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Hypovolemic Hypotonic Hyponatremia

by Amy Sussman, MD

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    00:01 So let's start with our patient who has hypovolemic hypotonic hyponatremia.

    00:06 That means that patient either has true volume depletion, because they have a low extracellular fluid volume, and that could be loss of fluid volume, or sodium from the ECF volume due to a variety of different regions.

    00:20 When that happens, ADH is stimulated from a nonosmotic mechanism.

    00:24 Remember, if we lose about 10% of our body volume, ADH will be stimulated in order to conserve our vascular volume.

    00:31 In so doing, it's going to retain free water in efforts to restore that ECF back to the appropriate volume.

    00:39 Physical exam will be very important in this population because we should see signs of volume depletion.

    00:45 The patient may be hypotensive, tachycardic, they'll have flat neck veins, or they might be orthostatic.

    00:54 When we think about some of the causes that cause true hypotonic hypovolemic hyponatremia, these are things like GI losses, gastro neuritis that causes stool losses or gastric losses.

    01:06 Again, with those losses you lose a lot of sodium and patient becomes hypovolemic.

    01:12 Blood losses, increase insensible losses, that means excessive sweating and burns.

    01:19 And all of these situations our urine sodium is going to be low less than 20 mEq/L, because we will have maximal reabsorption of sodium in that proximal and distal tubule.

    01:30 Why? Because RAAS is activated in these low volume states.

    01:36 We can also see this in renal sodium losses.

    01:39 So in patients who, for example, around diuretics, who become volume depleted.

    01:43 Adrenal insufficiency, where they have difficulty with sodium reabsorption at that principal cell or salt-wasting nephropathies, things like Bartter's and Gitelman's.

    01:52 In this situation, our patient will have a higher in sodium.

    01:56 But again, the ADH is activated because of their volume depletion.


    About the Lecture

    The lecture Hypovolemic Hypotonic Hyponatremia by Amy Sussman, MD is from the course Water Balance: Hypo- and Hypernatremia.


    Included Quiz Questions

    1. Adrenal insufficiency
    2. Burns
    3. Acute gastroenteritis with diarrhea
    4. Excessive sweating
    5. Blood loss

    Author of lecture Hypovolemic Hypotonic Hyponatremia

     Amy Sussman, MD

    Amy Sussman, MD


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