00:00
The symptoms: I think we've already talked
about these. The symptoms from deep venous
thrombosis and pulmonary embolism may be none.
00:10
The patients may be asymptomatic in at least
50%. The inflammatory process in the leg may
lead to some discomfort. There may also, of
course, be some edema. There may be tenderness
when you touch the thigh or the calf. When
there's pulmonary embolism, the patients complain
of shortness of breath. Heart rate and blood
pressure may be abnormal, with a fast heart
rate and a low blood pressure. And sometimes,
the clot in the lung results in damage to
the lung itself, and when that happens, you
have a pulmonary infarct. Like a myocardial
infarct, it's actually some death of pulmonary
tissue, and that results in pain that is pleuritic—that
is, it occurs or gets much worse when you
take a deep breath. When the patient has a
chest pain that they say, "Oh, I can't take
a deep breath, because it's going to hurt,"
that's pleuritic chest pain, and it's due
to irritation of the lung and the lining around
the lung.
The diagnosis: Again, physical exam sometimes
helps, although very often, the physical exam
is unremarkable. But you may see unilateral—one
leg or one ankle has—edema. You may have
tenderness when you palpate, or touch, the
calf. There may be some redness in the area
or warmth. Rarely, you can actually feel a
cord from the thrombosed vein. Homan's sign,
which is also rare, is when you bend the leg...
01:41
the foot up, and that stretches the gastrocnemius
muscle, stretches the vein, and it hurts.
01:48
But it's very rare, and it's not very sensitive
or specific, and we really don't do it much
anymore. I only put it in here because you
may hear about it in your teaching. It's not
a very useful physical finding. Unfortunately,
the majority of patients with DVT are asymptomatic,
and there's nothing on the physical exam that
shows you that it's there. So you need instrument-based
techniques. One of the clues, by the way,
that the patient may be having pulmonary embolism
is, as we talked about before, elevated heart
rate, increased respiratory rate, normal or
lowish blood pressure. And when one checks
the carbon dioxide and the oxygen in the blood,
they're both low. But these are, again, fairly
nonspecific findings that can occur with pneumonia
and heart failure.
So what are the tests that define and show
us that there's DVT? Well, you can actually
do an angiogram of the vein, called a venogram,
in which you squirt some dye in the vein,
and you see areas that… where the dye is
not going because there's blood clot there.
It's not really used all that often, because
we have many excellent noninvasive tests.
And it's time-consuming, uses dye, and causes...
03:02
has radiation exposure. Ultrasound is the
way, these days, that most cases of DVT are
diagnosed. It's low-cost. It's portable. It's
noninvasive. And you can see, with an ultrasound,
the vein can't be compressed because there's
clot in it. You can sometimes actually see
clot in the vein, and with a Doppler, you
can see that there's decreased flow in the
vein. There's a blood test, which is a breakdown
product of a clot in the vascular system,
called D-dimer. And when that's elevated,
it suggests that there's clotting going on
intravascularly. There is a test that measures
the volume change within the leg, called plethysmography.
03:46
This test was more popular in the past, but
not so much now. And of course, CT and MRI
can also show this.
So let's talk a little bit more about the
ultrasound test. It has two components. First
of all, there's a color-flow Doppler that
shows us when flow in the vein is abnormal.
It takes about 45 minutes to do that. Another
test that we do with that is we look at the
vein. We look for clot in the vein channel,
and then you try and squeeze the calf and
see whether the vein collapses. It should
collapse when you squeeze the calf. If the
vein doesn't collapse, it usually means that
there's a clot in there, because a normal
vein should collapse nicely. It is of interest
that clots that are in the popliteal vein
or below usually don't embolize, and they're
usually very small. But they can propagate.
They can increase in size, and so if you see
some clot in the popliteal vein, you need
to redo the ultrasound scan again three to
five days later, because the clot may have
increased in size, thus making it much higher
risk for pulmonary embolism. And again, as
I mentioned, the clot's identified by failure
of the vein to collapse when you squeeze it,
and the duplex ultrasound and the limited
compression are really very good tests for
diagnosing DVT. And this… these figures
are not easily seen, but on the one on the
left one, actually, there is a clot in the
vein, and the one on the right, there is failure
of the vein to com… to collapse when the
calf is squeezed.
There are a number of little tricks of the
trade. A good technician—a good ultrasound
deep venous thrombosis technician—can, as
I said, see augmentation of flow when they
compress the calf, and also, they look to
see if there's collapse of the vein when they
squeeze it. You can adjust the gain—that
is, how bright the image is—so you get a
better view of the vascular system. And again,
if there's plus–minus findings, you can
do the other side to see if it looks normal
compared to the side that you're thinking
has DVT. So there are a number of little tricks
that a very good ultrasound technician is
very accurate in finding deep venous thrombosis
with its potential for thromboembolism.