From the Guidelines
In heart failure-associated hyponatremia, plasma osmolality is typically normal or slightly decreased, usually ranging between 275-285 mOsm/kg, as evidenced by recent guidelines 1. This represents a dilutional hyponatremia caused by increased antidiuretic hormone (ADH) secretion and water retention. The pathophysiology involves decreased cardiac output leading to baroreceptor activation, which stimulates ADH release despite the lower serum sodium. Additionally, activation of the renin-angiotensin-aldosterone system promotes sodium and water retention, with water retention exceeding sodium retention.
Key Findings
- The 2022 AHA/ACC/HFSA guideline for the management of heart failure highlights the importance of addressing hyponatremia in heart failure patients, as it is associated with poor clinical and patient-reported outcomes 1.
- Treatment of hyponatremia in heart failure focuses on addressing the underlying heart failure with diuretics, ACE inhibitors, and fluid restriction.
- The use of vasopressin antagonists, such as tolvaptan, may be considered in the short term to improve serum sodium concentration in hypervolemic, hyponatremic states, as recommended in the 2013 ACCF/AHA guideline for the management of heart failure 1.
Treatment Approach
- Addressing the underlying heart failure with diuretics like furosemide (20-80 mg daily) and ACE inhibitors such as lisinopril (5-40 mg daily) is crucial in managing heart failure-associated hyponatremia.
- Fluid restriction (typically 1-1.5 L/day) is also an important aspect of treatment, although its effectiveness in improving clinical outcomes is limited, as noted in the 2022 AHA/ACC/HFSA guideline 1.
- In severe cases (sodium <125 mEq/L with neurological symptoms), careful administration of hypertonic saline may be necessary, but correction should not exceed 8 mEq/L in 24 hours to avoid osmotic demyelination syndrome.
From the Research
Plasma Osmolality Findings in Hyponatremia Associated with Heart Failure
- Hyponatremia in heart failure is often characterized by low plasma osmolality, indicating a dilutional effect on serum sodium concentrations 2, 3.
- The low plasma osmolality is typically caused by excess water retention, leading to dilutional hyponatremia, which is the most common form of hyponatremia in heart failure patients 3.
- Measurement of plasma osmolality can be a useful aid in differentiating between euvolemia and hypovolemia in patients with hyponatremia, and can help guide treatment decisions 4.
- In patients with heart failure, hyponatremia with low plasma osmolality is often associated with increased activity of arginine vasopressin (AVP), which increases free-water reabsorption in the renal collecting ducts, further diluting plasma sodium concentrations 5, 3.
- The urinary sodium concentration can also provide valuable information in diagnosing patients with low plasma osmolality, with high urinary sodium concentrations indicating renal disorders or other underlying conditions 4.