showed the need for a simple, rapid method for determination of serum water that would be applicable to sera with a high concentration of lipids. The method using Karl Fischer reagent (1) (3).previously described (7). The original and subnatant fluids were subjected to analysis.C. Gravimetric estimation of serum water:The water was evaporated and the weight loss used to calculate the serum water in grams per 100 ml. of serum (8). D. Calculation of serum water from serum protein:Serum water was calculated from the following formula, the derivation of which is explained elsewhere (8): Ws = 98.5 -0.745 P. in which W. = serum water in gm. per 100 ml. of serum, and P. = serum protein in gm. per 100 ml. E. Osmometric method for estimation of serum water:Theory: The osmotic pressure of serum is determined before and after the addition of a known amount of dry sodium chloride designed approximately to double the osmolarity of serum. The only change taking place upon this addition is an increase in the molal concentration of sodium chloride. Since the osmotic pressure of a solution is determined by the molal concentration of solute particles, the exact molal concentration of the added sodium chloride can be calculated from the increase it causes in the osmotic pressure of serum. Knowing both the absolute amount and the molal concentration of the added salt, the volume of water in which it was dissolved can then be calculated.A freezing point osmometer was used for the determination of osmotic pressure. Although osmotic pressure is not actually measured, advantage is taken of the proportionality between osmotic pressure and freezing point depression in such a way that the results are read directly as milliosmols per liter.Reagents: 1. 0.161 molar sodium chloride solution. Dilute 9.404 gm. dry sodium chloride (reagent grade) to one liter. Double distilled water.Special equipment: A Fiske Associates freezing-point osmometer was used for the determinations of osmolarity. Procedure: To prepare the dry sodium chloride exactly 2 ml. of the sodium chloride solution were pipetted into test tubes to be used later in the osmometer. These were brought to dryness in an oven at 980 C. and subsequently stored in a desiccator until ready for use. The addition of exactly 2 ml. of double-distilled water to the dry salt results in a 0.161 molal solution of sodium chlo-1483

The Nature of the Carbon Dioxide Titration Curve in the Normal Dog*

“…Sodium and potassium determinations were carried out on the Technicon autoanalyzer. Plasma water concentration was determined by the osmometric method (12). Extracellular fluid volume was estimated from chloride space utilizing a correction for the intracellular chloride shifts induced by hypercapnia (1).…”

New insights into the pathophysiology of the dysnatremias: a quantitative analysis

“…Rather, Edelman et al (14) empirically demonstrated that the [Na ϩ ] pw (as opposed to [Na ϩ ] p ) is equal to 1.11( Na e ϩ K e )/TBW Ϫ 25.6. Like all previous formulas, the Barsoum-Levine equation fails to consider the fact that plasma is 93% water (2,9), and it cannot account for the quantitative and physiological significance of the slope (1.11) and y-intercept (Ϫ25.6) in Eq. 1.…”

“…This formula has several advantages: 1) it accounts for all input and output sources of Na ϩ , K ϩ , and H 2 O (mass balance) that can result in a ⌬[Na ϩ ] p ; 2) it takes into consideration the fact that plasma is 93% water (2,9) and that the [Na ϩ ] pw ϭ 1.11(Na e ϩ K e )/TBW Ϫ 25.6 (Eq. 1); 3) it considers the therapy-induced change in TBW; 4) it is applicable for both hyponatremia and hypernatremia; 5) it calculates directly the amount of the infusate necessary to induce a given ⌬[Na ϩ ] p ; and 6) it may also be used to determine the inappropriateness of the selected fluid prescription in a given clinical situation (25).…”

Osmoregulation during Pregnancy in the Rat

“…The mean body weight of rats during gestational day [17][18][19][20] (average 10±3 pups per litter) was 283±27 g (n = 17) compared with 209±29 g (n = 19) in age-matched virgin controls (P < 0.001).…”