Medical Speech Pathology

Curiosity, Dialogue, and Knowledge

Hyponatremia and Cognition


A picture of neurons interacting with the blood stream to gather oxygen and glucose

Amid a network of blood vessels and star-shaped support cells, neurons in the brain signal each other. The mists of color show the flow of important molecules like glucose and oxygen.

What I didn’t know about the healthcare field when I started out was far greater than I imagined at the time.  I worked hard to do well in school and felt I had a better than average start.  Embarrassingly, sometimes you don’t know how important a new term is to you until a situation occurs much later that clarifies just how important it was all along.  For me, one such term was hyponatremia.

During one of our weekly team conference meetings, one of my fellow rehab therapists, an occupational therapist, asked the doctor for a cognitive evaluation on one of the new patients at the hospital. The doctor said, “Hmmm… looks like he has a sodium level of 122.  I don’t think speech can fix that.  Let’s see how he looks after we raise his sodium level.”

Two things happened at that moment:  I felt a small amount of joy at the thought of avoiding yet another pointless evaluation with an elderly orthopedic patient, and an equally humbling feeling that maybe I should have known a little more about labs than I did.  From discussions with many SLPs out there (rigorously scientific polling mind you), there are few of us that have any real understanding of lab work.  In some ways, that’s just fine.  Medicine is multidisciplinary for a reason, and that reason is that no one discipline, or doctor for that matter, can know all there is to know about every aspect of a patient’s care, especially if that patient has complicated health problems.  In other ways, not knowing a little about lab work is a real short coming when it comes to the differential diagnosis of complex cognitive issues with the elderly.

When doing training for work at a long term acute care hospital, I was told that three things topped the list for causes of delirium (or encephalopathy if you prefer): 1. Infection 2. Medications and 3. Metabolic Dysfunction. Hyponatremia falls under number 3. So what does having too little (hypo), salt (natr), in your blood (emia) have to do with cognitive function you ask?  In short, it causes the brain to swell.  As in the comparison here:

Cerebral edema in a patient following cytoreductive surgery and hyperthermic intraoperative intraperitoneal chemoperfusion.

Coronal section demonstrating normal grey and white matter with marked loss of luminal dimension in the ventricular system due to diffuse cortical edema.World Journal of Surgical Oncology 2006, 4:85 doi:10.1186/1477-7819-4-85

Coronal view without edema. Retrieved from the University of British Columbia- Anatomy of the Brain. Click on the image to redirect to their wonderful site.

Here’s a more full definition of hyponatremia (http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001431/):

Hyponatremia is a metabolic condition in which there is not enough sodium (salt) in the body fluids outside the cells. Sodium is found mostly in the body fluids outside the cells. It is very important for maintaining blood pressure. Sodium is also needed for nerves and muscles to work properly. When the amount of sodium in fluids outside cells drops, water moves into the cells to balance the levels. This causes the cells to swell with too much water. Although most cells can handle this swelling, brain cells cannot, because the skull bones confine them. Brain swelling causes most of the symptoms of hyponatremia.

Here’s a diagram demonstrating the relationship between sodium and potassium at the cellular level:

sodium-potassium_pump

diagram by Mariana Ruiz Villarreal retrieved from wikimedia.org

To flesh it out more fully, let’s think about the neuron.  The neuron’s communication system (action potentials) is mediated by a change in polarization and chemical interactions between Potassium (K+) and Sodium (Na+).  {See http://neuroscience.uth.tmc.edu/s1/chapter02.html for more in depth coverage of action potentials if you need the review like I did.}  Hyponatremia has a deleterious effect on action potentials by blocking the normal cycle from taking place.  If there isn’t enough sodium on the outside of the neuron to “reset” the action potential, then it cannot fire.  If it cannot fire, it does not communicate.  Couple this with all of that edema we saw illustrated above, and you have a terrible situation for cognitive function.

Another important note about this chemical imbalance is that if it happens quickly the effects are much more dramatic than if they happen very slowly.  Also note that sodium levels are slow to change normally and that means getting back to a healthy level may take some time.  Speak with your doctor about this condition for more information if you, your patient, or your loved one is suffering from it.

For more information on this subject and how it negatively effects more than just neurons, check out the links below:

http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001431/

http://en.wikipedia.org/wiki/Hyponatremia

http://www.mayoclinic.com/health/hyponatremia/DS00974

http://emedicine.medscape.com/article/242166-overview

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7 comments on “Hyponatremia and Cognition

  1. Lisa
    August 22, 2012

    Thank you for this informative article! Do you have any good resources for us SLPs who need a better understanding of labs? We have been trying to get more info and an inservice on this at my hospital.

    • Admin
      August 22, 2012

      Hello Lisa.

      I wish I had a great reference to point you to, but I don’t have one. This is one of the areas where I feel I was least prepared when I entered the work force, and I still am largely ignorant of what particular labs mean. Most of my knowledge comes from interactions between co-workers that do have training in lab results (nurses, doctors, registered dietitians, etc.) I hope to continue to find more answers, but I’ve not seen anything that is comprehensive and really aimed at the medical SLP. If I find anything, I’ll post about it. If you or other readers find anything, please send me the title/author. Thanks for commenting!

  2. Martha Carbone
    August 28, 2012

    Not sure if this link will work but the topic was in the Dec 2008 Perspectives for SID 13

    http://div13perspectives.asha.org/content/17/4/128.full.pdf+html

    • Admin
      August 29, 2012

      Awesome link! Thanks.

  3. Mo Jeffrey
    September 13, 2012

    I’ve recently become interested in this topic and have taken out a book from my library:
    Mosby’s Manual of Diagnostic and Laboratory Tests -Fourth Edition-
    by Kathleen Deska Pagana PhD RN, and Timothy J. Pagana MD FACS
    The book lists normal findings, indications, a test explanation, procedures, requirements, and related tests for just about every kind of study and chemical you can think of in the body. It’s a nursing book, but so far I have found it to be very helpful! I think amazon has it listed for something like $41, but you can probably get it used for cheaper. As an added bonus, if you’re working with someone who would benefit from evaluating their own lab values, then you can use it as a therapy tool for cognitive purposes :)

    • Admin
      September 13, 2012

      Fantastic! Thanks for the nice reference; I’ll check it out as soon as I have time and funds!

  4. Admin
    September 29, 2012

    Somewhat related to this post on hypnatremia, is the new series on lab values from khan academy… man I love this site! Here’s the link: http://www.khanacademy.org/science/healthcare-and-medicine/lab-values/v/introduction-to-lab-values-and-normal-ranges

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