Hyponatremia: New Insights into Risks, Prevention, and Treatment
Hyponatremia is the most common electrolyte abnormality in both children and adults. New research has begun to challenge some traditionally held views regarding this common condition. It is generally accepted that hospital-acquired hyponatremia affects approximately 25% of hospitalized patients.1-2
New research, primarily done in children, reveals that hospital-acquired hyponatremia is largely preventable.2 Hospital-acquired hyponatremia occurs as a consequence of administering hypotonic intravenous fluids and can be prevented by administering 0.9% sodium chloride (NaCl) when indicated.3-5
Another generally accepted view is that mild hyponatremia, serum sodium 125-135 mEq/L, is a relatively benign condition.6 There is now mounting evidence that mild hyponatremia is an independent predictor of mortality in adults7 and is an independent risk factor for falls and fractures in the elderly.8-9 There has been a long-standing controversy about the optimal treatment of symptomatic hyponatremia.
There is finally consensus on this topic, with experts now agreeing that the optimal treatment is the administration of 100 cc boluses of 3% sodium chloride, repeated as needed until neurologic symptoms improve.10-11 This rapid partial correction of hyponatremia effectively treats the condition and minimizes the risk of overcorrection.
Finally, there is a new class of medications, vasopressin 2 antagonists or vaptans, which are indicated for the treatment of euvolemic and hypervolemic asymptomatic hyponatremia.12 Below we will discuss these new advances and elaborate on how these changes can be immediately applied to clinical practice.
Hospital-acquired hyponatremia: A largely preventable condition
A long-standing practice in both children and adults dating back to the 1950's has been to administer hypotonic maintenance fluids.13-14 The basis for this is largely that it reflects normal dietary sodium consumption. The problem with this approach is that virtually all hospitalized patients are at risk for the development of hyponatremia due to numerous non-osmotic stimuli for arginine vasopressin (AVP) production that results in an inability to excrete free water.
Potential stimuli for AVP production in hospitalized patients include pain, stress, nausea, vomiting, volume depletion, and disease states associated with AVP excess, such as the post-operative state, pulmonary or central nervous system diseases, and malignancies.3 The administration of hypotonic fluids to patients with these potential stimuli for AVP production will predictably result in hyponatremia.
Recent studies have revealed that more than 75% of children and more than 50% of adults receive hypotonic intravenous fluids, which result in an associated incidence of hyponatremia of about 25%.15-16 The administration of hypotonic fluids has been associated with numerous deaths or permanent neurological injury from hyponatremic encephalopathy in otherwise healthy children and adults.2, 17-19
In 2003, we drew attention to this dangerous practice in children and posited that the most physiologic approach for the prevention of hospital-acquired hyponatremia would be to administer isotonic maintenance fluids (0.9% NaCl, Na 154 mEq/L), reserving hypotonic maintenance fluids for patients with either ongoing renal or extrarenal free water losses or hypernatremia.3
This concept caused great controversy in the pediatric community as hypotonic fluids were almost exclusively used and were an ingrained part of practice.20 Since that time there have been 22 studies—five retrospective and 17 prospective—in more than 2,000 hospitalized children evaluating this issue.2, 5, 21
All of these studies have confirmed that hypotonic fluids produce hyponatremia and that isotonic fluids prevent it, with the associated incidence of acute hyponatremia (Na less than 135 for 24-48 hours) being almost 30% with hypotonic fluids and less than 5% for isotonic fluids.
At this point, there remains little question that hypotonic fluids should be avoided in the vast majority of hospitalized patients and that 0.9% NaCl is the preferred maintenance intravenous fluid when needed. This simple change in practice would greatly reduce the incidence of hospital-acquired hyponatremia, virtually eliminate acute hospital-acquired hyponatremic encephalopathy, and translate into many saved lives in both children and adults.