The osmotic behaviour of the body cells in man; significance of changes of plasma-electrolyte levels in body-fluid disorders

Sodium Abnormalities in Cardiac Surgery With Cardiopulmonary Bypass in Adults: A Narrative Review

Perioperative sodium abnormalities or dysnatremia is not uncommon in patients presenting for cardiac surgery and is associated with increased morbidity and mortality. Both the disease process of heart failure and its treatment may contribute to abnormalities in serum sodium concentration. Serum sodium is the main determinant of serum osmolality, which in turn affects cell volume. Brain cells are particularly vulnerable to changes in serum osmolality because of the nondistensible cranium. The potentially catastrophic neurologic sequelae of rapidly correcting chronic dysnatremia and the time-sensitive nature of cardiac surgery can make the management of these patients challenging. The use of cardiopulmonary bypass to facilitate surgery adds another layer of complexity in the intraoperative management of sodium and water balance. This narrative review examines the definition and classification of dysnatremia. It also covers the etiology and pathophysiology of dysnatremia, implications during cardiac surgery requiring cardiopulmonary bypass, and the perioperative management of dysnatremia.

Using Electrolyte Free Water Balance to Rationalize and Treat Dysnatremias

Dysnatremias or abnormalities in plasma [Na+] are often termed disorders of water balance, an unclear physiologic concept often confused with changes in total fluid balance. However, most clinicians clearly recognize that hypertonic or hypotonic gains or losses alter plasma [Na+], while isotonic changes do not modify plasma [Na+]. This concept can be conceptualized as the electrolyte free water balance (EFWB), which defines the non-isotonic components of inputs and outputs to determine their effect on plasma [Na+]. EFWB is mathematically proportional to the rate of change in plasma [Na+] (dPNa/dt) and, therefore, is actively regulated to zero so that plasma [Na+] remains stable at its homeostatic set point. Dysnatremias are, therefore, disorders of EFWB and the relationship between EFWB and dPNa/dt provides a rationale for therapeutic strategies incorporating mass and volume balance. Herein, we leverage dPNa/dt as a desired rate of correction of plasma [Na+] to define a stepwise approach for the treatment of dysnatremias.

Salivary Markers for Quantitative Dehydration Estimation During Physical Exercise

Salivary markers have been proposed as noninvasive and easy-to-collect indicators of dehydrations during physical exercise. It has been demonstrated that threshold-based classifications can distinguish dehydrated from euhydrated subjects. However, considerable challenges were reported simultaneously, for example, high intersubject variabilities in these markers. Therefore, we propose a machine-learning approach to handle the intersubject variabilities and to advance from binary classifications to quantitative estimations of total body water (TBW) loss. For this purpose, salivary samples and reference values of TBW loss were collected from ten subjects during a 2-h running workout without fluid intake. The salivary samples were analyzed for previously investigated markers (osmolality, proteins) as well as additional unexplored markers (amylase, chloride, cortisol, cortisone, and potassium). Processing all these markers with a Gaussian process approach showed that quantitative TBW loss estimations are possible within an error of 0.34 l, roughly speaking, a glass of water. Furthermore, a data analysis illustrated that the salivary markers grow nonlinearly during progressive dehydration, which is in contrast to previously reported linear observations. This insight could help to develop more accurate physiological models for salivary markers and TBW loss. Such models, in turn, could facilitate even more precise TBW loss estimations in the future.

Dehydration: physiology, assessment, and performance effects

This article provides a comprehensive review of dehydration assessment and presents a unique evaluation of the dehydration and performance literature. The importance of osmolality and volume are emphasized when discussing the physiology, assessment, and performance effects of dehydration. The underappreciated physiologic distinction between a loss of hypo-osmotic body water (intracellular dehydration) and an iso-osmotic loss of body water (extracellular dehydration) is presented and argued as the single most essential aspect of dehydration assessment. The importance of diagnostic and biological variation analyses to dehydration assessment methods is reviewed and their use in gauging the true potential of any dehydration assessment method highlighted. The necessity for establishing proper baselines is discussed, as is the magnitude of dehydration required to elicit reliable and detectable osmotic or volume-mediated compensatory physiologic responses. The discussion of physiologic responses further helps inform and explain our analysis of the literature suggesting a ≥ 2% dehydration threshold for impaired endurance exercise performance mediated by volume loss. In contrast, no clear threshold or plausible mechanism(s) support the marginal, but potentially important, impairment in strength, and power observed with dehydration. Similarly, the potential for dehydration to impair cognition appears small and related primarily to distraction or discomfort. The impact of dehydration on any particular sport skill or task is therefore likely dependent upon the makeup of the task itself (e.g., endurance, strength, cognitive, and motor skill).

Body fluid dynamics: back to the future

Pioneering investigations conducted over a half century ago on tonicity, transcapillary fluid exchange, and the distribution of water and solute serve as a foundation for understanding the physiology of body fluid spaces. With passage of time, however, some of these concepts have lost their connectivity to more contemporary information. Here we examine the physical forces determining the compartmentalization of body fluid and its movement across capillary and cell membrane barriers, drawing particular attention to the interstitium operating as a dynamic interface for water and solute distribution rather than as a static reservoir. Newer work now supports an evolving model of body fluid dynamics that integrates exchangeable Na(+) stores and transcapillary dynamics with advances in interstitial matrix biology.

Osmotic equilibria in fibroblasts in tissue culture measured by immersion refractometry

Volume-osmotic pressure relationships at equilibrium have been obtained in chick heart fibroblasts grown in slide-coverslip cultures in a fluid medium consisting of heparinized plasma and embryo extract. The refractive index of the fibroblast gives a direct measure of its solid concentration, and the volume is estimated as the reciprocal of concentration. The volume is found to be linearly related to the reciprocal of the osmotic pressure over a range from 130 to 587 m-osm, provided the measurements are carried out rapidly at 38°C. The isotonic water content of the cells derived from the gradient of the regression line on the basis of the simple Boyle-van’t Hoff Law was found to be less than actual water content obtained by direct refractometry, i. e. the value of Ponder’s ℛ was 0⋅94 (s. d. 0⋅04). In cultures grown in a simple saline medium and measured at 22°C the volume was related linearly to the reciprocal of the osmotic pressure only between the limits of 330 and 191 m-osm. Outside these limits the volume was greater than expected and this was attributed to alterations in the semi-permeable properties of the cell membrane. The value of Ponder’s ℛ in these cultures was 1⋅15. The importance of the quantity, ℛ, as applied to cells other than the erythrocyte, is indicated. The value, 0⋅94 (s. d. 0⋅04), obtained in fibroblasts under physiological conditions is not explicable on the basis of the probable osmotic properties in vitro of the cell proteins. The discrepancy is within the experimental error, but it may also be due to abnormal osmotic behaviour of the cell proteins resulting from some form of intermolecular structure in the cytoplasm.

EXCHANGEABLE SODIUM, BODY POTASSIUM, AND BODY WATER IN PREVIOUSLY EDEMATOUS CARDIAC PATIENTS: EVIDENCE FOR OSMOTIC INACTIVATION OF CATION

Measurements have been made of total exchangeable sodium, total body potassium, and total body water in a group of 13 previously edematous patients with heart disease, and in 20 "control" patients. The data show that while both groups have the same quantity of water as the per cent of body weight and the same body potassium concentration, the cardiac group has an excess of exchangeable sodium when compared with the "controls." Since the excess sodium in the cardiac group cannot be attributed to the loss of potassium or the accumulation of water, the results of these studies are taken as evidence that osmotic inactivation of a considerable amount of some cation, probably sodium, has taken place. It is suggested that a likely site for cation binding is in the polyanionic constituents of the connective tissues.

Method for estimating rate of fat loss during treatment of obesity by calorie restriction

Rates of weight and fat loss in sixteen female and nine male obese patients during calorie restriction (655-789 kcal/day) for up to 120 days were studied by a method for estimating daily changes in body composition. Fat mass is calculated by subtracting daily fluid (calculated from sodium and potassium balances) and protein mass changes from daily weight changes. After the natriuresis of the first 4 days, there was a slower rate of weight loss between days 5 and 28 due largely to a decreasing contribution from fluid and protein losses. No significant change in the rate of weight loss could be shown after the first 28 days. The rate of fat loss did not change significantly from day 5 onwards suggesting no significant change in total energy expenditure during the study period. After 68 days, 93.4% of the weight loss was fat.

Non-radioisotopic estimate of body water and its spaces in hypertonic expansion

Mathematically rigorous formulae of apparent sodium volume of distribution for body water and of stable sodium chloride space for extracellular volume were derived and applied to data from five anuric dogs infused with hypertonic saline. The error of the formula used in the past to compute apparent sodium volume of distribution was also computed and the errors introduced in the calculation of sodium chloride space by the experimental methods applied were corrected. Apparent sodium volume of distribution, computed from a correct formula, is a measure of body water and corrected estimates of sodium chloride space agree with radio-sulphate space estimates of extracellular volume.