0:00:01.740,0:00:04.610
Now let's say that you[br]have a vial of plasma.

0:00:04.610,0:00:06.950
And I'm actually going[br]to label it as we go.

0:00:06.950,0:00:11.500
We've got some sodium[br]floating in here

0:00:11.500,0:00:15.270
and you've got some anion[br]in purple over here.

0:00:15.270,0:00:19.290
And this could be anything[br]that really binds to sodium.

0:00:19.290,0:00:23.200
So if this is some negatively[br]charged ion, maybe chloride,

0:00:23.200,0:00:26.900
or bicarb, those are[br]the two most common.

0:00:26.900,0:00:31.540
And you've also got, let's[br]say, some glucose in here.

0:00:31.540,0:00:40.610
And maybe some urea, or we[br]call it urea nitrogen as well.

0:00:40.610,0:00:42.940
So you've got a few things[br]floating around the plasma

0:00:42.940,0:00:44.550
and someone asks[br]you, well, what is

0:00:44.550,0:00:47.890
the total osmolarity[br]of the plasma?

0:00:47.890,0:00:49.670
And you know that[br]this is in units

0:00:49.670,0:00:56.290
of osmoles per liter[br]blood, Actually,

0:00:56.290,0:00:59.770
I should write liter[br]plasma to be more accurate.

0:00:59.770,0:01:02.450
Since that's what we're[br]talking about here.

0:01:02.450,0:01:06.475
So per one liter of plasma.

0:01:06.475,0:01:08.600
And these are the units[br]that we have to think about

0:01:08.600,0:01:10.260
to answer this[br]question, is, what

0:01:10.260,0:01:13.400
are the osmoles per[br]liter of plasma?

0:01:13.400,0:01:14.650
So let's go through this.

0:01:14.650,0:01:16.358
And I'm going to give[br]you some lab values

0:01:16.358,0:01:19.300
and we'll see how based on just[br]a few lab values and really

0:01:19.300,0:01:23.290
just four of the most[br]representative solutes,

0:01:23.290,0:01:25.550
or most important[br]solutes, we can

0:01:25.550,0:01:29.000
get a pretty close[br]guesstimate of the osmolarity.

0:01:29.000,0:01:32.245
So you don't actually need to[br]know every single osmole that's

0:01:32.245,0:01:32.870
in your plasma.

0:01:32.870,0:01:34.403
You can figure it[br]out based on four

0:01:34.403,0:01:35.600
of the most important ones.

0:01:35.600,0:01:37.825
So let's go with the[br]first one, sodium.

0:01:40.930,0:01:43.600
And let's say the lab tells[br]you, well, your sodium value--

0:01:43.600,0:01:47.280
and I'm going to write the labs[br]in kind of this grey color,

0:01:47.280,0:01:49.630
somehow that reminds[br]me of the lab--

0:01:49.630,0:01:52.580
let's say they say the sodium[br]value is 140 milliequivalents

0:01:52.580,0:01:53.920
per liter.

0:01:53.920,0:01:57.680
So how do you take that and[br]make it into osmoles per liter?

0:01:57.680,0:02:00.320
Well, our denominator[br]is already OK.

0:02:00.320,0:02:04.960
But immediately, you can[br]say, OK, well 140 millimoles

0:02:04.960,0:02:07.630
per liter is what that equals.

0:02:07.630,0:02:10.210
And you know that because[br]sodium is a monovalent.

0:02:10.210,0:02:11.680
It's only got one charge.

0:02:14.510,0:02:16.440
If it's monovalent,[br]then that means

0:02:16.440,0:02:19.546
that the equivalents[br]equal the moles.

0:02:19.546,0:02:20.920
And now that you're[br]in moles, you

0:02:20.920,0:02:22.920
can actually go[br]across to osmoles.

0:02:22.920,0:02:28.040
You could say 140 osmoles[br]or milliosmoles per liter.

0:02:28.040,0:02:31.900
And you know that because[br]once sodium is in water,

0:02:31.900,0:02:34.420
it acts the same way that[br]you would expect it to act.

0:02:34.420,0:02:36.400
It doesn't split[br]up or anything like

0:02:36.400,0:02:38.850
that because it's one particle.

0:02:38.850,0:02:42.480
So it acts as a single particle.

0:02:42.480,0:02:43.880
One particle.

0:02:43.880,0:02:45.850
So if it's one[br]particle, it's going

0:02:45.850,0:02:49.120
to have 140[br]milliosmoles per liter.

0:02:49.120,0:02:53.310
And we've effectively gotten one[br]quarter of this problem done.

0:02:53.310,0:02:57.390
Because all we need to do is[br]take the four different solutes

0:02:57.390,0:02:59.990
that we've identified[br]and add them up together.

0:02:59.990,0:03:01.740
So we've figured out sodium.

0:03:01.740,0:03:04.410
And now let's move[br]on to the anion.

0:03:04.410,0:03:08.100
And the trick to the anion is[br]just thinking of it as sodium.

0:03:08.100,0:03:10.580
It's almost the same as[br]sodium, but just the reverse.

0:03:10.580,0:03:13.260
So we know that it's[br]going to be 140.

0:03:13.260,0:03:17.320
We're going to use 140[br]as the number here.

0:03:17.320,0:03:24.020
Because our assumption is that[br]sodium is a positive charge

0:03:24.020,0:03:25.520
and for every one[br]positive charge,

0:03:25.520,0:03:27.440
you need one negative charge.

0:03:27.440,0:03:30.190
So we're going to assume that[br]all the negative charges are

0:03:30.190,0:03:31.490
coming from these anions.

0:03:31.490,0:03:33.400
And these would be[br]things like we said,

0:03:33.400,0:03:37.235
things like chloride or[br]bicarb, something like that.

0:03:37.235,0:03:39.110
So again, we don't[br]actually get these numbers

0:03:39.110,0:03:41.000
or even need these[br]numbers, we simply

0:03:41.000,0:03:45.200
take that 140 and[br]we multiply by 2

0:03:45.200,0:03:48.880
and assume that the other half[br]is going to be some anion.

0:03:48.880,0:03:51.260
Now we actually have[br]to convert units still.

0:03:51.260,0:03:56.400
We have to get over to[br]milliosmoles per liter.

0:03:56.400,0:03:58.910
And so we know that the anion[br]is going to be monovalent

0:03:58.910,0:04:02.370
and that gets us to millimoles.

0:04:02.370,0:04:04.340
And we use the same[br]logic as above.

0:04:04.340,0:04:06.920
We just say, OK, well[br]if that was millimoles

0:04:06.920,0:04:11.310
and it's still one particle,[br]meaning it's not splitting up

0:04:11.310,0:04:14.230
when it hits water and going[br]in two different directions,

0:04:14.230,0:04:19.550
in a sense, having[br]twice the effect,

0:04:19.550,0:04:22.770
we're going to end up with[br]140 milliosmoles per liter,

0:04:22.770,0:04:24.220
just as before.

0:04:24.220,0:04:26.840
So this is our second[br]part done, right?

0:04:26.840,0:04:28.020
So two parts are done.

0:04:28.020,0:04:31.360
We figured out the sodium[br]and we figured out the anion.

0:04:31.360,0:04:33.150
Now let's go over to glucose.

0:04:33.150,0:04:36.900
So let's figure out how to[br]get glucose as units from what

0:04:36.900,0:04:39.280
the lab gives us, which I'll[br]tell you in just a second,

0:04:39.280,0:04:41.250
into something more usable.

0:04:41.250,0:04:45.670
So how do we actually get[br]over to something usable?

0:04:45.670,0:04:51.060
Let me actually, switch over.

0:04:51.060,0:04:52.370
There we go.

0:04:52.370,0:04:53.670
Make some space on our canvas.

0:04:53.670,0:04:58.170
So let's say we have[br]our glucose here.

0:04:58.170,0:05:00.830
And the lab calls us[br]and says, hey, we just

0:05:00.830,0:05:05.610
got your lab result, it was[br]90 milligrams per deciliter.

0:05:05.610,0:05:08.580
It's actually a very,[br]very common lab value

0:05:08.580,0:05:12.590
or common range for[br]a glucose lab value.

0:05:12.590,0:05:14.020
One thing we have[br]to do right away

0:05:14.020,0:05:17.330
is figure out how to get[br]from milligrams to moles.

0:05:17.330,0:05:20.420
And you know that this is[br]what glucose looks like.

0:05:20.420,0:05:22.420
This is the formula for it.

0:05:22.420,0:05:25.860
So to get the overall[br]weight, the atomic weight,

0:05:25.860,0:05:27.600
you could say,[br]well, let's take 6,

0:05:27.600,0:05:29.580
because that's how[br]many carbons we have,

0:05:29.580,0:05:32.280
times the weight of[br]carbon, which is 12,

0:05:32.280,0:05:35.590
plus 12, because that's[br]what we have here,

0:05:35.590,0:05:38.390
times the weight of[br]hydrogen, which is 1,

0:05:38.390,0:05:43.590
plus 6, times the[br]weight of oxygen.

0:05:43.590,0:05:47.290
And that's going to equal--[br]this is 72, this is 12,

0:05:47.290,0:05:56.740
and this is 96, and add them all[br]up together, and we get-- 180.

0:05:56.740,0:06:01.320
So we have 180 atomic mass[br]units per glucose molecule.

0:06:01.320,0:06:03.190
Which means, if you[br]think back, which

0:06:03.190,0:06:13.510
means that one mole of[br]glucose equals 180 grams.

0:06:13.510,0:06:15.807
And since these[br]are way, way bigger

0:06:15.807,0:06:18.390
than, I mean this is grams, and[br]we're talking about milligrams

0:06:18.390,0:06:22.920
over here, so I'm going to[br]just switch it down by 1,000.

0:06:22.920,0:06:31.160
So one millimole of glucose[br]equals 180 milligrams.

0:06:31.160,0:06:33.400
All I did was divide by 1,000.

0:06:33.400,0:06:37.430
So now I can take this unit and[br]actually use our conversions.

0:06:37.430,0:06:41.240
I could say, well, let's[br]multiply that by 100

0:06:41.240,0:06:45.130
and-- let's say, one[br]millimole rather,

0:06:45.130,0:06:50.440
one millimole per 180[br]milligrams, that'll

0:06:50.440,0:06:52.360
cancel the milligrams out.

0:06:52.360,0:06:55.220
And I also have to get from[br]deciliters to liters, right?

0:06:55.220,0:06:59.930
So I've got to go 10[br]deciliters equals 1 liter.

0:06:59.930,0:07:02.310
And that'll cancel[br]my deciliters out.

0:07:02.310,0:07:06.180
So I'm left with-- and this[br]10 will get rid of that 0--

0:07:06.180,0:07:08.420
so I'm left with[br]90 divided by 18,

0:07:08.420,0:07:13.740
which is 5 millimoles per liter.

0:07:13.740,0:07:16.550
And, just as above, I[br]know that the glucose

0:07:16.550,0:07:20.680
will behave as one particle[br]in water, in solution.

0:07:20.680,0:07:25.770
So it's going to be 5 osmoles,[br]or milliosmoles, actually.

0:07:25.770,0:07:30.200
5 milliosmoles per liter.

0:07:30.200,0:07:32.040
And that's the[br]right units, right?

0:07:32.040,0:07:36.270
So I figured out another[br]part of my formula.

0:07:36.270,0:07:38.772
And I'll show you the actual[br]formula at the end of this,

0:07:38.772,0:07:40.730
but I wanted to work[br]through it piece by piece.

0:07:40.730,0:07:45.340
So we've done glucose now and[br]we're ready for our last bit,

0:07:45.340,0:07:50.200
so let's do our last one,[br]which is going to be urea.

0:07:50.200,0:07:54.230
Specifically, the lab is not[br]going to call us about urea,

0:07:54.230,0:07:58.030
it's going to call us[br]about blood urea nitrogen.

0:07:58.030,0:08:00.670
And actually, it[br]matters what this means.

0:08:00.670,0:08:03.660
So what that exactly[br]means is that they're

0:08:03.660,0:08:08.200
measuring the nitrogen[br]component of urea.

0:08:08.200,0:08:11.140
And so they'll call you and[br]say, well, we measured it

0:08:11.140,0:08:16.560
and the value came to 14[br]milligrams per deciliter.

0:08:16.560,0:08:18.340
Something like[br]that, so let's say

0:08:18.340,0:08:20.240
that's the amount[br]of urea we find

0:08:20.240,0:08:22.550
in our little tube of plasma.

0:08:22.550,0:08:26.090
How do we convert that to moles[br]per liter like we did before?

0:08:26.090,0:08:32.530
Well, again, it'll be helpful if[br]I draw out a molecule of urea.

0:08:32.530,0:08:34.360
So we have something like this.

0:08:34.360,0:08:36.330
A couple nitrogens.

0:08:36.330,0:08:37.940
And this is what[br]urea looks like.

0:08:37.940,0:08:39.159
It's a pretty small molecule.

0:08:39.159,0:08:42.140
A couple nitrogens,[br]carbon, and oxygen.

0:08:42.140,0:08:46.490
And these nitrogens have an[br]atomic mass unit of 14 apiece.

0:08:46.490,0:08:48.300
So that's 14.

0:08:48.300,0:08:51.440
And this is 14[br]over here, as well.

0:08:51.440,0:08:56.660
So what the lab actually[br]measures is just this part.

0:08:56.660,0:08:58.410
It's just measuring[br]the two nitrogens.

0:08:58.410,0:09:01.321
It's not measuring the weight[br]of the entire molecule.

0:09:01.321,0:09:03.820
So all it's going to give you[br]is the weight of the nitrogens

0:09:03.820,0:09:06.500
that are in the molecule.

0:09:06.500,0:09:11.000
So what that means is that we[br]say, OK, well, that tells us

0:09:11.000,0:09:22.430
that one molecule of urea is[br]going to be 28 atomic mass

0:09:22.430,0:09:28.450
units of-- I'm going to put[br]it in quotes-- urea nitrogen.

0:09:28.450,0:09:32.030
Because that's the part of[br]urea that we're measuring

0:09:32.030,0:09:36.040
and that means that[br]one mole of urea

0:09:36.040,0:09:44.250
is going to be 28[br]grams of urea nitrogen.

0:09:44.250,0:09:47.950
And because, again,[br]this is much, much more

0:09:47.950,0:09:50.260
than what we actually have,[br]let me divide by 1,000.

0:09:50.260,0:09:56.860
So one millimole equals 28[br]milligrams of urea nitrogen.

0:09:56.860,0:10:02.360
So that's how we figure[br]out the conversion.

0:10:02.360,0:10:04.240
And I do the exact[br]same thing as above.

0:10:04.240,0:10:06.419
I say, OK, well, let's[br]times-- let's say,

0:10:06.419,0:10:08.210
I want to get rid of[br]the milligrams, right?

0:10:08.210,0:10:14.790
So 1 millimole divided[br]by 28 milligrams,

0:10:14.790,0:10:17.090
and that'll get rid[br]of my milligrams.

0:10:17.090,0:10:22.620
And I'll take, let's say,[br]10 deciliters over 1 liter

0:10:22.620,0:10:25.550
and that'll help me get[br]rid of my deciliters.

0:10:25.550,0:10:31.470
And so then I'm left with[br]14 over 28, which is 0.5.

0:10:31.470,0:10:34.400
And then times 10, so that's 5.

0:10:34.400,0:10:39.380
5 millimoles per liter.

0:10:39.380,0:10:41.870
And as I've done[br]a couple times now

0:10:41.870,0:10:44.170
and we know that it's[br]the urea nitrogen

0:10:44.170,0:10:47.880
or the urea is going to act and[br]behave like one molecule or one

0:10:47.880,0:10:49.420
particle when it's[br]in water, it's

0:10:49.420,0:10:51.760
not going to split up[br]or anything like that,

0:10:51.760,0:10:53.510
so that means that[br]it's going to basically

0:10:53.510,0:10:58.540
be 5 milliosmoles per liter.

0:10:58.540,0:11:01.670
And so I figured out the[br]last part of my equation.

0:11:05.330,0:11:10.830
So going back to the[br]top, we have sodium.

0:11:10.830,0:11:13.810
And this turned[br]out to be a total

0:11:13.810,0:11:22.710
of 140 milliosmoles per liter.

0:11:22.710,0:11:30.330
And then for our anion, we had[br]140 milliosmoles per liter.

0:11:30.330,0:11:36.980
And then for our glucose, we[br]had 5 milliosmoles per liter.

0:11:36.980,0:11:42.790
And for our urea, we had[br]5 milliosmoles per liter.

0:11:42.790,0:11:49.460
So adding it all up, our total[br]comes to 140 times 2 plus 10.

0:11:49.460,0:11:52.030
So we get, if I do[br]my math correctly,

0:11:52.030,0:11:57.090
I think that's 290[br]milliosmoles per liter.

0:11:57.090,0:12:00.380
That's the answer[br]to our osmolarity.

0:12:00.380,0:12:01.970
Our total osmolarity[br]in the plasma

0:12:01.970,0:12:04.710
is 290 milliosmoles per liter.

0:12:04.710,0:12:07.030
Now that was kind of the[br]long way of doing it.

0:12:07.030,0:12:09.460
Let me give you a very,[br]very quick and dirty way

0:12:09.460,0:12:09.960
of doing it.

0:12:09.960,0:12:12.750
Let me actually make[br]some space up here.

0:12:12.750,0:12:15.380
You could do the exact same[br]problem, you could say,

0:12:15.380,0:12:24.900
well, this osmolarity[br]equals, you could say,

0:12:24.900,0:12:40.800
sodium times 2, plus[br]glucose, divided by 18,

0:12:40.800,0:12:45.450
plus BUN divided by 2.8.

0:12:45.450,0:12:48.370
And that takes all[br]of those conversions

0:12:48.370,0:12:49.650
and simplifies it down.

0:12:49.650,0:12:52.850
So if you ever get your sodium[br]value, your glucose value,

0:12:52.850,0:12:55.030
and your BUN, and you[br]want to quickly calculate

0:12:55.030,0:12:59.230
your osmolarity, now you[br]know the fast way to do it.