Hypovolemic Hypotonic Hyponatremia

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, gastroenteritis 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.