Hypertonic Saline for Hyponatremia: Meeting Goals and Avoiding Harm

Hyponatremia in the Context of Liver Disease

Hyponatremia is common in patients with liver disease and is associated with increased mortality, morbidity, and a reduced quality of life. In liver transplantation, the inclusion of hyponatremia in organ allocation scores has reduced waitlist mortality. Portal hypertension and the resulting lowering of the effective arterial blood volume are important pathogenetic factors, but in most patients with liver disease, hyponatremia is multifactorial. Treatment requires a multifaceted approach that tries to reduce electrolyte-free water intake, restore urinary dilution, and increase nonelectrolyte solute excretion. Albumin therapy for hyponatremia is a peculiarity of advanced liver disease. Its use appears to be increasing, while the vaptans are currently only given in selected cases. Osmotic demyelination is a special concern in patients with liver disease. Serial checks of serum sodium concentrations and urine volume monitoring are mandatory.

[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.

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

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

Treatment Guidelines for Hyponatremia: Stay the Course

International guidelines designed to minimize the risk of complications that can occur when correcting severe hyponatremia have been widely accepted for a decade. On the basis of the results of a recent large retrospective study of patients hospitalized with hyponatremia, it has been suggested that hyponatremia guidelines have gone too far in limiting the rate of rise of the serum sodium concentration; the need for therapeutic caution and frequent monitoring of the serum sodium concentration has been questioned. These assertions are reminiscent of a controversy that began many years ago. After reviewing the history of that controversy, the evidence supporting the guidelines, and the validity of data challenging them, we conclude that current safeguards should not be abandoned. To do so would be akin to discarding your umbrella because you remained dry in a rainstorm. The authors of this review, who represent 20 medical centers in nine countries, have all contributed significantly to the literature on the subject. We urge clinicians to continue to treat severe hyponatremia cautiously and to wait for better evidence before adopting less stringent therapeutic limits.

The Safety of Intravenous Peripheral Administration of 3% Hypertonic Saline: A Systematic Review and Meta-analysis

BACKGROUND AND OBJECTIVES

Three percent hypertonic saline (3% HTS) is used to treat several critical conditions such as severe and symptomatic hyponatremia and increased intracranial pressure. It has been traditionally administered through a central venous catheter (CVC). The avoidance of peripheral intravenous infusion of 3% HTS stems theoretically from the concern about the ability of the peripheral veins to tolerate hyperosmolar infusions. The aim of this systematic review and meta-analysis is to assess the rate of complications associated with the infusion of 3% HTS using peripheral intravenous access.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We conducted a systematic review and meta-analysis to assess the rate of complications related to the peripheral infusion of 3% HTS. We searched several databases for available studies that met the criteria until February 24th, 2022. We included ten studies conducted across three countries examining the incidence of infiltration, phlebitis, venous thrombosis, erythema, and edema. The overall event rate was calculated and transformed using the Freeman-Tukey arcsine method and pooled using the DerSimonian and Laird random-effects model. I ² was used to evaluate heterogeneity. Selected items from Newcastle-Ottawa Scale ¹² were used to assess the risk of bias in each included study.

RESULTS

A total of 1200 patients were reported to have received peripheral infusion of 3% HTS. The analysis showed that peripherally administered 3% HTS has a low rate of complications. The overall incidence of each of the complications was as follows: infiltration 3.3%, (95% C.I. = 1.8-5.1%), phlebitis 6.2% (95% C.I. = 1.1-14.3%), erythema 2.3% (95% C.I. = 0.3-5.4%) edema 1.8% (95% C.I. = 0.0-6.2%) and venous thrombosis 1% (95% C.I. = 0.0-4.8%). There was one incident of venous thrombosis preceded by infiltration resulting from peripheral infusion of 3% HTS.

CONCLUSION

Peripheral administration of 3% HTS is considered a safe and possibly preferred option as it carries a low risk of complications and is a less invasive procedure compared to CVC.

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.

Overcorrection and undercorrection with fixed dosing of bolus hypertonic saline for symptomatic hyponatremia

OBJECTIVE

Current guidelines recommend treating symptomatic hyponatremia with rapid bolus-wise infusion of fixed volumes of hypertonic saline regardless of body weight. We hypothesize that this approach is associated with overcorrection and undercorrection in patients with low and high body weight.

DESIGN

Single-center, retrospective cohort study.

METHODS

Data were collected on patients treated with ≥1 bolus 100 or 150 mL 3% NaCl for symptomatic hyponatremia between 2017 and 2021. Outcomes were overcorrection (plasma sodium rise > 10 mmol/L/24 h, > 18 mmol/L/48 h, or relowering therapy) and undercorrection (plasma sodium rise < 5 mmol/L/24 h). Low body weight and high body weight were defined according to the lowest (≤60 kg) and highest (≥80 kg) quartiles.

RESULTS

Hypertonic saline was administered to 180 patients and caused plasma sodium to rise from 120 mmol/L to 126.4 mmol/L (24 h) and 130.4 mmol/L (48 h). Overcorrection occurred in 32 patients (18%) and was independently associated with lower body weight, weight ≤ 60 kg, lower baseline plasma sodium, volume depletion, hypokalemia, and less boluses. In patients without rapidly reversible causes of hyponatremia, overcorrection still occurred more often in patients ≤ 60 kg. Undercorrection occurred in 52 patients (29%) and was not associated with body weight or weight ≥ 80 kg but was associated with weight ≥ 100 kg and lean body weight in patients with obesity.

CONCLUSION

Our real-world data suggest that fixed dosing of bolus hypertonic saline may expose patients with low and high body weight to more overcorrection and undercorrection, respectively. Prospective studies are needed to develop and validate individualized dosing models.

Hyponatremia Demystified: Integrating Physiology to Shape Clinical Practice

Hyponatremia is one of the most common problems encountered in clinical practice and one of the least-understood because accurate diagnosis and management require some familiarity with water homeostasis physiology, making the topic seemingly complex. The prevalence of hyponatremia depends on the nature of the population studied and the criteria used to define it. Hyponatremia is associated with poor outcomes including increased mortality and morbidity. The pathogenesis of hypotonic hyponatremia involves the accumulation of electrolyte-free water caused by either increased intake and/or decrease in kidney excretion. Plasma osmolality, urine osmolality, and urine sodium can help to differentiate among the different etiologies. Brain adaptation to plasma hypotonicity consisting of solute extrusion to mitigate further water influx into brain cells best explains the clinical manifestations of hyponatremia. Acute hyponatremia has an onset within 48 hours, commonly resulting in severe symptoms, while chronic hyponatremia develops over 48 hours and usually is pauci-symptomatic. However, the latter increases the risk of osmotic demyelination syndrome if hyponatremia is corrected rapidly; therefore, extreme caution must be exercised when correcting plasma sodium. Management strategies depend on the presence of symptoms and the cause of hyponatremia and are discussed in this review.

NaCl 3% bolus therapy as emergency treatment for severe hyponatremia: Comparison of 100 ml versus 250 ml

CONTEXT

The aim of initial treatment of severe hyponatremia is to rapidly increase serum sodium to reduce the complications of cerebral edema. The optimal strategy to achieve this goal safely is still under debate.

OBJECTIVE

To compare the efficacy and safety of 100 and 250 ml NaCl 3% rapid bolus therapy as initial treatment of severe hypotonic hyponatremia.

DESIGN

Retrospective analysis of patients admitted between 2017 and 2019.

SETTING

Teaching hospital in the Netherlands.

PATIENTS

130 adults with severe hypotonic hyponatremia, defined as serum sodium ≤ 120 mmol/L.

INTERVENTION

A bolus of either 100 ml (N = 63) or 250 ml (N = 67) NaCl 3% as initial treatment.

MAIN OUTCOME MEASURES

Successful treatment was defined as a rise in serum sodium ≥ 5 mmol/L within the first 4 hours after bolus therapy. Overcorrection of serum sodium was defined as an increase of more than 10 mmol/L in the first 24 hours.

RESULTS

The percentage of patients with a rise in serum sodium ≥ 5 mmol/L within 4 hours was 32% and 52% after a bolus of 100 and 250 ml, respectively (P=0.018). Overcorrection of serum sodium was observed after a median of 13 hours (range 9 - 17 hours) in 21% of patients in both treatment groups (P=0.971). Osmotic demyelination syndrome did not occur.

CONCLUSION

Initial treatment of severe hypotonic hyponatremia is more effective with a NaCl 3% bolus of 250 ml than of 100 ml and does not increase the risk of overcorrection.

Diagnosis and Management of Hyponatremia: A Review

IMPORTANCE

Hyponatremia is the most common electrolyte disorder and it affects approximately 5% of adults and 35% of hospitalized patients. Hyponatremia is defined by a serum sodium level of less than 135 mEq/L and most commonly results from water retention. Even mild hyponatremia is associated with increased hospital stay and mortality.

OBSERVATIONS

Symptoms and signs of hyponatremia range from mild and nonspecific (such as weakness or nausea) to severe and life-threatening (such as seizures or coma). Symptom severity depends on the rapidity of development, duration, and severity of hyponatremia. Mild chronic hyponatremia is associated with cognitive impairment, gait disturbances, and increased rates of falls and fractures. In a prospective study, patients with hyponatremia more frequently reported a history of falling compared with people with normal serum sodium levels (23.8% vs 16.4%, respectively; P < .01) and had a higher rate of new fractures over a mean follow-up of 7.4 years (23.3% vs 17.3%; P < .004). Hyponatremia is a secondary cause of osteoporosis. When evaluating patients, clinicians should categorize them according to their fluid volume status (hypovolemic hyponatremia, euvolemic hyponatremia, or hypervolemic hyponatremia). For most patients, the approach to managing hyponatremia should consist of treating the underlying cause. Urea and vaptans can be effective treatments for the syndrome of inappropriate antidiuresis and hyponatremia in patients with heart failure, but have adverse effects (eg, poor palatability and gastric intolerance with urea; and overly rapid correction of hyponatremia and increased thirst with vaptans). Severely symptomatic hyponatremia (with signs of somnolence, obtundation, coma, seizures, or cardiorespiratory distress) is a medical emergency. US and European guidelines recommend treating severely symptomatic hyponatremia with bolus hypertonic saline to reverse hyponatremic encephalopathy by increasing the serum sodium level by 4 mEq/L to 6 mEq/L within 1 to 2 hours but by no more than 10 mEq/L (correction limit) within the first 24 hours. This treatment approach exceeds the correction limit in about 4.5% to 28% of people. Overly rapid correction of chronic hyponatremia may cause osmotic demyelination, a rare but severe neurological condition, which can result in parkinsonism, quadriparesis, or even death.

CONCLUSIONS AND RELEVANCE

Hyponatremia affects approximately 5% of adults and 35% of patients who are hospitalized. Most patients should be managed by treating their underlying disease and according to whether they have hypovolemic, euvolemic, or hypervolemic hyponatremia. Urea and vaptans can be effective in managing the syndrome of inappropriate antidiuresis and hyponatremia in patients with heart failure; hypertonic saline is reserved for patients with severely symptomatic hyponatremia.