From the Guidelines
Postoperative hyponatremia should be managed based on the severity, onset speed, and symptoms, with careful monitoring and addressing underlying causes, and the goal of raising sodium by 4-6 mEq/L in the first 24 hours to relieve symptoms while avoiding correction faster than 8-10 mEq/L/day to prevent osmotic demyelination syndrome, as recommended by the most recent guidelines 1.
Causes of Postoperative Hyponatremia
- Excessive hypotonic fluid administration
- SIADH (syndrome of inappropriate antidiuretic hormone secretion)
- Diuretic use
- Stress response to surgery
Management of Postoperative Hyponatremia
- For mild asymptomatic hyponatremia (130-135 mEq/L), careful monitoring and addressing underlying causes may be sufficient
- For moderate hyponatremia (125-130 mEq/L), fluid restriction to 800-1000 mL/day is often recommended
- In symptomatic or severe cases (<125 mEq/L), 3% hypertonic saline may be administered at 1-2 mL/kg/hr initially
- Regular monitoring of serum sodium levels every 4-6 hours during correction is essential, along with tracking fluid intake/output and daily weights
- Discontinuing medications that may contribute to hyponatremia, such as certain antidepressants, anticonvulsants, or diuretics, should be considered when possible
Key Considerations
- Avoiding overcorrection of hyponatremia to prevent osmotic demyelination syndrome
- Using vasopressin receptor antagonists (vaptans) in certain cases, such as hypervolemic hyponatremia
- Considering the use of albumin infusion to improve serum sodium concentration
- Being aware of the potential risks and benefits of different treatment strategies, as outlined in recent studies 1
From the FDA Drug Label
The primary endpoint for these studies was the average daily AUC for change in serum sodium from baseline to Day 4 and baseline to Day 30 in patients with a serum sodium less than 135 mEq/L. Symptomatic patients, patients likely to require saline therapy during the course of therapy, patients with acute and transient hyponatremia associated with head trauma or postoperative state and patients with hyponatremia due to primary polydipsia, uncontrolled adrenal insufficiency or uncontrolled hypothyroidism were excluded Signs of postoperative salt intolerance include cellular dehydration, weakness, disorientation, anorexia, nausea, distention, deep respiration, oliguria and increased blood urea nitrogen.
The causes of postoperative hyponatremia are not directly stated in the provided drug labels, but exclusion criteria for the study of tolvaptan include patients with acute and transient hyponatremia associated with head trauma or postoperative state 2. The management of postoperative hyponatremia is not directly addressed in the provided drug labels, but sodium chloride (IV) label mentions that parenteral administration of quantities of sodium can result in adverse effects, particularly in patients with impaired renal or cardiac function 3. Tolvaptan has been shown to increase serum sodium levels in patients with euvolemic or hypervolemic hyponatremia, but its use in postoperative hyponatremia is not directly mentioned in the label 2.
- Key points to consider in management:
- Avoid overly rapid correction of serum sodium
- Fluid restriction may be necessary in some cases
- Monitor for signs of salt intolerance, such as cellular dehydration and weakness
From the Research
Causes of Postoperative Hyponatremia
- Hyponatremia is a common and potentially dangerous complication of transsphenoidal surgery 4
- The syndrome of inappropriate antidiuretic hormone secretion (SIADH) is the most frequent cause of hyponatremia in a hospital setting 5
- Hyponatremia can be caused by a variety of disorders and pathomechanisms, mostly related to malignancy, pulmonary, or neurologic disorders 6
- Nonosmotic release of arginine vasopressin (AVP) can lead to water retention and hyponatremia 7
Management of Postoperative Hyponatremia
- Prophylactic postoperative fluid restriction has been trialled as a method to reduce the incidence of postoperative hyponatremia 4
- Fluid restriction is commonly between 1000 and 1500 ml/day and limited to the first postoperative week 4
- The use of 3% hypertonic saline solution is proposed for acute correction of hyponatremia posing as a medical emergency 5
- Algorithm-based approaches have been developed for the therapy of SIADH-induced hyponatremia, including fluid restriction, solute, furosemide, and tolvaptan 5
- Vasopressin receptor-2 (VR2) antagonists, such as vaptans, have been shown to be efficacious in the treatment of SIADH 6
- Fluid restriction is widely endorsed as the first-line treatment for SIAD, but second-line therapy options are controversial 7