How do you manage a patient with hyponatremia, low urine sodium (<20), and third spacing, with a urine osmolality of 178?

From the Guidelines

The management of a patient with hyponatremia, low urine sodium (<20), and third spacing with a urine osmolality of 178 should prioritize fluid restriction, addressing the underlying cause, and cautious use of vaptans or albumin infusion as needed, with a focus on correcting serum sodium levels at a rate not exceeding 8 mEq/L in 24 hours to avoid osmotic demyelination syndrome, as recommended by the most recent guidelines 1.

Key Considerations

• The patient's presentation suggests hypovolemic hyponatremia with appropriate ADH release due to volume depletion.
• Begin with isotonic fluid resuscitation using 0.9% normal saline at a rate of 100-125 mL/hour to restore intravascular volume.
• The low urine sodium indicates sodium retention by the kidneys in response to decreased effective circulating volume, while the low urine osmolality (178) suggests the kidneys are attempting to excrete free water but are limited by overall volume depletion.

Monitoring and Treatment

• Monitor serum sodium every 4-6 hours initially, aiming for correction rates not exceeding 8 mEq/L in 24 hours to avoid osmotic demyelination syndrome.
• Once the patient is hemodynamically stable, identify and treat the underlying cause of third spacing, which may include conditions like cirrhosis, nephrotic syndrome, heart failure, or severe hypoalbuminemia.
• Albumin infusion (25%, 50-100 mL) may be beneficial if hypoalbuminemia is present, as it appears to improve serum sodium concentration, although more information is needed 1.
• Avoid hypotonic fluids and medications that impair free water excretion.
• Diuretics may be needed once intravascular volume is restored to mobilize third-spaced fluid, but should be used cautiously with close electrolyte monitoring.

Use of Vaptans

• Vaptans, such as tolvaptan, can be considered for short-term use (≤30 days) in patients with severe hyponatremia, as they have been shown to improve serum sodium concentration in conditions associated with high vasopressin levels, including cirrhosis 1.
• However, their use should be cautious, and patients should be closely monitored for potential side effects, such as thirst, dehydration, and renal impairment.

From the FDA Drug Label

Tolvaptan tablets are contraindicated in the following conditions: • Patients with autosomal dominant polycystic kidney disease (ADPKD) outside of FDA-approved REMS [see Warnings and Precautions ( 5.2)] • Unable to sense or respond to thirst • Hypovolemic hyponatremia • Taking strong CYP3A inhibitors [see Warnings and Precautions ( 5.5)] • Anuria • Hypersensitivity (e.g., anaphylactic shock, rash generalized) to tolvaptan or any components of the product [see Adverse Reactions ( 6)]

The patient has hyponatremia and is third spacing, which suggests hypervolemic hyponatremia. The urine sodium is less than 20, which is consistent with this diagnosis.

• Key consideration: Tolvaptan is indicated for the treatment of clinically significant hypervolemic and euvolemic hyponatremia.
• Important warning: Tolvaptan is contraindicated in hypovolemic hyponatremia. Given that the patient is third spacing, which is a form of hypervolemia, tolvaptan may be considered as a treatment option for hyponatremia in this patient, as long as the patient is closely monitored in a hospital setting due to the risk of too rapid correction of serum sodium 2. However, the presence of third spacing may affect the patient's volume status and require careful management to avoid overly rapid correction of hyponatremia. It is crucial to monitor serum sodium concentrations and neurologic status, especially during initiation and after titration of tolvaptan, to minimize the risk of osmotic demyelination syndrome 2. The dosage should be adjusted according to the patient's response, with a starting dose of 15 mg once daily and titration as needed to achieve the desired level of serum sodium, up to a maximum of 60 mg once daily 2.

From the Research

Management of Hyponatremia with Third Spacing

The management of a patient with hyponatremia, low urine sodium (<20), and third spacing, with a urine osmolality of 178, requires a careful approach.

• The patient's hyponatremia is likely due to a combination of factors, including elevated levels of arginine vasopressin (AVP) hormone and third spacing, which can lead to a decrease in serum sodium concentration 3.
• The low urine sodium (<20) suggests that the patient is likely hypovolemic, as the kidneys are trying to conserve sodium and water 4.
• The urine osmolality of 178 is lower than expected for a patient with hypovolemic hyponatremia, which may indicate that the patient has a degree of renal impairment or that the hyponatremia is due to a combination of factors 5.

Treatment Approach

• The treatment approach for this patient should focus on correcting the hyponatremia while also addressing the underlying causes of third spacing and hypovolemia.
• Fluid restriction and loop diuretics may be used to treat volume overload, but care must be taken to avoid overcorrection, which can lead to osmotic demyelination syndrome 3, 4.
• Vasopressin receptor antagonists may be considered to increase renal free water excretion and correct hyponatremia, but their use should be guided by the patient's volume status and renal function 5, 6.
• Hypertonic saline may be used to correct severe symptomatic hyponatremia, but the rate of correction should be carefully controlled to avoid overcorrection 3, 7.

Monitoring and Adjustments

• The patient's serum sodium concentration, urine osmolality, and urine sodium concentration should be closely monitored to guide treatment adjustments.
• The patient's volume status and renal function should also be closely monitored, as these can impact the treatment approach and the risk of complications 4, 6.
• Adjustments to the treatment plan should be made as needed to ensure that the patient's hyponatremia is corrected safely and effectively, while also addressing the underlying causes of third spacing and hypovolemia 3, 5, 7.