Thiazide-induced hyponatraemia: epidemiology and clues to pathogenesis

Evaluation of hyponatremia among older adults exposed to selective serotonin reuptake inhibitors and thiazide diuretics

OBJECTIVE

Hyponatremia is a common electrolyte disorder among older adults that can cause serious adverse effects. The purpose of this study was to assess the risk of hyponatremia with the concurrent use of selective serotonin reuptake inhibitors (SSRIs) and thiazide diuretics in an older population.

METHODS

Two retrospective nested case-control studies were conducted with exposure to an SSRI or a thiazide diuretic. Persons of interest were those enrolled in Medicare and who received parts A, B, and D benefits from 2017 to 2019 and who were receiving either an SSRI or thiazide diuretic. Cases were individuals with a diagnosis of hyponatremia. Controls had no documented history of hyponatremia. A logistic regression was conducted to determine the odds of hyponatremia.

RESULTS

Of the 551,298 patients receiving a SSRIs, the mean age was 77.8 years (Standard Deviation (SD) ± 8.0 years), 69% were female, and 91.23% were classified as White. We identified 701,007 individuals receiving a thiazide diuretic, with a mean age of 77.1 years (SD ± 7.2 years), 60.2% female, and 82.72% White. The prevalence of hyponatremia was 10.4% in patients taking thiazides alone and 9.0% in those taking SSRIs alone. On the other hand, patients on both medications had a hyponatremia prevalence of approximately 13.0%. Among SSRI users, the adjusted odds ratio (OR) of hyponatremia with concomitant use of thiazide diuretics was 1.24 (95% Confidence Interval (CI): 1.22-1.26). For thiazide users, the adjusted OR of hyponatremia with exposure to SSRIs was 1.27 (95% CI:1.24-1.29).

CONCLUSION

The concurrent use of thiazide diuretics and SSRIs is associated with an increased risk of hyponatremia in older populations.

[Features of water-electrolyte balance in persons of the older age group]

Age-related changes have a great influence on the regulation of water and electrolyte homeostasis in the body, which is regulated by a complex interaction of environmental factors, drinking behavior, the secretion of a number of hormones and hormone-like substances, as well as the innervation and functional state of the kidneys. It is well known that the changes that are part of physiological aging underlie fluid and electrolyte imbalances, exacerbated by the presence of age-related diseases, medications, or a number of external factors such as malnutrition, fluid intake, and the presence of dementia. This review considers literature data on the effect of normal aging on the development of pathology of the water-sodium balance, including dehydration of senile patients, hyponatremia, hypernatremia, changes in the secretion of antidiuretic hormone and the activity of elements of the renin-angiotensin-aldosterone system.

Laboratory medicine in arterial hypertension

In the initial diagnostics of arterial hypertension (AH) laboratory medicine is a cornerstone, along with a blood pressure (BP) measurement and an electrocardiogram. It mainly refers to routine blood and urine tests for diagnosis and monitoring primary hypertension and its associated conditions such as asymptomatic hypertension-mediated organ damage, chronic kidney disease and hypertensive disorders of pregnancy. In addition, long term non-fatal and fatal risks for cardiovascular (CV) events in hypertension are assessed based on clinical and laboratory data. Furthermore, laboratory medicine is involved in the management of hypertension, especially in monitoring the disease progression. However, antihypertensive drugs may interfere with laboratory test results. Diuretics, especially thiazides, can affect blood and urine sodium concentrations, or angiotensin-converting enzyme inhibitors and angiotensin receptor blockers can affect the blood biomarkers of the renin-angiotensin-aldosterone system (RAAS). It's dysfunction plays a critical role in primary aldosteronism (PA), the most common endocrine disorder in secondary hypertension, which accounts for only small proportion of AH in relative terms but substantial proportion of hypertensives in absolute terms, affecting younger population and carrying a higher risk of CV mortality and morbidity. When screening for PA, aldosterone-to-renin ratio still contributes massively to the increased incidence of the disease, despite certain limits. In conclusion, laboratory medicine is involved in the screening, diagnosis, monitoring and prognosis of hypertension. It is of great importance to understand the preanalytical and analytical factors influencing final laboratory result.

Women on diuretics have a higher risk of hospital admission because of hyponatremia than men

PURPOSE

Recent studies suggest that women are more susceptible to diuretic-induced hyponatremia resulting in hospital admission than men. The aim of this study was to confirm whether these sex differences in hyponatremia-related hospital admissions in diuretic users remain after adjusting for several confounding variables such as age, dose, and concurrent medication.

METHODS

In a case-control design nested in diuretic users, cases of hyponatremia associated hospital admissions between 2005 and 2017 were identified from the PHARMO Data Network. Cases were 1:10 matched to diuretic users as controls. Odds ratios (OR) with 95%CIs were calculated for women versus men and adjusted for potential confounders (age, number of diuretics, other hyponatremia-inducing drugs, chronic disease score) using unconditional logistic regression analysis. A subgroup analysis was performed for specific diuretic groups (thiazides, loop diuretics and aldosterone antagonists).

RESULTS

Women had a statistically significantly higher risk of a hospital admission associated with hyponatremia than men while using diuretics (OR 1.86, 95%CI 1.64-2.11). Adjusting for the potential confounders resulted in an increased risk for women compared to men (ORadj 2.65, 95% CI 2.31-3.04). This higher risk in women was also seen in the three subgroup analyses after adjustment.

CONCLUSION

Our findings show a higher risk of hyponatremia-related hospital admission in women than men while using diuretics. Further research is needed to understand the underlying mechanism of this sex difference to be able to provide sex-specific recommendations.

Pathophysiology of Drug-Induced Hyponatremia

Drug-induced hyponatremia caused by renal water retention is mainly due to syndrome of inappropriate antidiuresis (SIAD). SIAD can be grouped into syndrome of inappropriate antidiuretic hormone secretion (SIADH) and nephrogenic syndrome of inappropriate antidiuresis (NSIAD). The former is characterized by uncontrolled hypersecretion of arginine vasopressin (AVP), and the latter is produced by intrarenal activation for water reabsorption and characterized by suppressed plasma AVP levels. Desmopressin is useful for the treatment of diabetes insipidus because of its selective binding to vasopressin V2 receptor (V2R), but it can induce hyponatremia when prescribed for nocturnal polyuria in older patients. Oxytocin also acts as a V2R agonist and can produce hyponatremia when used to induce labor or abortion. In current clinical practice, psychotropic agents, anticancer chemotherapeutic agents, and thiazide diuretics are the major causes of drug-induced hyponatremia. Among these, vincristine and ifosfamide were associated with sustained plasma AVP levels and are thought to cause SIADH. However, others including antipsychotics, antidepressants, anticonvulsants, cyclophosphamide, and thiazide diuretics may induce hyponatremia by intrarenal mechanisms for aquaporin-2 (AQP2) upregulation, compatible with NSIAD. In these cases, plasma AVP levels are suppressed by negative feedback. In rat inner medullary collecting duct cells, haloperidol, sertraline, carbamazepine, and cyclophosphamide upregulated V2R mRNA and increased cAMP production in the absence of vasopressin. The resultant AQP2 upregulation was blocked by a V2R antagonist tolvaptan or protein kinase A (PKA) inhibitors, suggestive of the activation of V2R-cAMP-PKA signaling. Hydrochlorothiazide can also upregulate AQP2 in the collecting duct without vasopressin, either directly or via the prostaglandin E2 pathway. In brief, nephrogenic antidiuresis, or NSIAD, is the major mechanism for drug-induced hyponatremia. The associations between pharmacogenetic variants and drug-induced hyponatremia is an area of ongoing research.

A rare case of neurological dysfunction due to severe hyponatremia after carotid artery endarterectomy: A review of the clinical approach to hyponatremia

Development of severe hyponatremia after carotid endarterectomy procedure is rare. Several pathophysiological mechanisms related to the carotid endarterectomy procedure may infer an increased risk of developing this complication in specific populations.

Association between newly initiated thiazide diuretics and hospitalization due to hyponatremia

Purpose

Thiazide diuretics are the most common origin of drug-induced hyponatremia. However, population-based studies on clinical outcomes are lacking. We therefore explored the time course and absolute risk of thiazide-associated hospitalization due to hyponatremia in Sweden.

Methods

Population-based case-control study including patients hospitalized with a principal diagnosis of hyponatremia (n = 11,213) compared with controls (n = 44,801). Linkage of registers was used to acquire data. Multivariable regression was applied to explore time-dependent associations between thiazide diuretics and hospitalization due to hyponatremia. Attributable risks were calculated assessing the disease burden attributable to thiazides.

Results

Individuals initiating thiazide treatment were exposed to an immediate increase in risk for hospitalization with adjusted odds ratio (aOR) (95% CI) of 48 (28–89). The associations gradually declined reaching an aOR of 2.9 (2.7–3.1) for individuals treated for longer than 13 weeks. The attributable risk of hyponatremia-associated hospitalization due to thiazides of any treatment length was 27% (3095/11,213). Among 806 patients initiating treatment < 90 days before hospitalization, hyponatremia could be attributed to thiazides in 754. Based on nationwide data, 616,678 individuals were initiated on thiazides during the 8-year study period suggesting an absolute risk of 0.12% (754/661,678) for subsequent hospitalization with a main diagnosis of hyponatremia.

Conclusions

Thiazide diuretics attributed to more than one in four individuals hospitalized due to hyponatremia. The risk increase was very pronounced during the first month of treatment and then gradually declined, without returning to normal. However, the absolute risk for the development of hyponatremia demanding hospitalization may for most individuals be modest.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00228-020-03086-6.

Thiazide Diuretics and the Incidence of Osteoporotic Fracture: A Systematic Review and Meta-Analysis of Cohort Studies

Background: Thiazide diuretics may improve bone mineral density. However, results are inconsistent for studies evaluating the association between thiazides and risk of osteoporotic fracture. We performed an updated meta-analysis of cohort studies to determine the association between thiazides use and fracture risk.

Methods: Relevant studies were identified via systematic search of PubMed and Embase. A random-effect model was used for meta-analysis. Subgroup analyses were performed to explore the potential influences of study characteristics on the outcome.

Results: Seventeen cohort studies with 3,537,504 participants were included. The pooled results showed that use of thiazide diuretics at baseline did not significantly affect the risk of overall osteoporotic fracture incidence as compared with controls (risk ratio [RR]: 0.96, 95% confidence interval [CI]: 0.83 to 1.09, p = 0.51) with significant heterogeneity (p for Cochrane’s Q test < 0.001, I² = 90%). Results of subgroup analyses indicated that general status of the participants may be an important determinant for the association between thiazide diuretics and subsequent risk of osteoporotic fracture. Use of thiazide diuretics was associated with significantly reduced risk of fracture in patients with acute status including new-onset stroke or spinal cord injury (RR: 0.70, 95% CI: 0.57 to 0.86, p < 0.001), but not in those with good conditions such as community-dwelling population or hypertensive patients (p for subgroup difference = 0.02).

Conclusions: Use of thiazide diuretics is not associated with significantly affected risk of overall osteoporotic fracture. However, the association may be different according to the general status of the participants.

Mechanism of Thiazide Diuretic Arterial Pressure Reduction: The Search Continues

Thiazide diuretic (TZD)-mediated chronic reduction of arterial pressure is thought to occur through decreased total peripheral vascular resistance. Further, the decreased peripheral vascular resistance is accomplished through TZD activation of an extrarenal target, resulting in inhibition of vascular constriction. However, despite greater than five decades of investigation, little progress has been made into the identification of the TZD extrarenal target. Proposed mechanisms range from direct inhibition of constrictor and activation of relaxant signaling pathways in the vascular smooth muscle to indirect inhibition through decreased neurogenic and hormonal regulatory pathways. Surprisingly, particularly in view of this lack of progress, comprehensive reviews of the subject are absent. Moreover, even though it is well recognized that 1) several types of hypertension are insensitive to TZD reduction of arterial pressure and, further, TZD fail to reduce arterial pressure in normotensive subjects and animals, and 2) different mechanisms underlie acute and chronic TZD, findings derived from these models and parameters remain largely undifferentiated. This review 1) comprehensively describes findings associated with TZD reduction of arterial pressure; 2) differentiates between observations in TZD-sensitive and TZD-insensitive hypertension, normotensive subjects/animals, and acute and chronic effects of TZD; 3) critically evaluates proposed TZD extrarenal targets; 4) proposes guiding parameters for relevant investigations into extrarenal TZD target identification; and 5) proposes a working model for TZD chronic reduction of arterial pressure through vascular dilation.

Clinical and Molecular Features of Thiazide-Induced Hyponatremia

Purpose of Review

Hypertension affects more than 30% of the world’s adult population and thiazide (and thiazide-like) diuretics are amongst the most widely used, effective, and least costly treatments available, with all-cause mortality benefits equivalent to angiotensin-converting enzyme inhibitors or calcium channel antagonists. A minority of patients develop thiazide-induced hyponatremia (TIH) and this is largely unpredictable at the point of thiazide prescription. In some cases, TIH can cause debilitating symptoms and require hospital admission. Although TIH affects only a minority of patients exposed to thiazides, the high prevalence of hypertension leads to TIH being the most common cause of drug-induced hyponatremia requiring hospital admission in the UK. This review examines current clinical and scientific understanding of TIH. Consideration is given to demographic associations, limitations of current electrolyte monitoring regimens, clinical presentation, the phenotype evident on routine clinical blood and urine tests as well as more extensive analyses of blood and urine in research settings, recent genetic associations with TIH, and thoughts on management of the condition.

Recent Findings

Recent genetic and phenotyping analysis has suggested that prostaglandin E2 pathways in the collecting duct may have a role in the development of TIH in a subgroup of patients. Greater understanding of the molecular pathophysiology of TIH raises the prospect of pre-prescription TIH risk profiling and may offer novel insights into how TIH may be avoided, prevented and treated.

Summary

The rising prevalence of hypertension and the widespread use of thiazides mean that further understanding of TIH will continue to be a pressing issue for patients, physicians, and scientists alike for the foreseeable future.

A novel function of calcitonin gene-related peptide in body fluid Cl- homeostasis

Vertebrates need to maintain extracellular chloride (Cl(-)) concentrations to ensure the normal operation of physiological processes; the transition from aquatic to terrestrial environments necessitated the development of sophisticated mechanisms to ensure Cl(-) homeostasis in the face of fluctuating Cl(-) levels. Zebrafish calcitonin gene-related peptide (CGRP), unlike its splice variant calcitonin, does not respond to environmental Ca(2+) levels. This study aimed to test the hypothesis that CGRP is involved in the control of body fluid Cl(-) homeostasis. Acclimation to high-Cl(-) artificial water stimulated the mRNA expression of cgrp and the receptor (crlr1) when compared with low-Cl(-) CGRP knockdown induced upregulation of the Na(+)-Cl(-) co-transporter (ncc2b), while overexpression of CGRP resulted in the downregulation of ncc2b mRNA synthesis and a simultaneous decrease in Cl(-) uptake in embryos. Consistent with these findings, knockdown of either cgrp or crlr1 was found to increase the density of NCC2b-expressing cells in embryos. This is the first demonstration that CGRP acts as a hypochloremic hormone through suppressing NCC2b expression and the differentiation of NCC-expressing ionocytes. Elucidation of this novel function of CGRP in fish body fluid Cl(-) homeostasis promises to enhance our understanding of the related physiology in vertebrates.

Phenotypic and pharmacogenetic evaluation of patients with thiazide-induced hyponatremia

Thiazide diuretics are among the most widely used treatments for hypertension, but thiazide-induced hyponatremia (TIH), a clinically significant adverse effect, is poorly understood. Here, we have studied the phenotypic and genetic characteristics of patients hospitalized with TIH. In a cohort of 109 TIH patients, those with severe TIH displayed an extended phenotype of intravascular volume expansion, increased free water reabsorption, urinary prostaglandin E2 excretion, and reduced excretion of serum chloride, magnesium, zinc, and antidiuretic hormone. GWAS in a separate cohort of 48 TIH patients and 2,922 controls from the 1958 British birth cohort identified an additional 14 regions associated with TIH. We identified a suggestive association with a variant in SLCO2A1, which encodes a prostaglandin transporter in the distal nephron. Resequencing of SLCO2A1 revealed a nonsynonymous variant, rs34550074 (p.A396T), and association with this SNP was replicated in a second cohort of TIH cases. TIH patients with the p.A396T variant demonstrated increased urinary excretion of prostaglandin E2 and metabolites. Moreover, the SLCO2A1 phospho-mimic p.A396E showed loss of transporter function in vitro. These findings indicate that the phenotype of TIH involves a more extensive metabolic derangement than previously recognized. We propose one mechanism underlying TIH development in a subgroup of patients in which SLCO2A1 regulation is altered.

Hydrochlorothiazide in intensive care unit-acquired hypernatremia: A randomized controlled trial

PURPOSE

Thiazides are suggested as a treatment for intensive care unit (ICU)-acquired hypernatremia (IAH). The primary aim of the study was reducing serum sodium concentration (sNa) in patients with IAH with hydrochlorothiazide (HCT) in comparison to placebo. Secondary end points were a difference in urine sodium concentration (uNa) and duration of severe IAH.

MATERIALS

A monocentric, double-blind, placebo-controlled trial was conducted in 50 patients with IAH and urine potassium + uNa less than sNa in a spot urine sample. Patients were randomized to HCT 25 mg or placebo 1 qd for maximal 7 days. Patients on renal replacement therapy, on medication inducing diabetes insipidus, or with recent use of diuretics were excluded. IAH was defined as sNa of at least 143 mmol/L.

RESULTS

At baseline, sNa and uNa were comparable between groups. During the study period, sNa decreased significantly with median 4 mmol/L in both groups, with no significant difference between groups (P=.32). Median uNa increased significantly in both groups (46 [16-86] mmol/L in the HCT-group; 20 [10-66]mmol/L in the placebo group), with no difference between groups (P=.34). Median duration of sNa of at least 145 mmol/L was 3 days in both groups (P=.91).

CONCLUSION

HCT 25 mg 1 qd did not significantly affect sNa or uNa in patients with IAH.

Cicletanine-induced hyponatremia and hypokalemia in kidney transplant patients

Background

Cicletanine is an antihypertensive agent with vasorelaxant and diuretic properties. It has been widely used in European countries; however, cicletanine-associated electrolyte disturbances have yet to be defined. We investigated cicletanine-induced hyponatremia and hypokalemia in kidney transplant patients.

Methods

Data from a total of 68 kidney transplant recipients who were treated for hypertension with cicletanine were retrospectively analyzed. Cicletanine-induced hyponatremia and hypokalemia were defined as serum sodium < 135 mmol/L and potassium < 3.5 mmol/L, respectively, after the use of cicletanine.

Results

The average patient age was 50 (±11) years, and 44 (65%) were male. The daily dose of cicletanine was 171 ± 46 mg, and the duration of drug use was 215 ± 514 days. Hyponatremia occurred in 11 patients (16.2%), and hypokalemia occurred in 8 patients (11.8%). Three patients (4.4%) had hyponatremia and hypokalemia simultaneously. The duration of cicletanine administration was significantly longer in patients with hyponatremia than in those without hyponatremia (943 ± 958 vs. 74 ± 166 days, P < 0.05). The occurrence of hypokalemia was not affected by either daily dose or duration of drug use. Among 11 patients with hyponatremia, 10 were corrected within 2 weeks after withdrawal of the drug and 1 was spontaneously corrected. Among 8 cases of hypokalemia, 7 were corrected after withdrawal of the drug and 1 was spontaneously corrected.

Conclusion

We demonstrate that cicletanine may induce hyponatremia or hypokalemia in kidney transplant patients. Hyponatremia is more frequently associated with cicletanine than hypokalemia, and extended use of cicletanine may increase the risk of hyponatremia.

Acute Symptomatic Seizures Caused by Electrolyte Disturbances

In this narrative review we focus on acute symptomatic seizures occurring in subjects with electrolyte disturbances. Quite surprisingly, despite its clinical relevance, this issue has received very little attention in the scientific literature. Electrolyte abnormalities are commonly encountered in clinical daily practice, and their diagnosis relies on routine laboratory findings. Acute and severe electrolyte imbalances can manifest with seizures, which may be the sole presenting symptom. Seizures are more frequently observed in patients with sodium disorders (especially hyponatremia), hypocalcemia, and hypomagnesemia. They do not entail a diagnosis of epilepsy, but are classified as acute symptomatic seizures. EEG has little specificity in differentiating between various electrolyte disturbances. The prominent EEG feature is slowing of the normal background activity, although other EEG findings, including various epileptiform abnormalities may occur. An accurate and prompt diagnosis should be established for a successful management of seizures, as rapid identification and correction of the underlying electrolyte disturbance (rather than an antiepileptic treatment) are of crucial importance in the control of seizures and prevention of permanent brain damage.

A systematic review and meta-analysis of thiazide-induced hyponatraemia: time to reconsider electrolyte monitoring regimens after thiazide initiation?

AIMS

Hyponatraemia is one of the major adverse effects of thiazide and thiazide-like diuretics and the leading cause of drug-induced hyponatraemia requiring hospital admission. We sought to review and analyze all published cases of this important condition.

METHODS

Ovid Medline, Embase, Web of Science and PubMed electronic databases were searched to identify all relevant articles published before October 2013. A proportions meta-analysis was undertaken.

RESULTS

One hundred and two articles were identified of which 49 were single patient case reports. Meta-analysis showed that mean age was 75 (95% CI 73, 77) years, 79% were women (95% CI 74, 82) and mean body mass index was 25 (95% CI 20, 30) kg m(-2) . Presentation with thiazide-induced hyponatraemia occurred a mean of 19 (95% CI 8, 30) days after starting treatment, with mean trough serum sodium concentration of 116 (95% CI 113, 120) mm and serum potassium of 3.3 (95% CI 3.0, 3.5) mm. Mean urinary sodium concentration was 64 mm (95% CI 47, 81). The most frequently reported drugs were hydrochlorothiazide, indapamide and bendroflumethiazide.

CONCLUSIONS

Patients with thiazide-induced hyponatraemia were characterized by advanced age, female gender, inappropriate saliuresis and mild hypokalaemia. Low BMI was not found to be a significant risk factor, despite previous suggestions. The time from thiazide initiation to presentation with hyponatraemia suggests that the recommended practice of performing a single investigation of serum biochemistry 7-14 days after thiazide initiation may be insufficient or suboptimal. Further larger and more systematic studies of thiazide-induced hyponatraemia are required.

Molecular insights from dysregulation of the thiazide-sensitive WNK/SPAK/NCC pathway in the kidney: Gordon syndrome and thiazide-induced hyponatraemia

Human blood pressure is dependent on balancing dietary salt intake with its excretion by the kidney. Mendelian syndromes of altered blood pressure demonstrate the importance of the distal nephron in this process and of the thiazide-sensitive pathway in particular. Gordon syndrome (GS), the phenotypic inverse of the salt-wasting Gitelman syndrome, is a condition of hyperkalaemic hypertension that is reversed by low-dose thiazide diuretics or a low-salt diet. Variants within at least four genes [i.e. with-no-lysine(K) kinase 1 (WNK1), WNK4, kelch-like family member 3 (KLHL3) and cullin 3 (CUL3)] can cause the phenotype of GS. Details are still emerging for some of these genes, but it is likely that they all cause a gain-of-function in the thiazide-sensitive Na(+) -Cl(-) cotransporter (NCC) and hence salt retention. Herein, we discuss the key role of STE20/sporulation-specific protein 1 (SPS1)-related proline/alanine-rich kinase (SPAK), which functions as an intermediary between the WNKs and NCC and for which a loss-of-function mutation produces a Gitelman-type phenotype in a mouse model. In addition to Mendelian blood pressure syndromes, the study of patients who develop thiazide-induced-hyponatraemia (TIH) may give further molecular insights into the role of the thiazide-sensitive pathway for salt reabsorption. In the present paper we discuss the key features of TIH, including its high degree of reproducibility on rechallenge, possible genetic predisposition and mechanisms involving excessive saliuresis and water retention. Together, studies of Gordon syndrome and TIH may increase our understanding of the molecular regulation of sodium trafficking via the thiazide-sensitive pathway and have important implications for hypertensive patients, both in the identification of new antihypertensive drug targets and avoidance of hyponatraemic side-effects.

Case studies in fluid and electrolyte therapy

Disorders in serum sodium, hyponatremia and hypernatremia, are frequently encountered in both inpatient and outpatient settings. Many sodium disorders are iatrogenic, caused by inappropriate intravenous fluid management. The methods of prevention and treatment of serum disorders differ based on the underlying disease states. Nine cases are presented to illustrate different aspects of fluid management, with an emphasis on the prevention and treatment of disorders in serum sodium. Key concepts that are discussed are (1) when to use an isotonic fluid versus a hypotonic fluid, (2) when to restrict or liberalize maintenance intravenous fluids, (3) how to use 3% sodium chloride for the treatment of hyponatremic encephalopathy, (4) when to use desmospressin to prevent the overcorrection of chronic hyponatremia, and (5) strategies to treat different causes of hypernatremic dehydration in children.

Clinical review: practical approach to hyponatraemia and hypernatraemia in critically ill patients

Disturbances in sodium concentration are common in the critically ill patient and associated with increased mortality. The key principle in treatment and prevention is that plasma [Na+] (P-[Na+]) is determined by external water and cation balances. P-[Na+] determines plasma tonicity. An important exception is hyperglycaemia, where P-[Na+] may be reduced despite plasma hypertonicity. The patient is first treated to secure airway, breathing and circulation to diminish secondary organ damage. Symptoms are critical when handling a patient with hyponatraemia. Severe symptoms are treated with 2 ml/kg 3% NaCl bolus infusions irrespective of the supposed duration of hyponatraemia. The goal is to reduce cerebral symptoms. The bolus therapy ensures an immediate and controllable rise in P-[Na+]. A maximum of three boluses are given (increases P-[Na+] about 6 mmol/l). In all patients with hyponatraemia, correction above 10 mmol/l/day must be avoided to reduce the risk of osmotic demyelination. Practical measures for handling a rapid rise in P-[Na+] are discussed. The risk of overcorrection is associated with the mechanisms that cause hyponatraemia. Traditional classifications according to volume status are notoriously difficult to handle in clinical practice. Moreover, multiple combined mechanisms are common. More than one mechanism must therefore be considered for safe and lasting correction. Hypernatraemia is less common than hyponatraemia, but implies that the patient is more ill and has a worse prognosis. A practical approach includes treatment of the underlying diseases and restoration of the distorted water and salt balances. Multiple combined mechanisms are common and must be searched for. Importantly, hypernatraemia is not only a matter of water deficit, and treatment of the critically ill patient with an accumulated fluid balance of 20 litres and corresponding weight gain should not comprise more water, but measures to invoke a negative cation balance. Reduction of hypernatraemia/hypertonicity is critical, but should not exceed 12 mmol/l/day in order to reduce the risk of rebounding brain oedema.