Effective Osmolality Research Articles

A case of isolated and transient splenial lesion of the corpus callosum associated with disseminated Staphylococcus aureus infection

We report a 20-year-old man who presented with temporary encephalopathy. Serial brain MRI revealed an isolated and transient splenial lesion of the corpus callosum (SCC). He was subsequently diagnosed with septic metastasis of Staphylococcus aureus ( S. aureus) involving both lungs and multiple joints; however, there was no indication of S. aureus involvement of the meninges or brain parenchyma in CSF and MRI studies. Within 24 h of presentation, the serum sodium concentration and effective osmolality changed by approximately 10 mmol/L and 25 mOsm/kg H 2O, respectively. On the basis of the MRI findings, the changes in electrolyte concentration, and a review of relevant literature, an isolated and transient SCC in this case might be related to osmotic demyelination caused by fluid imbalance rather than direct invasion of S. aureus.

Relationships between glucose, sodium and effective osmolality in diabetic dogs and cats

AbstractObjective:To examine the relative contributions of sodium and glucose to serum effective osmolality and the presence of abnormalities of sodium and osmolality in diabetic dogs and cats.Design:Retrospective study.Setting:A university‐based referral hospital.Animals:Diabetic dogs (n=14) and cats (n=13) consecutively admitted to the hospital over a 6‐month period.Interventions:NoneMeasurements:Serum biochemistry assessments.Main results:The mean glucose concentration was higher in diabetic dogs than in diabetic cats. Total osmolality (OsmT), effective osmolality (OsmE), and the concentrations of sodium, potassium, blood urea notrogen, bicarbonate, and creatinine did not differ between species. Sodium abnormalities and hyperosmolality affected 44% and 81%, respectively, of the study group. However, marked hyperosmolality (OsmE>330 mOsm/L) was found in only 33% of the study group. Serum sodium correlated closely with OsmEin dogs and cats but serum glucose did not correlate with the OsmEin either species. Subsets of dogs (n=10) and cats (n=7) with diabetic ketosis (DK) were examined separately. DK dogs had significantly lower sodium concentrations than DK cats and the proportion of DK dogs with hyponatremia was nearly 3 times greater than DK cats. Severe hyperosmolality (OsmE>330 mOsm/L) was more common in DK cats than DK dogs.Conclusions:In diabetic dogs and cats, sodium, not glucose, was correlated with serum OsmEand marked elevation in pretreatment OsmEis uncommon. Compensatory reduction in serum sodium may be 1 mechanism for blunting changes in OsmEin the presence of marked hyperglycemia.

Changes in plasma osmolality in food poisoning

Changes in plasma osmolality may occur during acute intestinal infections due to dehydration (loss of water and/or electrolytes). Depending on whether the water and electrolyte deficit is primary, or a proportional loss of water and electrolytes, dehydration can be classified into three categories: hypertonic, hypotonic and isotonic. Thirty (30) patients with food poisoning were included in this research. All patients were hospitalized because of frequent vomiting, with resultant dehydration. A diagnosis of food poisoning was made based on the clinical picture, short incubation period and positive epidemiological history. Plasma osmolality was measured by a freezing point depression with an osmometer, while effective plasma osmolality was determined by using the following formula: EPO (eff. plasma osmolality) = 2 x serum sodium concentration + serum glucose level. Apart from plasma osmolality, other parameters were also measured in patients' sera: sodium, chloride, potassium, urea, glucose and hematocrit. In order to follow-up the changes in these parameters, they were also measured after treatment of the gastrointestinal disorder. Statistical analysis was performed using the equality of mean values for 2 basic groups. The statistical results showed that the values of total and effective plasma osmolality (TPO and EPO) among patients with gastrointestinal disorders were not significantly higher than values after the alimentary infection. Such results suggest that food poisoning is associated with disorders of water and electrolyte metabolism, that is isotonic type of dehydration.

Hyperglycemic Comas in Children: New Insights into Pathophysiology and Management

The hyperglycemic comas in pediatric patients, ketoacidosis (DKA), occurring with both type 1 and type 2 diabetes, and hyperglycemic hyperosmolar state (HHS), which occurs almost exclusively with type 2 diabetes, account for most of the diabetes related morbidity and mortality in childhood. DKA is defined as acidosis measured as venous pH 11 mmol/L. This is typically associated with glucosuria, ketonuria, and ketonemia. Near normal circulating glucose concentrations may occur rarely in DKA with partial treatment or with pregnancy [1]. HHS was formerly referred to as hyperglycemic hyperosmolar nonketotic state, but the nomenclature was changed to recognize the frequent presence of mild ketosis. Indeed, diabetic comas can be viewed as a continuum from DKA with normal osmolality to HHS without ketosis [2]. The emergence of type 2 diabetes in childhood, accounting for as much as 50% of newly-diagnosed diabetes in the 10–19 year age group, depending on socioeconomic and ethnic composition of the population, has resulted in an appreciation of HHS as no longer a condition seen rarely outside of elderly populations [3,4]. The criteria for HHS include plasma glucose concentration >33.3 mmol/L, serum bicarbonate concentration >15 mmol/L, no or small ketonuria, absent to small ketonemia, effective serum osmolality greater than 320 mOsm/kg, and stupor or coma [2].

Dogmas and controversies in the handling of nitrogenous wastes: excretion of nitrogenous wastes in human subjects.

Two major nitrogenous waste products, urea and ammonium (NH(4)(+)), are produced in humans when proteins are oxidized, and in this manuscript their excretions are examined from two perspectives. First, the specific physiology of each nitrogenous waste is reviewed and the current dogmas summarized. Second, their excretions are considered in the context of integrative physiology, i.e. the need to ensure that the urine composition is appropriate to minimize the risk of kidney stone formation. After the latter analysis, weak links in our understanding of the overall physiology become apparent and a conundrum is defined. The conundrum for the excretion of urea focuses on the fact that urea is not an effective osmole in the medullary-collecting duct when vasopressin acts. As a result, it appears that urinary urea cannot prevent a large decline in the urine flow rate and thereby minimize the risk of forming kidney stones in electrolyte-poor urine. The conundrum for the excretion of NH(4)(+) is: high rates of NH(4)(+) excretion require a low urine pH, yet a pH approximately 6.0 must be maintained in order to reduce the risk of precipitating uric acid in the urine. Possible ways of resolving these conundrums require novel physiological interpretations.

Influence of plasma amino acid level on vasopressin secretion

Vasopressin (VP) is known to be elevated in patients with diabetes mellitus (DM). While the influence of acute hyperglycemia has been ruled out, the mechanism or the osmotically active compound responsible for the increase in VP secretion is still not elucidated. Because the plasma level of several amino acids (AAs) is increased in DM, we evaluated whether AAs could represent an effective osmotic stimulus for VP secretion. In a cross-over study, eight healthy volunteers randomly received an infusion of isotonic saline (control) or mixed AA solution, i.v., at a low or a high rate (2 or 4.5 mg/min/kg BW, respectively). Plasma VP (P(VP)) was measured for two hours before and three hours during AA or control infusion. AA infusion induced a dose-dependent elevation in plasma AA concentration but did not alter P(VP). However, effective plasma osmolality (P(osm)) (osmolality minus urea concentration) remained unchanged because a concommittant fall in plasma sodium concentration (P(Na)), likely due to sodium-linked uptake of AA in peripheral cells, compensated for the rise in plasma AA. The stability of effective P(osm) may explain the lack of change observed in P(VP). Because sodium is a very efficient stimulus for VP secretion, it may be assumed that the fall in P(Na) occurring during AA infusion should have reduced VP secretion and thus P(VP). In this setting, the stability of P(VP) suggests that AAs induced an increase in VP secretion which counterbalanced the fall attributable to the decrease in P(Na). In conclusion, in acute experiments, AAs seem to represent an effective stimulus for VP secretion, almost equally potent as sodium. Further studies are needed to evaluate their contribution to the high P(VP) seen in the chronic setting of DM.

Trends in serum sodium concentration and effective osmolality during repair of paediatric diabetic ketoacidosis

Objective: To assess the effect of resuscitation fluid on trends in serum sodium and effective osmolality during repair of paediatric diabetic ketoacidosis. Design: Retrospective. Setting: A paediatric intensive care unit (PICU) in a tertiary academic medical centre. Subjects: Sixteen patients (age range: 7–20 years; mean: 14 +/− 3 years) admitted to the PICU over 19 months for 35 episodes of diabetic ketoacidosis. Interventions: We reviewed trends in serum sodium and effective osmolality as well as total fluid and sodium intake and mean resuscitation fluid sodium concentration (total sodium intake/total fluid intake) during the first day of therapy. Measurements and main results: Within the range of resuscitation fluid composition observed (mean resuscitation fluid [sodium]: 63–149 mmol/l), we noted a weak, positive correlation between trends in uncorrected serum [sodium] and mean resuscitation fluid [sodium]. No association was found between trends in corrected serum [sodium] or effective osmolality and fluid intake, sodium intake, or mean resuscitation fluid [sodium]. Near-isotonic resuscitation fluid (mean resuscitation fluid [sodium] >125 mmol/l) was associated with both positive and negative trends in uncorrected and corrected serum [sodium], as well as negative trends in effective osmolality. Trends in uncorrected serum [sodium] and effective osmolality were unrelated, while trends in corrected serum [sodium] and effective osmolality, though related, were not concordant in all episodes with a negative trend in effective osmolality. Conclusions: A strategy to limit precipitous declines in effective osmolality during repair of diabetic ketoacidosis should not rely solely on the trends in uncorrected or corrected serum [sodium] as markers of effective osmolality, or on changes in resuscitation fluid volume or content to bring about a change in effective osmolality.

Trends in serum sodium concentration and effective osmolality during repair of paediatric diabetic ketoacidosis

Trends in serum sodium concentration and effective osmolality during repair of paediatric diabetic ketoacidosis

The hyponatremic patient: A systematic approach to laboratory diagnosis

Hyponatremia (serum sodium < 134 mmol/L) is a common electrolyte disturbance. A history of concurrent illness and medication use as well as the assessment of extracellular volume status on physical examination may provide useful clues as to the pathogenesis of hyponatremia. Measurement of the effective serum tonicity is the first step in the laboratory evaluation. In patients with normal or elevated effective serum osmolality (280 mOsm/kg or greater) pseudohyponatremia should be excluded. In the hypo‐osmolar state, urine osmolality is used to determine whether water excretion is normal or impaired. A urine osmolality value of <100 mOsm/kg indicates complete and appropriate suppression of antidiuretic hormone secretion. A urine sodium level <20 mmol/L is indicative of hypovolemia, whereas a level >40 mmol/L is suggestive of the syndrome of inappropriate antidiuretic hormone secretion. Levels of hormones (thyroid‐stimulaing hormone and cortisol) and arterial blood gases should be determined in difficult cases ofhyponatremia. A clinical diagnostic algorithm for hyponatremia is included in this review article.

Pathogenesis and Diagnosis of Hyponatremia

This discussion emphasizes two aspects of hyponatremia: classification according to effective osmolality of the body fluid, and distinction between appropriate and inappropriate ADH secretion. Assessment of the effective osmolality is important because the main deleterious effect of hyponatremia is cell overhydration, which occurs only when the effective osmolality is reduced. Since most cases of hyponatremia are associated with low effective osmolality, cell overhydration is a hallmark of acute hyponatremia. On the other hand, one must be aware of other types of hyponatremia in which effective osmolality is either normal or even increased. Inappropriateness of ADH secretion is defined as ADH secretion that occurs despite low effective osmolality and normal or expanded effective vascular volume. ADH secretion that occurs in hyponatremia is deemed appropriate if the effective vascular volume is low. The use of laboratory parameters is much more reliable in determining effective vascular volume than is careful physical examination.

Effect of Extenders and Osmotic Pressure on Storage of Eggs of Ornamental Common Carp Cyprinus carpio at Ambient and Refrigerated Temperatures

AbstractThe eggs of ornamental (koi) common carp Cyprinus carpi0 were stored at ambient temperature (∼22–25 C) and at refrigerated temperatures (0–20 C) in extenders at different osmolalities. The treatments evaluated were dry (control), calcium‐free Hanks’balanced salt solution (C‐F HBSS), salt (NaCl), synthetic ovarian fluid (SOF), and Kurokura #2 (K2). In the first study, eggs were placed in extenders at osmolalities ranging from 130 to 450 mOsmol/kg and were fertilized after 2 h. The percentage of eyed embryos (our measure of fertilization capacity) was calculated 24 h later, and percent hatching was calculated at 60 h. Fertilization capacity of eggs suspended in C‐F HBSS (28%) or SOF (37%) was highest (P= 0.0001) at 250 mOsmol/kg, while eggs stored dry (control) had a fertilization capacity of 24%. Fertilization capacity of eggs suspended in NaCl (40%) or K2 (39%) was highest (P= 0.0001) at 200 mOsmol/kg. The percent of eyed embryos and percent hatch were found to be positively correlated (r= 0.9914). In the second study, eggs were stored in these extenders with the most effective osmolality from the previous study to evaluate percent eyed embryos and hatching over time. Samples of eggs were fertilized at every hour for 7 h. Eggs in the extenders C‐F HBSS and SOF yielded the highest (P= 0.0001) percent eyed embryos during 7 h. Percent hatch of these eggs was not significantly different (P= 0.1258) among treatments at each time interval. Eggs stored in the extenders SOF, C‐F HBSS, and NaCl had higher fertwzation capacity (P= 0.0271) at 7 h than did the dry control. Eggs were also stored at refigerated temperatures in these four extenders at the most effective osmolalities from the first study. A dry control (no extender) was also compared. The third study compared quality of eggs stored for 0, 2, 4, or 6 h in each of the extenders at 5 C or at ambient temperature (∼22–25 C). Eggs suspended in C‐F HBSS had significantly higher fertilization capacity at ambient temperature over time than did eggs stored in NaCl, SOF, K2, or the dry control. Eggs suspended in C‐F HBSS and the dry control had significantly higher fertilization capacity at 5 C over time than did eggs stored in NaCl, SOF, or K2. Eggs held dry had higher hatch at ambient temperatures (P= 0.0001) and at 5 C (P = 0.0002) over time than did eggs stored in any extender. At 6 h, fertlllvltion capacity with eggs in C‐F HBSS or K2 was higher than with NaCl, SOF, or the dry control. The fourth study used C‐F HBSS (250 mOsmol/kg) as the extender to evaluate fertilizing and hatching ability during storage at temperatures 0, 5, 10, 15, 20, or 25 C. Eggs were fertilized after 0, 1, 3, 6, 9, or 12 h of storage. Eggs stored at 15 C had significantly higher fertilization capacity (P= 0.0001) than at any other temperature. Eggs stored at 15 C and 10 C had significantly higher hatch (P= 0.0001) than at any other temperature. Fertilization capacity at 12 h was significantly higher in eggs stored at 10 C (33%) or 15 C (29%) than at any other temperature. Storage of koi carp eggs in C‐F HBSS at remgerated temperatures extended fertilizing ability for as long as 12 h compared to storage in NaCl, SOF, K2, or the dry control.

Osmolality and solute composition are strong regulators of AQP2 expression in renal principal cells.

The water permeability of the renal collecting duct is regulated by the insertion of aquaporin-2 (AQP2) into the apical plasma membrane of epithelial (principal) cells. Using primary cultured epithelial cells from the inner medulla of rat kidney (IMCD cells), we show that osmolality and solute composition are potent regulators of AQP2 mRNA and protein synthesis, as well as the classical cAMP-dependent pathway, but do not affect the arginine vasopressin-induced AQP2 shuttle. In the presence of the cAMP analog dibutyryl cAMP (DBcAMP, 500 microM), NaCl and sorbitol, but not urea, evoked a robust increase of AQP2 expression in IMCD cells, with NaCl being far more potent than sorbitol. cAMP-responsive element-binding protein phosphorylation increased with DBcAMP concentrations but was not altered by changes in osmolality. In the rat and human AQP2 promoter, we identified a putative tonicity-responsive element. We conclude that, in addition to the arginine vasopressin/cAMP-signaling cascade, a further pathway activated by elevated effective osmolality (tonicity) is crucial for the expression of AQP2 in IMCD cells, and we suggest that the effect is mediated via the tonicity-responsive element.

Water transport controversies--an overview.

The last 20 years have seen major advances in the understanding of the mechanisms and molecular bases of water transport across cell membranes. Prominent among these advances was the discovery of a family of transmembrane proteins that permeate exclusively or dominantly water (aquaporins), followed by structural studies identifying the intramolecular permeation pathway, as well as by studies directed to a detailed understanding of these molecules in health and disease. Agre and colleagues (Agre et al. 2002) discuss the molecular structure of aquaporins and the physiology and pathophysiology of aquaporins in diverse organs and tissues. Another important advance was the development of methods for rapid measurements of changes in cell volume. This resulted in accurate estimates of cell-membrane water permeability, and in the prediction that very small osmotic gradients would suffice to drive transepithelial transport, without the need for the existence of compartments of much higher osmolality than that of the bathing solution. Around 1990, faced with the question of what pathways and driving forces underlie net water fluxes across cell membranes, most physiologists working on animal cells would have had direct and clear answers. Water moves across the phospholipid moiety of the plasma membrane (although this membrane can be extremely water-tight in certain cases), and through water pores, in cells that express these proteins. The driving force is the difference in effective osmolality across the cell membrane. Enlightened physiologists working on epithelia would add that transepithelial water absorption or secretion is always a passive phenomenon, secondary to net solute transport in the same direction. Further, complicated compartment models, such as the standing osmotic gradient hypothesis, are unnecessary to explain water transport, because very small osmotic gradients, perhaps too small to measure directly, are a sufficient driving force. The question of how water fluxes are partitioned between transcellular and paracellular pathways remained difficult to answer because of the lack of direct measurements. The two central questions in the problem of water transport across simple or complex membranes are the pathway and the mechanism. Considering the cell membrane, one asks whether water permeates the lipid moiety and/or transmembrane proteins. These pathways are expected to have different properties, including the possibility that transmembrane water pores could also be permeable to other molecules. Concerning the driving force for water transport, in principle it could be primary active, secondary active or passive. At the time prior to the discoveries that provide the experimental bases for the Topical Reviews in this Special Issue, the virtually unanimous opinion of the experts would have been that water transport is passive. With respect to transepithelial water transport, the relative contributions of the transcellular and paracellular routes remain to be determined. There is no agreement on the molecular mechanism, i.e. whether there is secondary-active water transport at the cell membrane in addition to simple osmosis, or on the precise nature of osmotic water flow, i.e. is there truly isosmotic transport? This Special Issue highlights the current excitement in this area of physiology. Three current controversies in the field of water transport are discussed. In each case, the ‘controversial’ novel theory is presented (in the form of a Topical Review) and discussed critically in the form of a Perspective or a Research Paper. The three controversies presented in this Special Issue were debated at the XXXIV International Congress of Physiological Science in Christchurch, New Zealand.

Early osmoregulatory stimulation of neurohypophyseal hormone secretion and thirst after gastric NaCl loads.

Cerebral osmoreceptors mediate thirst and neurohypophyseal secretion stimulated by increases in the effective osmolality of plasma (P(osmol)). The present experiments determined whether an intragastric load of hypertonic saline (ig HS; 0.5 M NaCl, 4 ml) would potentiate these responses before induced increases in P(osmol) in the general circulation could be detected by cerebral osmoreceptors. Adult rats deprived of water overnight and then given intragastric HS consumed much more water in 15-30 min than rats given either pretreatment alone, even though systemic P(osmol) had not yet increased significantly because of the gastric load. In other rats pretreated with an intravenous infusion of 1 M NaCl (2 ml/h for 2 h), plasma levels of vasopressin and oxytocin were considerably elevated 15 and 25 min after intragastric HS treatment, whereas systemic P(osmol) was not increased further. These and other findings are consistent with previous reports that hepatic portal osmoreceptors (or Na(+) receptors) stimulate thirst and neurohypophyseal hormone secretion in euhydrated rats given gastric NaCl loads and indicate that these effects are potentiated when animals are dehydrated.

Mechanisms of transjunctional transport of NaCl and water in proximal tubules of mammalian kidneys.

Tight junctions and the intercellular space of proximal tubules are not accessible to direct measurements of fluid composition and transport rates, but morphological and functional data permit analysis of diffusion and osmosis causing transjunctional NaCl and water transport. In the S2 segment NaCl diffuses through tight junctions along a chloride gradient, but against a sodium gradient. Calculation in terms of modified Nernst-Fick diffusion equation after eliminating electrical terms shows that transport rates (300-500 pmol min-1 mm-1 tubule length) and transepithelial voltage of +2 mV are in agreement with observations. Diffusion coefficients are Dtj=1500 microm2 s-1 in the S1 segment, and Dtj=90-100 microm2 s-1 in the S2 segment where apical intercellular NaCl concentration is 132 mM, 1 mM below complete stop (Dtj=0 and Donnan equilibrium). Tight junctions with gap distance 6 A are impermeable to mannitol (effective molecular radius 4 A); reflection coefficients are sigma=0.92 for NaHCO3 and sigma=0.28 for NaCl, because of difference in anion size. The osmotic force is provided by a difference in effective transjunctional osmolality of 10 mOsm kg-1 in the S1 segment and 30 mOsm kg-1 in the S2 segment, where differences in transjunctional concentration contribute with 21 mOsm kg-1 for NaHCO3 and -4 mOsm kg-1 for NaCl. Transjunctional difference of 30 mOsm kg-1 causes a volume flow of 2 nL min-1 mm-1 tubule length. Luminal mannitol concentration of 30 mM stops all volume flow and diffusive and convective transport of NaCl. In conclusion, transjunctional diffusion and osmosis along gradients generated by transcellular transport of other solutes account for all NaCl transport in proximal tubules.

Body fluid osmolality and tonicity in preterm infants.

In adult patients, a recent physiological approach for the osmoregulatory system based on body fluid tonicity (the so-called effective osmolality) seems to provide better information on water movements than does the classical body fluid osmolality. To evaluate whether plasma or urinary tonicities could give a better assessment of osmoregulation than plasma and urine osmolalities in sick preterm infants cared for in a NICU. A prospective study was conducted in 30 preterm infants (BW=1284+/-377 g; GA=28.8+/-1.7 weeks). Fifteen consecutive 8-h urine collections were performed for each infant from the 8th h of life (450 periods). A plasma sample was obtained at the end of each urine collection. Sodium, potassium, creatinine, osmolality and tonicity were measured or calculated in urine and blood samples as often as possible. Hypernatremia (PNa=146-149 mmol/l) was observed in seven infants (23.3%) and in 5.9% of the periods. Fifty-three percent of the infants and 20.4% of the periods presented with plasma hyperosmolality (>300 mosmol/kg H2O). The relationship between Posm and PNa was significant, but the clinical relevance was weak (r(2)=0.411; P<0.001). Plasma osmolality (Posm) positively correlated with urine osmolality (Uosm), but did not correlate significantly with CH2O/100 ml GFR. Plasma tonicity (2x(PNa+PK)) positively correlated with both urine tonicity (2x(UNa+UK)) and effective water clearance (EWC/100 ml GFR). On an individual basis, the linear relationship between urine and plasma osmolalities was significantly weaker than the relationship between urine and plasma tonicities. This study suggests that the calculation of plasma and urine tonicities allows a better assessment of water movements in body fluid compartments than plasma and urine osmolalities.

Room C, 10/17/2000 9: 00 AM - 11: 00 AM (PS) Measured, Calculated and Effective Plasma Osmolality in Neurointensive Care Patients

Room C, 10/17/2000 9: 00 AM - 11: 00 AM (PS) Measured, Calculated and Effective Plasma Osmolality in Neurointensive Care Patients

Festschrift for Professor Claude Jacobs. Recent developments in conductivity monitoring of haemodialysis session.

On-line monitoring of dialysate conductivity is now a standard equipment (called 'Diascan') of the dialysis monitor Integra (Hospal, Italy). From the record of the dialysate conductivity at the dialyser inlet and outlet, the Diascan calculates the values of patient's plasma conductivity and of ionic dialysance which is a weighed average of the dialysances of all ions of quantitative importance in plasma and dialysate. Because there is an equivalence between the transfer characteristics of urea and electrolytes, the ionic dialysance reflects the urea clearance corrected for recirculation. Because the conductivity of a solution is related to the concentrations of the ions and thus to the effective osmolality, the plasma conductivity is a reflection of the plasma sodium concentration. The determination of ionic dialysance and plasma conductivity by the Diascan module is fully automatic and totally inexpensive, does not require any blood or dialysate sampling and therefore can be repeated every 15 or 30 min during each dialysis session. Some clinical applications of conductivity modelling are presented: (i) the repeated measurement of ionic dialysance allows the quantification of the dialysis dose actually delivered to the patient from the beginning of the session; (ii) the measurement of ionic dialysance with blood lines in normal and reversed positions permits the easy estimation of the blood flow rate in the vascular access of the haemodialysed patient; (iii) the on-line monitoring of ionic dialysance allows the development of new methods of haemodialysis with simultaneous infusion of ions; (iv) the on-line monitoring of ionic dialysance and patient's plasma conductivity facilitates the automatic optimization of the dialysate conductivity for each individual patient.

Hyponatremia, hyposmolality, and hypotonicity: tables and fables.

The difficulty that nonnephrologists sometimes have with the differential diagnosis of hyponatremic patients often results from misinterpreting the significance of measured and calculated serum osmolalities, effective serum osmolalities (tonicities), and the influence of various normal (eg, serum urea nitrogen) and abnormal (eg, ethanol) solutes. Among the more commonly held misconceptions are that high serum urea or alcohol levels will, by analogy with glucose, cause hyponatremia, and that a normal (or elevated) measured serum osmolality in a hyponatremic patient excludes the possibility of hypotonicity. This article describes typical and deliberately comparative data of the serum levels of sodium, glucose, urea nitrogen, and mannitol and/or ethanol (if present); calculated and measured osmolality; effective osmolality; and the potential risk of hypotonicity-induced cerebral edema for each of 6 prototypical hyponatremic states. This provides a helpful educational tool for untangling these interrelationships and for clarifying the differences among various hyponatremic conditions.

Disorders of the effective osmolality in central nervous system injury

Disorders of the effective osmolality in central nervous system injury