Point-of-care ultrasound to evaluate volume status in severe hyponatremia

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.

Point-of-care ultrasound is a useful adjunct tool to a clinician's assessment in the evaluation of severe hyponatraemia

INTRODUCTION

Hyponatraemia is the most common electrolyte disorder in inpatients resulting mainly from an imbalance in water homeostasis. Intravascular fluid status assessment is pivotal but is often challenging given multimorbidity, polypharmacy and diuretics use. We evaluated the utility of point-of-care ultrasound (POCUS) as an adjunct tool to standard practice for fluid assessment in severe hyponatraemia patients.

METHODS

Patients presenting with severe hyponatremia (Serum Sodium [Na] < 120 mmol/L; Normal range: 135-145 mol/L), managed by standard care were included. Hyponatraemia biochemistry work-up and POCUS examination were undertaken. Both clinician and POCUS independently assigned one of the three fluid status groups of hypovolaemia, hypervolaemia or euvolaemia. The final diagnosis of three fluid status groups at admission was made at the time of discharge by retrospective case review. Clinician's (standard of care) and POCUS fluid assessments were compared to that of the final diagnosis at the time of discharge.

RESULTS

n = 19 patients were included. Median Na on admission was 113 mmol/L (109-116), improved to 129 ± 3 mmol/L on discharge. POCUS showed the higher degree of agreement with the final diagnosis (84%; n = 16/19), followed by the clinician (63%; n = 12/19). A trend towards higher accuracy of POCUS compared to clinician assessment of fluid status was noted (84% vs. 63%, p = 0.1611). Biochemistry was unreliable in 58% (n = 11/19) likely due to renal failure, polypharmacy or diuretic use. Inappropriate emergency fluid management was undertaken in 37% (n = 7/19) of cases based on initial clinician assessment. Thirst symptom correlated to hypovolaemia in 80% (4/5) cases.

CONCLUSION

As subjective clinical and biochemistry assessments of fluid status are often unreliable due to co-morbidities and concurrent use of medications, POCUS can be a rapid objective diagnostic tool to assess fluid status in patients with severe hyponatraemia, to guide accurate emergency fluid management.

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.

Precision medicine: "Point of Care Ultrasound" (PoCUS) in the diagnostic approach to the patient with hyponatremia

Hyponatremia is a multifactorial disorder defined as a decrease in plasma sodium concentration. Its differential diagnosis requires an adequate evaluation of the extracellular volume (ECV). However, ECV determination, simply based on the clinical history, vital signs, physical examination, and laboratory findings can leads to misdiagnosis and inappropriate treatment. The use of Point-of-Care Ultrasound (POCUS), through the combination of Lung Ultrasound (LUS), Venous Excess UltraSound (VExUS) and Focused Cardiac Ultrasound (FoCUS), allows a much more accurate holistic assessment of the patient's ECV status in combination with the other parameters.

[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.

The Role of Ultrasonographic Inferior Vena Cava Measurement in the Volume-Based Classification of Patients With Hyponatremia

OBJECTIVES

To demonstrate the role of inferior vena cava (IVC) collapsibility in the assessment of volume status in hyponatremic critically ill patients in the emergency department (ED) with bedside IVC imaging and to predict volume status with response to fluid therapy.

METHODS

A prospective 110 hypotonic hyponatremic patients aged >18 years with a serum sodium level under 125 mEq/L and at least one symptom of hyponatremia, who presented or referred to the ED was conducted. Demographical, clinical, and laboratory characteristics with bedside measurement of IVC diameter of patients were recorded. Volume status was divided into 3 subgroups: hypovolemic-G1, euvolemic-G2, and hypervolemic-G3. An ED trainee with a certification to perform basic and advanced ultrasonography (USG) training carried out the USG examinations. A diagnostic algorithm approach was made according to the results.

RESULTS

Symptom severity was significantly greater in the hypervolemic group than the other groups (P = .009 and P = .034, respectively). Systolic blood pressure (SBP) and mean arterial pressure (MAP) were significantly lower in the hypovolemic group compared with the other groups (P < .001 and P = .003, respectively). There was a significant difference between the ultrasonographically measured IVC min, IVC max, and mean IVC values across the three volume-based groups (P < .001).

CONCLUSION

Considering the diversity of physical examination (PE) findings, with the highly heterogenous nature of hyponatremia, a new measurable algorithm can be developed on the basis of contemporary hyponatremic patient management guidelines.

Demystifying hyponatremia: A clinical guide to evaluation and management

Hyponatremia (serum sodium <135 mEq/L) is a frequent electrolyte abnormality complicating the clinical care of hospitalized patients. Hyponatremia has been associated with an increased risk of mortality. Hyponatremia can be seen in patients with euvolemia, hypovolemia, or hypervolemia. Evaluation of hyponatremia relies on clinical assessment and estimation of serum sodium, urine electrolytes, and serum and urine osmolality in addition to other case-specific laboratory parameters. In addition, point-of-care ultrasonography is an important adjunct to physical assessment in estimation of volume status. Understanding the pathophysiology of the underlying process can lead to a timely diagnosis and appropriate management of hyponatremia.

Use of Venous Excess UltraSound (VExUS) score in hyponatraemia management in critically ill patient

Hyponatraemia is the most prevalent electrolyte disorder in the neurocritical care setting and is associated with a significant morbimortality. Cerebral salt wasting and inappropriate antidiuretic hormone secretion syndrome have been classically described as the two most frequent entities responsible for hyponatraemia in neurocritical care patients. An accurate aetiological diagnosis of hypotonic hyponatraemia requires a proper volume status assessment. Nevertheless, determination of volume status based on physical examination, laboratory findings and imaging modalities have several limitations and can lead to improperly diagnosis and hyponatraemia mismanagement. Point-of-care ultrasound (POCUS), specifically Venous Excess UltraSound (VExUS) score, is a fast and valuable tool to evaluate venous congestion at the bedside and identify hypervolaemia, helping the physicians in therapeutic decision making in a patient with hyponatraemia. We report a case where the use of POCUS, and more specifically VExUS, can be helpful in volume status assessment, complementing the complex management of multifactorial hyponatraemia in a neurocritical patient.