Body fluids and salt metabolism - Part I

ABSTRACT: There is a high frequency of diarrhea and vomiting in childhood. As a consequence the focus of the present review is to recognize the different body fluid compartments, to clinically assess the degree of dehydration, to know how the equilibrium between extracellular fluid and intracellular fluid is maintained, to calculate the effective blood osmolality and discuss both parenteral fluid requirments and repair.

[Hyponatraemia in patients with neurosurgical disorders: SIADH or cerebral salt wasting syndrome?]

Patients with neurosurgical disorders often present with hyponatraemia. Two mechanisms account for hyponatraemia in these patients: the Syndrome of Inappropriate Secretion of Antidiuretic Hormone (SIADH) and Cerebral Salt Wasting Syndrome (CSWS). The two entities differ in their volume status. In SIADH, volume is expanded due to ADH-mediated renal water retention, but in CSWS, volume is diminished as a consequence of renal salt wasting, most likely attributable to an increased secretion of Brain Natriuretic Peptide (BNP) and Artrial Natriuretic Peptide (ANP). Since it is clinically difficult to distinguish between these two entities, fluid management has to be performed carefully. Salt and fluid replacement appears to be indicated in CSWS, whereas fluid restriction might be the primary approach in patients with SIADH.

Disorders of serum sodium in emergency patients: salt in the soup of emergency medicine

Electrolyte disorders are common and potentially fatal laboratory findings in emergency patients. Approximately 20 % of patients in the emergency department present with either hyponatremia or hypernatremia. Recently it was shown that disorders of serum sodium are not only an expression of the severity of the underlying disease but independent predictors for the outcome of patients. They directly influence patient daily life by causing not only gait and concentration disturbances but also an increased tendency to fall together with a reduced bone mass. Given these new data it is even more important to detect and adequately correct dysnatremia in patients in the emergency department. Acute, symptomatic dysnatremia should be corrected promptly by use of 3 % NaCl for hyponatremia and 5 % glucose for hypernatremia. A close monitoring of serum sodium concentration is, however, essential in any case of correction of hyponatremia or hypernatremia in order to avoid rapid overcorrection and subsequent complications. A profound knowledge of the mechanisms underlying the development of hyponatremia, e.g. diuretics, syndrome of inappropriate antidiuretic hormone secretion (SIADH), heart failure and cirrhosis of the liver and hypernatremia, e.g. dehydration, infusions, diuretics and osmotic diuresis is essential. The present article describes the epidemiology, etiology and correction of hyponatremia and hypernatremia on the basis of current knowledge with special emphasis on emergency department patients.

Body salt and water balances in cardiothoracic surgery patients with intensive care unit-acquired hyponatremia

PURPOSE Hyponatremia is frequently observed in intensive care unit (ICU) patients, but there is still lack information on the physiological mechanisms of development. MATERIALS AND METHODS In this retrospective analysis we performed tonicity balances in 54 patients with ICU acquired hyponatremia. We calculated fluid and solute in and outputs during 24 hours in 106 patient days with decreasing serum-sodium levels. RESULTS We could observe a positive fluid balance as a single reason for hyponatremia in 25% of patients and a negative solute balance in 57%. In 18% both factors contributed to the decrease in serum-sodium. Hyponatremic patients had renal water retention, measured by electrolyte free water clearance calculation in 79% and positive input of free water in 67% as reasons for decline of serum-sodium. The theoretical change of serum sodium during 24 hours according to the calculations of measured balances correlated well with the real change of serum sodium (r = 0.78, P < .01). CONCLUSIONS Balance studies showed that renal water retention together with renal sodium loss and high electrolyte free water input are the major contributors to the development of hyponatremia. Control of renal water and sodium handling by urine analysis may contribute to a better fluid management in the ICU population.

Common noncoding UMOD gene variants induce salt-sensitive hypertension and kidney damage by increasing uromodulin expression

Hypertension and chronic kidney disease (CKD) are complex traits representing major global health problems1,2. Multiple genome-wide association studies have identified common variants in the promoter of the UMOD gene3–9, which encodes uromodulin, the major protein secreted in normal urine, that cause independent susceptibility to CKD and hypertension. Despite compelling genetic evidence for the association between UMOD risk variants and disease susceptibility in the general population, the underlying biological mechanism is not understood. Here, we demonstrate that UMOD risk variants increased UMOD expression in vitro and in vivo. Uromodulin overexpression in transgenic mice led to salt-sensitive hypertension and to the presence of age-dependent renal lesions similar to those observed in elderly individuals homozygous for UMOD promoter risk variants. The link between uromodulin and hypertension is due to activation of the renal sodium cotransporter NKCC2. We demonstrated the relevance of this mechanism in humans by showing that pharmacological inhibition of NKCC2 was more effective in lowering blood pressure in hypertensive patients who are homozygous for UMOD promoter risk variants than in other hypertensive patients. Our findings link genetic susceptibility to hypertension and CKD to the level of uromodulin expression and uromodulin’s effect on salt reabsorption in the kidney. These findings point to uromodulin as a therapeutic target for lowering blood pressure and preserving renal function.

Coupling of eastern and western subpolar North Atlantic: salt transport in the Irminger Current

Salt transport in the Irminger Current and thus the coupling between eastern and western subpolar North Atlantic plays an important role for climate variability across a wide range of time scales. High-resolution ocean modeling and observations indicate that 5 salinities in the eastern subpolar North Atlantic decrease with enhanced circulation of the North Atlantic subpolar gyre (SPG). This has led to the perception that a stronger SPG also transports less salt westward. In this study, we analyze a regional ocean model and a comprehensive global coupled climate model, and show that a stronger SPG transports more salt in the Irminger Current irrespective of lower salinities in its 10 source region. The additional salt converges in the Labrador Sea and the Irminger Basin by eddy transports, increases surface salinity in the western SPG, and favors more intense deep convection. This is part of a positive feedback mechanism with potentially large implications for climate variability and predictability.

Liquid–Vapor Interface of Formic Acid Solutions in Salt Water: A Comparison of Macroscopic Surface Tension and Microscopic in Situ X-ray Photoelectron Spectroscopy Measurements

The liquid–vapor interface is difficult to access experimentally but is of interest from a theoretical and applied point of view and has particular importance in atmospheric aerosol chemistry. Here we examine the liquid–vapor interface for mixtures of water, sodium chloride, and formic acid, an abundant chemical in the atmosphere. We compare the results of surface tension and X-ray photoelectron spectroscopy (XPS) measurements over a wide range of formic acid concentrations. Surface tension measurements provide a macroscopic characterization of solutions ranging from 0 to 3 M sodium chloride and from 0 to over 0.5 mole fraction formic acid. Sodium chloride was found to be a weak salting out agent for formic acid with surface excess depending only slightly on salt concentration. In situ XPS provides a complementary molecular level description about the liquid–vapor interface. XPS measurements over an experimental probe depth of 51 Å gave the C 1s to O 1s ratio for both total oxygen and oxygen from water. XPS also provides detailed electronic structure information that is inaccessible by surface tension. Density functional theory calculations were performed to understand the observed shift in C 1s binding energies to lower values with increasing formic acid concentration. Part of the experimental −0.2 eV shift can be assigned to the solution composition changing from predominantly monomers of formic acid to a combination of monomers and dimers; however, the lack of an appropriate reference to calibrate the absolute BE scale at high formic acid mole fraction complicates the interpretation. Our data are consistent with surface tension measurements yielding a significantly more surface sensitive measurement than XPS due to the relatively weak propensity of formic acid for the interface. A simple model allowed us to replicate the XPS results under the assumption that the surface excess was contained in the top four angstroms of solution.

Salt intake in children and its consequences on blood pressure.

Sodium is the most abundant extracellular cation and therefore pivotal in determining fluid balance. At the beginning of life, a positive sodium balance is needed to grow. Newborns and preterm infants tend to lose sodium via their kidneys and therefore need adequate sodium intake. Among older children and adults, however, excessive salt intake leads to volume expansion and arterial hypertension. Children who are overweight, born preterm, or small for gestational age and African American children are at increased risk of developing high blood pressure due to a high salt intake because they are more likely to be salt sensitive. In the developed world, salt intake is generally above the recommended intake also among children. Although a positive sodium balance is needed for growth during the first year of life, in older children, a sodium-poor diet seems to have the same cardiovascular protective effects as among adults. This is relevant, since: (1) a blood pressure tracking phenomenon was recognized; (2) the development of taste preferences is important during childhood; and (3) salt intake is often associated with the consumption of sugar-sweetened beverages (predisposing children to weight gain).

A Compact Tetrathiafulvalene-Benzothiadiazole Dyad and Its Highly Symmetrical Charge-Transfer Salt: Ordered Donor π-Stacks Closely Bound to Their Acceptors

A compact and planar donor–acceptor molecule 1 comprising tetrathiafulvalene (TTF) and benzothiadiazole (BTD) units has been synthesised and experimentally characterised by structural, optical, and electrochemical methods. Solution-processed and thermally evaporated thin films of 1 have also been explored as active materials in organic field-effect transistors (OFETs). For these devices, hole field-effect mobilities of μFE=(1.3±0.5)×10−3 and (2.7±0.4)×10−3 cm2 V s−1 were determined for the solution-processed and thermally evaporated thin films, respectively. An intense intramolecular charge-transfer (ICT) transition at around 495 nm dominates the optical absorption spectrum of the neutral dyad, which also shows a weak emission from its ICT state. The iodine-induced oxidation of 1 leads to a partially oxidised crystalline charge-transfer (CT) salt {(1)2I3}, and eventually also to a fully oxidised compound {1I3}⋅1/2I2. Single crystals of the former CT compound, exhibiting a highly symmetrical crystal structure, reveal a fairly good room temperature electrical conductivity of the order of 2 S cm−1. The one-dimensional spin system bears compactly bonded BTD acceptors (spatial localisation of the LUMO) along its ridge.