Hyponatremia: A Clinical and Practical Approach

INTRODUCTION

Hyponatremia is defined as a serum sodium %3C;135 mEq/L.¹ This condition is a chronic and constant nightmare to clinicians and pathologists due to its varied or broader etiopathogenesis. Multiple etiologies and variety of symptoms make it a puzzle which cannot be solved easily. Varying and ever-changing guidelines did not help the cause. These articles pave light to the disorder and its management. Hyponatremia is the electrolyte disorder typically present in day-to-day life of physician, with a stated occurrence of 15–30%.² It creates substantial diagnostic and management trouble for clinicians. This state has many reasons and influencing factors. The important and immediate attention should be given for the prompt and correct identification of the reason and its management. In the delicate setting, management frequently has to be started before an optimistic judgment can be made and results of helpful biochemical investigations are obtainable. Both over treatment and under treatment can create overwhelming effects on cerebral function.³

A frequent clinical problem, hyponatremia commonly increases in hospitalized patients. Although morbidity varies extensively in severity, grave problems can occur from the disorder itself as well as from mistake in management.⁴

MATERIALS AND METHODS

The review article was searched based on MESH terms, hyponatremia, causes, pathogenesis, and management. The data search was extensively done on PubMed, Google scholar, and Google sites.

PREVALENCE

Hyponatremia (serum sodium level <135 mEq/L) is the most frequent electrolyte defect in hospitalized patients with the stated occurrence in range 5% to almost 35% in foreign countries.^5,6

Increased mortality, duration of hospital stay, and emerging of complications are unknown implications of hyponatremia.^7,8

CAUSES OF HYPONATREMIA^9–11

SYMPTOMS OF HYPONATREMIA^11,14

Acute hyponatremia has a typical start of symptoms in less than 48 hours. Patients build up neurological features causing from cerebral edema causing seizures, altered mentation leading to coma, and death.

CHRONIC HYPONATREMIA

Hyponatremia just beginning over %3E;48 hours. Major chunk of patient population is suffering from this. The serum sodium concentration is usually above 120 mEq/L. There is a protective adaptive mechanism of brain to reduce the degree of cerebral edema. Hence, in chronic hyponatremia, patients may appear symptom less. Mild hyponatremia can cause vague nausea vomiting, and rarely subclinical neurologic defect may be present when the serum sodium is between 120 mEq/L and 130 mEq/L. Hyponatremia in the elder person may be obviously visible with recurrent falls and gait instabilities.

Hyponatremia is divided as pseudohyponatremia, true and translocational hyponatremia.

Normal serum osmolality is 280–295 mOsm/kg. Pseudohyponatremia is due to hypertriglyceridemia or multiple myeloma. In regular subjects, the plasma water is 93% of the plasma volume. Plasma water part falls lower than 80% in cases with noticeable hyperlipidemia (triglycerides >1500 mg/dL) or hyperproteinemia (protein >10 mg/dL).¹⁵ Rise in blood urea causes the hyponatremia in renal failure.¹⁶

True hyponatremia is having a fall in serum osmolality and is divided into hypervolemic, hypovolemic, and euvolemic based on volume status.^17–19

TYPES OF HYPONATREMIA¹²

MANAGEMENT OF HYPONATREMIA

The management of hyponatremia depended mainly on its commencement, etiology, and symptomatology. Early assessment of any patient with hyponatremia engages in recognition of the start of the state (acute or chronic), the occurrence of features, and evaluation of quantity grade. A previous analysis of disease of liver, kidney, and heart has to be seen, as well as earlier electrolytes to differentiate acute from chronic hyponatremia. Any blood loss or extracellular fluid should be identified. An exact drug history and history of signs of headache, nausea, seizures, and confusion, which point to raised intracranial pressure should be noted. On physical examination, a precise measurement of the patient’s volume status is significant.

Measurement or investigation of^27–31

• Serum osmolality,
• Urine osmolality,
• Urine sodium,
• Serum sodium,
• Urine to serum electrolyte ratio,
• Fractional excretion of sodium,
• Serum uric acid and urea concentrations,
• Acid-base and potassium balance,
• Saline infusion,
• Thyroid investigations, adrenal stimulation tests, CT/MRI brain, and imaging of chest.

Each investigation will be needed to differentiate the different types of hyponatremia.

The treatment of hyponatremia will be based on the volume status, length of hyponatremia (whether acute less than or equal to 48 hour or chronic more than 48 hours), presence or absence of symptoms, and cause of hyponatremia.^32,33

STUDIES RELATED TO HYPONATREMIA (TABLE 1)

Elderly patients in USA were included in a study on their demographic profile with regards to hyponatremia and it showed that SIADH, diuretics, and SSRIs were common causes and it had significant age-related morbidity and mortality.³⁴

In a study done in India among patients staying in hospital, confusion, headache, and tiredness were the most frequent symptoms, of them two patients had seizures, and 20% patients showed no symptoms. Nausea was significantly more frequent in patients with hyponatremia. Twenty-two patients (31.4%) had hyponatremia during their stay in the hospital. Most had multiple causative factors, reduced eating being the most common (82.9%), followed by augmented losses of blood (65.7%), and various factors (70.0%). Drugs, fluid excess, and unsuitable Ryle’s tube feeds more usually precipitated hyponatremia in patients.³⁵

Shapiro et al. did a study which was done for about 5 months in the medicine wards. Eighty-six patients aged more than 65 years with serum sodium levels less than or equal to 125 mEq/L were incorporated. The occurrence of hyponatremia was 6.2%. The frequent reason of hyponatremia was the syndrome of inappropriate antidiuretic hormone secretion (SIADH) causing euvolemic hyponatremia.³⁶

A study was conducted among patients in hospital and found the result of severe hyponatremia with regards to mortality and duration of hospital stay, on the whole death, was 27% in hyponatremic patients in comparison to 9% in nonhyponatremic patients, and length of admission was longer in hyponatremic patients.³⁷

In a study, patients who had severe hyponatremia were evaluated in comparison with patients who gained severe hyponatremia in a 3-month hospital stay. In hospital-gained hyponatremia, treatment started significantly later and the duration of hospitalization was longer. Factors that added to hospital-gained hyponatremia incorporated: thiazide diuretics, drugs stimulating antidiuretic hormone, surgery, and hypotonic intravenous fluids.³⁸

In a study done on occurrence of hyponatremia with seasonal variations as a primary outcome, it showed raised occurrence of hyponatremia during summer when the outdoor temperatures were highest and especially prevalent in elderly female patients.³⁹

STUDIES RELATED TO MANAGEMENT OF HYPONATREMIA

In a study with oral conivaptan, a V1A/V2-receptor antagonist, 83 patients with serum [Na] less than 130 mEq/L were randomly assigned to placebo or conivaptan 40 or 80 mg/day for 5 days. Oral conivaptan was efficient in rising serum sodium and it had greatest effect on euvolemic hyponatremia.⁴⁰

In a study, the effects of VPA-985, an orally active vasopressin V2 receptor antagonist, in patients with cirrhosis and dilutional hyponatremia were investigated. Normalization of serum sodium concentration was attained in 27% and 50% of patients in the VPA-985 100 mg/day and 200 mg/day groups, respectively, but in none of the patients in the placebo group.⁴¹

In an analysis done by Alessandro Peri, he has stated that concurring with previous trails, vaptans had an ability to maintain serum sodium level post discharge from hospital, which have been diagnosed and corrected as euvolemic and hypervolemic hyponatremia.⁴²

SUMMARY

The correct diagnosis and cause of hyponatremia are essential in management of patients particularly hospitalized patients. The electrolyte imbalance if correctly diagnosed and treated can avoid mortality and reduce morbidity. Normal saline outlines the root of management for hypovolemic hyponatremia, while 3% NaCl and fluid limit are important for euvolemic hyponatremia. Hypervolemic hyponatremia responds well to fluid constraint and diuretic drugs.

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