New approach to disturbances in the plasma sodium concentration

Edelman Gamblegrams: a tool to teach and learn disorders of water/plasma tonicity homeostasis

This article introduces an innovative teaching and learning tool called "Edelman Gamblegrams" that aims to help medical learners better understand disorders related to water/plasma tonicity homeostasis, i.e., hyponatremia and hypernatremia. Gamblegrams, named after physician James L. Gamble, are bar diagrams displaying the relative abundance of extracellular anions and cations and are commonly used in the analysis of acid-base disorders. The Edelman equation represents the physiological variables that determine plasma sodium concentration, namely, total body sodium mass, total body potassium mass, and total body water volume. Edelman Gamblegrams inspired by traditional Gamblegrams but using the components of the Edelman equation, visually demonstrate how sodium, potassium, and water contribute to plasma sodium concentration under normal and pathological conditions. Scenarios that lead to hypotonic hyponatremia and hypernatremia in Edelman Gamblegrams are also discussed. Furthermore, examples of how these visual aids can enhance understanding of the pathogenesis of dysnatremias are also presented. Overall, the use of Edelman Gamblegrams has the potential to improve comprehension and retention of concepts related to water/plasma tonicity homeostasis.NEW & NOTEWORTHY This article introduces a new teaching tool called "Edelman Gamblegrams," modeled after the conventional Gamblegrams used in acid-base disorder analysis and using the independent physiological variables that determine the plasma sodium concentration (Edelman equation), that aims to help medical learners understand disorders related to water/plasma tonicity homeostasis.

Hypernatremia in Hyperglycemia: Clinical Features and Relationship to Fractional Changes in Body Water and Monovalent Cations during Its Development

In hyperglycemia, the serum sodium concentration ([Na]S) receives influences from (a) the fluid exit from the intracellular compartment and thirst, which cause [Na]S decreases; (b) osmotic diuresis with sums of the urinary sodium plus potassium concentration lower than the baseline euglycemic [Na]S, which results in a [Na]S increase; and (c), in some cases, gains or losses of fluid, sodium, and potassium through the gastrointestinal tract, the respiratory tract, and the skin. Hyperglycemic patients with hypernatremia have large deficits of body water and usually hypovolemia and develop severe clinical manifestations and significant mortality. To assist with the correction of both the severe dehydration and the hypovolemia, we developed formulas computing the fractional losses of the body water and monovalent cations in hyperglycemia. The formulas estimate varying losses between patients with the same serum glucose concentration ([Glu]S) and [Na]S but with different sums of monovalent cation concentrations in the lost fluids. Among subjects with the same [Glu]S and [Na]S, those with higher monovalent cation concentrations in the fluids lost have higher fractional losses of body water. The sum of the monovalent cation concentrations in the lost fluids should be considered when computing the volume and composition of the fluid replacement for hyperglycemic syndromes.

Diagnostic and Therapeutic Strategies to Severe Hyponatremia in the Intensive Care Unit

Hyponatremia is the most common electrolyte abnormality encountered in critically ill patients and is linked to heightened morbidity, mortality, and healthcare resource utilization. However, its causal role in these poor outcomes and the impact of treatment remain unclear. Plasma sodium is the main determinant of plasma tonicity; consequently, hyponatremia commonly indicates hypotonicity but can also occur in conjunction with isotonicity and hypertonicity. Plasma sodium is a function of total body exchangeable sodium and potassium and total body water. Hypotonic hyponatremia arises when total body water is proportionally greater than the sum of total body exchangeable cations, that is, electrolyte-free water excess; the latter is the result of increased intake or decreased (kidney) excretion. Hypotonic hyponatremia leads to water movement into brain cells resulting in cerebral edema. Brain cells adapt by eliminating solutes, a process that is largely completed by 48 h. Clinical manifestations of hyponatremia depend on its biochemical severity and duration. Symptoms of hyponatremia are more pronounced with acute hyponatremia where brain adaptation is incomplete while they are less prominent in chronic hyponatremia. The authors recommend a physiological approach to determine if hyponatremia is hypotonic, if it is mediated by arginine vasopressin, and if arginine vasopressin secretion is physiologically appropriate. The treatment of hyponatremia depends on the presence and severity of symptoms. Brain herniation is a concern when severe symptoms are present, and current guidelines recommend immediate treatment with hypertonic saline. In the absence of significant symptoms, the concern is neurologic sequelae resulting from rapid correction of hyponatremia which is usually the result of a large water diuresis. Some studies have found desmopressin useful to effectively curtail the water diuresis responsible for rapid correction.

Hypertonic Saline Infusion for Hyponatremia: Limitations of the Adrogué-Madias and Other Formulas

Hypertonic saline infusion is used to correct hyponatremia with severe symptoms. The selection of the volume of infused hypertonic saline ( VInf ) should address prevention of overcorrection or undercorrection. Several formulas computing this VInf have been proposed. The limitations common to these formulas consist of (1) failure to include potential determinants of change in serum sodium concentration ([ Na ]) including exchanges between osmotically active and inactive sodium compartments, changes in hydrogen binding of body water to hydrophilic compounds, and genetic influences and (2) inaccurate estimates of baseline body water entered in any formula and of gains or losses of water, sodium, and potassium during treatment entered in formulas that account for such gains or losses. In addition, computing VInf from the Adrogué-Madias formula by a calculation assuming a linear relation between VInf and increase in [ Na ] is a source of errors because the relation between these two variables was proven to be curvilinear. However, these errors were shown to be negligible by a comparison of estimates of VInf by the Adrogué-Madias formula and by a formula using the same determinants of the change in [ Na ] and the curvilinear relation between this change and VInf . Regardless of the method used to correct hyponatremia, monitoring [ Na ] and changes in external balances of water, sodium, and potassium during treatment remain imperative.

Salt and Water: A Review of Hypernatremia

Serum sodium disorders are generally a marker of water balance in the body. Thus, hypernatremia is most often caused by an overall deficit of total body water. Other unique circumstances may lead to excess salt, without an impact on the body's total water volume. Hypernatremia is commonly acquired in both the hospital and community. As hypernatremia is associated with increased morbidity and mortality, treatment should be initiated promptly. In this review, we will discuss the pathophysiology and management of the main types of hypernatremia, which can be categorized as either a loss of water or gain of sodium that can be mediated by renal or extrarenal mechanisms.

Clinical Approach to Euvolemic Hyponatremia

Euvolemic hyponatremia is frequently encountered in hospitalized patients and the syndrome of inappropriate antidiuretic hormone secretion (SIADH) is the most common cause in most patients. SIADH diagnosis is confirmed by decreased serum osmolality, inappropriately elevated urine osmolality (>100 mosmol/L), and elevated urine sodium (Na) levels. Patients should be screened for thiazide use and adrenal or thyroid dysfunction should be ruled out before making a diagnosis of SIADH. Clinical mimics of SIADH like cerebral salt wasting and reset osmostat should be considered in some patients. The distinction between acute (<48 hours) versus chronic (>48 hours or without baseline labs) hyponatremia and clinical symptomatology are important to initiate proper therapy. Acute hyponatremia is a medical emergency and osmotic demyelination syndrome (ODS) occurs commonly when rapidly correcting any chronic hyponatremia. Hypertonic (3%) saline should be used in patients with significant neurologic symptoms and maximal correction of serum Na level should be limited to <8 mEq over 24 hours to prevent the ODS. Simultaneous administration of parenteral desmopressin is one of the best ways to prevent overly rapid Na correction in high-risk patients. Free water restriction combined with increased solute intake (e.g., urea) is the most effective therapy to treat patients with SIADH. 0.9% saline acts as a hypertonic solution in patients with hyponatremia and should be avoided in the treatment of SIADH due to rapid fluctuations in serum Na levels. Dual effects of 0.9% saline resulting in rapid correction of serum Na during infusion (inducing ODS) and post-infusion worsening of serum Na levels are described in the article with clinical examples.

Predictive correction of serum sodium concentration with formulas derived from the Edelman equation in patients with severe hyponatremia

Severe hyponatremia can cause life-threatening cerebral edema. Treatment comprises rapid elevation of serum sodium concentration; however, overcorrection can result in osmotic demyelination. This study investigated potential factors, including predictive correction based on the Edelman equation, associated with appropriate correction in 221 patients with a serum sodium concentration ≤ 120 mEq/L who were admitted to a hospital in Nagoya, Japan. Appropriate correction was defined as an elevation in serum sodium concentration in the range of 4-10 mEq/L in the first 24 h and within 18 mEq/L in the first 48 h after the start of the correction. Appropriate corrections were made in 132 (59.7%) of the 221 patients. Multivariate analysis revealed that predictive correction with an infusate and fluid loss formula derived from the Edelman equation was associated with appropriate correction of serum sodium concentration (adjusted odds ratio, 7.84; 95% confidence interval, 2.97-20.64). Relative without its use, the predictive equation results in a lower proportion of undercorrection (14.3% vs. 48.0%, respectively) and overcorrection (1.0% vs. 12.2%, respectively). These results suggest that predictive correction of serum sodium concentrations using the formula derived from the Edelman equation can play an essential role in the appropriate management of patients with severe hyponatremia.

Evaluation and management of hypernatremia in adults: clinical perspectives

Hypernatremia is an occasionally encountered electrolyte disorder, which may lead to fatal consequences under improper management. Hypernatremia is a disorder of the homeostatic status regarding body water and sodium contents. This imbalance is the basis for the diagnostic approach to hypernatremia. We summarize the eight diagnostic steps of the traditional approach and introduce new biomarkers: exclude pseudohypernatremia, confirm glucose-corrected sodium concentrations, determine the extracellular volume status, measure urine sodium levels, measure urine volume and osmolality, check ongoing urinary electrolyte free water clearance, determine arginine vasopressin/copeptin levels, and assess other electrolyte disorders. Moreover, we suggest six steps to manage hypernatremia by replacing water deficits, ongoing water losses, and insensible water losses: identify underlying causes, distinguish between acute and chronic hypernatremia, determine the amount and rate of water administration, select the type of replacement solution, adjust the treatment schedule, and consider additional therapy for diabetes insipidus. Physicians may apply some of these steps to all patients with hypernatremia, and can also adapt the regimens for specific causes or situations.

Dysnatremia in Gastrointestinal Disorders

The primary solute of the milieu intérieur is sodium and accompanying anions. The solvent is water. The kidneys acutely regulate homeostasis in filtration, secretion, and resorption of electrolytes, non-electrolytes, and minerals while balancing water retention and clearance. The gastrointestinal absorptive and secretory functions enable food digestion and water absorption needed to sustain life. Gastrointestinal perturbations including vomiting and diarrhea can lead to significant volume and electrolyte losses, overwhelming the renal homeostatic compensatory mechanisms. Dysnatremia, potassium and acid-base disturbances can result from gastrointestinal pathophysiologic processes. Understanding the renal and gastrointestinal contributions to homeostatis are important for the clinical evaluation of perturbed volume disturbances.

Edelman Revisited: Concepts, Achievements, and Challenges

The key message from the 1958 Edelman study states that combinations of external gains or losses of sodium, potassium and water leading to an increase of the fraction (total body sodium plus total body potassium) over total body water will raise the serum sodium concentration ([Na]_S), while external gains or losses leading to a decrease in this fraction will lower [Na]_S. A variety of studies have supported this concept and current quantitative methods for correcting dysnatremias, including formulas calculating the volume of saline needed for a change in [Na]_S are based on it. Not accounting for external losses of sodium, potassium and water during treatment and faulty values for body water inserted in the formulas predicting the change in [Na]_S affect the accuracy of these formulas. Newly described factors potentially affecting the change in [Na]_S during treatment of dysnatremias include the following: (a) exchanges during development or correction of dysnatremias between osmotically inactive sodium stored in tissues and osmotically active sodium in solution in body fluids; (b) chemical binding of part of body water to macromolecules which would decrease the amount of body water available for osmotic exchanges; and (c) genetic influences on the determination of sodium concentration in body fluids. The effects of these newer developments on the methods of treatment of dysnatremias are not well-established and will need extensive studying. Currently, monitoring of serum sodium concentration remains a critical step during treatment of dysnatremias.

The management of acute and chronic hyponatraemia

Hyponatraemia is the most common electrolyte abnormality encountered in clinical practice; despite this, the work-up and management of hyponatraemia remain suboptimal and varies among different specialist groups. The majority of data comparing hyponatraemia treatments have been observational, up until recently. The past two years have seen the publication of several randomised control trials investigating hyponatraemia treatments, both for chronic and acute hyponatraemia. In this article, we aim to provide a background to the physiology, cause and impact of hyponatraemia and summarise the most recent data on treatments for acute and chronic hyponatraemia, highlighting their efficacy, tolerability and adverse effects.

Intravenous Infusion of Sterile Water for the Treatment of Hypernatraemia

Little research has been carried out into the infusion of intravenous sterile water for the treatment of hypernatraemia, and it remains a contentious issue. We conducted a review of the literature and extract results following an extensive search of Medline 1946, Embase 1974, ProQuest, evidence-based practice resources, national and international guideline sites and the publications of various professional bodies. The review is presented on the infusion of sterile water (hypotonic fluid) to lower serum sodium level in those circumstances when enteral supplementation of water is not possible, such as in postoperative patients or when other isotonic fluids (such as 5% dextrose in water infusion) are less than ideal—for example, hyperglycaemic patients on an insulin infusion. Absence of guidelines has limited the use of sterile water, even as an off-label drug when it can be administered relatively safely via a central line.

Polyuria in adults. A diagnostic approach based on pathophysiology

Polyuria is a common clinical condition characterized by a urine output that is inappropriately high (more than 3 L in 24 h) for the patient's blood pressure and plasma sodium levels. From a pathophysiological point of view, it is classified into two types: polyuria due to a greater excretion of solutes (urine osmolality >300 mOsm/L) or due to an inability to increase solute concentration (urine osmolality <150 mOsm/L). Sometimes both mechanisms can coexist (urine osmolality 150-300 mOsm/L). Polyuria is a diagnostic challenge and its proper treatment requires an evaluation of the medical record, determination of urine osmolality, estimation of free water clearance, use of water deprivation tests in aqueous polyuria, and measurement of electrolytes in blood and urine in the case of osmotic polyuria.

High Na+ Salt Diet and Remodeling of Vascular Smooth Muscle and Endothelial Cells

Our knowledge on essential hypertension is vast, and its treatment is well known. Not all hypertensives are salt-sensitive. The available evidence suggests that even normotensive individuals are at high cardiovascular risk and lower survival rate, as blood pressure eventually rises later in life with a high salt diet. In addition, little is known about high sodium (Na⁺) salt diet-sensitive hypertension. There is no doubt that direct and indirect Na⁺ transporters, such as the Na/Ca exchanger and the Na/H exchanger, and the Na/K pump could be implicated in the development of high salt-induced hypertension in humans. These mechanisms could be involved following the destruction of the cell membrane glycocalyx and changes in vascular endothelial and smooth muscle cells membranes’ permeability and osmolarity. Thus, it is vital to determine the membrane and intracellular mechanisms implicated in this type of hypertension and its treatment.

Use of Urine Electrolytes and Urine Osmolality in the Clinical Diagnosis of Fluid, Electrolytes, and Acid-Base Disorders

We discuss the use of urine electrolytes and urine osmolality in the clinical diagnosis of patients with fluid, electrolytes, and acid-base disorders, emphasizing their physiological basis, their utility, and the caveats and limitations in their use. While our focus is on information obtained from measurements in the urine, clinical diagnosis in these patients must integrate information obtained from the history, the physical examination, and other laboratory data.

Urine Electrolytes in the Intensive Care Unit: From Pathophysiology to Clinical Practice

Assessment of urine concentrations of sodium, chloride, and potassium is a widely available, rapid, and low-cost diagnostic option for the management of critically ill patients. Urine electrolytes have long been suggested in the diagnostic workup of hypovolemia, kidney injury, and acid-base and electrolyte disturbances. However, due to the wide range of normal reference values and challenges in interpretation, their use is controversial. To clarify their potential role in managing critical patients, we reviewed existing evidence on the use of urine electrolytes for diagnostic and therapeutic evaluation and assessment in critical illness. This review will describe the normal physiology of water and electrolyte excretion, summarize the use of urine electrolytes in hypovolemia, acute kidney injury, acid-base, and electrolyte disorders, and suggest some practical flowcharts for the potential use of urine electrolytes in daily critical care practice.

Fatal case of hospital-acquired hypernatraemia in a neonate: lessons learned from a tragic error

A 3-week-old boy with viral gastroenteritis was by error given 200 mL 1 mmol/mL hypertonic saline intravenously instead of isotonic saline. His plasma sodium concentration (PNa) increased from 136 to 206 mmol/L. Extreme brain shrinkage and universal hypoperfusion despite arterial hypertension resulted. Treatment with glucose infusion induced severe hyperglycaemia. Acute haemodialysis decreased the PNa to 160 mmol/L with an episode of hypoperfusion. The infant developed intractable seizures, severe brain injury on magnetic resonance imaging and died. The most important lesson is to avoid recurrence of this tragic error. The case is unique because a known amount of sodium was given intravenously to a well-monitored infant. Therefore the findings give us valuable data on the effect of fluid shifts on the PNa, the circulation and the brain’s response to salt intoxication and the role of dialysis in managing it. The acute salt intoxication increased PNa to a level predicted by the Edelman equation with no evidence of osmotic inactivation of sodium. Treatment with glucose in water caused severe hypervolaemia and hyperglycaemia; the resulting increase in urine volume exacerbated hypernatraemia despite the high urine sodium concentration, because electrolyte-free water clearance was positive. When applying dialysis, caution regarding circulatory instability is imperative and a treatment algorithm is proposed.

Understanding dysnatremia

Dysnatremia—either hyponatremia or hypernatremia—is frequently encountered in the clinical practice and often poses a diagnostic and therapeutic challenge for physicians. Despite their frequent occurrence, disorders of the water and sodium balance in the human body have puzzled many physicians over the years and often remain elusive for those lacking experience in their interpretation and management. In this article, we derive a transparent governing equation that can be used by clinicians to describe how a change in relevant physiological parameters will affect the plasma sodium concentration. As opposed to many existing models, our model takes both input and output into account, and integrates osmolarity and tonicity. Our governing equation should be considered a means for clinicians to get a better qualitative understanding of the relationship between the plasma sodium concentration and the variables that influence it for a wide range of scenarios.

Trajectories of Serum Sodium on In-Hospital and 1-Year Survival among Hospitalized Patients

BACKGROUND AND OBJECTIVES

This study aimed to investigate the association between in-hospital trajectories of serum sodium and risk of in-hospital and 1-year mortality in patients in hospital.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This is a single-center cohort study. All adult patients who were hospitalized from years 2011 through 2013 who had available admission serum sodium and at least three serum sodium measurements during hospitalization were included. The trend of serum sodium during hospitalization was analyzed using group-based trajectory modeling; the five main trajectories were grouped as follows: (1) stable normonatremia, (2) uncorrected hyponatremia, (3) borderline high serum sodium, (4) corrected hyponatremia, and (5) fluctuating serum sodium. The outcome of interest was in-hospital mortality and 1-year mortality. Stable normonatremia was used as the reference group for outcome comparison.

RESULTS

A total of 43,539 patients were analyzed. Of these, 47% had stable normonatremia, 15% had uncorrected hyponatremia, 31% had borderline high serum sodium, 3% had corrected hyponatremia, and 5% had fluctuating serum sodium trajectory. In adjusted analysis, there was a higher in-hospital mortality among those with uncorrected hyponatremia (odds ratio [OR], 1.33; 95% CI, 1.06 to 1.67), borderline high serum sodium (OR, 1.66; 95% CI, 1.38 to 2.00), corrected hyponatremia (OR, 1.50; 95% CI, 1.02 to 2.20), and fluctuating serum sodium (OR, 4.61; 95% CI, 3.61 to 5.88), compared with those with the normonatremia trajectory. One-year mortality was higher among those with uncorrected hyponatremia (hazard ratio [HR], 1.28; 95% CI, 1.19 to 1.38), borderline high serum sodium (HR, 1.18; 95% CI, 1.11 to 1.26), corrected hyponatremia (HR, 1.24; 95% CI, 1.08 to 1.42), and fluctuating serum sodium (HR, 2.10; 95% CI, 1.89 to 2.33) compared with those with the normonatremia trajectory.

CONCLUSIONS

More than half of patients who had been hospitalized had an abnormal serum sodium trajectory during hospitalization. This study demonstrated that not only the absolute serum sodium levels but also their in-hospital trajectories were significantly associated with in-hospital and 1-year mortality. The highest in-hospital and 1-year mortality risk was associated with the fluctuating serum sodium trajectory.

PODCAST

This article contains a podcast at https://www.asn-online.org/media/podcast/CJASN/2020_03_25_CJN.12281019.mp3.

Sodium-Based Osmotherapy in Continuous Renal Replacement Therapy: a Mathematical Approach

Cerebral edema, in a variety of circumstances, may be accompanied by states of hyponatremia. The threat of brain injury from hypotonic stress-induced astrocyte demyelination is more common when vulnerable patients with hyponatremia who have end stage liver disease, traumatic brain injury, heart failure, or other conditions undergo overly rapid correction of hyponatremia. These scenarios, in the context of declining urinary output from CKD and/or AKI, may require controlled elevations of plasma tonicity vis-à-vis increases of the plasma sodium concentration. We offer a strategic solution to this problem via sodium-based osmotherapy applied through a conventional continuous RRT modality: predilution continuous venovenous hemofiltration.

Hyponatremia in Patients Undergoing CAPD: Role of Water Gain and/or Malnutrition

Background

Hyponatremia has a number of different causes; some may have serious untoward implications for patients undergoing chronic ambulatory peritoneal dialysis (CAPD).

Objective

To determine the pathophysiology of hyponatremia in patients on CAPD.

Methods

A retrospective analysis was carried out on 210 patients on CAPD. We selected patients with 2 – 4 consecutive periods when the plasma sodium concentration was ≤130 mmol/L and again when it was > 133 mmol/L. Exclusion criteria included hyperglycemia, orthostatic hypotension, edema, and inadequate records.

Results

An electrolyte-free water gain appeared to be the main cause of hyponatremia in only 1 of 5 patients because this was the only patient with a significant increase in body weight. In 1 patient, there was weight loss in the hyponatremic period, suggesting tissue catabolism was present. In 3 patients, there was neither weight gain nor evidence for a contracted extracellular fluid volume in the hyponatremic period, suggesting that intracellular potassium and phosphate loss could be the major mechanism for their hyponatremia.

Conclusion

When hyponatremia is due to a catabolic state, its management should aim to restore intracellular fluid composition ( i.e., to correct malnutrition).

A Physiological Analysis of Hyponatremia: Implications for Patients on Peritoneal Dialysis

The basis for hyponatremia is a negative balance for sodium (Na+) plus potassium (K+) and/or a positive balance for water. In patients with normal renal function, vasopressin is needed to prevent the excretion of electrolyte-free water. Vasopressin is not important when there is little residual renal function. If hyponatremia is accompanied by a quantitatively appropriate gain in weight, this implies that a gain of electrolyte-free water was the basis for hyponatremia. In the absence of this weight gain, a loss of salts is to be suspected. If the extracellular fluid (ECF) volume is obviously low, hyponatremia is due to a deficit of NaCl, unless there is a deficit of K+. With a KCl deficit and a contracted ECF volume, there should also be a large shift of Na+ into cells, so metabolic alkalosis would not be an expected finding. In contrast, those patients with no change in weight who have a normal or expanded ECF volume are subdivided into those with a gain of solutes restricted to the ECF compartment (glucose, mannitol), or those with a deficit of solutes of intracellular fluid origin, which implies that a catabolic state (malnutrition) may be present.

Prediction of dysnatremias in critically ill patients based on the law of conservation of mass. Comparison of existing formulae

Background

We aimed to examine the predictive value of a novel mathematical formula based on the law of conservation of mass in calculating sodium changes in intensive care unit patients and compare its performance with previously published formulae.

Methods

178 patients were enrolled from 01/2010 to 10/2013. Plasma and urine were collected in two consecutive 8-hour intervals and the sodium was measured. The predicted sodium concentration was calculated based on previous equations and our formula. The two 8-hour period (epoch 1 and 2) results were compared. Variability of predicted values among the measured range of serum sodium levels were provided by Bland-Altman plots with bias and precision statistics. Comparison of the results was performed with the statistical model of the Percentage Similarity.

Results

47.19% patients had dysnatremias. The bias ± SD with 95% limits of agreement for sodium levels were -1.395±3.491 for epoch 1 and -1.623 ±11.1 for epoch 2 period. Bland-Altman analysis for the epoch 1 study period had the following results: -0.8079±3.447 for Adrogué–Madias, 0.56±9.687 for Barsoum–Levine, 0.1412±3.824 for EFWC and 0.294±4.789 for Kurtz–Nguyen formula. The mean similarity, SD and coefficient variation for the methods compared with the measured sodium are: 99.56%, 3.873, 3.89% epoch 1, 99.56%, 1.255, 1.26% for epoch 2, 99.77%, 1.245, 1.26% for Adrogue-Madias, 100.1%, 1.337, 1.34% for Barsoum-Levine, 100.1%, 1.704, 1.7% for Nguyen, 100.1%, 1.370, 1.37% for ECFW formula.

Conclusions

The law of conservation of mass can be successfully applied for the prediction of sodium changes in critically ill patients.

[Hyponatremia in Liver Cirrhosis]

Hyponatremia is a commonly observed complication that is related to hypoalbuminemia and portal hypertension in patients with advanced liver cirrhosis. Hyponatremia in patients with liver cirrhosis is mostly dilutional hyponatremia and is defined when the serum sodium concentration is below 130 meq/L. The risk of complications increases significantly in cirrhotic patients with hyponatremia, which includes spontaneous bacterial peritonitis, hepatorenal syndrome, and hepatic encephalopathy. In addition, hyponatremia is associated with increased morbidity and mortality in patients with cirrhosis, and is an important prognostic factor before and after liver transplantation. The conventional therapies of hyponatremia are albumin infusion, fluid restriction and loop diuretics, but these are frequently ineffective. This review investigates the pathophysiology and various therapeutic modalities, including selective vasopressin receptor antagonists, for the management of hyponatremia in patients with liver cirrhosis.

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.

Predictors of failure to respond to fluid restriction in SIAD in clinical practice; time to re-evaluate clinical guidelines?

BACKGROUND

Fluid restriction is recommended as first line therapy for Syndrome of Inappropriate Antidiuresis (SIAD), despite of lack of good evidence base to support its use, and poor efficacy in clinical practice and in the literature.

AIM

We set out to determine how many patients with well-defined SIAD had pre-treatment criteria which would predict failure to fluid restriction.

DESIGN AND METHODS

This was a consecutive, prospective evaluation of 183 patients with a diagnosis of SIAD in two different hospitals. Full ascertainment of the diagnostic criteria for SIAD was obtained in all patients.

RESULTS

About 47% of patients had a urine volume <1500 ml in 24 h, 41% had initial urine osmolality > 500 mOsm/kg, 26% a Furst-equation ratio > 1. About 59% had one criterion predicting failure to respond to fluid restriction, 37% two criteria, and 3% three criteria.

CONCLUSIONS

Our data suggest that up to 60% of patients with SIAD had criteria which recent clinical guidelines suggest would predict nonresponse to fluid restriction. This may explain why the recommended first line therapy for SIAD has been shown to be ineffective.

Diagnosis and Treatment of Hyponatremia: Compilation of the Guidelines

Hyponatremia is a common water balance disorder that often poses a diagnostic or therapeutic challenge. Therefore, guidelines were developed by professional organizations, one from within the United States (2013) and one from within Europe (2014). This review discusses the diagnosis and treatment of hyponatremia, comparing the two guidelines and highlighting recent developments. Diagnostically, the initial step is to differentiate hypotonic from nonhypotonic hyponatremia. Hypotonic hyponatremia is further differentiated on the basis of urine osmolality, urine sodium level, and volume status. Recently identified parameters, including fractional uric acid excretion and plasma copeptin concentration, may further improve the diagnostic approach. The treatment for hyponatremia is chosen on the basis of duration and symptoms. For acute or severely symptomatic hyponatremia, both guidelines adopted the approach of giving a bolus of hypertonic saline. Although fluid restriction remains the first-line treatment for most forms of chronic hyponatremia, therapy to increase renal free water excretion is often necessary. Vasopressin receptor antagonists, urea, and loop diuretics serve this purpose, but received different recommendations in the two guidelines. Such discrepancies may relate to different interpretations of the limited evidence or differences in guideline methodology. Nevertheless, the development of guidelines has been important in advancing this evolving field.

Health effects of desalinated water: Role of electrolyte disturbance in cancer development

This review contends that "healthy" water in terms of electrolyte balance is as important as "pure" water in promoting public health. It considers the growing use of desalination (demineralization) technologies in drinking water treatment which often results in tap water with very low concentrations of sodium, potassium, magnesium and calcium. Ingestion of such water can lead to electrolyte abnormalities marked by hyponatremia, hypokalemia, hypomagnesemia and hypocalcemia which are among the most common and recognizable features in cancer patients. The causal relationships between exposure to demineralized water and malignancies are poorly understood. This review highlights some of the epidemiological and in vivo evidence that link dysregulated electrolyte metabolism with carcinogenesis and the development of cancer hallmarks. It discusses how ingestion of demineralized water can have a procarcinogenic effect through mediating some of the critical pathways and processes in the cancer microenvironment such as angiogenesis, genomic instability, resistance to programmed cell death, sustained proliferative signaling, cell immortalization and tumorigenic inflammation. Evidence that hypoosmotic stress-response processes can upregulate a number of potential oncogenes is well supported by a number studies. In view of the rising production and consumption of demineralized water in most parts of the world, there is a strong need for further research on the biological importance and protean roles of electrolyte abnormalities in promoting, antagonizing or otherwise enabling the development of cancer. The countries of the Gulf Cooperative Council (GCC) where most people consume desalinated water would be a logical place to start this research.

Diagnosis and Management of Hyponatremia

Appropriate treatment of hyponatremic disorders is de pendent on an understanding of the mechanisms that cause these abnormalities. This article offers a patho physiological approach to hypoosmolar syndromes. Common causes of hyponatremia are reviewed with particular emphasis on congestive heart failure, ad vanced liver disease, diuretic use, and the syndrome of inappropriate antidiuretic hormone secretion. New con cepts in treatment are discussed with the aid of clinical examples that emphasize critical information. A number of recent studies have questioned the safety of rapidly correcting hyponatremia; recommendations based on our current understanding of these risks are proposed. Pitfalls in the diagnosis and management of patients with hyponatremic disorders are also discussed.

Diagnosis and treatment of hypernatremia

Hypernatremia is defined as a serum sodium level above 145 mmol/L. It is a frequently encountered electrolyte disturbance in the hospital setting, with an unappreciated high mortality. Understanding hypernatremia requires a comprehension of body fluid compartments, as well as concepts of the preservation of normal body water balance. The human body maintains a normal osmolality between 280 and 295 mOsm/kg via Arginine Vasopressin (AVP), thirst, and the renal response to AVP; dysfunction of all three of these factors can cause hypernatremia. We review new developments in the pathophysiology of hypernatremia, in addition to the differential diagnosis and management of this important electrolyte disorder.

Am I Drinking Enough? Yes, No, and Maybe

Adequate fluid intake can be dually defined as a volume of fluid (from water, beverages, and food) sufficient to replace water losses and provide for solute excretion. A wide range of fluid intakes are compatible with euhydration, whereby total body water varies narrowly from day to day by 600 to 900 mL (<1% body mass). One measure of fluid intake adequacy involves enough fluid to prevent meaningful body water deficits outside this euhydration range (i.e., dehydration). Another measure of fluid intake adequacy involves enough fluid to balance the renal solute load, which can vary widely inside the euhydration range. The subtle but important distinction between the 2 types of adequacy may explain some of the ambiguity surrounding the efficacy of hydration status markers. Both perspectives of fluid intake adequacy are discussed in detail and a simple tool is reviewed that may help healthy, active, low-risk populations answer the question, "Am I drinking enough?" Key Teaching Points • Adequate fluid intake can be dually defined as a volume of fluid (from water, beverages, and food) sufficient to replace water losses and provide for solute excretion. • Fluid needs can differ greatly among individuals due to variation in the factors that influence both water loss and solute balance; thus, adequacy is consistent with a wide range of fluid intakes and is better gauged using hydration assessment methods. • Adequacy of fluid intake for replacing meaningful water losses (dehydration) can be assessed simply, inexpensively, and with reasonable fidelity among healthy, active, low-risk individuals. • Adequacy of fluid intake for solute excretion per se can also be assessed among individuals but is more difficult to define and less practical to measure.

Prevention of hospital-acquired hyponatraemia: individualised fluid therapy

BACKGROUND

Large amounts of fluids are daily prescribed to hospitalised patients across different medical specialities. Unfortunately, inappropriate fluid administration commonly causes iatrogenic hyponatraemia with associated increase in morbidity and mortality.

METHODS/RESULTS

Fundamental for prevention of hospital-acquired hyponatraemia is an understanding of what determines plasma sodium concentration (P-[Na(+) ]) in the individual patient. P-[Na(+) ] is determined by balances of water and cations according to Edelman. This paper discusses the mechanisms influencing water and cation balances. In the hospitalised patient, non-osmotic antidiuretic hormone secretion is frequent and results in a reduced renal electrolyte-free water clearance (EFWC). This condition puts the patient at risk of hyponatraemia upon infusion of fluids that are hypotonic such as 5% glucose, Darrow-glucose, NaKglucose and 0.45% NaCl in 5% glucose. It is suggested that individualised fluid therapy includes the following: Firstly, bolus therapy with Ringer-acetate/Ringer-lactate/0.9% NaCl in the hypovolaemic patient to minimise the risk of fluid under-/overload. Secondly, P-[Na(+) ] should be monitored together with the balances influencing P-[Na(+) ]. This may include EFWC in patients at additional risk of hyponatraemia. In patients with potentially reduced intracranial compliance (e.g. meningitis, intracranial bleeding, cerebral contusion and brain oedema), even a small decrease in P-[Na(+) ] induced by slightly hypotonic fluids like Ringer-acetate/Ringer-lactate can increase the intracranial pressure dramatically. Consequently, 0.9 % NaCl is recommended as first-line fluid for such patients.

CONCLUSIONS

The occurrence of hospital-acquired hyponatraemia may be reduced by prescribing fluids, type and amount, with the same dedication as shown for other drugs.

Clinical and Genetic Factors Associated With Thiazide-Induced Hyponatremia

Thiazide diuretics are associated with an increased risk of hyponatremia. The aim of this study was to investigate possible predictors of thiazide-induced hyponatremia.A total of 48 patients admitted to the ward or to the emergency department due to severe thiazide-induced hyponatremia (Na < 125 mmol/L) were enrolled in our study as the case group. Another 211 hypertensive patients with normal sodium levels after treatment with thiazide diuretics were selected as the control group. Twelve tag single nucleotide polymorphism markers were selected from the Potassium Channel, Inwardly Rectifying Subfamily J, Member 1 (KCNJ1) gene: rs1231254, rs2238009, rs1148058, rs675482, rs673614, rs12795437, rs2855800, rs2509585, rs3016774, rs881333, rs4529890, and rs7116606. Clinical and genetic parameters between patients with thiazide-induced hyponatremia and the control group were compared. Logistic regression was used to analyze data.The patients with thiazide-induced hyponatremia were older (P < 0.001), predominantly female (P = 0.008), had a lower mean body mass index (BMI) (P < 0.001), and more commonly used angiotensin II receptor antagonist (P < 0.001) and spironolactone (P = 0.007) compared with the control groups. Analysis with multivariate logistic regression revealed that age (odds ratio [OR], 1.13; 95% confidence interval [CI], 1.08-1.19, P < 0.001), female gender (OR, 4.49; 95% CI, 1.54-13.11, P = 0.006), BMI (OR, 0.80; 95% CI, 0.69-0.93, P = 0.003), and KCNJ1 rs2509585 C/T or T/T polymorphisms (OR, 5.75; 95% CI, 1.25-26.45, P = 0.03) were independent predictors for thiazide-induced hyponatremia.Older female patients with lower BMIs and KCNJ1 rs2509585 C/T or T/T polymorphisms were more likely to develop thiazide-induced hyponatremia.

Employment of vasopressin receptor antagonists in management of hyponatraemia and volume overload in some clinical conditions

WHAT IS KNOWN AND OBJECTIVE

Hyponatraemia, the most common electrolyte imbalance occurring in hospitalized subjects, is usually classified as hypovolaemic, euvolaemic or hypervolaemic. Hyponatraemia is a predictor of death among subjects with chronic heart failure and cirrhosis. The inappropriate secretion of the antidiuretic hormone (AVP) seems to be of pivotal importance in the decline of serum sodium concentration in these clinical conditions. The objective of this review was to summarize recent progress in management of hyponatraemia in SIADH, cirrhosis and heart failure.

METHODS

Literature searches were conducted on the topics of hyponatraemia and vasopressin receptor antagonists, using PubMed, pharmaceutical company websites and news reports. The information was evaluated for relevance and quality, critically assessed and summarized.

RESULTS AND DISCUSSION

The initial treatment of severe hyponatraemia is directed towards the prevention or management of neurological manifestations and consists of an intravenous infusion of hypertonic saline. Fluid restriction is indicated in oedematous states. Diuretics alone or in combination with other specific drugs remain the main strategy in the management of volume overload in heart failure. In resistant cases, ultrafiltration can lead to effective removal of isotonic fluid preventing new episodes of decompensation; however, aquapheresis is associated with increased costs and other limits. In several trials, the efficacy of vasopressin receptor antagonists in euvolaemic patients (inappropriate antidiuretic hormone secretion) or in hypervolaemic hyponatraemia (chronic heart failure, cirrhosis) has been evaluated. It was found that vaptans, which promote aquaresis, were superior to a placebo in raising and maintaining serum sodium concentrations in these subjects.

WHAT IS NEW AND CONCLUSIONS

Combined with conventional therapy, vasopressin receptor antagonists (AVP-R antagonists) are able to increase the excretion of electrolyte-free water and the sodium concentration. Further studies are needed to assess efficacious outcomes of aquaresis compared with aquapheresis and with conventional therapy.

Hyponatremia in cirrhosis: Pathophysiology and management

Hyponatremia is frequently seen in patients with ascites secondary to advanced cirrhosis and portal hypertension. The development of ascites in patients with cirrhosis is multi-factorial. Portal hypertension and the associated systemic vasodilation lead to activation of the sodium-retaining neurohumoral mechanisms which include the renin-angiotensin-aldosterone system, sympathetic nervous system and antidiuretic hormone (ADH). The net effect is the avid retention of sodium and water to compensate for the low effective circulatory volume resulting in the development of ascites. Although not apparent in the early stages of cirrhosis, the progression of cirrhosis and ascites leads to impairment of the kidneys to eliminate solute- free water. This leads to additional compensatory mechanisms including non-osmotic secretion of ADH, also known as arginine vasopressin, further worsening excess water retention and thereby hyponatremia. Hyponatremia is associated with increased morbidity and mortality in patients with cirrhosis, and is an important prognostic marker both before and after liver transplant. The management of hyponatremia in this setting is a challenge as conventional therapy for hyponatremia including fluid restriction and loop diuretics are frequently inefficacious. In this review, we discuss the pathophysiology and various treatment modalities, including selective vasopressin receptor antagonists, for the management of hyponatremia in patients with cirrhosis.

Increase in urinary sodium excretion in spinal cord injury patients in the emergency department

OBJECTIVE

Spinal cord injury (SCI) is a pathological condition known to produce hyponatremia. The aim of this study was to elucidate the dynamics of urinary sodium excretion in patients with spinal cord injury.

METHODS

SCI patients undergoing intensive care management were enrolled in this study. These patients were divided into two groups: those with Frankel Grade A spinal cord injury manifesting complete, severe motor disorders (FA group) and those with incomplete spinal cord injury (non-FA group). The occurrence of episode of hyponatremia (serum sodium <135 mmol/L), hypotension, and bradycardia during the first 14 hospital days was counted and fractional excretion of sodium (FENa) was calculated on the 1st, 7th, and 14th hospital days.

RESULTS

Thirty-four patients (FA group, n = 9; non-FA group, n = 25) were included. Eight patients (88.9 %) in the FA group and three patients (12 %) in the non-FA group experienced at least one episode of hyponatremia during the first 14 hospital days. In the FA group, the FENa was significantly increased on the 7th and 14th hospital days compared to the 1st hospital day. FENa on the 14th hospital day was a significant independent predictor of hyponatremic episodes. Hypotension and bradycardia as the symptoms of sympathetic blockade differed significantly as independent predictors of increased FENa on the 14th hospital day.

CONCLUSION

Urinary sodium excretion calculated by FENa increased in patients with severe spinal cord injury. Sympathetic blockade due to SCI may increase urine sodium excretion and lead to hyponatremia.

AVP-induced increase in AQP2 and p-AQP2 is blunted in heart failure during cardiac remodeling and is associated with decreased AT1R abundance in rat kidney

AIM

The objective was to examine the renal effects of long-term increased angiotensin II and vasopressin plasma levels in early-stage heart failure (HF). We investigated the regulations of the V2 vasopressin receptor, the type 1A angiotensin II receptor, the (pro)renin receptor, and the water channels AQP2, AQP1, AQP3, and AQP4 in the inner medulla of rat kidney.

METHODS

HF was induced by coronary artery ligation. Sixty-eight rats were allocated to six groups: Sham (N = 11), HF (N = 11), sodium restricted sham (N = 11), sodium restricted HF (N = 11), sodium restricted sham + DDAVP (N = 12), and sodium restricted HF + DDAVP (N = 12). 1-desamino-8-D-arginine vasopressin (0.5 ng h-1 for 7 days) or vehicle was administered. Pre- and post-treatment echocardiographic evaluation was performed. The rats were sacrificed at day 17 after surgery, before cardiac remodeling in rat is known to be completed.

RESULTS

HF rats on standard sodium diet and sodium restriction displayed biochemical markers of HF. These rats developed hyponatremia, hypo-osmolality, and decreased fractional excretion of sodium. Increase of AQP2 and p(Ser256)-AQP2 abundance in all HF groups was blunted compared with control groups even when infused with DDAVP and despite increased vasopressin V2 receptor and Gsα abundance. This was associated with decreased protein abundance of the AT1A receptor in HF groups vs. controls.

CONCLUSION

Early-stage HF is associated with blunted increase in AQP2 and p(Ser256)-AQP2 despite of hyponatremia, hypo-osmolality, and increased inner medullary vasopressin V2 receptor expression. Decreased type 1A angiotensin II receptor abundance likely plays a role in the transduction of these effects.

Body sodium, potassium and water in peritoneal dialysis-associated hyponatremia

OBJECTIVE

This report presents a method quantitatively analyzing abnormalities of body water and monovalent cations (sodium plus potassium) in patients on peritoneal dialysis (PD) with true hyponatremia.

METHODS

It is well known that in the face of euglycemia serum sodium concentration is determined by the ratio between the sum of total body sodium plus total body potassium on the one hand and total body water on the other. We developed balance equations that enabled us to calculate excesses or deficits, relative to the state of eunatremia and dry weight, in terms of volumes of water and volumes of isotonic solutions of sodium plus potassium when patients presented with hyponatremia. We applied this method retrospectively to 5 episodes of PD-associated hyponatremia (serum sodium concentration 121-130 mEq/L) and compared the findings of the method with those of the clinical evaluation of these episodes.

RESULTS

Estimates of the new method and findings of the clinical evaluation were in agreement in 4 of the 5 episodes, representing euvolemic hyponatremia (normal total body sodium plus potassium along with water excess) in 1 patient, hypovolemic hyponatremia (deficit of total body sodium plus potassium along with deficit of total body water) in 2 patients, and hypervolemic hyponatremia (excess of total body sodium along with larger excess of total body water) in 1 patient. In the 5(th) patient, in whom the new method suggested the presence of water excess and a relatively small deficit of monovalent cations, the clinical evaluation had failed to detect the cation deficit.

CONCLUSIONS

Evaluation of imbalances in body water and monovalent cations in PD-associated hyponatremia by the method presented in this report agrees with the clinical evaluation in most instances and could be used as a guide to the treatment of hyponatremia. Prospective studies are needed to test the potential clinical applications of this method.

Hyponatremia: pathophysiology, classification, manifestations and management

Hyponatremia has complex pathophysiology, is frequent and has potentially severe clinical manifestations, and its treatment is associated with high risks. Hyponatremia can be hypertonic, isotonic or hypotonic. Hypotonic hyponatremia has multiple etiologies, but only two general mechanisms of development, defective water excretion, usually because of elevated serum vasopressin levels, or excessive fluid intake. The acute treatment of symptomatic hypotonic hyponatremia requires understanding of its targets and risks and requires continuous monitoring of the patient's clinical status and relevant serum biochemical values. The principles of fluid restriction, which is the mainstay of management of all types of hypotonic hyponatremia, should be clearly understood and followed. Treatment methods specific to various categories of hyponatremia are available. The indications and risks of these treatments should also be well understood. Rapid correction of chronic hypotonic hyponatremia may lead to osmotic demyelination syndrome, which has severe clinical manifestations, and may lead to permanent neurological disability or death. Prevention of this syndrome should be a prime concern of the treatment of hypotonic hyponatremia.

The ideal crystalloid - what is 'balanced'?

PURPOSE OF REVIEW

This review explores the contemporary definition of the term 'balanced crystalloid' and outlines optimal design features and their underlying rationale.

RECENT FINDINGS

Crystalloid interstitial expansion is unavoidable, but also occurs with colloids when there is endothelial glycocalyx dysfunction. Reduced chloride exposure may lessen kidney dysfunction and injury with a possible mortality benefit. Exact balance from an acid-base perspective is achieved with a crystalloid strong ion difference of 24 mEq/l. This can be done simply by replacing 24 mEq/l of chloride in 0.9% sodium chloride with bicarbonate or organic anion bicarbonate substitutes. Potassium, calcium and magnesium additives are probably unnecessary. Large volumes of mildly hypotonic crystalloids such as lactated Ringer's solution reduce extracellular tonicity in volunteers and increase intracranial pressure in nonbrain-injured experimental animals. A total cation concentration of 154 mmol/l with accompanying anions provides isotonicity. Of the commercial crystalloids, Ringer's acetate solution is close to balanced from both acid-base and tonicity perspectives, and there is little current evidence of acetate toxicity in the context of volume loading, in contrast to renal replacement.

SUMMARY

The case for balanced crystalloids is growing but unproven. A large randomized controlled trial of balanced crystalloids versus 0.9% sodium chloride is the next step.