In this episode I will discuss the management of hyponatremia:
I am excited to announce that I now have a 6-hour program with ACPE continuing education credits on the subject of Inpatient Emergency Response Training for Pharmacists. This program provides comprehensive training on the role of a pharmacist at inpatient medical emergencies.
Pharmacists who complete this program will develop the confidence and skills necessary to respond to code blue and rapid response calls. Attendees will also be better prepared to successfully pass the healthcare provider ACLS class. The program covers emergency response, highlights of the BLS/ACLS guidelines, ECG recognition, patient assessment, airway pharmacology, and the care of patients with septic shock. To find out more go to pharmacyjoe.com/codebluetraining.
Hyponatremia
Hyponatremia is a common finding in ICU patients. It can be caused by either too much total body water, or not enough total body sodium. Hyponatremia (serum sodium level less than 135 mEq/L) can be found in as many as 1 out of every 6 patients in the ICU. Severe hyponatremia (serum sodium level less than 125 mEq/L) can be found in as many as 1 out of every 10 patients in the ICU.
Severe, symptomatic hyponatremia
The first decision point when deciding on a course of treatment for a patient in the ICU with hyponatremia is to determine whether they have severe, symptomatic hyponatremia.
Mild hyponatremia may be asymptomatic or is associated with symptoms such as headache, lethargy, and dizziness. Severe, symptomatic hyponatremia is characterized by a serum sodium < 125 mEq/L and symptoms such as seizure, mental status changes, respiratory depression, coma or obtundation.
Without immediate treatment, severe, symptomatic hyponatremia can lead to cerebral edema, respiratory failure, permanent brain injury, or death. Such symptoms are generally seen when the hyponatremia develops acutely rather than chronically.
When a patient has severe, symptomatic hyponatremia, it should be promptly treated with hypertonic 3% saline. The simplest method is to give a 100 mL IV bolus of 3% saline, repeated up to 2 more times until symptoms resolve. Once symptoms resolve, it is important to determine what the cause of hyponatremia is before selecting the next course of treatment.
Determining the cause
The first decision point to determine the cause of hyponatremia is to check the serum osmolality. A normal serum osmolality is 280 to 285 mOsm.
If the serum osmolality is normal or high, there is something in the patient’s blood that is causing an osmotic shift of water into the extracellular space. This osmotic shift causes a dilutional hyponatremia due to the increased water in the blood. Excessive protein, lipid, glucose, mannitol, sorbitol, or contrast media are all potential causes of this dilutional hyponatremia.
If the serum osmolality is low, the next step is to evaluate the patient’s volume status.
If the patient is hypovolemic, the treatment is generally to give sodium in the form of IV normal saline or salt tablets. Diuretic use, Addison’s disease, and vomiting or diarrhea are common causes of this type of hyponatremia.
If the patient is hypervolemic, the treatment is fluid restriction with either diuresis or dialysis. Heart failure, cirrhosis, and renal failure are common causes of this type of hyponatremia. Because these patients have normal total body sodium and excessive total body water, they cannot be treated successfully with treatments that add saline such as IV fluids or salt tablets.
If the patient is euvolemic, they should be treated with fluid restriction. To further narrow down the cause of hyponatremia in an euvolemic patient, the urine osmolality should be checked. If the urine osmolality is high, the patient likely has SIADH or Addison’s Disease. If the urine osmolality is low, the patient likely has polydipsia or low solute intake such as found in “beer potomania.”
Rate of correction
Regardless of the type of hyponatremia, care should be made to not correct the serum sodium too quickly. An increase of 9 mEq in the first 24 hours and 18 mEq in the first 48 hours is safe, but more aggressive correction can lead to osmotic demyelination and permanent brain damage.
Several previous episodes deal with various aspects of the treatment of hyponatremia:
To learn why giving normal saline to a patient with SIADH causes the sodium to drop lower, go to episode 32.
To learn how to re-lower the serum sodium if you correct it too quickly, go to episode 173.
To learn about the effectiveness of the vaptans in neurocritical patients, go to episode 175.
If you like this post, check out my book – A Pharmacist’s Guide to Inpatient Medical Emergencies: How to respond to code blue, rapid response calls, and other medical emergencies.
Leave a Reply