Which type of fluid is best? Ringer’s lactate has a sodium concentration of 128 mmol/L, which is more isotonic to the hyponatremic patient. Administering Ringer’s lactate will likely result in a slower rise in serum sodium than normal saline and therefore have a lower risk of causing ODS. I therefore recommend Ringer’s lactate as the fluid of choice for resuscitation of the hypovolemic/hyponatremic patient.

For hyponatremic patients deemed to be hypervolemic, management includes sodium restriction, free water restriction, and diuretics.

Euvolemic patients with hyponatremia do not require any particular treatment to defend intravascular volume, and management should concentrate on preventing worsening hyponatremia. The syndrome of inappropriate antidiuretic hormone (ADH) secretion (SIADH) is hyponatremia and hypo-osmolality secondary to secretion of ADH despite normal or increased plasma volume. This results in impaired water excretion. It is important to understand that SIADH is a result of an excess of water rather than a deficiency of sodium. SIADH is usually caused by a medication, cancer, respiratory illness, or central nervous system illness.

3. Prevent worsening hyponatremia. After restoring adequate circulating volume, the goal is to prevent further exacerbation of the hyponatremia by strict fluid restriction and an IV saline lock. It is vital to communicate this to the patient’s family and health care team. Water can literally kill the patient!

4. Prevent rapid overcorrection: the rule of 100s. It is important to understand that the fluid itself that is given to the hyponatremic patient is not the cause of a rapid increase in the serum sodium but rather the free water diuresis that results shortly afterwards. Thus, monitoring the urine output is key in preventing overcorrection and possible complications. To prevent rapid overcorrection:

1. Insert a urinary catheter and monitor ins and outs.
2. If urine output >100 cc/hour, send a STAT urine osmolarity and sodium.
3. If urine osmolarity <100, consider 1 mg desmopressin (DDAVP) IV.
4. Continue following steps 2–4 as per urine output.

Correcting Hyponatremia: the Rule of 6s

“Six in six hours for severe symptoms, then stop. Six a day makes sense for safety.”

If you need to rapidly increase serum sodium due to a neurological emergency, do not correct more than 6 mmol. Do not exceed an increase of sodium of more than 6 mmol/day. While different sources will cite different ranges, targeting six is a conservative approach.

Ascertain the Cause of Hyponatremia

• Assess the chief complaint: Search for conditions that can increase output or decrease intake such as vomiting and diarrhea, pain, or altered level of awareness.
• Review the medication list: Search for those that cause SIADH, especially thiazide diuretics and selective serotonin reuptake inhibitors. Patients who have been on chronic steroids may have adrenal insufficiency as a cause for their hyponatremia.
• Evaluate the past medical history: Look for a history of end organ failure (congestive heart failure, liver failure, or renal failure) or cancers (a common cause of SIADH).
• Evaluate the lab work: Assess the glucose (hyperglycemia), potassium (hyperkalemia may suggest adrenal insufficiency), and thyroid-stimulating hormone (hypothyroidism).

Next time a weak and dizzy older person presents to your emergency department with a serum sodium concentration in the boots, simply follow this algorithm (see Figure 1) so that your patient will make a smooth recovery and you won’t be asked by the admitting physician a week later, “Do you remember that hyponatremic patient you saw the other day?”