Changes in Body Fluid Compartment

00:01 Now that we have the ability to do a lot of the measurements, let's go through some body fluid compartment changes.

00:10 These body fluid compartments can be broken up in a very simplistic manner into 2 boxes.

00:16 We are going to use the ECF as the extracellular fluid compartment and that's about 14 liters for a 70-kg male.

00:26 The intracellular fluid compartment is a larger box.

00:30 It has about 28 liters if we think about this from the 70-kg male.

00:34 Osmolality will go from 0 to 285, and 285 is the osmolality of blood, typically.

00:43 So having this box in place, let's go through a number of clinical examples of various changes in body water.

00:53 We are going to call a contraction a decrease in body water and an expansion as an increase in total body water.

01:03 So our first one is a hypo-osmotic volume expansion.

01:08 So let's walk through what this means.

01:11 Volume expansion means that you're going to increase the volume, which means the X axis [denotions] will be larger.

01:20 If it is hypo-osmotic, you will now move osmolality down.

01:26 This particular case of a hypo-osmotic volume expansion can be done by drinking excess water.

01:36 It will normally not change arterial pressure too much because the body is very good about getting rid of it.

01:43 But if you are able to measure blood pressure, very transiently you would see a very small increase.

01:49 And then we go back to normal.

01:53 Sodium levels would go down.

01:56 And the reason why sodium levels go down is because we're measuring it as a concentration.

02:01 So simply you're diluting the sodium that you do have.

02:06 So you haven't lost any sodium, but now you have more volume that you are dissolving it in.

02:13 Total protein levels also go down for the same reason.

02:17 You haven't changed the number of proteins, but now you've changed the volume so they are less concentrated.

02:24 This one is a little bit tricky, but hematocrit doesn't change very much.

02:29 You don't change the number of red blood cells.

02:32 You think that similar to total proteins that they should go down, right? Because red blood cell number should decrease, just like the concentration should decrease, just like the total proteins are.

02:46 The reason why hematocrit is not observed as decreasing is because you're causing those cells to swell.

02:54 So when you're making a hematocrit measurement, you're measuring the same number of red blood cells, but now these red blood cells are bigger, and therefore count for more percent.

03:04 So you mask any decrease.

03:09 The endocrine response to hypo-osmotic volume expansion is a decrease in aldosterone, and a decrease in arginine vasopressin antidiuretic hormone.

03:21 The goal in this case would be to lose water so that you will become more euvolemic again.

03:30 Our next condition is a hypo-osmotic volume contraction.

03:35 So contractions are going to be a decrease in the total body water.

03:41 Hypo-osmotic means that you've also lost now the osmolality.

03:46 What happens to this if we would measure the blood parameters? Blood pressure decreases because you've lost volume.

03:55 Sodium concentration also decreases.

03:59 Total protein levels increase, and the reason why total protein levels increase is because you haven't changed the number of proteins.

04:08 You've just lost more fluid than you have protein.

04:12 Hematocrit also increase.

04:15 The endocrine response to this type of hypo-osmotic volume contraction is an increase in aldosterone.

04:23 So if you increase aldosterone, then that goal will try to be to increase sodium levels.

04:30 And there really is no large change for antidiuretic hormone arginine vasopressin.

04:37 So sometimes you can observe a small decrease but more likely is that there's no change.

04:48 Now, let's look at some iso-osmotic volume changes.

04:52 The first is an iso-osmotic volume expansion.

04:55 So this is simply a gain in iso-osmotic fluid.

04:59 So that could be something as simple as, if you're hooked up to an IV and you infused into a person some 0.9% saline or isotonic saline, would be a great example of iso-osmotic volume expansion.

05:15 This involves an increased measurement in blood pressure.

05:19 No change in sodium. Why no change in sodium? Because you're infusing in the same concentration of sodium that's normally in the plasma.

05:30 So you're just increasing volume but you are not changing osmolality.

05:34 You get a decrease in total proteins. Why? Because total proteins again have not changed, you just have now more volume, you're diluting them.

05:45 Same with red blood cell number, you decrease red blood cell concentration simply because you're adding volume even though the number of red blood cells haven't changed.

05:56 The endocrine response to this is a decrease in aldosterone levels and no real change in arginine vasopressin antidiuretic hormone.

06:07 And the reason for this is because since there hasn't been a change in osmolality which is the primary stimulus for arginine vasopressin antidiuretic hormone, you don't get a change in this variable.

06:21 Now let's go back to iso-osmotic volume contraction.

06:25 So in this case, you're taking the normal volume diagram and you're just losing ECF volume.

06:32 No change in ICF.

06:37 In this condition, you get a decrease in arterial blood pressure.

06:42 No real change in sodium.

06:45 You get an increase in total proteins.

06:48 An increase in hematrocrit.

06:50 And the reason is because you haven't changed the number of plasma proteins or red blood cells, you just concentrated them more.

07:00 A good clinical example of this is, let's say after a person has been sick with a GI disorder and you have either vomited a lot or had a lot of diarrhea.

07:11 Volume contraction is typically iso-osmotic in nature.

07:16 The endocrine response to this is an increase in aldosterone.

07:21 No real change in antidiuretic hormone.

07:26 Why? Because again, you haven't changed the osmolality, so there's no stimulus to release antidiuretic hormone or arginine vasopressin.

07:38 Hyper-osmotic volume expansion.

07:41 So in this particular one, you're not only increasing the volume, but you're also increasing the osmolality.

07:48 So this is a very big response.

07:52 And what happens to something like blood pressure? It increases.

07:56 'Cause you've increased the total amount of circulating fluid volume.

08:00 You're also increasing the sodium levels.

08:05 Total protein and hematocrit both decrease and this is because even though you haven't changed the number of total proteins or red blood cells, you're now putting more solvent out there and diluting them in terms of the blood.

08:24 The endocrine response is a decrease in aldosterone and no real change in arginine vasopressin antidiuretic hormone.

08:35 The reason why that doesn't change is now that you've increased the osmolality but you've also increased the volume, and those two things cancel each other out.

08:44 Now we come to hyper-osmotic volume contraction.

08:48 So what's the volume contraction? You're going to lose both ECF and ICF, and you're going to have a higher amount of osmolality.

08:58 A great example for this is dehydration through a lack of drinking and an increase in sweat production.

09:06 How does this change you blood pressure if you're in a dehydrated state? There's a decrease in blood pressure because circulatory volume is lower.

09:16 There is an increase in sodium concentration.

09:20 This is because you have now concentrated sodium to a greater degree because of loss of volume.

09:27 And that volume loss was mainly hypotonic solutions.

09:34 There's an increase in the total protein concentration because again you're concentrating your proteins even though their absolute number hasn't changed.

09:44 The hematocrit is something that we have to talk a little bit more about because there's no change in hematocrit.

09:52 Remember hematocrit should be following total proteins.

09:55 It should concentrate to a greater degree.

09:58 But in this case, it's masked.

10:01 And the reason why it occurs, is even though you've lost volume and you should be concentrating the number of red blood cells, each individual red blood cell is shrinking or becoming smaller.

10:13 So when you look at them in terms of percent, it looks like they haven't changed, because they are smaller red blood cells and therefore, the volume change of both the ECF and ICF are similar enough that you don't observe a hematocrit change.

10:32 The endocrine response is an increase in aldosterone and an increase in arginine vasopressin antidiuretic hormone.

10:40 So let's go through those very briefly.

10:43 If you have a hyper-osmotic condition, your stimulus for arginine vasopressin antidiuretic hormone goes up.

10:51 It also occurs to increase aldosterone levels because you have a decrease in arterial blood pressure and a decrease in ECF volume.

11:00 So in this dehydrated condition, you have increases in aldosterone, where you want to reabsorb sodium, and you have increases in ADH (antidiuretic hormone) to reabsorb water.

11:13 So now we've gone through a number of volume contractions and expansions and these can be either hyper-osmotic, iso-osmotic, or hypo-osmotic.

11:23 It's important to be able to track these, and we do track them by measuring the blood levels of various ions, we measure blood pressure, we measure blood protein concentrations.

11:35 All of those help us assess our body fluid compartments and what types of changes we're going to have and then the predictions you can do medically to alleviate those problems.