1
00:00:01,740 --> 00:00:04,610
Now let's say that you
have a vial of plasma.

2
00:00:04,610 --> 00:00:06,950
And I'm actually going
to label it as we go.

3
00:00:06,950 --> 00:00:11,500
We've got some sodium
floating in here

4
00:00:11,500 --> 00:00:15,270
and you've got some anion
in purple over here.

5
00:00:15,270 --> 00:00:19,290
And this could be anything
that really binds to sodium.

6
00:00:19,290 --> 00:00:23,200
So if this is some negatively
charged ion, maybe chloride,

7
00:00:23,200 --> 00:00:26,900
or bicarb, those are
the two most common.

8
00:00:26,900 --> 00:00:31,540
And you've also got, let's
say, some glucose in here.

9
00:00:31,540 --> 00:00:40,610
And maybe some urea, or we
call it urea nitrogen as well.

10
00:00:40,610 --> 00:00:42,940
So you've got a few things
floating around the plasma

11
00:00:42,940 --> 00:00:44,550
and someone asks
you, well, what is

12
00:00:44,550 --> 00:00:47,890
the total osmolarity
of the plasma?

13
00:00:47,890 --> 00:00:49,670
And you know that
this is in units

14
00:00:49,670 --> 00:00:56,290
of osmoles per liter
blood, Actually,

15
00:00:56,290 --> 00:00:59,770
I should write liter
plasma to be more accurate.

16
00:00:59,770 --> 00:01:02,450
Since that's what we're
talking about here.

17
00:01:02,450 --> 00:01:06,475
So per one liter of plasma.

18
00:01:06,475 --> 00:01:08,600
And these are the units
that we have to think about

19
00:01:08,600 --> 00:01:10,260
to answer this
question, is, what

20
00:01:10,260 --> 00:01:13,400
are the osmoles per
liter of plasma?

21
00:01:13,400 --> 00:01:14,650
So let's go through this.

22
00:01:14,650 --> 00:01:16,358
And I'm going to give
you some lab values

23
00:01:16,358 --> 00:01:19,300
and we'll see how based on just
a few lab values and really

24
00:01:19,300 --> 00:01:23,290
just four of the most
representative solutes,

25
00:01:23,290 --> 00:01:25,550
or most important
solutes, we can

26
00:01:25,550 --> 00:01:29,000
get a pretty close
guesstimate of the osmolarity.

27
00:01:29,000 --> 00:01:32,245
So you don't actually need to
know every single osmole that's

28
00:01:32,245 --> 00:01:32,870
in your plasma.

29
00:01:32,870 --> 00:01:34,403
You can figure it
out based on four

30
00:01:34,403 --> 00:01:35,600
of the most important ones.

31
00:01:35,600 --> 00:01:37,825
So let's go with the
first one, sodium.

32
00:01:40,930 --> 00:01:43,600
And let's say the lab tells
you, well, your sodium value--

33
00:01:43,600 --> 00:01:47,280
and I'm going to write the labs
in kind of this grey color,

34
00:01:47,280 --> 00:01:49,630
somehow that reminds
me of the lab--

35
00:01:49,630 --> 00:01:52,580
let's say they say the sodium
value is 140 milliequivalents

36
00:01:52,580 --> 00:01:53,920
per liter.

37
00:01:53,920 --> 00:01:57,680
So how do you take that and
make it into osmoles per liter?

38
00:01:57,680 --> 00:02:00,320
Well, our denominator
is already OK.

39
00:02:00,320 --> 00:02:04,960
But immediately, you can
say, OK, well 140 millimoles

40
00:02:04,960 --> 00:02:07,630
per liter is what that equals.

41
00:02:07,630 --> 00:02:10,210
And you know that because
sodium is a monovalent.

42
00:02:10,210 --> 00:02:11,680
It's only got one charge.

43
00:02:14,510 --> 00:02:16,440
If it's monovalent,
then that means

44
00:02:16,440 --> 00:02:19,546
that the equivalents
equal the moles.

45
00:02:19,546 --> 00:02:20,920
And now that you're
in moles, you

46
00:02:20,920 --> 00:02:22,920
can actually go
across to osmoles.

47
00:02:22,920 --> 00:02:28,040
You could say 140 osmoles
or milliosmoles per liter.

48
00:02:28,040 --> 00:02:31,900
And you know that because
once sodium is in water,

49
00:02:31,900 --> 00:02:34,420
it acts the same way that
you would expect it to act.

50
00:02:34,420 --> 00:02:36,400
It doesn't split
up or anything like

51
00:02:36,400 --> 00:02:38,850
that because it's one particle.

52
00:02:38,850 --> 00:02:42,480
So it acts as a single particle.

53
00:02:42,480 --> 00:02:43,880
One particle.

54
00:02:43,880 --> 00:02:45,850
So if it's one
particle, it's going

55
00:02:45,850 --> 00:02:49,120
to have 140
milliosmoles per liter.

56
00:02:49,120 --> 00:02:53,310
And we've effectively gotten one
quarter of this problem done.

57
00:02:53,310 --> 00:02:57,390
Because all we need to do is
take the four different solutes

58
00:02:57,390 --> 00:02:59,990
that we've identified
and add them up together.

59
00:02:59,990 --> 00:03:01,740
So we've figured out sodium.

60
00:03:01,740 --> 00:03:04,410
And now let's move
on to the anion.

61
00:03:04,410 --> 00:03:08,100
And the trick to the anion is
just thinking of it as sodium.

62
00:03:08,100 --> 00:03:10,580
It's almost the same as
sodium, but just the reverse.

63
00:03:10,580 --> 00:03:13,260
So we know that it's
going to be 140.

64
00:03:13,260 --> 00:03:17,320
We're going to use 140
as the number here.

65
00:03:17,320 --> 00:03:24,020
Because our assumption is that
sodium is a positive charge

66
00:03:24,020 --> 00:03:25,520
and for every one
positive charge,

67
00:03:25,520 --> 00:03:27,440
you need one negative charge.

68
00:03:27,440 --> 00:03:30,190
So we're going to assume that
all the negative charges are

69
00:03:30,190 --> 00:03:31,490
coming from these anions.

70
00:03:31,490 --> 00:03:33,400
And these would be
things like we said,

71
00:03:33,400 --> 00:03:37,235
things like chloride or
bicarb, something like that.

72
00:03:37,235 --> 00:03:39,110
So again, we don't
actually get these numbers

73
00:03:39,110 --> 00:03:41,000
or even need these
numbers, we simply

74
00:03:41,000 --> 00:03:45,200
take that 140 and
we multiply by 2

75
00:03:45,200 --> 00:03:48,880
and assume that the other half
is going to be some anion.

76
00:03:48,880 --> 00:03:51,260
Now we actually have
to convert units still.

77
00:03:51,260 --> 00:03:56,400
We have to get over to
milliosmoles per liter.

78
00:03:56,400 --> 00:03:58,910
And so we know that the anion
is going to be monovalent

79
00:03:58,910 --> 00:04:02,370
and that gets us to millimoles.

80
00:04:02,370 --> 00:04:04,340
And we use the same
logic as above.

81
00:04:04,340 --> 00:04:06,920
We just say, OK, well
if that was millimoles

82
00:04:06,920 --> 00:04:11,310
and it's still one particle,
meaning it's not splitting up

83
00:04:11,310 --> 00:04:14,230
when it hits water and going
in two different directions,

84
00:04:14,230 --> 00:04:19,550
in a sense, having
twice the effect,

85
00:04:19,550 --> 00:04:22,770
we're going to end up with
140 milliosmoles per liter,

86
00:04:22,770 --> 00:04:24,220
just as before.

87
00:04:24,220 --> 00:04:26,840
So this is our second
part done, right?

88
00:04:26,840 --> 00:04:28,020
So two parts are done.

89
00:04:28,020 --> 00:04:31,360
We figured out the sodium
and we figured out the anion.

90
00:04:31,360 --> 00:04:33,150
Now let's go over to glucose.

91
00:04:33,150 --> 00:04:36,900
So let's figure out how to
get glucose as units from what

92
00:04:36,900 --> 00:04:39,280
the lab gives us, which I'll
tell you in just a second,

93
00:04:39,280 --> 00:04:41,250
into something more usable.

94
00:04:41,250 --> 00:04:45,670
So how do we actually get
over to something usable?

95
00:04:45,670 --> 00:04:51,060
Let me actually, switch over.

96
00:04:51,060 --> 00:04:52,370
There we go.

97
00:04:52,370 --> 00:04:53,670
Make some space on our canvas.

98
00:04:53,670 --> 00:04:58,170
So let's say we have
our glucose here.

99
00:04:58,170 --> 00:05:00,830
And the lab calls us
and says, hey, we just

100
00:05:00,830 --> 00:05:05,610
got your lab result, it was
90 milligrams per deciliter.

101
00:05:05,610 --> 00:05:08,580
It's actually a very,
very common lab value

102
00:05:08,580 --> 00:05:12,590
or common range for
a glucose lab value.

103
00:05:12,590 --> 00:05:14,020
One thing we have
to do right away

104
00:05:14,020 --> 00:05:17,330
is figure out how to get
from milligrams to moles.

105
00:05:17,330 --> 00:05:20,420
And you know that this is
what glucose looks like.

106
00:05:20,420 --> 00:05:22,420
This is the formula for it.

107
00:05:22,420 --> 00:05:25,860
So to get the overall
weight, the atomic weight,

108
00:05:25,860 --> 00:05:27,600
you could say,
well, let's take 6,

109
00:05:27,600 --> 00:05:29,580
because that's how
many carbons we have,

110
00:05:29,580 --> 00:05:32,280
times the weight of
carbon, which is 12,

111
00:05:32,280 --> 00:05:35,590
plus 12, because that's
what we have here,

112
00:05:35,590 --> 00:05:38,390
times the weight of
hydrogen, which is 1,

113
00:05:38,390 --> 00:05:43,590
plus 6, times the
weight of oxygen.

114
00:05:43,590 --> 00:05:47,290
And that's going to equal--
this is 72, this is 12,

115
00:05:47,290 --> 00:05:56,740
and this is 96, and add them all
up together, and we get-- 180.

116
00:05:56,740 --> 00:06:01,320
So we have 180 atomic mass
units per glucose molecule.

117
00:06:01,320 --> 00:06:03,190
Which means, if you
think back, which

118
00:06:03,190 --> 00:06:13,510
means that one mole of
glucose equals 180 grams.

119
00:06:13,510 --> 00:06:15,807
And since these
are way, way bigger

120
00:06:15,807 --> 00:06:18,390
than, I mean this is grams, and
we're talking about milligrams

121
00:06:18,390 --> 00:06:22,920
over here, so I'm going to
just switch it down by 1,000.

122
00:06:22,920 --> 00:06:31,160
So one millimole of glucose
equals 180 milligrams.

123
00:06:31,160 --> 00:06:33,400
All I did was divide by 1,000.

124
00:06:33,400 --> 00:06:37,430
So now I can take this unit and
actually use our conversions.

125
00:06:37,430 --> 00:06:41,240
I could say, well, let's
multiply that by 100

126
00:06:41,240 --> 00:06:45,130
and-- let's say, one
millimole rather,

127
00:06:45,130 --> 00:06:50,440
one millimole per 180
milligrams, that'll

128
00:06:50,440 --> 00:06:52,360
cancel the milligrams out.

129
00:06:52,360 --> 00:06:55,220
And I also have to get from
deciliters to liters, right?

130
00:06:55,220 --> 00:06:59,930
So I've got to go 10
deciliters equals 1 liter.

131
00:06:59,930 --> 00:07:02,310
And that'll cancel
my deciliters out.

132
00:07:02,310 --> 00:07:06,180
So I'm left with-- and this
10 will get rid of that 0--

133
00:07:06,180 --> 00:07:08,420
so I'm left with
90 divided by 18,

134
00:07:08,420 --> 00:07:13,740
which is 5 millimoles per liter.

135
00:07:13,740 --> 00:07:16,550
And, just as above, I
know that the glucose

136
00:07:16,550 --> 00:07:20,680
will behave as one particle
in water, in solution.

137
00:07:20,680 --> 00:07:25,770
So it's going to be 5 osmoles,
or milliosmoles, actually.

138
00:07:25,770 --> 00:07:30,200
5 milliosmoles per liter.

139
00:07:30,200 --> 00:07:32,040
And that's the
right units, right?

140
00:07:32,040 --> 00:07:36,270
So I figured out another
part of my formula.

141
00:07:36,270 --> 00:07:38,772
And I'll show you the actual
formula at the end of this,

142
00:07:38,772 --> 00:07:40,730
but I wanted to work
through it piece by piece.

143
00:07:40,730 --> 00:07:45,340
So we've done glucose now and
we're ready for our last bit,

144
00:07:45,340 --> 00:07:50,200
so let's do our last one,
which is going to be urea.

145
00:07:50,200 --> 00:07:54,230
Specifically, the lab is not
going to call us about urea,

146
00:07:54,230 --> 00:07:58,030
it's going to call us
about blood urea nitrogen.

147
00:07:58,030 --> 00:08:00,670
And actually, it
matters what this means.

148
00:08:00,670 --> 00:08:03,660
So what that exactly
means is that they're

149
00:08:03,660 --> 00:08:08,200
measuring the nitrogen
component of urea.

150
00:08:08,200 --> 00:08:11,140
And so they'll call you and
say, well, we measured it

151
00:08:11,140 --> 00:08:16,560
and the value came to 14
milligrams per deciliter.

152
00:08:16,560 --> 00:08:18,340
Something like
that, so let's say

153
00:08:18,340 --> 00:08:20,240
that's the amount
of urea we find

154
00:08:20,240 --> 00:08:22,550
in our little tube of plasma.

155
00:08:22,550 --> 00:08:26,090
How do we convert that to moles
per liter like we did before?

156
00:08:26,090 --> 00:08:32,530
Well, again, it'll be helpful if
I draw out a molecule of urea.

157
00:08:32,530 --> 00:08:34,360
So we have something like this.

158
00:08:34,360 --> 00:08:36,330
A couple nitrogens.

159
00:08:36,330 --> 00:08:37,940
And this is what
urea looks like.

160
00:08:37,940 --> 00:08:39,159
It's a pretty small molecule.

161
00:08:39,159 --> 00:08:42,140
A couple nitrogens,
carbon, and oxygen.

162
00:08:42,140 --> 00:08:46,490
And these nitrogens have an
atomic mass unit of 14 apiece.

163
00:08:46,490 --> 00:08:48,300
So that's 14.

164
00:08:48,300 --> 00:08:51,440
And this is 14
over here, as well.

165
00:08:51,440 --> 00:08:56,660
So what the lab actually
measures is just this part.

166
00:08:56,660 --> 00:08:58,410
It's just measuring
the two nitrogens.

167
00:08:58,410 --> 00:09:01,321
It's not measuring the weight
of the entire molecule.

168
00:09:01,321 --> 00:09:03,820
So all it's going to give you
is the weight of the nitrogens

169
00:09:03,820 --> 00:09:06,500
that are in the molecule.

170
00:09:06,500 --> 00:09:11,000
So what that means is that we
say, OK, well, that tells us

171
00:09:11,000 --> 00:09:22,430
that one molecule of urea is
going to be 28 atomic mass

172
00:09:22,430 --> 00:09:28,450
units of-- I'm going to put
it in quotes-- urea nitrogen.

173
00:09:28,450 --> 00:09:32,030
Because that's the part of
urea that we're measuring

174
00:09:32,030 --> 00:09:36,040
and that means that
one mole of urea

175
00:09:36,040 --> 00:09:44,250
is going to be 28
grams of urea nitrogen.

176
00:09:44,250 --> 00:09:47,950
And because, again,
this is much, much more

177
00:09:47,950 --> 00:09:50,260
than what we actually have,
let me divide by 1,000.

178
00:09:50,260 --> 00:09:56,860
So one millimole equals 28
milligrams of urea nitrogen.

179
00:09:56,860 --> 00:10:02,360
So that's how we figure
out the conversion.

180
00:10:02,360 --> 00:10:04,240
And I do the exact
same thing as above.

181
00:10:04,240 --> 00:10:06,419
I say, OK, well, let's
times-- let's say,

182
00:10:06,419 --> 00:10:08,210
I want to get rid of
the milligrams, right?

183
00:10:08,210 --> 00:10:14,790
So 1 millimole divided
by 28 milligrams,

184
00:10:14,790 --> 00:10:17,090
and that'll get rid
of my milligrams.

185
00:10:17,090 --> 00:10:22,620
And I'll take, let's say,
10 deciliters over 1 liter

186
00:10:22,620 --> 00:10:25,550
and that'll help me get
rid of my deciliters.

187
00:10:25,550 --> 00:10:31,470
And so then I'm left with
14 over 28, which is 0.5.

188
00:10:31,470 --> 00:10:34,400
And then times 10, so that's 5.

189
00:10:34,400 --> 00:10:39,380
5 millimoles per liter.

190
00:10:39,380 --> 00:10:41,870
And as I've done
a couple times now

191
00:10:41,870 --> 00:10:44,170
and we know that it's
the urea nitrogen

192
00:10:44,170 --> 00:10:47,880
or the urea is going to act and
behave like one molecule or one

193
00:10:47,880 --> 00:10:49,420
particle when it's
in water, it's

194
00:10:49,420 --> 00:10:51,760
not going to split up
or anything like that,

195
00:10:51,760 --> 00:10:53,510
so that means that
it's going to basically

196
00:10:53,510 --> 00:10:58,540
be 5 milliosmoles per liter.

197
00:10:58,540 --> 00:11:01,670
And so I figured out the
last part of my equation.

198
00:11:05,330 --> 00:11:10,830
So going back to the
top, we have sodium.

199
00:11:10,830 --> 00:11:13,810
And this turned
out to be a total

200
00:11:13,810 --> 00:11:22,710
of 140 milliosmoles per liter.

201
00:11:22,710 --> 00:11:30,330
And then for our anion, we had
140 milliosmoles per liter.

202
00:11:30,330 --> 00:11:36,980
And then for our glucose, we
had 5 milliosmoles per liter.

203
00:11:36,980 --> 00:11:42,790
And for our urea, we had
5 milliosmoles per liter.

204
00:11:42,790 --> 00:11:49,460
So adding it all up, our total
comes to 140 times 2 plus 10.

205
00:11:49,460 --> 00:11:52,030
So we get, if I do
my math correctly,

206
00:11:52,030 --> 00:11:57,090
I think that's 290
milliosmoles per liter.

207
00:11:57,090 --> 00:12:00,380
That's the answer
to our osmolarity.

208
00:12:00,380 --> 00:12:01,970
Our total osmolarity
in the plasma

209
00:12:01,970 --> 00:12:04,710
is 290 milliosmoles per liter.

210
00:12:04,710 --> 00:12:07,030
Now that was kind of the
long way of doing it.

211
00:12:07,030 --> 00:12:09,460
Let me give you a very,
very quick and dirty way

212
00:12:09,460 --> 00:12:09,960
of doing it.

213
00:12:09,960 --> 00:12:12,750
Let me actually make
some space up here.

214
00:12:12,750 --> 00:12:15,380
You could do the exact same
problem, you could say,

215
00:12:15,380 --> 00:12:24,900
well, this osmolarity
equals, you could say,

216
00:12:24,900 --> 00:12:40,800
sodium times 2, plus
glucose, divided by 18,

217
00:12:40,800 --> 00:12:45,450
plus BUN divided by 2.8.

218
00:12:45,450 --> 00:12:48,370
And that takes all
of those conversions

219
00:12:48,370 --> 00:12:49,650
and simplifies it down.

220
00:12:49,650 --> 00:12:52,850
So if you ever get your sodium
value, your glucose value,

221
00:12:52,850 --> 00:12:55,030
and your BUN, and you
want to quickly calculate

222
00:12:55,030 --> 00:12:59,230
your osmolarity, now you
know the fast way to do it.