Epidemiology, clinical and economic outcomes of admission hyponatremia among hospitalized patients

Hyponatremia's Impact on Patients and Health Systems

Purpose

To define hyponatremia, discuss its incidence and epidemiology, and summarize the frequency and prognostic implications of hyponatremia in selected clinical conditions.

Summary

Hyponatremia is the most common electrolyte abnormality encountered in clinical practice. Hyponatremia is commonly defined as a serum sodium concentration of <136 mEq/L. There are 3 different types of hyponatremia: hypovolemia, euvolemia, and hypervolemia. Epidemiologic studies reveal that hyponatremia is a common problem in hospitalized patients whether it is present at admission or is hospital acquired. The disorder increases the risk of admission to the intensive care unit, hospital length of stay, and morbidity and mortality. Hyponatremia appears to be a marker for severe underlying disease with a poor prognosis. Congestive heart failure, pneumonia, cirrhosis, and neurologic disease are among the serious clinical conditions known to be associated with hyponatremia. Chronic hyponatremia presents its own set of challenges; even in mild disease that is often asymptomatic, patients are at heightened risk for falls, gait disturbances, attention deficits, and fracture.

Conclusion

Hyponatremia is the most common electrolyte disorder encountered in clinical practice and is associated with significant morbidity and mortality, especially at lower serum sodium concentrations. The disorder has a substantial impact on hospital length of stay with a direct impact on health care costs. Further, as this discussion illustrates, hyponatremia represents a significant clinical burden in all forms – mild, moderate, and severe – with subsequent clinical consequences.

Risk of thiazide-induced hyponatremia in patients with hypertension

BACKGROUND

Although hyponatremia is a well-recognized complication of treatment with thiazide diuretics, the risk of thiazide-induced hyponatremia remains uncertain in routine care.

METHODS

We conducted a retrospective cohort study using a multicenter clinical research registry to identify 2613 adult outpatients that were newly treated for hypertension between January 1, 2000 and December 31, 2005 at 2 teaching hospitals in Boston, Massachusetts, and followed them for up to 10 years.

RESULTS

Two hundred twenty patients exposed to ongoing thiazide therapy were compared with 2393 patients who were not exposed. In the exposed group, 66 (30%) developed hyponatremia (sodium ≤130 mmol/L). The adjusted incidence rate of hyponatremia was 140 cases per 1000 person-years for patients treated with thiazides, compared with 87 cases per 1000 person-years in those without thiazides. Patients exposed to thiazides were more likely to develop hyponatremia (adjusted incidence rate ratio, 1.61; 95% confidence interval [CI], 1.15-2.25). There was no significant difference in the risk of hospitalizations associated with hyponatremia (adjusted rate ratio, 1.04; 95% CI, 0.46-2.32) or mortality (adjusted rate ratio, 0.41; 95% CI, 0.12-1.42). The number needed to harm (to result in one excess case of incident hyponatremia in 5 years) was 15.02 (95% CI, 7.88-160.30).

CONCLUSIONS

Approximately 3 in 10 patients exposed to thiazides who continue to take them develop hyponatremia.

Hyponatremia in hospitalized cancer patients and its impact on clinical outcomes

BACKGROUND

Hyponatremia is the most common electrolyte abnormality in clinical practice, yet little is known about its frequency in patients with cancer or its impact on their clinical outcomes.

STUDY DESIGN

Retrospective analysis of prospectively collected data.

SETTING & PARTICIPANTS

Patients with cancer admitted to the University of Texas M.D. Anderson Cancer Center in 2006 for 3 months.

PREDICTOR

Serum sodium levels categorized as eunatremia (serum sodium, 135-147 mEq/L) and mild (134-130 mEq/L), moderate (129-120 mEq/L), and severe (<120 mEq/L) hyponatremia.

OUTCOMES

(1) Length of hospital stay and (2) 90-day mortality.

RESULTS

In 4,702 admissions in 3,357 patients with cancer, hyponatremia (serum sodium <135 mEq/L) was noted in 47% of admissions. It was mild in 36%, moderate in 10%, and severe in 1%. Hyponatremia was acquired during the hospital stay in 24%. Using the first admission data, mean length of stay was 5.6 ± 5.0 days for patients with eunatremia and 9.9 ± 9.2, 13.0 ± 14.1, and 11.5 ± 12.6 days for those with mild, moderate, and severe hyponatremia, respectively. The respective HRs in the multivariate Cox model for longer hospital stay, using patients with eunatremia as reference, were 1.92 (95% CI, 1.75-2.13; P < 0.01), 2.94 (95% CI, 2.56-3.45; P < 0.01), and 2.32 (95% CI, 1.32-4.00; P = 0.01). 283 (8.4%) deaths occurred during 90 days, and in the multivariate model, the respective HRs for 90-day mortality for mild, moderate, and severe hyponatremia were 2.04 (95% CI, 1.42-2.91; P < 0.01); 4.74 (95% CI, 3.21-7.01; P < 0.01), and 3.46 (95% CI, 1.05-11.44; P = 0.04). These findings were consistent when analyses were repeated with sodium levels in tertiles.

LIMITATIONS

Observational study, retrospective, inability to adjust for all comorbid conditions.

CONCLUSION

Hyponatremia in patients with cancer is associated with longer hospital stay and higher mortality. Whether long-term correction of hyponatremia would improve these outcomes remains to be determined.

Hyponatremia in hospitalized patients: the potential role of tolvaptan

Hyponatremia (typically defined as serum sodium level < 135 mEq/L) is a common electrolyte abnormality among hospitalized patients. Whether present at admission or acquired during hospitalization, hyponatremia is associated with higher mortality and longer hospital stays. Failure to adequately investigate and treat hyponatremia may also be associated with adverse outcomes. The presence and severity of clinical symptoms largely depend on the rate and extent of the decline in serum sodium; rapid or large decreases may cause serious neurologic complications. The approach to treatment depends on the presence and severity of symptoms, the timing of their onset, the underlying etiology, and the patient's volume status. Patients with euvolemic or hypervolemic hyponatremia usually have inappropriately elevated levels of arginine vasopressin, which stimulates water reabsorption even in the presence of low serum osmolality. Tolvaptan is an orally active, selective V2-receptor antagonist that blocks the effects of arginine vasopressin in the renal collecting duct to promote aquaresis without increasing sodium or potassium excretion; as a result, it increases serum sodium in a controlled manner. Tolvaptan offers a mechanism-based treatment option for patients with euvolemic or hypervolemic hyponatremia who have serum sodium levels < 125 mEq/L or persistent symptoms resistant to fluid restriction.

The Therapeutic Use of Vaptans for the Treatment of Dilutional Hyponatremia

Hyponatremia is a very common electrolyte abnormality. Dilutional hyponatremia is very difficult to treat effectively due to the complications of conventional treatment. Arginine-vasopressin (AVP) plays an integral role in circulatory and water homeostasis. AVP is a hormone released in response to increases in plasma tonicity or decreases in plasma volume in an attempt to maintain the plasma osmolality between 284 and 295 mOsm/L. AVP receptor antagonists or “vaptans” are a new class of drugs that allow for the safe and efficacious treatment of dilutional hyponatremia. Conivaptan, a mixed V1a/V2 receptor antagonist, and tolvaptan, a selective V2 receptor antagonist, are the only 2 vaptans approved by the US Food and Drug Administration.

Vaptans are not the mainstay of treatment in hyponatremia: perhaps not yet

Two vasopressin antagonists ('vaptans') are now in the market for the treatment of euvolemic (Europe) or euvolemic and hypervolemic (United States) hyponatremia: conivaptan for intravenous use and tolvaptan for oral application. Although their specificity and effectiveness are considered established, their indications are not. At present, we do not know which symptoms of hyponatremia and which degree of hyponatremia should serve as indications for vaptans. Other areas of uncertainty relate to the following unanswered questions: do vaptans shorten the duration of hospitalization? Is it justifiable to use them to prevent relapse of hyponatremia in (chronic) SIAD(H)? (In this text we use the abbreviation SIAD(H) instead of the recently proposed abbreviation SIAD to emphasize that vaptans will work only in the presence of ADH ('SIADH') but not in the syndrome of nephrogenic antidiuresis.) Do they decrease the high mortality associated with hyponatremia? How do we justify the cost of chronic vaptan therapy? The optimal vaptan regimen (dose, timing of controls) to treat SIAD(H) is currently not established, as is the procedure to be recommended in a too rapid correction rate of (chronic) hyponatremia. Until these requirements shall be met by additional studies, we are hesitant to consider vaptans a treatment of choice for the appropriate hyponatremias.

Hyponatraemia in cases of children with pneumonia

INTRODUCTION

Hyponatraemia is the most common electrolyte imbalance seen in clinical practice, and a common laboratory finding in children with community-acquired pneumonia (CAP). This study aimed to identify the incidence of hyponatraemia in cases of CAP, to find predictive tools in order to classify the severity and outcome of CAP and to explore possible differences of clinical importance between the two sexes.

MATERIAL AND METHODS

The medical files of 54 children (66.4% males), 4.67 ±2.88 years old, were retro-prospectively reviewed.

RESULTS

35/54 (64.8%) children with pneumonia had normal values of sodium at admission, 18/54 (33.3%) had mild hyponatraemia and 1 child (1.9%) moderate hyponatraemia. Increased heart rhythm and tachypnoea at admission were correlated with lower values of sodium (z= -2.664, p = 0.007 and z = -1.705, p = 0.089 respectively). No differences were found between the two sexes concerning the characteristics of pneumonia or the range of sodium in serum at admission. A correlation was found between sodium admission values and: a) C-reactive protein (p = 0.000), and b) leukocyte count (p = 0.006). Sedimentation rate (p = 0.021) was also considered as a possible risk factor affecting the value of sodium at admission to hospital. Finally, a negative association was also observed between the degree of hyponatraemia and the duration of hospitalization (z = -3.398, p = 0.001).

CONCLUSIONS

Although studies in larger population groups are needed, in our study increased heart rhythm, tachypnoea, leucocyte count, C-reactive protein, and also erythrocyte sedimentation rate could be considered as possible risk factors influencing the degree of hyponatraemia, and thus the outcome of hospitalized children with CAP.

Managing hyponatremia in cirrhosis

The development of hyponatremia represents an ominous event in the progression of cirrhosis to end-stage liver disease. It usually develops in those with refractory ascites and is a manifestation of the non-osmotic release of arginine vasopressin (AVP). In the hospitalized cirrhotic patient, hyponatremia is associated with increased disease severity and mortality. In this article, we review the pathophysiology of hyponatremia, its clinical implications, evaluation, and treatment.

Prognostic importance of hyponatremia in patients with acute pulmonary embolism

RATIONALE

Although associated with adverse outcomes in other cardiopulmonary conditions, the prognostic value of hyponatremia, a marker of neurohormonal activation, in patients with acute pulmonary embolism (PE) is unknown.

OBJECTIVES

To examine the associations between hyponatremia and mortality and hospital readmission rates for patients hospitalized with PE.

METHODS

We evaluated 13,728 patient discharges with a primary diagnosis of PE from 185 hospitals in Pennsylvania (January 2000 to November 2002). We used random-intercept logistic regression to assess the independent association between serum sodium levels at the time of presentation and mortality and hospital readmission within 30 days, adjusting for patient (race, insurance, severity of illness, use of thrombolytic therapy) and hospital factors (region, size, teaching status).

MEASUREMENTS AND MAIN RESULTS

Hyponatremia (sodium ≤135 mmol/L) was present in 2,907 patients (21.1%). Patients with a sodium level greater than 135, 130-135, and less than 130 mmol/L had a cumulative 30-day mortality of 8.0, 13.6, and 28.5% (P < 0.001), and a readmission rate of 11.8, 15.6, and 19.3% (P < 0.001), respectively. Compared with patients with a sodium greater than 135 mmol/L, the adjusted odds of dying were significantly greater for patients with a sodium 130-135 mmol/L (odds ratio [OR], 1.53; 95% confidence interval [CI], 1.33-1.76) and a sodium less than 130 mmol/L (OR, 3.26; 95% CI, 2.48-4.29). The adjusted odds of readmission were also increased for patients with a sodium of 130-135 mmol/L (OR, 1.28; 95% CI, 1.12-1.46) and a sodium less than 130 mmol/L (OR, 1.44; 95% CI, 1.02-2.02).

CONCLUSIONS

Hyponatremia is common in patients presenting with PE, and is an independent predictor of short-term mortality and hospital readmission.

[Incidence of hyponatremia and its causes in neurological patients]

INTRODUCTION

Hyponatremia is considered the most frequent electrolyte disorder found in hospitalized patients and seems to be a prognostic factor during hospitalization.

METHODS

A prospective observational study was carried out in consecutive neurological patients admitted to our hospital over a 3-month period. Blood and urinary ionogram and osmolality were determined at entry and 3-5 days after admission in all patients with hyponatremia.

RESULTS

Of the 130 patients admitted, 19 (14.6%) had hyponatremia. The causes of hyponatremia were as follows: inappropriate fluid replacement in 4 patients (21%), antihypertensive drugs in 4 (21%), syndrome of inappropriate secretion of antidiuretic hormone in 4 (21%), cerebral salt wasting syndrome in 2 (10%), and edematous status caused by liver disease in one and digestive loss in one (5%) each. Mortality was one (5%) and 0 (0%) among patients with and without hyponatremia, respectively.

CONCLUSION

Hyponatremia is common in hospitalized neurological patients and can be misdiagnosed as a worsening of the main illness.

The critical link of hypervolemia and hyponatremia in heart failure and the potential role of arginine vasopressin antagonists

BACKGROUND

Hypervolemia and hyponatremia resulting from activation of the neurohormonal system and impairment of renal function are prominent features of decompensated heart failure. Both conditions share many pathophysiologic and prognostic features and each has been associated with increased morbidity and mortality. When both conditions coexist, therapeutic options are limited.

METHODS AND RESULTS

This review presents a concise digest of the pathophysiology, clinical significance, and pharmacological therapy of hyponatremia complicating heart failure with a special emphasis on vasopressin antagonists and their aquaretic effects in the absence of neurohormonal activation along with their ability to correct hyponatremia.

CONCLUSIONS

Hypervolemia and hyponatremia share many pathophysiologic and prognostic features in heart failure. Vasopressin antagonists provide a viable option for their management and a potentially unique role when both conditions coexists.

Conivaptan and its role in the treatment of hyponatremia

Hyponatremia is the most common electrolyte abnormality in hospitalized patients and is associated with increased morbidity and mortality. The recognition of the central role that arginin vasopressin plays in the pathogenesis of hyponatremia and the discovery that its actions are mediated by stimulation of V(1A) and V(2) receptors have led to the development of a new class of drugs, the arginin vasopressin antagonists. Conivaptan is a nonselective V(1A) and V(2) receptors antagonist that was the first of this class to be approved by the FDA for the management of euvolemic and hypervolemic hyponatremia. Its short-term safety and efficacy for the correction of hyponatremia have been established by multiple double-blind, randomized, controlled studies. Blocking the effects of arginin vasopressin on V(2) receptors produces aquaresis--the electrolyte-sparing excretion of water--an ideal approach to correct hypervolemic hyponatremia. The nonselectivity of conivaptan offers a theoretical advantage for its use in heart failure that may merit further exploration.

Mortality after hospitalization with mild, moderate, and severe hyponatremia

BACKGROUND

Hyponatremia is the most common electrolyte abnormality in hospitalized individuals.

METHODS

To investigate the association between serum sodium concentration and mortality, we conducted a prospective cohort study of 98,411 adults hospitalized between 2000 and 2003 at 2 teaching hospitals in Boston, Massachusetts. The main outcome measures were in-hospital, 1-year, and 5-year mortality. Multivariable logistic regression and Cox proportional hazards models were used to compare outcomes in patients with varying degrees of hyponatremia against those with normal serum sodium concentration.

RESULTS

Hyponatremia (serum sodium concentration <135 mEq/L) was observed in 14.5% of patients on initial measurement. Compared with patients with normonatremia (135-144 mEq/L), those with hyponatremia were older (67.0 vs 63.1 years, P <.001) and had more comorbid conditions (mean Deyo-Charlson Index 1.9 vs 1.4, P <.001). In multivariable-adjusted models, patients with hyponatremia had an increased risk of death in hospital (odds ratio 1.47, 95% confidence interval [CI], 1.33-1.62), at 1 year (hazard ratio 1.38, 95% CI, 1.32-1.46), and at 5 years (hazard ratio 1.25, 95% CI, 1.21-1.30). The increased risk of death was evident even in those with mild hyponatremia (130-134 mEq/L; odds ratio 1.37, 95% CI, 1.23-1.52). The relationship between hyponatremia and mortality was pronounced in patients admitted with cardiovascular disease, metastatic cancer, and those admitted for procedures related to the musculoskeletal system. Resolution of hyponatremia during hospitalization attenuated the increased mortality risk conferred by hyponatremia.

CONCLUSION

Hyponatremia, even when mild, is associated with increased mortality.

Hyponatremia in the intensive care unit

Hyponatremia is a common electrolyte disturbance encountered in the intensive care unit setting. The underlying etiology is multifactorial and includes processes that lead to both a baroreceptor-mediated and a baroreceptor independent increase in antidiuretic hormone release. Patients with hyponatremia have an increased mortality rate and therefore an understanding of the cause and treatment of this disorder is of paramount importance.

Epidemiology of hyponatremia

Hyponatremia is the most common electrolyte abnormality encountered in clinical practice with wide-ranging prognostic implications in a variety of conditions. This review summarizes the available literature on the epidemiology of hyponatremia in both hospitalized and ambulatory-based patients. Particular attention is given to hyponatremia in the geriatric population, drug-induced hyponatremia, exercise-associated hyponatremia, and the medical costs of hyponatremia. The frequency and outcomes of hyponatremia in congestive heart failure, cirrhosis, pneumonia, and human immunodeficiency virus infection also are reviewed. Although the knowledge on hyponatremia has expanded in the past few decades, the disorder largely remains an underdiagnosed condition. Substantial additional work is needed to improve the awareness of hyponatremia among medical professionals. The advent of vasopressin-receptor antagonists as a plausible treatment option for some forms of euvolemic and hypervolemic hyponatremia now offers the opportunity to gain further insights into the prognostic impact of hyponatremia and its management in various clinical settings.

Monitoring of drug-associated electrolyte disturbances in a hospital

PURPOSE

The aim of our study was to find drug-associated changes in serum levels of major electrolytes using clinical-event monitoring method.

METHODS

During 1-year period, electrolyte disturbances in serum samples from patients of Clinical Center Kragujevac, Serbia, were monitored in central biochemical facility. A sample of 982 patients was randomly selected from total population of 43,120 patients whose electrolyte serum levels were measured in the facility during the study period.

RESULTS

Clinically important drug-associated electrolyte disturbances were detected in 181 patient. There were 25 significant associations between the drugs and electrolyte values outside the reference range. However, only four causal connections were established: use of normal saline infusion with hypernatremia (OR 6.97, 95%CI 2.24-21.67), theophylline with acid-base disturbances (7.75, 1.46-41.02), polygeline infusion with decrease in bicarbonate levels (4.08, 1.42-11.73), and association of risperidone and hypocalcemia (4.10, 1.42-11.81).

CONCLUSION

Although clinical-event monitoring method is far from optimal, it could quantify the known risks and provide evidence for credible hypothesis of drug adverse reactions, based on both relevant biological pathways and reasonable clinical thinking, as it was the case in our study.

Economic impact of hyponatremia in hospitalized patients: a retrospective cohort study

BACKGROUND

Hyponatremia is the most common electrolyte abnormality seen in general hospital patients, with an incidence of 1% to 6% in the United States.

OBJECTIVE

We aimed to evaluate the impact of varying levels of hyponatremia at admission on length of stay (LOS) and cost of care in adult hospitalized patients.

METHODS

A retrospective cohort study was conducted using an existing clinical database from a large academic-setting hospital. All adult admissions from January 2004 through May 2005 with serum sodium level at admission of < or = 134 mEq/L were separated into 2 cohorts: patients with moderate-to-severe hyponatremia (serum sodium level at admission of < or = 129 mEq/L, n = 547) and patients with mild-to-moderate hyponatremia (serum sodium level of 130-134 mEq/L, n = 1500). ICD-9 diagnosis codes for these 2047 admissions with hyponatremia were used to identify a cohort of 7573 admissions with the same principal admitting diagnoses and a serum sodium level of 135 to 145 mEq/L. Differences in hospital LOS, intensive care unit (ICU) admission rate, and median total costs per admission between cohorts were examined using multiple linear regression, logistic, and quantile regression models.

RESULTS

Admissions with hyponatremia had significantly longer hospital LOS than those admitted without hyponatremia (median LOS: moderate-to-severe hyponatremia, 8 days; mild-to-moderate hyponatremia, 8 days; normal, 6 days; P < 0.001). Patients with more severe hyponatremia were also more likely to be admitted to the ICU during the hospital stay (moderate-to-severe hyponatremia, 32%; mild-to-moderate hyponatremia, 26%; normal, 22%; P < 0.001). These trends were also reflected in the total costs per admission, with median costs of $16,606 for moderate-to-severe hyponatremia cases, $14,266 for mild-to-moderate hyponatremia cases, and $13,066 for normal admissions (P < 0.001).

CONCLUSIONS

Hyponatremia at admission was associated with increased LOS and cost of care for hospitalized patients. Interventions or pharmacotherapies for the prompt treatment of hyponatremia could potentially reduce morbidity and LOS, thereby reducing the utilization of health care resources.