Prediction of plasma sodium changes in the acutely ill patients: the potential role of tissue sodium content

BACKGROUND

Rapid correction of dysnatremias can result in neurological complications. Therefore, various formulas are available to predict changes in plasma sodium concentration ([Na+]) after treatment, but these have been shown to be inaccurate. This could be explained by sodium acumulation in skin and muscle tissue, which is not explicitly considered in these formulas. We assessed the association between clinical and biochemical factors related to tissue sodium accumulation and the discrepancy between predicted and measured plasma [Na+].

METHODS

We used data from an intensive care unit (ICU) cohort with complete data on sodium, potassium, and water balance. The predicted plasma [Na+] was calculated using the Barsoum-Levine (BL) and the Nguyen-Kurtz (NK) formula. We calculated the discrepancy between predicted and measured plasma sodium and fitted a linear mixed-effect model to investigate its association with factors related to tissue sodium accumulation.

RESULTS

We included 594 ICU days of sixty-three patients in our analysis. The mean plasma [Na+] at baseline was 147±6 mmol/L. The median (IQR) discrepancy between predicted and measured plasma [Na+] was 3.14 mmol/L (1.48, 5.55) and 3.53 mmol/L (1.81, 6.44) for the BL and NK formulas, respectively. For both formulas, estimated total body water (p=0.027), initial plasma [Na+] (p<0.001) and plasma [Na+] change (p<0.001) were associated with the discrepancy between predicted and measured plasma [Na+].

CONCLUSION

In this ICU cohort, initial plasma [Na+], total body water, and plasma [Na+] changes, all factors that are related to tissue sodium accumulation, were associated with the inaccurateness of plasma [Na+] prediction.

[Consensus recommendations on the diagnosis and treatment of hyponatremia from the Austrian Society for Nephrology 2024]

Hyponatremia is a disorder of water homeostasis. Water balance is maintained by the collaboration of renal function and cerebral structures, which regulate thirst mechanisms and secretion of the antidiuretic hormone. Measurement of serum-osmolality, urine osmolality and urine-sodium concentration help to diagnose the different reasons for hyponatremia. Hyponatremia induces cerebral edema and might lead to severe neurological symptoms, which need acute therapy. Also, mild forms of hyponatremia should be treated causally, or at least symptomatically. An inadequate fast increase of the serum sodium level should be avoided, because it raises the risk of cerebral osmotic demyelination. Basic pathophysiological knowledge is necessary to identify the different reasons for hyponatremia which need different therapeutic procedures.

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.

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.

Ratio Profile: Physiologic Approach to Estimating Appropriate Intravenous Fluid Rate to Manage Hyponatremia in the Syndrome of Inappropriate Antidiuresis

A hyponatremic patient with the syndrome of inappropriate antidiuresis (SIAD) gets normal saline (NS), and the plasma sodium decreases, paradoxically. To explain, desalination is often invoked: if urine is more concentrated than NS, the fluid's salts are excreted while some water is reabsorbed, exacerbating hyponatremia. But comparing concentrations can be deceiving. They should be converted to quantities because mass balance is key to unlocking the paradox. The [sodium] equation can legitimately be used to track all of the sodium, potassium, and water entering and leaving the body. Each input or output "module" can be counterbalanced by a chosen iv fluid so that the plasma sodium stays stable. This equipoise is expressed in terms of the iv fluid's infusion rate, an easy calculation called the ratio profile. Knowing the infusion rate that maintains steady state, we can prescribe the iv fluid at a faster rate in order to raise the plasma sodium. Rates less than the ratio profile may risk a paradox, which essentially is caused by an iv fluid underdosing. Selecting an iv fluid that is more concentrated than urine is not enough to prevent paradoxes; even 3% saline can be underdosed. Drinking water adds to the ratio profile and is underestimated in its ability to provoke a paradox. In conclusion, the quantitative approach demystifies the paradoxical worsening of hyponatremia in SIAD and offers a prescriptive guide to keep the paradox from happening. The ratio profile method is objective and quickly deployable on rounds, where it may change patient management for the better.

Reconsidering the Edelman equation: impact of plasma sodium concentration, edema and body weight

BACKGROUND

Guidelines recommend treatment of dysnatremias to be guided by formulas based on the Edelman equation. This equation describes the relation between plasma sodium concentration and exchangeable cations. However, this formula does not take into account clinical parameters that have recently been associated with local tissue sodium accumulation, which occurs without concurrent water retention. We investigated to what extent such clinical factors affect the Edelman equation and dysnatremia treatment.

METHODS

We performed a post-hoc analysis with original data of the Edelman study. Linear regression was used to examine the effect of age, sex, weight, edema, total body water (TBW) and heart and kidney failure on the Edelman equation. With attenuated correction, we corrected for measurement errors of both variables. Using piecewise regression, we analyzed whether the Edelman association differs for different plasma sodium concentrations.

RESULTS

Data was available for 82 patients; 57 males and 25 females with a mean (SD) age of 57 (15) years. The slope of the Edelman equation was significantly affected by weight (p=0.01) and edema (p=0.03). Also, below and above plasma sodium levels of 133 mmol/L the slope of the Edelman equation was significantly different (1.25 x0025vs 0.58x0025, p<0.01).

CONCLUSION

Edelman's equation's coefficients are significantly affected by weight, edema and plasma sodium, possibly reflecting differences in tissue sodium accumulation capacity. The performance of Edelman-based formulas in clinical settings may be improved by taking these clinical characteristics into account.

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.

Hyponatraemia and hypernatraemia: Disorders of Water Balance in Neurosurgery

Disorders of tonicity, hyponatraemia and hypernatraemia, are common in neurosurgical patients. Tonicity is sensed by the circumventricular organs while the volume state is sensed by the kidney and peripheral baroreceptors; these two signals are integrated in the hypothalamus. Volume is maintained through the renin-angiotensin-aldosterone axis, while tonicity is defended by arginine vasopressin (antidiuretic hormone) and the thirst response. Edelman found that plasma sodium is dependent on the exchangeable sodium, potassium and free-water in the body. Thus, changes in tonicity must be due to disproportionate flux of these species in and out of the body. Sodium concentration may be measured by flame photometry and indirect, or direct, ion-sensitive electrodes. Only the latter method is not affected by changes in plasma composition. Classification of hyponatraemia by the volume state is imprecise. We compare the tonicity of the urine, given by the sodium potassium sum, to that of the plasma to determine the renal response to the dysnatraemia. We may then assess the activity of the renin-angiotensin-aldosterone axis using urinary sodium and fractional excretion of sodium, urate or urea. Together, with clinical context, these help us determine the aetiology of the dysnatraemia. Symptomatic individuals and those with intracranial catastrophes require prompt treatment and vigilant monitoring. Otherwise, in the absence of hypovolaemia, free-water restriction and correction of any reversible causes should be the mainstay of treatment for hyponatraemia. Hypernatraemia should be corrected with free-water, and concurrent disorders of volume should be addressed. Monitoring for overcorrection of hyponatraemia is necessary to avoid osmotic demyelination.

Improving on the Adrogué-Madias Formula

The Adrogué-Madias (A-M) formula is correct as written, but technically, it only works when adding 1 L of an intravenous (IV) fluid. For all other volumes, the A-M algorithm gives an approximate answer, one that diverges further from the truth as the IV volume is increased. If 1 L of an IV fluid is calculated to change the serum sodium by some amount, then it was long assumed that giving a fraction of the liter would change the serum sodium by a proportional amount. We challenged that assumption and now prove that the A-M change in [sodium] ([Na]) is not scalable in a linear way. Rather, the Δ[Na] needs to be scaled in a way that accounts for the actual volume of IV fluid being given. This is accomplished by our improved version of the A-M formula in a mathematically rigorous way. Our equation accepts any IV fluid volume, eliminates the illogical infinities, and most importantly, incorporates the scaling step so that it cannot be forgotten. However, the nonlinear scaling makes it harder to obtain a desired Δ[Na]. Therefore, we reversed the equation so that clinicians can enter the desired Δ[Na], keeping the rate of sodium correction safe, and then get an answer in terms of the volume of IV fluid to infuse. The improved equation can also unify the A-M formula with the corollary A-M loss equation wherein 1 L of urine is lost. The method is to treat loss as a negative volume. Because the new equation is just as straightforward as the original formula, we believe that the improved form of A-M is ready for immediate use, alongside frequent [Na] monitoring.

ICU acquired hypernatremia treated by enteral free water - A retrospective cohort study

PURPOSE

ICU acquired hypernatremia (IAH) is associated with increased morbidity and mortality, however treatment remains controversial. This study aims to determine the effect of enteral free water suppletion in patients with IAH.

MATERIALS AND METHODS

Retrospective single center study in a tertiary ICU.

INCLUSION CRITERIA

patients with IAH and treatment with enteral free water.

EXCLUSION CRITERIA

patients with renal replacement therapy, diabetic ketoacidosis or hyperosmolar hyperglycaemic state.

PRIMARY OUTCOME

change in plasma sodium (in mmol/l) after 5 days treatment. Responders were defined as patients with a decrease in sodium level of 5 mmol/l or more.

RESULTS

In total 382 consecutive patients were included. The median sodium level at the start of water therapy was 149 mmol/l (IQR 147-150). The median volume of enteral water was 4423 ml (IQR 3349-5379 ml) after 5 days and mean sodium decrease was 1.87 mmol/l (SD 4.84). There was no significant correlation between the volume of enteral water and sodium decrease (r² = 0.01).

CONCLUSIONS

Treatment with enteral free water did not result in a clinically relevant decrease in serum sodium level in patients with IAH. In addition, the volume of enteral free water and the use of diuretics was unrelated with sodium change over 5 days.

Renal Function is a Major Determinant of ICU-acquired Hypernatremia: A Balance Study on Sodium Handling

Background and Objectives

The development of ICU-acquired hypernatremia (IAH) is almost exclusively attributed to ‘too much salt and too little water’. However, intrinsic mechanisms also have been suggested to play a role. To identify the determinants of IAH, we designed a prospective controlled study.

Methods

Patients with an anticipated length of stay ICU > 48 hours were included. Patients with hypernatremia on admission and/or on renal replacement therapy were excluded. Patients without IAH were compared with patients with borderline hypernatremia (≥ 143 mmol/L, IAH 143) and more severe hypernatremia (≥ 145 mmol/L, IAH 145).

Results

We included 89 patients, of which 51% developed IAH 143 and 29% IAH 145. Sodium intake was high in all patients. Fluid balances were slightly positive and comparable between the groups. Patients with IAH 145 were more severely ill on admission, and during admission, their sodium intake, cumulative sodium balances, serum creatinine and copeptin levels were higher. According to the free water clearance, all the patients conserved water. On multivariate analysis, the baseline serum creatinine was an independent risk factor for the development of IAH 143 and IAH 145. Also, the copeptin levels remained significant for IAH 143 and IAH 145. Sodium intake remained only significant for patients with IAH 145.

Conclusions

Our data support the hypothesis that IAH is due to the combination of higher sodium intake and a urinary concentration deficit, as a manifestation of the renal impairment elicited by severe illness.

Pharmacotherapy of sodium disorders in neurocritical care

PURPOSE OF REVIEW

To describe the pathophysiology and pharmacotherapy of dysnatremia in neurocritical care patients.

RECENT FINDINGS

Sodium disorders may affect approximately half of the neurocritical care patients and are associated with worse neurological outcome and increased risk of death. Pharmacotherapy of sodium disorders in neurocritical care patients may be challenging and is guided by a careful investigation of water and sodium balance.

SUMMARY

In case of hyponatremia, because of excessive loss of sodium, fluid challenge with isotonic solution, associated with salt intake is the first-line therapy, completed with mineralocorticoids if needed. In case of hyponatremia because of SIADH, fluid restriction is the first-line therapy followed by urea if necessary. Hypernatremia should always be treated with hypotonic solutions according to the free water deficit, associated in case of DI with desmopressin. The correction speed should take into consideration the symptoms associated with dysnatremia and the rapidity of the onset.

Clinical impact of tissue sodium storage

In recent times, the traditional nephrocentric, two-compartment model of body sodium has been challenged by long-term sodium balance studies and experimental work on the dermal interstitium and endothelial surface layer. In the new paradigm, sodium can be stored without commensurate water retention in the interstitium and endothelial surface layer, forming a dynamic third compartment for sodium. This has important implications for sodium homeostasis, osmoregulation and the hemodynamic response to salt intake. Sodium storage in the skin and endothelial surface layer may function as a buffer during periods of dietary depletion and excess, representing an extra-renal mechanism regulating body sodium and water. Interstitial sodium storage may also serve as a biomarker for sodium sensitivity and cardiovascular risk, as well as a target for hypertension treatment. Furthermore, sodium storage may explain the limitations of traditional techniques used to quantify sodium intake and determine infusion strategies for dysnatraemias. This review is aimed at outlining these new insights into sodium homeostasis, exploring their implications for clinical practice and potential areas for further research for paediatric and adult populations.

Equivalent Efficacy and Decreased Rate of Overcorrection in Patients With Syndrome of Inappropriate Secretion of Antidiuretic Hormone Given Very Low-Dose Tolvaptan

Rationale & Objective

Euvolemic hyponatremia often occurs due to the syndrome of inappropriate antidiuretic hormone secretion (SIADH). Vasopressin 2 receptor antagonists may be used to treat SIADH. Several of the major trials used 15 mg of tolvaptan as the lowest effective dose in euvolemic and hypervolemic hyponatremia. However, a recent observational study suggested an elevated risk for serum sodium level overcorrection with 15 mg of tolvaptan in patients with SIADH.

Study Design

A retrospective chart review study comparing outcomes in patients with SIADH treated with 15 versus 7.5 mg of tolvaptan.

Settings & Participants

Patients with SIADH who were treated with a very low dose of tolvaptan (7.5 mg) at a single center compared with patients using a 15-mg dose from patient-level data from the observational study described previously.

Predictors

Tolvaptan dose of 7.5 versus 15 mg daily.

Outcomes

Appropriate response to tolvaptan, defined as an initial increase in serum sodium level > 3 mEq/L, and overcorrection of serum sodium level (>8 mEq/L per day, and >10 mEq/L per day in sensitivity analyses).

Analytical Approach

Descriptive study with additional outcomes compared using t tests and F-tests (Fischer's Exact χ2 Test).

Results

Among 18 patients receiving 7.5 mg of tolvaptan, the mean rate of correction was 5.6 ± 3.1 mEq/L per day and 2 (11.1%) patients corrected their serum sodium levels by >8 mEq/L per day, with 1 of these increasing by >12 mEq/L per day. Of those receiving tolvaptan 7.5 mg, 14 had efficacy, with increases ≥ 3 mEq/L; similar results were seen with the 15-mg dose (21 of 28). There was a statistically significant higher chance of overcorrection with the use of 15 versus 7.5 mg of tolvaptan (11 of 28 vs 2 of 18; P = 0.05; and 10 of 28 vs 1 of 18; P = 0.03, for >8 mEq/L per day and >10 mEq/L per day, respectively).

Limitations

Small sample size, retrospective, and nonrandomized.

Conclusions

Tolvaptan, 7.5 mg, daily corrects hyponatremia with similar efficacy and less risk for overcorrection in patients with SIADH versus 15 mg of tolvaptan.

Effects of Water Loading on Observed and Predicted Plasma Sodium, and Fluid and Urine Cation Excretion in Healthy Individuals

RATIONALE & OBJECTIVE

The discovery of sodium storage without concurrent water retention suggests the presence of an additional compartment for sodium distribution in the body. The osmoregulatory role of this compartment under hypotonic conditions is not known.

STUDY DESIGN

Experimental interventional study.

SETTING & PARTICIPANTS

Single-center study of 12 apparently healthy men.

INTERVENTION

To investigate whether sodium can be released from its nonosmotic stores after a hypotonic fluid load, a water-loading test (20mL water/kg in 20 minutes) was performed.

OUTCOMES

During a 240-minute follow-up, we compared the observed plasma sodium concentration ([Na⁺]) and fluid and urine cation excretion with values predicted by the Barsoum-Levine and Nguyen-Kurtz formulas. These formulas are used for guidance of fluid therapy during dysnatremia, but do not account for nonosmotic sodium stores.

RESULTS

30 minutes after water loading, mean plasma [Na⁺] decreased 3.2±1.6 (SD) mmol/L, after which plasma [Na⁺] increased gradually. 120 minutes after water loading, plasma [Na⁺] was significantly underestimated by the Barsoum-Levine (-1.3±1.4mmol/L; P=0.05) and Nguyen-Kurtz (-1.5±1.5mmol/L; P=0.03) formulas. In addition, the Barsoum-Levine and Nguyen-Kurtz formulas overestimated urine volume, while cation excretion was significantly underestimated, with a cation gap of 57±62 (P=0.009) and 63±63mmol (P=0.005), respectively. After 240 minutes, this gap was 28±59 (P=0.2) and 34±60mmol (P=0.08), respectively.

LIMITATIONS

The compartment from which the mobilized sodium originated was not identified, and heterogeneity in responses to water loading was observed across participants.

CONCLUSIONS

These data suggest that healthy individuals are able to mobilize osmotically inactivated sodium after an acute hypotonic fluid load. Further research is needed to expand knowledge about the compartment of osmotically inactivated sodium and its role in osmoregulation and therapy for dysnatremias.

FUNDING

This investigator-initiated study was partly supported by a grant from Unilever Research and Development Vlaardingen, The Netherlands B.V. (MA-2014-01914).

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.

Estimation of sodium and chloride storage in critically ill patients: a balance study

BACKGROUND

Nonosmotic sodium storage has been reported in animals, healthy individuals and patients with hypertension, hyperaldosteronism and end-stage kidney disease. Sodium storage has not been studied in ICU patients, who frequently receive large amounts of sodium chloride-containing fluids. The objective of our study was to estimate sodium that cannot be accounted for by balance studies in critically ill patients. Chloride was also studied. We used multiple scenarios and assumptions for estimating sodium and chloride balances.

METHODS

We retrospectively analyzed patients admitted to the ICU after cardiothoracic surgery with complete fluid, sodium and chloride balance data for the first 4 days of ICU treatment. Balances were obtained from meticulously recorded data on intake and output. Missing extracellular osmotically active sodium (MES) was calculated by subtracting the expected change in plasma sodium from the observed change in plasma sodium derived from balance data. The same method was used to calculate missing chloride (MEC). To address considerable uncertainties on the estimated extracellular volume (ECV) and perspiration rate, various scenarios were used in which the size of the ECV and perspiration were varied.

RESULTS

A total of 38 patients with 152 consecutive ICU days were analyzed. In our default scenario, we could not account for 296 ± 35 mmol of MES in the first four ICU days. The range of observed MES in the five scenarios varied from 111 ± 27 to 566 ± 41 mmol (P < 0.001). A cumulative value of 243 ± 46 mmol was calculated for MEC in the default scenario. The range of cumulative MEC was between 62 ± 27 and 471 ± 56 mmol (P = 0.001 and P = 0.003). MES minus MEC varied from 1 ± 51 to 123 ± 33 mmol in the five scenarios.

CONCLUSIONS

Our study suggests considerable disappearance of osmotically active sodium in critically ill patients and is the first to also suggest rather similar disappearance of chloride from the extracellular space. Various scenarios for insensible water loss and estimated size for the ECV resulted in considerable MES and MEC, although these estimates showed a large variation. The mechanisms and the tissue compartments responsible for this phenomenon require further investigation.

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.

Recommendations for active correction of hypernatremia in volume-resuscitated shock or sepsis patients should be taken with a grain of salt: A systematic review

Background:

Healthcare-acquired hypernatremia (serum sodium >145 mEq/dL) is common among critically ill and other hospitalized patients and is usually treated with hypotonic fluid and/or diuretics to correct a “free water deficit.” However, many hypernatremic patients are eu- or hypervolemic, and an evolving body of literature emphasizes the importance of rapidly returning critically ill patients to a neutral fluid balance after resuscitation.

Objective:

We searched for any randomized- or observational-controlled studies evaluating the impact of active interventions intended to correct hypernatremia to eunatremia on any outcome in volume-resuscitated patients with shock and/or sepsis.

Data sources:

We performed a systematic literature search with studies identified by searching MEDLINE, Embase, Cochrane Central Register of Controlled Trials, Cochrane Database of Systematic Reviews, ClinicalTrials.gov, Index-Catalogue of the Library of the Surgeon General’s Office, DARE (Database of Reviews of Effects), and CINAHL and scanning reference lists of relevant articles with abstracts published in English.

Data synthesis:

We found no randomized- or observational-controlled trials measuring the impact of active correction of hypernatremia on any outcome in resuscitated patients.

Conclusion:

Recommendations for active correction of hypernatremia in resuscitated patients with sepsis or shock are unsupported by clinical research acceptable by modern evidence standards.

Management of severe dehydration

The presented case is one of severe dehydration and acute kidney injury with significant resultant complications that required considerable fluid and electrolyte replacement. Approaches to fluid resuscitation in the context of hypernatraemia and the hyperosmolar state were considered and then judiciously combined to manage a complex case with a successful outcome. Conflicting guidance in this domain is discussed with recommendations for a future management strategy that is tailored to individual patients.

Graded interference with the direct potentiometric measurement of sodium by hemoglobin

OBJECTIVES

Sodium concentration is measured by either indirect (I_Na) or direct potentiometry (D_Na), on chemistry and gas panels, respectively. A spurious difference between these methods (ΔNa=I_Na-D_Na) can be confusing to the clinician. For example, variation in serum total protein (TP) is well known to selectively interfere with I_Na. Red cells have been suggested to interfere with D_Na, but both positive and negative interference have been reported. In this study, the effect of gas panel hemoglobin (Hb) on ΔNa was examined.

METHODS

ΔNa was calculated in 772 pairs of closely-timed chemistry and gas panels (median: 4min. apart), retrospectively collected from our critical care units, with 1 pair per patient. Hb was treated as a categorical or continuous variable and tested for linear and non-linear effects, with adjustment for 3 known influences on ΔNa-TP, bicarbonate (tCO₂), and the chemistry-gas panel glucose difference (ΔGlu).

RESULTS

Hb ranged from 3.5 to 22.0g/dL [35-220g/L]. In categorical analysis, ΔNa increased with Hb, and the effect was essentially linear. By simple regression, ΔNa rose 0.06±0.03[SE]mmol/L per 1g/dL [10g/L] increase in Hb (p<0.05), but confounding was suspected because Hb also correlated (p<10^-3) with TP, tCO₂, and ΔGlu. Using multiple regression to adjust for the confounders, ΔNa rose 0.15±0.03mmol/L per 1g/dL [10g/L] rise in Hb (p<10^-6).

CONCLUSIONS

Increasing Hb spuriously decreases D_Na and increases ΔNa. A linear correction for this artifact can reduce the discordance between I_Na and D_Na, promoting their interchangeable use.

Transurethral Resection of the Prostate, Bladder Explosion and Hyponatremic Encephalopathy: A Rare Case Report of Malpractice

We present an original case report of a bladder explosion during a TURP intervention for benign prostatic hypertrophy, that was brought on by the absorption of about 5 liters of glycine 1.5% and then onset of a severe hyponatremia. The quick and inappropriate correction of this electrolyte imbalance led the onset of encephalopathy and the death of the patient. The authors discuss the pathogenesis of these uncommon diseases and, considering the most recent Italian Legislation, they highlight the importance to respect good clinical practice standards and guidelines to ensure the most appropriate treatments for the patient and remove any assumptions of medical liability.

The utility and accuracy of four equations in predicting sodium levels in dysnatremic patients

BACKGROUND

Improper correction of hyponatremia can cause severe complications, including osmotic demyelination syndrome (ODS). The Adrogué-Madias equation (AM), the Barsoum-Levine (BL) equation, the Electrolyte Free Water Clearance (EFWC) equation and the Nguyen-Kurtz (NK) equation are four derived equations based on the empirically derived Edelman equation for predicting sodium at a later time (Na2) from a known starting sodium (Na1), fluid/electrolyte composition and input and output volumes.

METHODS

Our retrospective study included 43 data points from 31 mostly hyponatremic patients. We calculated Na2 based on five sets of rules that were progressively more precisely calculated. Sets A-D included all 31 patients and 43 data points and set E was based on 15 patients and 27 data points.

RESULTS

The root mean square error was calculated and found to be between 4.79 and 6.37 mmol/L (mEq/L) for all sets. Bland-Altman analysis showed high variability and discrepancies between the predicted and actual Na2.

CONCLUSIONS

Like similar studies in hypernatremic patients, the data suggest that hyponatremic modeling equations are not reliably accurate in predicting Na2 from Na1 and available clinical data regarding sodium, potassium and fluid balance over longer time frames (12-30 h). Our study was retrospective and was done in an inpatient setting and thus was subject to limitations and laboratory measurement variability, but showed that all four equations are not able to reliably predict Na2 from Na1 and inputs across a 12-30 h period.

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.

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.

Integrating Murine and Clinical Trials with Cabozantinib to Understand Roles of MET and VEGFR2 as Targets for Growth Inhibition of Prostate Cancer

PURPOSE

We performed parallel investigations in cabozantinib-treated patients in a phase II trial and simultaneously in patient-derived xenograft (PDX) models to better understand the roles of MET and VEGFR2 as targets for prostate cancer therapy.

EXPERIMENTAL DESIGN

In the clinical trial, radiographic imaging and serum markers were examined, as well as molecular markers in tumors from bone biopsies. In mice harboring PDX intrafemurally or subcutaneously, cabozantinib effects on tumor growth, MET, PDX in which MET was silenced, VEGFR2, bone turnover, angiogenesis, and resistance were examined.

RESULTS

In responsive patients and PDX, islets of viable pMET-positive tumor cells persisted, which rapidly regrew after drug withdrawal. Knockdown of MET in PDX did not affect tumor growth in mice nor did it affect cabozantinib-induced growth inhibition but did lead to induction of FGFR1. Inhibition of VEGFR2 and MET in endothelial cells reduced the vasculature, leading to necrosis. However, each islet of viable cells surrounded a VEGFR2-negative vessel. Reduction of bone turnover was observed in both cohorts.

CONCLUSIONS

Our studies demonstrate that MET in tumor cells is not a persistent therapeutic target for metastatic castrate-resistant prostate cancer (CRPC), but inhibition of VEGFR2 and MET in endothelial cells and direct effects on osteoblasts are responsible for cabozantinib-induced tumor inhibition. However, vascular heterogeneity represents one source of primary therapy resistance, whereas induction of FGFR1 in tumor cells suggests a potential mechanism of acquired resistance. Thus, integrated cross-species investigations demonstrate the power of combining preclinical models with clinical trials to understand mechanisms of activity and resistance of investigational agents.

Undercorrection of hypernatremia is frequent and associated with mortality

Background

About 1% of patients admitted to the Emergency Department (ED) have hypernatremia, a condition associated with a mortality rate of 20 to 60%. Management recommendations originate from intensive care unit studies, in which patients and medical diseases differ from those in ED.

Methods

We retrospectively studied clinical characteristics, treatments, and outcomes of severely hypernatremic patients in the ED and risk factors associated with death occurrence during hospitalization.

Results

During 2010, 85 cases of severe hypernatremia ≥150 mmol/l were admitted to ED. Hypernatremia occurred in frail patients: mean age 79.7 years, 55% institutionalized, 28% with dementia.

Twenty four percent of patients died during hospitalization. Male gender and low mean blood pressure (MBP) were independently associated with death, as well as slow natremia correction speed, but not the severity of hyperosmolarity at admission. Infusion solute was inappropriate for 45% of patients with MBP <70 mmHg who received hypotonic solutes and 22% of patients with MBP ≥70 mmHg who received isotonic solutes or were not perfused.

Conclusions

This is the first study assessing outcome of hypernatremic patients in the ED according to the treatment provided. It appears that not only a too quick, but also a too slow correction speed is associated with an increased risk of death regardless of initial natremia. Medical management of hypernatremic patients must be improved regarding evaluation and treatment.

Prognostic value of amplitude-integrated electroencephalography in neonates with hypernatremic dehydration

OBJECTIVES

Hypernatremic dehydration in neonates is a condition that develops due to inadequate fluid intake and it may lead to cerebral damage. We aimed to determine whether there was an association between serum sodium levels on admission and aEEG patterns and prognosis, as well as any association between aEEG findings and survival rates and long-term prognosis.

METHOD

The present study included all term infants hospitalized for hypernatremic dehydration in between January 2010 and May 2011. Infants were monitored by aEEG. At 2 years of age, we performed a detailed evaluation to assess the impact of hypernatremic dehydration on the neurodevelopmental outcome.

RESULTS

Twenty-one infants were admitted to the neonatal intensive care unit for hypernatremic dehydration. A correlation was found between increased serum sodium levels and aEEG abnormalities. Neurodevelopmental assessment was available for 17 of the 21 infants. The results revealed that hypernatremic dehydration did not adversely affect the long-term outcomes.

CONCLUSION

The follow-up of newborns after discharge is key to determine the risks associated with hypernatremic dehydration. Our results suggest that hypernatremic dehydration had no impact on the long-term outcome. In addition, continuous aEEG monitoring could provide information regarding early prognosis and mortality.

Urine output and resultant osmotic water shift are major determinants of plasma sodium level in syndrome of inappropriate antidiuretic hormone secretion

Although various formulas predicting plasma sodium level ([Na]) are proposed for correction of hyponatremia, it seems that an anticipated [Na] frequently exceeds or falls below the measured [Na], especially in syndrome of inappropriate antidiuretic hormone secretion (SIADH). The causative factors of the fluctuation have never been investigated clearly. The aim of this study was to identify the determining factors for accurate prediction of [Na] by comparing data from previously proposed formulas and a novel osmotic compartment model (O-C model). The O-C model, which simulates the amounts of osmoles in extracellular and intracellular fluids, can estimate resultant osmotic water shift (OWS) and [Na]. The accuracy of representative formulas was verified in a point-to-point study using blood and urine samples obtained every 4 hours from 9 patients. Among 161 measurement points, a large fluctuation of urine volume and urine sodium level was observed. The gap between anticipated and measured [Na] in the widely used Adrogue-Madias formula was -0.5 ± 0.1 mEq/L/4 h (mean ± standard error), showing a marked tendency to underestimate [Na]. The gap in the O-C model including OWS was 0.1 ± 0.1 mEq/L/4 h, and that in the O-C model eliminating OWS was 1.9 ± 0.2 mEq/L/4 h, indicating that measurement of urine output and estimation of resulting OWS are essential for a superior prediction of [Na] in SIADH. A simulation study with the O-C model including OWS unveiled a distinctive correction pattern of [Na] dependent on the urine volume and urine sodium level, providing a useful choice for the proper type and rate of infusion.

Safety and efficacy of intravenous hypotonic 0.225% sodium chloride infusion for the treatment of hypernatremia in critically ill patients

BACKGROUND

The purpose of this study was to evaluate the safety and efficacy of central venous administration of a hypotonic 0.225% sodium chloride (one-quarter normal saline [¼ NS]) infusion for critically ill patients with hypernatremia.

METHODS

Critically ill, adult patients with traumatic injuries and hypernatremia (serum sodium [Na] >150 mEq/L) who were given ¼ NS were retrospectively studied. Serum sodium, fluid balance, free water intake, sodium intake, and plasma free hemoglobin concentration (fHgb) were assessed.

RESULTS

Twenty patients (age, 50 ± 18 years; Injury Severity Score, 29 ± 12) were evaluated. The ¼ NS infusion was given at 1.5 ± 1.0 L/d for 4.6 ± 1.6 days. Serum sodium concentration decreased from 156 ± 4 to 143 ± 6 mEq/L (P < .001) over 3-7 days. Total sodium intake was decreased from 210 ± 153 to 156 ± 112 mEq/d (P < .05). Daily net fluid balance was not significantly increased. Plasma fHgb increased from 4.9 ± 5.4 mg/dL preinfusion to 8.9 ± 7.4 mg/dL after 2.6 ± 1.3 days of continuous intravenous (IV) ¼ NS in 10 patients (P = .055). An additional 10 patients had a plasma fHgb of 10.2 ± 9.0 mg/dL during the infusion. Hematocrit and hemoglobin decreased (26% ± 3% to 24% ± 2%, P < .001 and 9.1 ± 1.1 to 8.2 ± 0.8 g/dL, P < .001, respectively).

CONCLUSIONS

Although IV ¼ NS was effective for decreasing serum sodium concentration, evidence for minor hemolysis warrants further research to establish its safety before its routine use can be recommended.

[Severe hypernatremia. Case report, pathophysiology and therapy]

The case of a female patient with a suprasellar optic glioma is reported, who was admitted to the intensive care unit due to decompensated diabetes insipidus with hypernatremia of 194 mmol/l. The sodium concentration was reduced slowly over 4 days and the patient recovered without sequelae. Based on this case the article deals with the pathophysiology and therapy of hypernatremia. An increase in extracellular osmolarity leads to augmented production of intracellular osmolytes in order to maintain the cell volume constant. Due to this counterregulation correction of the sodium concentration must be done with caution.

[Disorders in sodium-water balance]

Water balance control is aimed at normalizing cellular hydration, and sodium balance control at normalizing extracellular volume. Water balance control is based on the regulation of body fluid tonicity, while the control of sodium balance is based on the regulation of effective arterial volume. Disorders of water balance act on cellular hydration: primary disorders induce a proportional change in tonicity; secondary disorders are induced by a change in tonicity or effective arterial volume. Disorders of sodium balance act on extracellular volume: primary disorders of sodium balance induce a change in effective arterial volume; secondary disorders are induced by a change in effective arterial volume. Physical examination of the patient allows assessing the extracellular volume and the severity of the sodium balance disorder. Natremia - that generally reflects tonicity - allows to assess cellular hydration and to determine the type of water balance disorder. In the case of natremia disturbance, the assessment of both the tonicity and the extracellular volume allows the determination of the type of water and/or sodium balance disorder that is necessary for prescribing the adequate therapy.

Pitfalls in the management of severe hyponatraemia

The correction of severe hyponatraemia is complicated by practical and theoretical limitations of formulae used to predict response to treatment, and random errors in the measurement of sodium concentration. We report the case of an elderly woman with a symptomatic serum sodium concentration of 93 mmol/l. Correction of serum sodium unintentionally exceeded conventional targets but, as in the majority of such cases, there were no neurological sequelae.

A clinical approach to the treatment of chronic hypernatremia

Hypernatremia is a commonly encountered electrolyte disorder occurring in both the inpatient and outpatient settings. Community-acquired hypernatremia typically occurs at the extremes of age, whereas hospital-acquired hypernatremia affects patients of all age groups. Serum sodium concentration is linked to water homeostasis, which is dependent on the thirst mechanism, arginine vasopressin, and kidney function. Because both hypernatremia and the rate of correction of hypernatremia are associated with significant morbidity and mortality, prompt effective treatment is crucial. Chronic hypernatremia can be classified into 3 broad categories, hypovolemic, euvolemic, and hypervolemic forms, with each form having unique treatment considerations. In this teaching case, we provide a clinically based quantitative approach to the treatment of both hypervolemic and hypovolemic hypernatremia, which occurred in the same patient during the course of a prolonged illness.

Electrolyte-free water clearance versus modified electrolyte-free water clearance: do the results justify the effort?

BACKGROUND

Calculation of electrolyte-free water clearance (EFWC) allows for quantification of renal losses of free water and was shown to be helpful in the differential diagnosis of dysnatremias and might help in the correction of the electrolyte disorders. A modified EFWC formula (MEFWC) was described to be more accurate than the conventional one; however, it has never been evaluated clinically.

METHODS

In order to evaluate the performance of MEFWC compared to EFWC under clinical circumstances, we gathered data from a total of 912 patient days of 138 critically ill patients. EFWC and MEFWC were calculated on the basis of these data. Additionally, from data of critically ill patients, we calculated a prediction of serum sodium based on the Edelman equation using either EFWC or MEFWC and compared results.

RESULTS

Altogether, 343 normonatremic, 124 hyponatremic and 445 hypernatremic days were analyzed. Results for EFWC and MEFWC correlated significantly (R = 0.98). In patients with hyponatremia, the absolute difference between EFWC and MEFWC was significantly larger than in patients with normonatremia (437 vs. 256 ml, p < 0.01). The absolute difference between EFWC and MEFWC correlated significantly with the level of serum sodium (R = -0.41). The mean difference in the prediction of serum sodium change as calculated based on the Edelman equation between the formula using EFWC and the formula using MEFWC was 0.7 mmol/l (SD 0.68) and was highest in hyponatremia and lowest in hypernatremia.

CONCLUSION

Results of EFWC and MEFWC were comparable in critically ill patients. Under normal circumstances, the use of the more complicated MEFWC is not justified. In hyponatremia, the difference between EFWC and MEFWC is larger and thus might justify the use of the more complicated formula.

Normal saline is a safe initial rehydration fluid in children with diarrhea-related hypernatremia

To demonstrate safety and efficacy of using normal saline (NS) for initial volume expansion (IVE) and rehydration in children with diarrhea-related hypernatremic dehydration (DR-HD), forty eight patients with DR-HD were retrospectively studied. NS was used as needed for IVE and for initial rehydration. Fluid deficit was given over 48 h. Median Na(+) level on admission was 162.9 mEq/L (IQR 160.8-165.8). The median average hourly drop at 6 and 24 h was 0.53 mEq/L/h (0.48-0.59) and 0.52 mEq/L/h (0.47-0.57), respectively. Compared to children not needing IVE, receiving ≥40 ml/kg IVE was associated with a higher average hourly drop of Na(+) at 6 h (0.51 vs. 0.58 mEq/L/h, p = 0.013) but not at 24 h (p = 0.663). The three patients (6.3%) with seizures had a higher average hourly drop of Na(+) at 6 and 24 h (p = 0.084 and 0.021, respectively). Mortality (4/48, 8.3%) was not related to Na(+) on admission or to its average hourly drop at 6 or 24 h. Children receiving ≥40 ml/kg IVE were more likely to die (OR 3.3; CI, 1.5-7.2).

CONCLUSION

In children with DR-HD, NS is a safe rehydration fluid with a satisfactory rate of Na(+) drop and relatively low incidence of morbidity and mortality. Judicious use of IVE should be exerted and closer monitoring should be guaranteed for children requiring large volumes for IVE and for those showing rapid initial drop of serum Na(+) to avoid neurological complications and poor outcome.